document_title: Nuclear fusion

question_text: which elements are primarily involved in the suns fusion reaction

question_tokens: which elements are primarily involved in the suns fusion reaction

text: Nuclear fusion

text: Process[edit]

text: The release of energy with the fusion of light elements is due to the interplay of two opposing forces: the nuclear force, which combines together protons and neutrons, and the Coulomb force, which causes protons to repel each other. Protons are positively charged and repel each other by the Coulomb force, but they can nonetheless stick together, demonstrating the existence of another, short-range, force referred to as nuclear attraction.[2] Light nuclei (or nuclei smaller than iron and nickel) are sufficiently small and proton-poor allowing the nuclear force to overcome repulsion. This is because the nucleus is sufficiently small that all nucleons feel the short-range attractive force at least as strongly as they feel the infinite-range Coulomb repulsion. Building up nuclei from lighter nuclei by fusion releases the extra energy from the net attraction of particles. For larger nuclei, however, no energy is released, since the nuclear force is short-range and cannot continue to act across  longer atomic length scales. Thus, energy is not released with the fusion of such nuclei; instead, energy is required as input for such processes.

text: Fusion powers stars and produces virtually all elements in a process called nucleosynthesis. The Sun is a main-sequence star, and, as such, generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core, the Sun fuses 620 million metric tons of hydrogen and makes 606 million metric tons of helium each second. The fusion of lighter elements in stars releases energy and the mass that always accompanies it. For example, in the fusion of two hydrogen nuclei to form helium, 0.7% of the mass is carried away in the form of kinetic energy of an alpha particle or other forms of energy, such as electromagnetic radiation.[3]

text: It takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen. When accelerated to high enough speeds, nuclei can overcome this electrostatic repulsion and brought close enough such that the attractive nuclear force is greater than the repulsive Coulomb force. The strong force grows rapidly once the nuclei are close enough, and the fusing nucleons can essentially "fall" into each other and the result is fusion and net energy produced. The fusion of lighter nuclei, which creates a heavier nucleus and often a free neutron or proton, generally releases more energy than it takes to force the nuclei together; this is an exothermic process that can produce self-sustaining reactions.

text: Energy released in most nuclear reactions is much larger than in chemical reactions, because the binding energy that holds a nucleus together is greater than the energy that holds electrons to a nucleus. For example, the ionization energy gained by adding an electron to a hydrogen nucleus is 6982217896002232000♠13.6 eV—less than one-millionth of the 6988281983061712000♠17.6 MeV released in the deuterium–tritium (D–T) reaction shown in the adjacent diagram. The complete conversion of one gram of matter would release 9×1013 joules of energy. Fusion reactions have an energy density many times greater than nuclear fission; the reactions produce far greater energy per unit of mass even though individual fission reactions are generally much more energetic than individual fusion ones, which are themselves millions of times more energetic than chemical reactions. Only direct conversion of mass into energy, such as that caused by the annihilatory collision of matter and antimatter, is more energetic per unit of mass than nuclear fusion.

text: Research into using fusion for the production of electricity has been pursued for over 60 years. Successful accomplishment of controlled fusion has been stymied by scientific and technological difficulties; nonetheless, important progress has been made. At present, controlled fusion reactions have been unable to produce break-even (self-sustaining) controlled fusion.[4] The two most advanced approaches for it are magnetic confinement (toroid designs) and inertial confinement (laser designs).

text: Workable designs for a toroidal reactor that theoretically will deliver ten times more fusion energy than the amount needed to heat plasma to the required temperatures are in development (see ITER). The ITER facility is expected to finish its construction phase in 2019. It will start commissioning the reactor that same year and initiate plasma experiments in 2020, but is not expected to begin full deuterium-tritium fusion until 2027.[5]

text: The US National Ignition Facility, which uses laser-driven inertial confinement fusion, was designed with a goal of break-even fusion; the first large-scale laser target experiments were performed in June 2009 and ignition experiments began in early 2011.[6][7]

text: Nuclear fusion in stars[edit]

text: An important fusion process is the stellar nucleosynthesis that powers stars and the Sun. In the 20th century, it was recognized that the energy released from nuclear fusion reactions accounted for the longevity of stellar heat and light. The fusion of nuclei in a star, starting from its initial hydrogen and helium abundance, provides that energy and synthesizes new nuclei as a byproduct of the fusion process.  Different reaction chains are involved, depending on the mass of the star (and therefore the pressure and temperature in its core).

text: Around 1920, Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars.[8][9] At that time, the source of stellar energy was a complete mystery; Eddington correctly speculated that the source was fusion of hydrogen into helium, liberating enormous energy according to Einstein's equation E = mc2. This was a particularly remarkable development since at that time fusion and thermonuclear energy, and even that stars are largely composed of hydrogen (see metallicity), had not yet been discovered. Eddington's paper, based on knowledge at the time, reasoned that:

text:
The leading theory of stellar energy, the contraction hypothesis, should cause stars' rotation to visibly speed up due to conservation of angular momentum. But observations of Cepheid variable stars showed this was not happening.
The only other known plausible source of energy was conversion of matter to energy; Einstein had shown some years earlier that a small amount of matter was equivalent to a large amount of energy.
Francis Aston had also recently shown that the mass of a helium atom was about 0.8% less than the mass of the four hydrogen atoms which would, combined, form a helium atom, suggesting that if such a combination could happen, it would release considerable energy as a byproduct.
If a star contained just 5% of fusible hydrogen, it would suffice to explain how stars got their energy. (We now know that most 'ordinary' stars contain far more than 5% hydrogen)
Further elements might also be fused, and other scientists had speculated that stars were the "crucible" in which light elements combined to create heavy elements, but without more accurate measurements of their atomic masses nothing more could be said at the time.

tag: ol

text: All of these speculations were proven correct in the following decades.

text: The primary source of solar energy, and similar size stars, is the fusion of hydrogen to form helium (the proton-proton chain reaction), which occurs at a solar-core temperature of 14 million kelvin. The net result is the fusion of four protons into one alpha particle, with the release of two positrons and two neutrinos (which changes two of the protons into neutrons), and energy. In heavier stars, the CNO cycle and other processes are more important. As a star uses up a substantial fraction of its hydrogen, it begins to synthesize heavier elements. The heaviest elements are synthesized by fusion that occurs as a more massive star undergoes a violent supernova at the end of its life, a process known as supernova nucleosynthesis.

text: Requirements[edit]

text: A substantial energy barrier of electrostatic forces must be overcome before fusion can occur. At large distances, two naked nuclei repel one another because of the repulsive electrostatic force between their positively charged protons. If two nuclei can be brought close enough together, however, the electrostatic repulsion can be overcome by the quantum effect in which nuclei can tunnel through coulomb forces.

text: When a nucleon such as a proton or neutron is added to a nucleus, the nuclear force attracts it to all the other nucleons of the nucleus (if the atom is small enough), but primarily to its immediate neighbours due to the short range of the force. The nucleons in the interior of a nucleus have more neighboring nucleons than those on the surface. Since smaller nuclei have a larger surface area-to-volume ratio, the binding energy per nucleon due to the nuclear force generally increases with the size of the nucleus but approaches a limiting value corresponding to that of a nucleus with a diameter of about four nucleons. It is important to keep in mind that nucleons are quantum objects. So, for example, since two neutrons in a nucleus are identical to each other, the goal of distinguishing one from the other, such as which one is in the interior and which is on the surface, is in fact meaningless, and the inclusion of quantum mechanics is therefore necessary for proper calculations.

text: The electrostatic force, on the other hand, is an inverse-square force, so a proton added to a nucleus will feel an electrostatic repulsion from all the other protons in the nucleus. The electrostatic energy per nucleon due to the electrostatic force thus increases without limit as nuclei atomic number grows.

text: The net result of the opposing electrostatic and strong nuclear forces is that the binding energy per nucleon generally increases with increasing size, up to the elements iron and nickel, and then decreases for heavier nuclei. Eventually, the binding energy becomes negative and very heavy nuclei (all with more than 208 nucleons, corresponding to a diameter of about 6 nucleons) are not stable. The four most tightly bound nuclei, in decreasing order of binding energy per nucleon, are 62Ni, 58Fe, 56Fe, and 60Ni.[10] Even though the nickel isotope, 62Ni, is more stable, the iron isotope 56Fe is an order of magnitude more common. This is due to the fact that there is no easy way for stars to create 62Ni through the alpha process.

