Polarized fusion and potential in situ tests of fuel polarization survival in a tokamak plasma

Baylor, L. R.; Deur, A.; Eidietis, N. W.; Heidbrink, W. W.; Jackson, G.L.; Liu, Jie; Lowry, Michael M; Miller, Wilson; Pace, D. C.; Sandorfi, A. M.; Smith, S. P.; Tafti, Sina; Wei, K.; Wei, X.; Zheng, X.

doi:10.1088/1741-4326/acc3ae

Cited by 3 publications

(21 citation statements)

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“…For deuterium, one approach uses an H-D capsule and another approach uses a 7 Li-D capsule. The expected values for the H-D capsule are 0.4 for the vector polarization and 0.12 for the tensor polarization [10]. The 7 Li-D capsule can potentially deliver larger values of 0.70 and 0.41 for the vector and tensor polarizations, respectively.…”

Section: Accuracy Estimatesmentioning

confidence: 98%

“…The first practical complication is that current technology cannot produce fuel pellets with 100% polarization. A reasonable value for vector polarization of 3 He is 0.65 [10]. For deuterium, one approach uses an H-D capsule and another approach uses a 7 Li-D capsule.…”

Section: Accuracy Estimatesmentioning

confidence: 99%

“…(Significant dσ − /dΩ tensor polarization variation is not presently available.) Although these are likely values using existing technology, new schemes discussed in [10] should be able to produce P V D = 1 and P T D = 1 and possibly even P T D = −2 but require extensive research and investment [10]. Figures 12(a A second practical complication is detector count rates.…”

Section: Accuracy Estimatesmentioning

confidence: 99%

“…For a poloidal array of three 3.6 MeV alpha detectors, the uncertainty associated with counting statistics in inferring either P V D P He in a thermonuclear experiment or P T D in a beamplasma experiment is very small (<0.01), implying that systematic errors will determine the ultimate resolution. D P He coefficient is inferred from data similar to figure 13, assuming that P T D is given by equation (10). Each symbol and error bar is from an ensemble of trials with randomly generated counting statistics.…”

Section: Accuracy Estimatesmentioning

confidence: 99%

“…A companion paper [10] considers many important issues with minimal coverage here, including a historical overview of research on spin polarized fusion in tokamaks, details of the relevant nuclear physics, depolarization mechanisms, and benefits for a fusion reactor. The preparation and delivery of polarized fuel pellets is discussed in considerable detail.…”

Section: Introductionmentioning

confidence: 99%

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Conceptual design of DIII-D experiments to diagnose the lifetime of spin polarized fuel

2023

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In magnetic fusion experiments, the cross sections for the D-T and D-3He fusion reactions are increased by as much as 50% if the fuel remains spin polarized parallel to the magnetic field. The goal of this study is to assess the feasibility of lifetime measurements of spin polarization, in magnetic fusion relevant conditions, on the DIII-D tokamak using relative changes in charged fusion product (CFP) loss measurements that depend upon the differential fusion cross section dσ/dΩ. Relative measurements that capture changes in the escaping CFP pitch, poloidal, and energy distributions are studied in two realistic TRANSP calculated plasma scenarios: 1) vector-polarized 3He and D pellets are injected into a hot hydrogen plasma to produce thermonuclear reactions, and 2) a tensor-polarized deuterium pellet is injected into an L-mode hydrogen background plasma that includes unpolarized 3He neutral beam injection (NBI). Ideal CFP signals in both scenarios show substantial pitch sensitivity to polarization for 14.7 MeV proton detection at a poloidal angle of -56° (on the outer wall in the ion ∇B direction), and strong sensitivity to polarization for 3.6 MeV alpha flux detection by an array of poloidal detectors. Energy-resolved measurements of 14.7 MeV protons are also sensitive to the degree of polarization for the -56° port in the beam-plasma scenario. A realistic assessment of CFP signals in the thermonuclear scenario show count rates in the range of 2×104 cps for pitch-resolved proton detection and 2×105 cps for alpha flux measurements. Reduced chi-squared χr 2 calculations show polarization lifetime measurements are feasible for either proton or alpha detection of both enhanced or suppressed polarization for the thermonuclear scenario. Measurements of gamma rays produced in the weak D + 3He → γ + 5Li branch complement the CFP measurements.

