NEUTRON DIAGNOSTICS IN COMPACT HELICAL SYSTEM

An efficient neutron diagnostic system has been established and applie d to deuterium experiments on compact helical system. A neutron counte r was installed at the center of the torus, and the detection efficien cy was about two orders of magnitude higher than the values of most to roidal fusion devices. The effect of the stray magnetic field on the o peration of a proportional counter was experimentally confirmed to be negligibly small. The ion temperature, as low as 400 eV, was obtained from neutron measurement with a time resolution of 1 ms. The decay tim e of neutron emission rate after the termination of a 1% deuterium-dop ed beam was measured and the confinement time of neutral beam-injected fast ions was estimated. The fast ion confinement was clearly improve d by strengthening the toroidal magnetic field. (C) 1997 American Inst itute of Physics.