text: An exception to this general trend is the helium-4 nucleus, whose binding energy is higher than that of lithium, the next heaviest element. This is because protons and neutrons are fermions, which according to the Pauli exclusion principle cannot exist in the same nucleus in exactly the same state. Each proton or neutron's energy state in a nucleus can accommodate both a spin up particle and a spin down particle. Helium-4 has an anomalously large binding energy because its nucleus consists of two protons and two neutrons, so all four of its nucleons can be in the ground state. Any additional nucleons would have to go into higher energy states.  Indeed, the helium-4 nucleus is so tightly bound that it is commonly treated as a single particle in nuclear physics, namely, the alpha particle.

text: The situation is similar if two nuclei are brought together. As they approach each other, all the protons in one nucleus repel all the protons in the other. Not until the two nuclei actually come close enough for long enough so the strong nuclear force can take over (by way of tunneling) is the repulsive electrostatic force overcome. Consequently, even when the final energy state is lower, there is a large energy barrier that must first be overcome. It is called the Coulomb barrier.

text: The Coulomb barrier is smallest for isotopes of hydrogen, as their nuclei contain only a single positive charge. A diproton is not stable, so neutrons must also be involved, ideally in such a way that a helium nucleus, with its extremely tight binding, is one of the products.

text: Using deuterium-tritium fuel, the resulting energy barrier is about 0.1 MeV. In comparison, the energy needed to remove an electron from hydrogen is 13.6 eV, about 7500 times less energy. The (intermediate) result of the fusion is an unstable 5He nucleus, which immediately ejects a neutron with 14.1 MeV. The recoil energy of the remaining 4He nucleus is 3.5 MeV, so the total energy liberated is 17.6 MeV. This is many times more than what was needed to overcome the energy barrier.

text: The reaction cross section σ is a measure of the probability of a fusion reaction as a function of the relative velocity of the two reactant nuclei. If the reactants have a distribution of velocities, e.g. a thermal distribution, then it is useful to perform an average over the distributions of the product of cross section and velocity. This average is called the 'reactivity', denoted <σv>. The reaction rate (fusions per volume per time) is <σv> times the product of the reactant number densities:

text:
If a species of nuclei is reacting with a nucleus like itself, such as the DD reaction, then the product

n

1

n

2

{\displaystyle n_{1}n_{2}}

 must be replaced by

(
1

/

2
)

n

2

{\displaystyle (1/2)n^{2}}

.

text:
⟨
σ
v
⟩

{\displaystyle \langle \sigma v\rangle }

 increases from virtually zero at room temperatures up to meaningful magnitudes at temperatures of 10–100 keV. At these temperatures, well above typical ionization energies (13.6 eV in the hydrogen case), the fusion reactants exist in a plasma state.

text:
The significance of

⟨
σ
v
⟩

{\displaystyle \langle \sigma v\rangle }

 as a function of temperature in a device with a particular energy confinement time is found by considering the Lawson criterion.  This is an extremely challenging barrier to overcome on Earth, which explains why fusion research has taken many years to reach the current advanced technical state.[11]

text: Methods for achieving fusion[edit]

text: Thermonuclear fusion[edit]

text: If matter is sufficiently heated (hence being plasma), fusion reactions may occur due to collisions with extreme thermal kinetic energies of the particles. Thermonuclear weapons produce what amounts to an uncontrolled release of fusion energy. Controlled thermonuclear fusion energy has yet to be achieved.

text: Inertial confinement fusion[edit]

text: Inertial confinement fusion (ICF)  is a method aimed at releasing fusion energy by heating and compressing a fuel target, typically a pellet containing deuterium and tritium.

text: Inertial electrostatic confinement[edit]

text: Inertial electrostatic confinement is a set of devices that use an electric field to heat ions to fusion conditions.  The most well known is the fusor.  Starting in 1999, a number of amateurs have been able to do amateur fusion using these homemade devices.[12][13][14][15]  Other IEC devices include: the Polywell, MIX POPS[16] and Marble concepts.[17]

text: Beam-beam or beam-target fusion[edit]

text: If the energy to initiate the reaction comes from accelerating one of the nuclei, the process is called beam-target fusion; if both nuclei are accelerated, it is beam-beam fusion.

text: Accelerator-based light-ion fusion is a technique using particle accelerators to achieve particle kinetic energies sufficient to induce light-ion fusion reactions. Accelerating light ions is relatively easy, and can be done in an efficient manner—requiring only a vacuum tube, a pair of electrodes, and a high-voltage transformer; fusion can be observed with as little as 10 kV between the electrodes. The key problem with accelerator-based fusion (and with cold targets in general) is that fusion cross sections are many orders of magnitude lower than Coulomb interaction cross sections. Therefore, the vast majority of ions expend their energy emitting bremsstrahlung radiation and the ionization of atoms of the target. Devices referred to as sealed-tube neutron generators are particularly relevant to this discussion. These small devices are miniature particle accelerators filled with deuterium and tritium gas in an arrangement that allows ions of those nuclei to be accelerated against hydride targets, also containing deuterium and tritium, where fusion takes place, releasing a flux of neutrons. Hundreds of neutron generators are produced annually for use in the petroleum industry where they are used in measurement equipment for locating and mapping oil reserves.

text: Muon-catalyzed fusion[edit]

text: Muon-catalyzed fusion is a fusion process that occurs at ordinary temperatures. It was studied in detail by Steven Jones in the early 1980s. Net energy production from this reaction has been unsuccessful because of the high energy required to create muons, their short 2.2 µs half-life, and the high chance that a muon will bind to the new alpha particle and thus stop catalyzing fusion.[18]

text: Other principles[edit]

text: Some other confinement principles have been investigated.

text: Antimatter-initialized fusion uses small amounts of antimatter to trigger a tiny fusion explosion. This has been studied primarily in the context of making nuclear pulse propulsion, and pure fusion bombs feasible. This is not near becoming a practical power source, due to the cost of manufacturing antimatter alone.

text: Pyroelectric fusion was reported in April 2005 by a team at UCLA. The scientists used a pyroelectric crystal heated from −34 to 7 °C (−29 to 45 °F), combined with a tungsten needle to produce an electric field of about 25 gigavolts per meter to ionize and accelerate deuterium nuclei into an erbium deuteride target.  At the estimated energy levels,[19] the D-D fusion reaction may occur, producing helium-3 and a 2.45 MeV neutron. Although it makes a useful neutron generator, the apparatus is not intended for power generation since it requires far more energy than it produces.[20][21][22][23]

text:
Hybrid nuclear fusion-fission (hybrid nuclear power) is a proposed means of generating power  by use of a combination of nuclear fusion and fission processes. The concept dates to the 1950s, and was briefly advocated by Hans Bethe during the 1970s, but largely remained unexplored until a revival of interest in 2009, due to the delays in the realization of pure fusion.[24]
Project PACER, carried out at Los Alamos National Laboratory (LANL) in the mid-1970s, explored the possibility of a fusion power system that would involve exploding small hydrogen bombs (fusion bombs) inside an underground cavity. As an energy source, the system is the only fusion power system that could be demonstrated to work using existing technology. However it would also require a large, continuous supply of nuclear bombs, making the economics of such a system rather questionable.

text: Important reactions[edit]

text: Astrophysical reaction chains[edit]

text: At the temperatures and densities in stellar cores the rates of fusion reactions are notoriously slow. For example, at solar core temperature (T ≈ 15 MK) and density (160 g/cm3), the energy release rate is only 276 μW/cm3—about a quarter of the volumetric rate at which a resting human body generates heat.[25] Thus, reproduction of stellar core conditions in a lab for nuclear fusion power production is completely impractical. Because nuclear reaction rates depend on density as well as temperature and most fusion schemes operate at relatively low densities, those methods are strongly dependent on higher temperatures. The fusion rate as a function of temperature (exp(−E/kT)), leads to the need to achieve temperatures in terrestrial reactors 10–100 times higher temperatures than in stellar interiors: T ≈ 0.1–1.0×109 K.

text: Criteria and candidates for terrestrial reactions[edit]

text: In artificial fusion, the primary fuel is not constrained to be protons and higher temperatures can be used, so reactions with larger cross-sections are chosen. Another concern is the production of neutrons, which activate the reactor structure radiologically, but also have the advantages of allowing volumetric extraction of the fusion energy and tritium breeding. Reactions that release no neutrons are referred to as aneutronic.

