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

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_eE 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.On leave from RCA David Sarnoff Research Center, Princeton, New Jersey 08540.On assignment from Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831.On leave from Idaho National Engineering Laboratory, EG&G Idaho, Inc., Idaho Falls, Idaho 83415.