Neutron profile measurements for trace tritium experiments

The JET neutron profile monitor was used to study the transport of tritium into a magnetically confined deuterium plasma. Trace amounts of tritium wer e introduced through a gas valve beyond the plasma edge into a variety of p lasma confinement regimes. The d(t, n)alpha fusion cross section is two ord ers of magnitude greater than the d(t, n)He-3 cross section and so a puff o f tritium which has a negligible effect on the plasma nevertheless produces a large d-t neutron signal. The profile monitor consists of two cameras ea ch made up of a fan-shaped array of collimated lines of sight. It was used to measure the d-d and d-t neutron profiles simultaneously. This article de scribes the detection system, its operation and assesses the difficulties d ue to scattered neutrons. The profiles can be used to determine tritium den sity and transport coefficients. (C) 1999 American Institute of Physics. [S 0034-6748(99)58901-6].