text: To be a useful energy source, a fusion reaction must satisfy several criteria. It must:

text: Few reactions meet these criteria. The following are those with the largest cross sections:[26]

text:
(1)
21D
+
31T
→
42He
(
3.5 MeV
)
+
n0
(
14.1 MeV
)

(2i)
21D
+
21D
→
31T
(
1.01 MeV
)
+
p+
(
3.02 MeV
)

50%

(2ii)

→
32He
(
0.82 MeV
)
+
n0
(
2.45 MeV
)

50%

(3)
21D
+
32He
→
42He
(
3.6 MeV
)
+
p+
(
14.7 MeV
)

(4)
31T
+
31T
→
42He

+
2 n0

+
11.3 MeV

(5)
32He
+
32He
→
42He

+
2 p+

+
12.9 MeV

(6i)
32He
+
31T
→
42He

+
p+
+
n0

+
12.1 MeV

57%

(6ii)

→
42He
(
4.8 MeV
)
+
21D
(
9.5 MeV
)

43%

(7i)
21D
+
63Li
→
2 42He
+
22.4 MeV

(7ii)

→
32He
+
42He

+
n0

+
2.56 MeV

(7iii)

→
73Li
+
p+

+
5.0 MeV

(7iv)

→
74Be
+
n0

+
3.4 MeV

(8)
p+
+
63Li
→
42He
(
1.7 MeV
)
+
32He
(
2.3 MeV
)

(9)
32He
+
63Li
→
2 42He
+
p+

+
16.9 MeV

(10)
p+
+
115B
→
3 42He

+
8.7 MeV

text:
Nucleosynthesis
Stellar nucleosynthesis
Big Bang nucleosynthesis
Supernova nucleosynthesis
Cosmic ray spallation

Related topics
Astrophysics
Nuclear fusion
R-process
S-process
Nuclear fission
vte

text: For reactions with two products, the energy is divided between them in inverse proportion to their masses, as shown. In most reactions with three products, the distribution of energy varies. For reactions that can result in more than one set of products, the branching ratios are given.

text: Some reaction candidates can be eliminated at once. The D-6Li reaction has no advantage compared to p+-115B because it is roughly as difficult to burn but produces substantially more neutrons through 21D-21D side reactions. There is also a p+-73Li reaction, but the cross section is far too low, except possibly when Ti > 1 MeV, but at such high temperatures an endothermic, direct neutron-producing reaction also becomes very significant. Finally there is also a p+-94Be reaction, which is not only difficult to burn, but 94Be can be easily induced to split into two alpha particles and a neutron.

text: In addition to the fusion reactions, the following reactions with neutrons are important in order to "breed" tritium in "dry" fusion bombs and some proposed fusion reactors:

text:
n0
+
63Li
→
31T
+
42He + 4.784 MeV

n0
+
73Li
→
31T
+
42He + n0 – 2.467 MeV

text: The latter of the two equations was unknown when the U.S. conducted the Castle Bravo fusion bomb test in 1954. Being just the second fusion bomb ever tested (and the first to use lithium), the designers of the Castle Bravo "Shrimp" had understood the usefulness of Lithium-6 in tritium production, but had failed to recognize that Lithium-7 fission would greatly increase the yield of the bomb. While Li-7 has a small neutron cross-section for low neutron energies, it has a higher cross section above 5 MeV.[27]  The 15 Mt yield was 150% greater than the predicted 6 Mt and caused unexpected exposure to fallout.

text: To evaluate the usefulness of these reactions, in addition to the reactants, the products, and the energy released, one needs to know something about the cross section. Any given fusion device has a maximum plasma pressure it can sustain, and an economical device would always operate near this maximum. Given this pressure, the largest fusion output is obtained when the temperature is chosen so that <σv>/T2 is a maximum. This is also the temperature at which the value of the triple product nTτ required for ignition is a minimum, since that required value is inversely proportional to <σv>/T2 (see Lawson criterion). (A plasma is "ignited" if the fusion reactions produce enough power to maintain the temperature without external heating.) This optimum temperature and the value of <σv>/T2 at that temperature is given for a few of these reactions in the following table.

text:
fuel
T [keV]
<σv>/T2 [m3/s/keV2]

21D-31T
13.6
1.24×10−24

21D-21D
15
1.28×10−26

21D-32He
58
2.24×10−26

p+-63Li
66
1.46×10−27

p+-115B
123
3.01×10−27

text: Note that many of the reactions form chains. For instance, a reactor fueled with 31T and 32He creates some 21D, which is then possible to use in the 21D-32He reaction if the energies are "right". An elegant idea is to combine the reactions (8) and (9). The 32He from reaction (8) can react with 63Li in reaction (9) before completely thermalizing. This produces an energetic proton, which in turn undergoes reaction (8) before thermalizing. Detailed analysis shows that this idea would not work well,[citation needed] but it is a good example of a case where the usual assumption of a Maxwellian plasma is not appropriate.

text: Neutronicity, confinement requirement, and power density[edit]

text: Any of the reactions above can in principle be the basis of fusion power production. In addition to the temperature and cross section discussed above, we must consider the total energy of the fusion products Efus, the energy of the charged fusion products Ech, and the atomic number Z of the non-hydrogenic reactant.

text: Specification of the 21D-21D reaction entails some difficulties, though. To begin with, one must average over the two branches (2i) and (2ii). More difficult is to decide how to treat the 31T and 32He products. 31T burns so well in a deuterium plasma that it is almost impossible to extract from the plasma. The 21D-32He reaction is optimized at a much higher temperature, so the burnup at the optimum 21D-21D temperature may be low. Therefore, it seems reasonable to assume the 31T but not the 32He gets burned up and adds its energy to the net reaction, which means the total reaction would be the sum of (2i), (2ii), and (1):

text: For calculating the power of a reactor (in which the reaction rate is determined by the D-D step), we count the 21D-21D fusion energy per D-D reaction as Efus = (4.03 MeV + 17.6 MeV)×50% + (3.27 MeV)×50% = 12.5 MeV and the energy in charged particles as Ech = (4.03 MeV + 3.5 MeV)×50% + (0.82 MeV)×50% = 4.2 MeV. (Note: if the tritium ion reacts with a deuteron while it still has a large kinetic energy, then the kinetic energy of the helium-4 produced may be quite different from 3.5 MeV,[28] so this calculation of energy in charged particles is only an approximation of the average.) The amount of energy per deuteron consumed is 2/5 of this, or 5.0 MeV (a specific energy of about 225 million MJ per kilogram of deuterium).

text: Another unique aspect of the 21D-21D reaction is that there is only one reactant, which must be taken into account when calculating the reaction rate.

text: With this choice, we tabulate parameters for four of the most important reactions

text:
fuel
Z
Efus [MeV]
Ech [MeV]
neutronicity

21D-31T
1
17.6
3.5
0.80

21D-21D
1
12.5
4.2
0.66

21D-32He
2
18.3
18.3
≈0.05

p+-115B
5
8.7
8.7
≈0.001

text: The last column is the neutronicity of the reaction, the fraction of the fusion energy released as neutrons. This is an important indicator of the magnitude of the problems associated with neutrons like radiation damage, biological shielding, remote handling, and safety. For the first two reactions it is calculated as (Efus-Ech)/Efus. For the last two reactions, where this calculation would give zero, the values quoted are rough estimates based on side reactions that produce neutrons in a plasma in thermal equilibrium.

text: Of course, the reactants should also be mixed in the optimal proportions. This is the case when each reactant ion plus its associated electrons accounts for half the pressure. Assuming that the total pressure is fixed, this means that particle density of the non-hydrogenic ion is smaller than that of the hydrogenic ion by a factor 2/(Z+1). Therefore, the rate for these reactions is reduced by the same factor, on top of any differences in the values of <σv>/T2. On the other hand, because the 21D-21D reaction has only one reactant, its rate is twice as high as when the fuel is divided between two different hydrogenic species, thus creating a more efficient reaction.

text: Thus there is a "penalty" of (2/(Z+1)) for non-hydrogenic fuels arising from the fact that they require more electrons, which take up pressure without participating in the fusion reaction. (It is usually a good assumption that the electron temperature will be nearly equal to the ion temperature. Some authors, however discuss the possibility that the electrons could be maintained substantially colder than the ions. In such a case, known as a "hot ion mode", the "penalty" would not apply.) There is at the same time a "bonus" of a factor 2 for 21D-21D because each ion can react with any of the other ions, not just a fraction of them.

text: We can now compare these reactions in the following table.

