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Sep 24 – 29, 2023
US/Eastern timezone

A research program to measure the lifetime of spin polarized nuclei in magnetically confined fusion plasmas

Sep 25, 2023, 11:30 AM
30m
Grand Ballroom 3 (Durham Convention Center)

Grand Ballroom 3

Durham Convention Center

Talk Plenary Plenary

Speaker

W.W. Heidbrink

Description

The use of spin polarized fuel could increase D-T fusion reactivity by a factor of 1.5 and, owing to alpha heating, increase fusion Q in ITER even more [1]. The use of polarized D 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 [1]. Dynamically polarized 7Li-D pellets can achieve 70% vector polarization for the deuterium [1]. The polarization lifetimes in cooled 3He fuel capsules are days, while only minutes for 7Li-D [1]. (This is still much greater than the ~10 second duration of a plasma shot in a research tokamak such as DIII-D.) Cryogenically-frozen pellets can be injected vertically into tokamaks by special injectors that minimize depolarizing field gradients. The use of a Sona transition [2] to polarize neutral beams is also under investigation. Theoretically [3], nuclei remain polarized in a hot fusion plasma for much longer than the particle confinement time but the predictions have never been tested experimentally. Measurements that exploit spin-induced changes in differential cross section are more sensitive than measurements of the reaction rate alone [4]. One possible experimental scenario uses an unpolarized 3He fast-ion population (~80 keV) and tensor-polarized deuterium pellets; in another, both species are polarized in a thermonuclear plasma with ion temperatures above 10 keV. Modeling shows that a Ti>10 keV DIII-D plasma generates 14.7 MeV proton and 3.6 MeV alpha signals that are sensitive to depolarization with high accuracy [4]; additionally, nearly all reactor-relevant depolarization mechanisms are accessible for study in DIII-D. With a sufficiently intense polarized beam, accurate measurements of the depolarization rate could also be performed in the Wisconsin HTS Axisymmetric Mirror. Experiments in a compact spherical tokamak are also under investigation.
[1] L.R. Baylor et al., Nucl. Fusion 63 (2023) doi 10.1088/1741-4326/acc3ae
[2] R. Engels et al., Eur. Phys. J. D 75:257 (2021).
[3] R.M. Kulsrud et al., Nucl. Fusion 26 (1986) 1443.
[4] A.V. Garcia et al., Nucl. Fusion 63 (2023) 026030.

Primary author

Co-authors

A.M. Sandorfi (University of Virginia) A.V. Garcia (UC Irvine) C.B. Forest (University of Wisconsin, Madison) G.W. Miller (University of Virginia) L.R. Baylor (Oak Ridge National Laboratory) M. Büscher (Forschungsszentrum Jülich & Heinrich-Heine Universität Düsseldorf) M. Gryaznevich (Tokamak Energy) R.W. Engels (Forschungsszentrum Jülich & GSI Helmholtzzentrum für Schwerionenforschung) X. Wei (Jefferson Lab) X. Zhang (University of Virginia)

Presentation materials