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Section: Accuracy Estimatesmentioning

confidence: 98%

Section: Accuracy Estimatesmentioning

confidence: 99%

Section: Accuracy Estimatesmentioning

confidence: 99%

Section: Accuracy Estimatesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Conceptual design of DIII-D experiments to diagnose the lifetime of spin polarized fuel

2023

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Simultaneous enhancement of tritium burn efficiency and fusion power with low-tritium spin-polarized fuel

Parisi,

Diallo,

Schwartz

2024

Nucl. Fusion

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This study demonstrates that using spin-polarized deuterium-tritium (D-T) fuel with more deuterium than tritium can increase tritium burn efficiency (TBE) by at least an order of magnitude without compromising fusion power output, compared to unpolarized fuel. Although previous studies show that a low tritium fraction can enhance TBE, this strategy resulted in reduced fusion power density. The surprising improvement in TBE at fixed power reported here is due to the TBE increasing nonlinearly with decreasing tritium fraction but the fusion power density increasing roughly linearly with D-T cross section. A study is performed for an ARC-like tokamak producing 481 MW of fusion power with unpolarized 53:47 D-T fuel, finding the minimum startup tritium inventory ($I_{\mathrm{startup,min}}$) is 0.69 kg. By spin-polarizing half of the fuel and using a 60:40 D-T mix, $I_{\mathrm{startup,min}}$ is reduced to 0.08 kg, and fully spin-polarizing the fuel with a 63:37 D-T mix further reduces $I_{\mathrm{startup,min}}$ to 0.03 kg. Some ARC-like scenarios {are predicted to} achieve plasma ignition with relatively modest spin polarization. These findings indicate that, with advancements in helium divertor pumping efficiency, TBE values of approximately 10-40\% could be achieved using low-tritium-fraction and spin-polarized fuel with minimal power loss. This would dramatically lower tritium startup inventory requirements and reduce the amount of on-site tritium. More generally than just for spin-polarized fuels, {increased} plasma performance can be used to increase TBE. This strongly motivates the development of spin-polarized fuels and low-tritium-fraction operation for burning plasmas.

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A research program to measure the lifetime of spin polarized fuel

Heidbrink,

Baylor,

Büscher

et al. 2024

Front. Phys.

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The use of spin polarized fuel could increase the deuterium-tritium (D-T) fusion cross section by a factor of 1.5 and, owing to alpha heating, increase the fusion power by an even larger factor. Issues associated with the use of polarized fuel in a reactor are identified. Theoretically, nuclei remain polarized in a hot fusion plasma. The similarity between the Lorentz force law and the Bloch equations suggests polarization can be preserved despite the rich electromagnetic spectrum present in a magnetic fusion device. The most important depolarization mechanisms can be tested in existing devices. The use of polarized deuterium and 3He in an experiment avoids the complexities of handling tritium, while encompassing the same nuclear reaction spin-physics, making it a useful proxy to study issues associated with full D-T implementation. 3He fuel with 65% polarization can be prepared by permeating optically-pumped 3He into a shell pellet. Dynamically polarized 7Li-D pellets can achieve 70% vector polarization for the deuterium. Cryogenically-frozen pellets can be injected into fusion facilities by special injectors that minimize depolarizing field gradients. Alternatively, polarized nuclei could be injected as a neutral beam. Once injected, the lifetime of the polarized fuel is monitored through measurements of escaping charged fusion products. Multiple experimental scenarios to measure the polarization lifetime in the DIII-D tokamak and other magnetic-confinement facilities are discussed, followed by outstanding issues that warrant further study.

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Polarized fusion and potential in situ tests of fuel polarization survival in a tokamak plasma

Cited by 3 publications

References 103 publications

Conceptual design of DIII-D experiments to diagnose the lifetime of spin polarized fuel

Conceptual design of DIII-D experiments to diagnose the lifetime of spin polarized fuel

Simultaneous enhancement of tritium burn efficiency and fusion power with low-tritium spin-polarized fuel

A research program to measure the lifetime of spin polarized fuel

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