The diffusion of fast ions in Ohmic TFTR discharges

W W Heidbrink,Cris W Barnes,Y Kusama,G W Hammett,H K Park,L C Johnson,S S Medley,D Mccune,S D Scott,J D Strachan,M C Zarnstorff,A L Roquemore,G Taylor

doi:10.1063/1.859796

W W Heidbrink, Cris W Barnes + Show 11 more

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https://doi.org/10.1063/1.859796

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Abstract

Short duration (20 msec) neutral deuterium beams are injected into the TFTR tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. I, p. 51]. The subsequent confinement, thermalization, and diffusion of the beam ions are studied with multichannel neutron and charge exchange diagnostics. The central fast-ion diffusion (&lt;0.05 m2/sec ) is an order of magnitude smaller than typical thermal transport coefficients.

Highlights

Two requirements for an ignited D-T fusion reactor are sufficient energy confinement of the thermal plasma and confinement of fusion-product alphas while they thermalize
A likely explanation for the difference between thermal transport and fast-ion transport is that beam ions do not stay in resonance with the fluctuations responsible for thermal transport since their drift orbit displacements exceed the radial correlation length A, of the fluctuations.5’2’ (A similar process may account for enhanced high-energy runaway electron confinement.*’ ) If one assumes that this explanation is correct, the observed ratio of D /xe implies that the fluctuations responsible for transport have a radial scale length significantly smaller thanpf- 1 cm
In contrast to the thermal transport, the central beam-ion diffusion coefficient is consistent with the diffusion predicted by neoclassical theory [D- 0( 0.01 m*/sec) 1. (The neoclassical pinch velocity is negligible.) The diffusion of off-axis banana-trapped ions does exceed the neoclassical prediction

Summary

The diffusion of fast ions in Ohmic TFTR discharges

Taylor Plasma PhysicsLaboratory, Princeton Universiry Princeton, New Jersey08543. Short duration (20 msec) neutral deuterium beams are injected into the TFTR tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol I, p. The subsequent confinement, thermalization, and diffusion of the beam ions are studied with multichannel neutron and charge exchange diagnostics. The central fast-ion diffusion ( co. m2/sec) is an order of magnitude smaller than typical thermal transport coefficients

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