text:
fuel
<σv>/T2
penalty/bonus
inverse reactivity
Lawson criterion
power density (W/m3/kPa2)
inverse ratio of power density

21D-31T
1.24×10−24
1
1
1
34
1

21D-21D
1.28×10−26
2
48
30
0.5
68

21D-32He
2.24×10−26
2/3
83
16
0.43
80

p+-63Li
1.46×10−27
1/2
1700

0.005
6800

p+-115B
3.01×10−27
1/3
1240
500
0.014
2500

text: The maximum value of <σv>/T2 is taken from a previous table. The "penalty/bonus" factor is that related to a non-hydrogenic reactant or a single-species reaction. The values in the column "inverse reactivity" are found by dividing 1.24×10−24 by the product of the second and third columns. It indicates the factor by which the other reactions occur more slowly than the 21D-31T reaction under comparable conditions. The column "Lawson criterion" weights these results with Ech and gives an indication of how much more difficult it is to achieve ignition with these reactions, relative to the difficulty for the 21D-31T reaction. The next-to-last column is labeled "power density" and weights the practical reactivity by Efus. The final column indicates how much lower the fusion power density of the other reactions is compared to the 21D-31T reaction and can be considered a measure of the economic potential.

text: Bremsstrahlung losses in quasineutral, isotropic plasmas[edit]

text: The ions undergoing fusion in many systems will essentially never occur alone but will be mixed with electrons that in aggregate neutralize the ions' bulk electrical charge and form a plasma. The electrons will generally have a temperature comparable to or greater than that of the ions, so they will collide with the ions and emit x-ray radiation of 10–30 keV energy, a process known as Bremsstrahlung.

text: The huge size of the Sun and stars means that the x-rays produced in this process will not escape and will deposit their energy back into the plasma. They are said to be opaque to x-rays. But any terrestrial fusion reactor will be optically thin for x-rays of this energy range. X-rays are difficult to reflect but they are effectively absorbed (and converted into heat) in less than mm thickness of stainless steel (which is part of a reactor's shield). This means the bremsstrahlung process is carrying energy out of the plasma, cooling it.

text: The ratio of fusion power produced to x-ray radiation lost to walls is an important figure of merit. This ratio is generally maximized at a much higher temperature than that which maximizes the power density (see the previous subsection). The following table shows estimates of the optimum temperature and the power ratio at that temperature for several reactions:

text:
fuel
Ti (keV)
Pfusion/PBremsstrahlung

21D-31T
50
140

21D-21D
500
2.9

21D-32He
100
5.3

32He-32He
1000
0.72

p+-63Li
800
0.21

p+-115B
300
0.57

text: The actual ratios of fusion to Bremsstrahlung power will likely be significantly lower for several reasons. For one, the calculation assumes that the energy of the fusion products is transmitted completely to the fuel ions, which then lose energy to the electrons by collisions, which in turn lose energy by Bremsstrahlung. However, because the fusion products move much faster than the fuel ions, they will give up a significant fraction of their energy directly to the electrons. Secondly, the ions in the plasma are assumed to be purely fuel ions. In practice, there will be a significant proportion of impurity ions, which will then lower the ratio. In particular, the fusion products themselves must remain in the plasma until they have given up their energy, and will remain some time after that in any proposed confinement scheme. Finally, all channels of energy loss other than Bremsstrahlung have been neglected. The last two factors are related. On theoretical and experimental grounds, particle and energy confinement seem to be closely related. In a confinement scheme that does a good job of retaining energy, fusion products will build up. If the fusion products are efficiently ejected, then energy confinement will be poor, too.

text: The temperatures maximizing the fusion power compared to the Bremsstrahlung are in every case higher than the temperature that maximizes the power density and minimizes the required value of the fusion triple product. This will not change the optimum operating point for 21D-31T very much because the Bremsstrahlung fraction is low, but it will push the other fuels into regimes where the power density relative to 21D-31T is even lower and the required confinement even more difficult to achieve. For 21D-21D and 21D-32He, Bremsstrahlung losses will be a serious, possibly prohibitive problem. For 32He-32He, p+-63Li and p+-115B the Bremsstrahlung losses appear to make a fusion reactor using these fuels with a quasineutral, isotropic plasma impossible. Some ways out of this dilemma are considered—and rejected—in fundamental limitations on plasma fusion systems not in thermodynamic equilibrium.[29][30]  This limitation does not apply to non-neutral and anisotropic plasmas; however, these have their own challenges to contend with.

text: Mathematical description[edit]

text: To determine the rate of fusion reactions, the value of most interest is the cross section, which describes the probability that particle with fuse by giving a characteristic area of interaction. In a classical picture, the cross section is the radius of the nuclei  (on order of a femtometer) and can only occur when the particles have enough energy to overcome the Coulomb barrier and approach within this radius (Needing energy on the order of a MeV). This greatly overestimates the energy needed for fusion reactions to occur because it doesn't include quantum effects of the smeared radius as the DeBroglie wavelength as well as quantum tunnelling. An estimation of the fusion cross section is often broken into three pieces:

text:
Where

σ

g
e
o
m
e
t
r
y

{\displaystyle \sigma _{geometry}}

 is the geometric cross section, T is the barrier transparency and R is the reaction characteristics of the reaction.

text:
σ

g
e
o
m
e
t
r
y

{\displaystyle \sigma _{geometry}}

 is of the order of the square of the de-Broglie wavelength

σ

g
e
o
m
e
t
r
y

≈

λ

2

=

(

ℏ

2

m

r

v

)

2

∝

1
ϵ

{\displaystyle \sigma _{geometry}\approx \lambda ^{2}={\bigg (}{\frac {\hbar ^{2}}{m_{r}v}}{\bigg )}^{2}\propto {\frac {1}{\epsilon }}}

 where

m

r

{\displaystyle m_{r}}

 is the reduced mass of the system and

ϵ

{\displaystyle \epsilon }

 is the center of mass energy of the system.

text:
T can be approximated by the Gamow transparency, which has the form:

T
≈

e

−

ϵ

G

/

ϵ

{\displaystyle T\approx e^{-{\sqrt {\epsilon _{G}/\epsilon }}}}

 where

ϵ

G

=
(
π
α

Z

1

Z

2

)

2

×
2

m

r

c

2

{\displaystyle \epsilon _{G}=(\pi \alpha Z_{1}Z_{2})^{2}\times 2m_{r}c^{2}}

 is the Gamow factor.

text:
R contains all the nuclear physics of the specific reaction and takes very different values depending on the nature of the interaction. However, for most reactions, the variation of

R
(
ϵ
)

{\displaystyle R(\epsilon )}

 is small compared to the variation from the Gamow factor and so is approximated by a function called the Astrophysical S-factor,

S
(
ϵ
)

{\displaystyle S(\epsilon )}

, which is weakly varying in energy. Putting these dependencies together, one estimation for the fusion cross section as a function of energy takes the form:


document_title: Once Upon a Time (TV series)

question_text: where is the tv series once upon a time filmed

question_tokens: where is the tv series once upon a time filmed

root

text: Once Upon a Time (TV series)

text: Series overview[edit]

text: For the first six seasons, the series originally took place in the fictional seaside town of Storybrooke, Maine, in which the residents are actually characters from various fairy tales and other stories that were transported to the real world town and robbed of their original memories by the Evil Queen Regina (Lana Parrilla) who used a powerful curse obtained from Rumplestiltskin (Robert Carlyle). The residents of Storybrooke, where Regina is mayor, have lived an unchanging existence for 28 years, unaware of their own lack of aging. The town's only hope lies with a bail-bonds person named Emma Swan (Jennifer Morrison), the daughter of Snow White (Ginnifer Goodwin) and Prince Charming (Josh Dallas), who was transported from the Enchanted Forest to the real world via a magic tree as an infant before she could be cursed. As such, she is the only person who can break the curse and restore the characters' lost memories. She is aided by her son, Henry (Jared S. Gilmore), with whom she was recently reunited after giving him up for adoption upon his birth, and his Once Upon a Time book of fairy tales that holds the key to breaking the curse. Henry is also the adopted son of Regina, providing a source of both conflict and common interest between the two women.

tag: p

text: In the seventh season reboot, an adult Henry Mills (Andrew J. West), along with Regina, Captain Hook (Colin O'Donoghue) and Rumplestiltskin, are found years later in the Seattle neighborhood of Hyperion Heights, where characters from a different realm were brought under a new curse. Hoping to restore her family's memories, Lucy (Alison Fernandez) must convince her parents, Henry and Cinderella (Dania Ramirez), of the true nature of Hyperion Heights, in the midst of emerging dangers involving Lady Tremaine (Gabrielle Anwar) and Mother Gothel (Emma Booth).

