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

Garcia, Alvin; Heidbrink, W. W.; Sandorfi, A. M.

doi:10.1088/1741-4326/acaf0d

Cited by 3 publications

(57 citation statements)

References 46 publications

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Section: Strategies For Detecting Polarization In a Plasmamentioning

confidence: 99%

“…An alternate detection strategy envisioned in a companion paper [26], exploits the polarization dependence in the angular distribution of emitted fragments (figure 4). Simulations in [26] show that the pitch at the tokamak wall, taken as the arccos of the parallel component of the ion velocity v || /v, is strongly correlated with the polar reaction angle at birth. Since the dependence of the cross section on this angle is strongly polarization dependent, as in equation ( 4) and figure 4, the shape of the v || /v velocity distribution at a fixed location on the tokamak wall varies with polarization.…”

Section: Strategies For Detecting Polarization In a Plasmamentioning

confidence: 99%

“…In this section we model how changes in fusion yields due to polarization would be reflected at the walls of the DIII-D tokamak. (The effects of changes in the angular distribution are treated separately in [26].) Our goal here is to demonstrate that the basic enhancements of equation ( 10) are reflected at the plasma-facing wall, despite the highly variable orbits of the charged fusion products through the tokamak.…”

Section: Simulation Of Polarization-dependent Fusion Yieldsmentioning

confidence: 99%

“…We consider a notional DIII-D experiment heated by hydrogen neutral beam injection into a majority high ion-temperature hydrogen plasma with minority 3 He and D populations from polarized pellets. These plasma characteristics have not yet been achieved in DIII-D. (Some of the associated challenges are discussed further in the companion paper [26].) Modeling begins with plasma characteristics from sh-96369, a past DIII-D shot with a solid D 2 pellet injection through the HFS V + 1 vertical port at t = 4550 ms [21], into a deuterium plasma.…”

Section: Plasma Parameters For Modeling and Simulationmentioning

confidence: 99%

“…Section 6 continues with a simulation of projected polarization-dependent changes in the fusion product yields reaching the plasma-facing walls. (A companion paper simulates a polarization life-time experiment through measurements of changes in fusion angular distributions, as reflected in the pitch angles of fusion products reaching the outer walls [26]. )…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2023

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The use of spin-polarized fusion fuels would provide a significant boost towards the ignition of a burning plasma. The cross section for D+T→ α+n, would be increased by 1.5 if the fuels were injected with parallel polarization. Furthermore, our simulations demonstrate additional non-linear power gains in large-scale machines such as ITER, due to increased alpha heating. Such benefits require the survival of spin polarizations for periods comparable to the particle confinement time. During the 1980s, calculations predicted that polarizations could survive a plasma environment, although concerns persisted regarding the cumulative impacts of wall recycling. In that era, technical challenges prevented direct tests and left the large scale fueling of a power reactor beyond reach. Over the last decades, this situation has dramatically changed. Detailed simulations of ITER have predicted negligible wall recycling in a high-power reactor, and recent advances in laser-driven sources project the capability of producing large quantities of ~100% polarized D and T. The remaining crucial step is an in-situ demonstration of polarization survival in a plasma. For this, we outline a measurement strategy using the isospin-mirror reaction, D+3He→ α+p. Polarized 3He avoids the complexities of handling tritium, while encompassing the same spin-physics. We evaluate two methods of delivering deuterium, using dynamically polarized Lithium-Deuteride (with vector polarization PV D of 70%) or frozen-spin Hydrogen-Deuteride (with PV D of 40%), together with a method of injecting optically-pumped 3He (with 65% polarization). Pellets of these materials all have long polarization decay times (~6 minutes for LiD at 2K, ~2 months for HD at 2K, and ~3 days for 3He at 77K), all far greater than a plasma shot in a research tokamak such as DIII-D. Both species can be propelled from a single cryogenic injection gun. We review plasma requirements and strategies for detecting polarization survival. Polarization alters both fusion yields and the angular distribution of fusion products, and each of these provides a potential signal. In this paper we simulate a selection of shots with similar characteristics in a future high-Tion H plasma, and find ratios of yields from shots with fuel spins parallel and antiparallel reaching 1.3 (HD+3He) to 1.6 (LiD+3He) over a wide range of poloidal angles. (A companion paper finds sensitivity to fusion product angular distributions as reflected in the pitch angles of protons and alphas reaching the plasma facing wall.)

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Section: Strategies For Detecting Polarization In a Plasmamentioning

confidence: 99%

Section: Strategies For Detecting Polarization In a Plasmamentioning

confidence: 99%

Section: Simulation Of Polarization-dependent Fusion Yieldsmentioning

confidence: 99%

Section: Plasma Parameters For Modeling and Simulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

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

Cited by 3 publications

References 46 publications

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

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

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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