Polarized fusion, its Implications and plans for Direct Measurements in a Tokamak

Sandorfi, A. M.; Deur, A.; Hanretty, C.; Jackson, G.L.; Lanctot, M.; Liu, J.; Lowry, M.; Miller, Greg; Pace, D. C.; Smith, S.P.; Wei, K.; Wei, Xu; Zheng, X.J.

doi:10.2172/1963207

Cited by 2 publications

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“…Finally, cryogenic injection guns have been demonstrated to convey pellets into the core of tokamak plasmas with high efficiencies [21]. The combination of these technologies that have matured since the original Kulsrud et al paper [4] can now be used to test the long-standing prediction of polarization survival, using the D + 3 He → α + p reaction [13,22]. As discussed below (section 2), the 5 He and 5 Li compound states in the D + T → α + n and D + 3 He → α + p reactions have a nearly identical low-energy structure.…”

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: Introductionmentioning

confidence: 99%

“…Various details are included that may appear redundant to one group or another, but are included here for the sake of the broader audience. General concepts and preliminary progress on some aspects of this work have been reported in [13,22,25,27,28].…”

Section: Introductionmentioning

confidence: 99%