text: Episodes usually have one segment that details the characters' past lives that, when serialized, adds a piece to the puzzle about the characters and their connection to the events that preceded the curse and its consequences. The other, set in the present day, follows a similar pattern with a different outcome but also offers similar insights.

text: Season 1 (2011–12)[edit]

text: The first season premiered on October 23, 2011. The Evil Queen interrupts the wedding of Snow White and Prince Charming to announce that she will cast a curse on everyone that will leave her with the only happy ending. The majority of the characters are transported to the town of Storybrooke, Maine, where they have been stripped of their original memories and identities as fairy tale characters. On her 28th birthday, Emma Swan, the daughter of Snow White and Prince Charming, is brought to Storybrooke by her biological son Henry Mills in the hopes of breaking the curse cast by his adoptive mother, the Evil Queen Regina.

text: Season 2 (2012–13)[edit]

text: The second season premiered on September 30, 2012.[8] Despite Emma having broken the curse, the characters are not returned to the fairy tale world, and must deal with their own dual identities. With the introduction of magic into Storybrooke by Mr. Gold, the fates of the two worlds become intertwined, and new threats emerge in the form of Captain Hook (Colin O'Donoghue), Regina's mother Cora (Barbara Hershey), also known as the Queen of Hearts, and sinister operatives from the real world with an agenda to destroy magic.

text: Season 3 (2013–14)[edit]

text: The third season premiered on September 29, 2013. It was split into two volumes, with the first eleven episodes running from September to December 2013, and the later half from March to May 2014. In the first volume, the main characters travel to Neverland to rescue Henry, who has been kidnapped by Peter Pan (Robbie Kay) as part of a plan to obtain the "Heart of the Truest Believer" from him. Their increasing power struggle with Pan continues in Storybrooke, which ultimately results in the complete reversal of the original curse. All the characters are returned to their original worlds, leaving Emma and Henry to escape to New York City. In the second volume, the characters are mysteriously brought back to a recreated Storybrooke with their memories of the previous year removed, and the envious Wicked Witch of the West (Rebecca Mader) from the Land of Oz appears with a plan to change the past. Once again, Emma is needed to save her family.

text: Season 4 (2014–15)[edit]

text: The fourth season premiered on September 28, 2014. It was also split into two volumes, with the first eleven episodes running from September to December 2014, and the later half from March to May 2015. A new storyline incorporating elements from Frozen was revealed when the time travel events of the previous season lead to the accidental arrival of Elsa (Georgina Haig) from the Enchanted Forest of the past to present-day Storybrooke. As she searches for her sister Anna (Elizabeth Lail) with the aid of the main characters, they encounter the Snow Queen (Elizabeth Mitchell).[9] Meanwhile, Regina seeks the Author of Henry's Once Upon a Time book so that she can finally have her happy ending. However, Mr. Gold, with the help of Cruella De Vil (Victoria Smurfit), Maleficent (Kristin Bauer van Straten), and Ursula (Merrin Dungey), has his own plan to rewrite the rules governing the fates of all heroes and villains. Henry and Emma race to restore reality and the truth before the twisted inversion becomes permanent. However, the price leads to the ultimate sacrifice.

text: Season 5 (2015–16)[edit]

text: The fifth season was announced on May 7, 2015,[10] and premiered on September 27, 2015. It was once again split into two volumes with the first volume ran from September to December 2015, and the second volume from March to May 2016. The characters embark on a quest to Camelot to find the Sorcerer Merlin (Elliot Knight) in order to free Emma from the powers of an ancient darkness that threatens to destroy everything. To complicate matters, King Arthur (Liam Garrigan) is determined to forever alter the balance between light and darkness using the legendary Excalibur. As history and destiny collide, unsuspected consequences lead the characters to the Underworld where they encounter souls of those with unfinished business and must face Hades (Greg Germann). In an attempt to restore order to the chaos that has culminated, the characters' dangerous manipulations of magic lead to an exacerbation of the war between light and darkness, with the separation of Regina and her Evil Queen persona, as well as the arrival of Dr. Jekyll (Hank Harris) and Mr. Hyde (Sam Witwer).

text: Season 6 (2016–17)[edit]

text: The sixth season was announced on March 3, 2016, and premiered on September 25, 2016. The characters must defend Storybrooke from the combined threat of Mr. Hyde and an unleashed Evil Queen and the mysterious fate of saviors leads to Emma learning about Aladdin (Deniz Akdeniz).[11] The ongoing war between light and darkness ultimately leads to the arrival of the Black Fairy (Jaime Murray) as well as the final battle that was prophesied before the casting of the original curse.

text: Season 7 (2017)[edit]

text: In May 2017, the series was renewed for a seventh season consisting of 22 episodes,[12] which marks the beginning of a soft reboot.[13][14][15] Years later, Lucy (Alison Fernandez) arrives in the neighborhood of Hyperion Heights in Seattle, Washington with her Once Upon a Time book to find her father Henry Mills (Andrew J. West) who is needed by his family.[16][17][18] Characters from the New Enchanted Forest[19] were brought to Hyperion Heights under a new curse and are caught in a rising conflict involving Cinderella (Dania Ramirez) and Lady Tremaine (Gabrielle Anwar) whose dangerous history with Mother Gothel (Emma Booth) is also revealed.

text: Episodes[edit]

text:
Season
Episodes
Originally aired
Nielsen ratings

First aired
Last aired
Viewers
(millions)
Viewers
rank
18–49
rating/share
18-49
rank

1
22
October 23, 2011 (2011-10-23)
May 13, 2012 (2012-05-13)
11.71
28[20]
4.1/10
18[21]

2
22
September 30, 2012 (2012-09-30)
May 12, 2013 (2013-05-12)
10.24
35[22]
3.6/9
18[23]

3
22
September 29, 2013 (2013-09-29)
May 11, 2014 (2014-05-11)
9.38
35[24]
3.3/8
12[25]

4
22
September 28, 2014 (2014-09-28)
May 10, 2015 (2015-05-10)
8.98
50[26]
3.2/7
17[26]

5
23
September 27, 2015 (2015-09-27)
May 15, 2016 (2016-05-15)
6.32
69[27]
2.2/7
34[27]

6
22
September 25, 2016 (2016-09-25)
May 14, 2017 (2017-05-14)
4.39
105[28]
1.5/5
70[28]

7
22[29]
October 6, 2017 (2017-10-06)
TBA
TBA
TBA
TBA
TBA

tag: table

text: Once Upon a Time's first season received "generally favorable" reviews from critics. Metacritic gave it a score of 66 out of 100 based on 26 reviews. The pilot episode was watched by 12.93 million viewers and achieved an adult 18–49 rating/share of 4.0/10. The second season premiered on September 30, 2012, to an audience of 11.36 million viewers, while the third season began on September 29, 2013, opening to 8.52 million viewers. In May 2014, ABC renewed the show for its fourth season, premiering in September 2014 to an audience of 9.47 million viewers. The series was renewed for a fifth season in May 2015 and for a sixth season in March 2016.[30] On May 11, 2017, ABC renewed the series for a 22-episode seventh season.[31]

text: Cast[edit]

text:
Ginnifer Goodwin as Snow White / Mary Margaret Blanchard (seasons 1–6)[32][33]
Jennifer Morrison as Emma Swan (seasons 1–6)[32][33][34]
Lana Parrilla as Evil Queen / Regina Mills / Roni[32][35]
Josh Dallas as Pauper[36] / Prince Charming / David Nolan (seasons 1–6)[32][33]
Jared S. Gilmore as Henry Mills (seasons 1–6)[33][37]
Raphael Sbarge as Jiminy Cricket / Dr. Archibald Hopper (main season 1; recurring seasons 2–3, 6)
Jamie Dornan as Huntsman / Sheriff Graham Humbert (season 1)
Robert Carlyle as Rumplestiltskin / Crocodile / Beast / Mr. Gold[32] / Weaver
Eion Bailey as Pinocchio / August Wayne Booth (main season 1; recurring seasons 2, 4, 6)
Emilie de Ravin as Belle / Lacey (main seasons 2–6; recurring season 1)[32][33][38]
Meghan Ory as Red Riding Hood / Wolf / Ruby (main season 2; recurring seasons 1, 3, 5)[39]
Colin O'Donoghue as Killian Jones / Captain Hook / Rogers (seasons 2–)[32]
Michael Raymond-James as Baelfire / Neal Cassidy (main season 3; recurring season 2)
Michael Socha as Will Scarlet / Knave of Hearts / White King (season 4)
Rebecca Mader as Zelena / Wicked Witch of the West / Kelly (main seasons 5–6; recurring seasons 3–4, 7)[32][40][41]
Sean Maguire as Robin Hood (main season 5; recurring season 3–4, 6)[32][40]
Andrew J. West as Henry Mills (season 7)
Dania Ramirez as Cinderella / Jacinda (season 7)
Gabrielle Anwar as Rapunzel / Lady Tremaine / Victoria Belfrey (season 7)
Alison Fernandez as Lucy (season 7)
Mekia Cox as Tiana / Sabine (season 7)

