Fusion-neutron production in the TFTR with Deuterium neutral-beam injection

Abstract

We report measurements of the fusion reaction rate in the Tokamak Fusion Test Reactor (TFTR) covering a wide range of plasma conditions and injected neutral-beam powers up to 6.3 MW. The fusion neutron production rate in beam-injected plasmas decreases slightly with increasing plasma density n_e, even though the energy confinement parameter n_eτ_E generally increases with density. The measurements indicate and Fokker-Planck simulations show that with increasing density the source of fusion neutrons evolves from mainly beam-beam and beam-target reactions at very low n_e to a combination of beam-target and thermonuclear reactions at high n_e. At a given plasma current, the reduction in neutron source strength at higher n_e is due to both a decrease in electron temperature and in beam-beam reaction rate. The Fokker-Planck simulations also show that at low n_e, plasma rotation can appreciably reduce the beam-target reaction rate for experiments with coinjection only. The variation of neutron source strength with plasma and beam parameters is as expected for beam-dominated regimes. However, the Fokker-Planck simulations systematically overestimate the measured source strength by a factor of 2–3; the source of this discrepancy has not yet been identified.