tag: ul

text: Development and production[edit]

text: Conception[edit]

text: Adam Horowitz and Edward Kitsis conceived the show in 2004 before joining the writing staff of Lost, but wanted to wait until that series was over to focus on this project.[42]

text:
The idea is to take these characters that we all know collectively and try to find things about them that we haven't explored before. Sometimes it's a story point, sometimes it's a thematic connection, sometimes it's a dilemma they face in both worlds that is similar. We are not generally retelling the exact same story as the fairy tale world.
“
”

— Executive producer Adam Horowitz[43]

tag: div

text: Eight years before the Once Upon a Time pilot (the two had just completed their work on Felicity, in 2002), Kitsis and Horowitz became inspired to write fairy tales out of a love of "mystery and excitement of exploring lots of different worlds."[44] They presented the premise to networks, but were refused because of its fantastic nature.[45] From their time on Lost, the writers learned to look at the story in a different way,[45] namely that "character has to trump mythology."[43]

text: They explained,

text: "As people, you've got to see what the void in their heart or in their lives is to care about them ... For us, this was as much about the character journeys and seeing what was ripped from them in coming to Storybrooke – going at it that way as opposed to making it the 'break-the-curse show.'"[46]

text: Despite the comparisons and similarities to Lost, the writers intend them to be very different shows.[45] To them, Lost concerned itself with redemption, while Once Upon a Time is about "hope".[47] Lost co-creator Damon Lindelof aids in the development of the series as a consultant, but has no official credit on the show. Kitsis and Horowitz have called him a "godfather" to the series.[48][49] To differentiate the storytelling from what the audience already knew, the writing staff decided to begin the pilot with the end of the typical Snow White fairytale.[46] Themes concerning family and motherhood were emphasized, in contrast to the focus on fatherhood in Lost. Kitsis and Horowitz sought to write strong female characters, rather than the classic damsel in distress. Horowitz stated their desire to approach each character the same way, asking themselves, "How do we make these icons real, make them relatable?"[45]

text: The pilot is meant to be the "template of the series".[44] Kitsis confirmed that every week will contain flashbacks between both worlds,[43] as they "love the idea of going back and forth and informing what the character is missing in their life."[50] The writers' desire to present a "mash up" of many small characters can be seen in a scene of the pilot, in which there is a war council featuring Geppetto, Pinocchio, and Grumpy. Horowitz elaborated, "One of the fun things for us coming up with these stories is thinking of ways these different characters can interact in ways they never have before."[45] Since then, the creators have added more elements, and given its ties to Disney, have managed to expand the universe to include more recent material, by throwing out hints that they might look ahead at incorporating characters from Brave and Frozen in future episodes, if they get the green light from Disney.[51] The Season 3 finale introduced Elsa in the final minutes of the episode.[52]

text: The general premise, importing the Snow White core characters into the "real world", was previously seen on ABC television in the short-lived 1980s comedy The Charmings. The show also has a similar premise to Bill Willingham's ten-year-old comic series Fables, to which ABC bought the rights in 2008 but never made it past planning stages. After Fables fans raised controversy over possible appropriation, the show writers initially denied a link, but later said they may have "read a couple issues" of the comic book but while the two concepts are "in the same playground", they are "telling a different story."[50] Bill Willingham responded to the controversy in an interview, where he stated he did not feel the show was plagiarism and said: "Maybe they did remember reading Fables back then, but didn't want to mention it because we've become a very litigious people."[50][53]

text: Casting[edit]

text: Secondary character casting director, Samuel Forsyth, started the casting process in 2010. Horowitz stated that everyone they initially wanted for roles in the series accepted their roles after being sent a script.[44][45] Ginnifer Goodwin was cast as Snow White / Mary Margaret Blanchard,[54] who appreciated that she would be playing a strong character that was fleshed out for the audience. Goodwin had stated in interviews that she would love to play Snow White, and called her acceptance of the role "a no-brainer."[55] Both Kitsis and Horowitz are self-described big fans of Goodwin's previous series, Big Love, and wrote the part of Snow White with her in mind.[45] Josh Dallas, who portrays Prince Charming / David Nolan, was pleased the writers took "some dramatic license" with his character, believing the prince had become more real. He explained,

text: "Prince Charming just happens to be a name. He's still a man with the same emotions as any other man. He's a Prince, but he's a Prince of the people. He gets his hands dirty. He's got a kingdom to run. He has a family to protect. He has an epic, epic love for Snow White. He's like everybody else. He's human."[55]

text: Jennifer Morrison was hired for the part of Emma Swan.[56] The actress explained her character as someone who "help[s] her son Henry whom she abandoned when he was a baby and who seems like he's a little bit emotionally dysfunctional", but noted that Emma does not start out believing in the fairytale universe.[55] Ten-year old Jared Gilmore, known for his work on Mad Men, took the role of her son, Henry.[56] The role of The Evil Queen/ Regina was given to Lana Parrilla.[57]

text:
"There's always two stories being told when playing Regina. There's the threat of her knowing she's an evil queen and then there's just the pure simple fact that the biological mother has stepped into her world and the threat of losing her son is just enormous. That's a fear that I think any adopted mother would have. I think that's going to really help the audience relate to Regina in some level."

—Lana Parrilla[55]

text: The role of Rumplestiltskin / Mr. Gold was given to Robert Carlyle,[58] after having been written with him in mind, though the writers initially thought he would not accept the part.[43] Horowitz recalled Carlyle's prison sequence, which was the actor's first day on the set as "mind-blowing ... You could see Ginny actually jump, the first time he did that character. It was fantastic!"[44] Jamie Dornan portrayed the Huntsman / Sheriff Graham[59] as a series regular before being killed off in the seventh episode,[60] while Eion Bailey was cast as Pinocchio / August Wayne Booth[59] in a recurring role,[61] starting in the show's ninth episode, "True North", where he was credited as "Stranger", he was promoted to series regular status for the fifteenth episode, "Red-Handed".[62] Raphael Sbarge portrayed Jiminy Cricket / Dr. Archie Hopper.[59]

text: For the second season, Meghan Ory and Emilie de Ravin were promoted to series regulars as Red Riding Hood / Ruby[63] and Belle / Lacey[64] respectively, while Bailey made guest appearances in two episodes after departing the series[65][66] and Sbarge joined the recurring cast.[67] Colin O'Donoghue was cast as Captain Killian "Hook" Jones,[68] and was upped to series regular for the fourteenth episode of the season.[69]

text: For the third season, Michael Raymond-James was promoted to a series regular as Neal Cassidy,[70] while Ory did not return as a series regular due to commitments to the TV series, Intelligence.[71]

text: For the fourth season, Michael Socha was brought onto the show as Will Scarlet / Knave of Hearts from the show's spin-off, Once Upon a Time in Wonderland,[72][73] while Raymond-James was dropped from the regular cast[74] when the writers decided to kill off his character.[74] Bailey returned in a recurring arc towards the end of the season after being absent from the show since the second season.[75]

text: For the fifth season, Rebecca Mader[40] and Sean Maguire[40] were announced to have been promoted to series regulars as Zelena / Wicked Witch of the West and Robin Hood respectively, while Socha was confirmed to not be returning as a series regular.[76] Ory also returned to the series in a recurring capacity after being absent since the third-season finale.[39]

text: Before the series was renewed for a seventh season, Jennifer Morrison announced that, if the series were to be renewed, she would not be returning as a series regular for that season but agreed to return for one episode to wrap up Emma Swan's storyline.[77] Later that week, actress Rebecca Mader announced that she would also be leaving the series after the sixth season wrapped. It was later announced that Ginnifer Goodwin, Josh Dallas, Jared S. Gilmore and Emilie de Ravin would also be leaving the show after the sixth season's finale aired. Along with departures, Andrew J. West and Alison Fernandez were announced to be joining the seventh season of the show as series regulars after guest starring in the previous season's finale. They will portray an older Henry Mills and his daughter Lucy respectively. In July 2017, actresses Dania Ramirez and Gabrielle Anwar were announced to be joining the cast of the seventh season as series regulars, playing new iterations of Cinderella and Lady Tremaine, respectively. In September 2017, Mekia Cox, who portrays Tiana, was promoted to a series regular.[78]

text: Filming[edit]

text: Principal photography for the series takes place in Vancouver, British Columbia.[79][80] The village of Steveston in the adjacent city of Richmond doubles as Storybrooke for the series, with props and exterior sets disguising the existing businesses and buildings. During filming, all brightly-colored objects (flowers, etc.) are hidden to reinforce the story village's spell-subdued character. Certain sets are additionally filmed in separate studios, including the interior of Mr. Gold's pawn shop and the clock tower, which are not found in Steveston.[81]

text: Setting[edit]

text: This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2016) (Learn how and when to remove this template message)

text: Main settings[edit]

text: During the first six seasons, the Enchanted Forest was one of the main setting of the series. The Enchanted Forest is a realm within Fairy Tale Land, but the actual spread and scope of the realm is not known. However, they were later united during the Ogre Wars, which played a part in the formation of the War Council that was formed by Prince Charming and served as the catalysts in the backstories involving Rumpelstiltskin and the Evil Queen. Several independent kingdoms are implied by an array of different rulers. Most of the stories detailed their earlier lives before ascension to power and being influenced by their mentors through their upbringings.

text: The Land Without Magic, commonly known as the Real World, is another main setting, shown as a place devoid with magic, and not connected to the others. It is often said that travelling to the Land Without Magic is hard, but possible, such as magical doors created by the Apprentice, magic beans, or the Dark Curse. During the first six seasons, Storybrooke, Maine was the main setting, serving as an isolated town separated from the rest of the world, where the cursed inhabitants are trapped by various forces. During the series’ seventh season, the setting shifted to Hyperion Heights, Seattle, where unlike Storybrooke, its cursed inhabitants are living among ordinary people.

text: During the seventh season, the New Enchanted Forest[82] is shown as the main setting, alongside with Hyperion Heights. As a world of its own, it is divided into several independent kingdoms with different rulers. The inhabitants are in-conflict with each other, most notably between Cinderella, Lady Tremaine, Drizella, a resistance led by Tiana, and the Coven of the Eight led by Mother Gothel. Most flashbacks shown are involving events happened before the original curse and before the latest curse that brought everyone to Hyperion Heights.

text: Expanded settings[edit]

text: The realms and worlds featured in the series are mostly based on many fairy tales, mythologies and real life locations and are magical, unlike the real world which is dubbed the Land Without Magic. Just like the Enchanted Forest, the other realms and worlds were affected by the Evil Queen’s curse, but indirectly, merely freezing them in time and state for twenty-eight years.

text: Some of the worlds within the universe are mostly based fairy tales where witchcraft plays a vital role in the lands. Known worlds are Fairy Tale Land,[83] Wonderland,[83] Neverland,[83] the Land of Oz,[83] the Book Realm,[84] the Land of Untold Stories,[83] the World Behind the Mirror,[85] the Dark Realm,[86] the Wish Realm,[86] the New Enchanted Forest,[87] the Edge of Realms,[88] and New Wonderland.[89]

text: There are also worlds known as the Realms of Storytelling.[90] These realms are mostly based on the Land Without Magic, taking the name of a certain location and a certain time period. Known worlds are the Land Without Color,[83] 19th Century London,[91] Victorian England,[92] Kansas,[93] 1920s England,[94] 19th Century France,[95] and the Land Without Stories.[96]

text: Additionally, several spiritual worlds exist in the universe. These worlds are known to not sustain living inhabitants, merely souls of the living in some and the deceased in others, with exception of the deities. Such worlds are the Dreamscape,[97] the Netherworld,[98] the Underworld,[99] the Worst Place,[100] and Mount Olympus.[101]

text: Cultural references[edit]

text: As a nod to the ties between the production teams of Once Upon a Time and Lost, the former show contains allusions to Lost, and is expected to continue alluding to Lost throughout its run.[50] For example, many items found in the Lost universe, such as Apollo candy bars, Oceanic Airlines, Ajira Airways, the TV series Exposé and MacCutcheon Whiskey, can be seen in Once Upon a Time.[102]

text: Music[edit]

text: Mark Isham composed the series' theme and music. On February 14, 2012, an extended play album featuring four cues from the score was released by ABC Studios.[103] On May 1, 2012, a full-length 25-track official soundtrack album was released by Intrada Records to accompany season one.[104] On August 13, 2013, another full-length 25-track official soundtrack album was released by Intrada to accompany season two.[105] Since December 2015, Mark Isham had begun to release music that was previously not released from the third, fourth and fifth seasons on his Soundcloud account.

text:
[show]Season 1 Soundtrack

No.
Title
Length

1.
"Once Upon a Time Orchestral Suite"
4:13

2.
"Henry's Proposal"
1:17

3.
"The Queen's Curse"
2:46

4.
"Jiminy Cricket"
3:11

5.
"Dealing With Rumplestiltskin"
3:26

6.
"Belle's Story"
2:37

7.
"Dwarves"
2:45

8.
"The Huntsman"
4:31

9.
"Things Are Changing in Storybrooke"
1:47

10.
"Cinderella"
1:44

11.
"Wedding Dance"
1:21

12.
"Advising Ashley"
2:26

13.
"If The Shoe Fits"
1:35

14.
"Unhappy Endings"
3:46

15.
"Emma And Henry"
1:43

16.
"The Siren"
5:07

17.
"The Man with the Wooden Box"
1:11

18.
"Hope Will Return"
1:48

19.
"Rumplestiltskin in Love"
2:19

20.
"The Genie's Wishes"
1:58

21.
"The Road To True Love"
2:50

22.
"The Family Compass"
2:00

23.
"Burn The Witch"
2:34

24.
"What The Queen Loves Most"
2:30

25.
"The Clock Moves"
1:12

text:
[show]Season 2 Soundtrack

No.
Title
Length

1.
"Sleeping Beauty"
2:29

2.
"True Love"
4:45

3.
"Magic"
3:12

4.
"We Are Both"
1:41

5.
"Meet the Jefferson"
2:37

6.
"Ruby and Granny"
1:54

7.
"A Real Boy"
2:26

8.
"The Hedge Maze"
4:13

9.
"Regina's True Love"
2:29

10.
"Storybrooke Reunions"
2:12

11.
"The Duelists"
1:21

12.
"The Lady Jack"
0:45

13.
"In a Burning Room"
4:16

14.
"Tallahassee"
2:21

15.
"This Boy Will Be Your Undoing"
2:46

16.
"Science!"
1:23

17.
"To Neverland!"
1:58

18.
"Cora's Waltz"
2:19

19.
"Snow White in Black"
2:45

20.
"How Magic Is Made"
3:33

21.
"One Perfect Day After Another"
2:37

22.
"Bae and the Shadow"
2:45

23.
"Tamara Shows Her True Colors"
4:20

24.
"The Adventure Begins"
2:14

25.
"Main Title"
0:14

text: Broadcast[edit]

text: The series has been licensed to over 190 countries.[106] In Australia, Once Upon a Time first aired on Seven Network, starting on May 15, 2012. In Canada it airs on CTV from October 23, 2011. It premiered on Channel 5 in the United Kingdom on April 1, 2012.[107] On December 17, 2013, it was confirmed that Channel 5 would not be picking the series up for the third season airing in the UK.[107] On March 14, 2015, Netflix picked up the show in the United Kingdom and Republic of Ireland, subsequently showing all seasons and premiering each new episode on Wednesdays after their initial showing on Sundays on ABC.

text: Reception[edit]

text: Critical response[edit]

text: Critical response to the first season was generally positive. On Metacritic, it was given a score of 66 out of 100 with "generally favorable reviews".[108] E!'s Kristin dos Santos cited the show as one of the five new shows of the 2011–2012 season to watch.[109] Matthew Gilbert of The Boston Globe gave the show a "C+" grade commenting

text: "From a pair of Lost producers, this is a love-or-hate proposition. The ambition is impressive, as it asks us to imagine Goodwin's Snow White and Parrilla's Evil Queen as moderns. But Morrison is a wooden lead, and the back stories – a random collection of fairy tales -- don't promise to surprise."[110]

text: In a review from the St. Louis Post-Dispatch, TV critic Gail Pennington hailed it as one of the "Most Promising Shows of The Fall" and, unlike Gilbert, had high marks for Morrison.[111] USA Today's Robert Blanco placed the series on its top ten list, declaring that "There's nothing else on the air quite like it."[112] Mary McNamara of the Los Angeles Times preferred the series to another fairy-tale themed drama, Grimm, citing that the premise takes its time building up the charm and that the producer "has that part nailed". She also gave excellent reviews for Morrison's character: "Her Emma is predictably cynical and prickly – fairy-tale princess, my Aunt Fanny – but she's sharp and lively enough to keep audiences begging for 'just a few more pages' before they go to bed."[113]

text: Several feminist outlets were pleased with the show for its feminist twist on fairy tales. Avital Norman Nathman of Bitch stated that she liked the show for "infusing a feminist sensibility" into the stories.[114] Genie Leslie at Feministing commented that Emma was a "badass", that she liked how Emma was "very adamant that women be able to make their own decisions about their lives and their children", and how Emma was a "well-rounded" character who was "feminine, but not 'girly'".[115] Natalie Wilson from Ms. praised the show for a strong, "kick-butt" female lead, for including multiple strong women who take turns doing the saving with the men, for subverting the fetishization of true love, and for dealing with the idea of what makes a mother in a more nuanced fashion. Wilson went on to state of the lead: "Her pursuit of a 'happy ending' is not about finding a man or going to a ball all gussied up, but about detective work, about building a relationship with her son Henry, and about seeking the 'truth' as to why time stands still in the corrupt Storybrooke world."[116]

text: Ratings[edit]

text: The first season premiered as the top-rated drama series. The pilot episode was watched by 13 million viewers and received a 4.0 rating/share among 18- to 49-year-olds.[117] It was the season's highest-rated drama debut among the age range and ABC's biggest debut in five years.[118][119] With DVR viewers, the premiere climbed to 15.5 million viewers and a 5.2 rating/share in adults 18–49.[120] The show's next three episodes had consistent ratings every week with over 11 million viewers.[121][122][123] The series has become the number one non-sports program in the U.S. with viewers and young adults on Sunday nights.[124]

text:
Season
Timeslot (ET)
Episodes
First aired
Last aired
TV season
Rank
Avg. viewers
(millions)
18–49 rating
(average)

Date
Viewers
(millions)
Date
Viewers
(millions)

1
Sunday 8:00 pm
22
October 23, 2011 (2011-10-23)
12.93[125]
May 13, 2012 (2012-05-13)
9.66[126]
2011–12
28
11.71[127]
4.1/10[128]

2
22
September 30, 2012 (2012-09-30)
11.36[129]
May 12, 2013 (2013-05-12)
7.33[130]
2012–13
35
10.24[131]
3.6/9[132]

3
22
September 29, 2013 (2013-09-29)
8.52[133]
May 11, 2014 (2014-05-11)
6.80[134]
2013–14
35
9.38[135]
3.3/8[136]

4
22
September 28, 2014 (2014-09-28)
9.47[137]
May 10, 2015 (2015-05-10)
5.51[138]
2014–15
50
8.98[139]
3.2/7[139]

5
23
September 27, 2015 (2015-09-27)
5.93[140]
May 15, 2016 (2016-05-15)
4.07[141]
2015–16
69
6.32[27]
2.2[27]

6
22
September 25, 2016 (2016-09-25)
3.99[142]
May 14, 2017 (2017-05-14)
2.95[143]
2016–17
105
4.39[144]
1.5/5[28]

7
Friday 8:00 pm
22[145]
October 6, 2017 (2017-10-06)
3.26[146]
TBA
TBD
2017–18
TBD
TBD
TBD

text: Awards and nominations[edit]

text: Once Upon a Time was nominated for a 2012 People's Choice Award for "Favorite New TV Drama", but lost to Person of Interest.[147] The show was nominated at the 39th People's Choice Awards in four categories: Favorite Network TV Drama, Favorite Sci-Fi/Fantasy Show, Favorite TV Fan Following, and Favorite TV Drama Actress (Ginnifer Goodwin); it lost to another ABC show Grey's Anatomy in the first category, Supernatural in the second two, and Ellen Pompeo (from Grey's Anatomy) in the last category. the show was nominated at 40th People's Choice Awards, but lost to Beauty and the Beast and The Vampire Diaries, respectively.

text: The show was also nominated for "Best Genre Series" at the 2011 Satellite Awards, but lost to American Horror Story.[148] The show was nominated in this category again at the 2012 Satellite Awards, but lost to The Walking Dead.[149]

text: The program also received three nominations at the 2012 Visual Effects Society Awards, but all lost to Boardwalk Empire, Gears of War 3, and Terra Nova.[150]

text: At the 38th Saturn Awards, the series received a nomination for Best Network Television Series and Parrilla was nominated for Best Supporting Actress on Television, but lost to Fringe and Michelle Forbes, respectively.[151]

text: The program was nominated for the former award again at the 39th Saturn Awards, but lost to new series Revolution.[152]

text: Jared S. Gilmore was nominated for Best Performance by an Younger Actor on Television at 40th Saturn Awards, but lost to Chandler Riggs for The Walking Dead

text: The show received trophies for "Favorite New TV Drama" and "Favorite Villain" for Lana Parrilla by the TV Guide.[153]

text: The show was nominated at the 2012 Teen Choice Awards, but lost to The Vampire Diaries, Pretty Little Liars and Awkward and the show was also nominated at 2013 Teen Choice Awards, but lost to The Vampire Diaries and Pretty Little Liars.

text: The show was nominated again 2014 Teen Choice Awards, but lost to The Vampire Diaries and Dylan O'Brien, respectively.

text: It was also nominated at the 64th Creative Arts Primetime Emmy Awards, but lost to Game of Thrones and The Walking Dead and the show was nominated again at 65th Primetime Creative Arts Emmy Awards, but lost to The Borgias and Game of Thrones.

text: Tie-in material[edit]

text: Novels[edit]

text: In 2013, Disney-owned Hyperion Books published Reawakened by Odette Beane, a novelization of storylines from the first season, expanded to include new perspectives. The narrative is from the points-of-view of Emma Swan in Storybrooke and Snow White in the Enchanted Forest. The novel was published on April 28, 2013, as an ebook and May 7, 2013, in paperback form.[154]

text: In 2015, production company Kingswell Teen published Red's Untold Tale, by Wendy Toliver, a novel telling a story of Red's past that was not seen in the show. The novel was published on September 22, 2015 and consisted of 416 pages.

text: In 2017, Kingswell Teen published a second novel, Regina Rising, also written by Wendy Toliver, which depicts the life of a sixteen year old Regina. The novel was published on April 25, 2017.

text: Comic books[edit]

text: A comic book, titled Once Upon a Time: Shadow of the Queen, was released on September 4, 2013, in both digital and hardcover forms. The story was written by Dan Thomsen and Corinna Bechko, with art by Nimit Malavia, Vasilis Lolos, Mike Del Mundo, Stephanie Hans and Mike Henderson. Shadow of the Queen details what happens after the Evil Queen takes the Huntsman's heart. She forces the Huntsman to commit evil, and try to capture Snow White yet again. The Huntsman faces his past, and also meets Red Riding Hood, who is trying to cope with her beastly alter ego. Together, they team up and try to save Snow White before all is too late.[155]

text: On April 14, 2014, a sequel to the first comic book called Once Upon a Time: Out of the Past was released.[156]

text: Spin-off[edit]

text: In February 2013, Kitsis & Horowitz, along with producers Zack Estrin and Jane Espenson, developed a spin-off focusing on Lewis Carroll's Wonderland.[157] The series was called Once Upon a Time in Wonderland. A "teaser presentation" began shooting in April 2013, and the pilot was shot in late July or August.[158] On May 10, 2013, ABC announced that it had approved the spin-off and on May 14, 2013, announced that the spin-off would air in the Thursday night 8:00pm time slot instead of making it a fill-in for the parent series.[159] The series premiered on October 10, 2013, but was cancelled[160] after a single-season thirteen-episode run that ended on April 3, 2014.[161]