Neutron profile measurements in the Joint European Torus

The prototype neutron profile monitor was in use at the Joint European Torus (JET) from 1987 until the end of 1994, when it was upgraded to incorporate features which experience showed to be desirable. For ohmic and ion cyclotron resonance frequency (ICRF)-heated discharges, the profile monitor provides useful information on ion temperatures and deuterium densities. However, most JET discharges involve beam heating, for which charge exchange recombination spectroscopy provides high quality ion temperature profile data, so that analysis of neutron profile monitor data has been diverted to other matters, such as the following: the examination of the effects of beam deposition and density profiles on the neutron emissivity profile; the extraction of information on fast particle diffusion from a study of the bum-up of D-D reaction fusion product tritons; the interpretation of results from the first tritium experiment; studies of gamma-ray emission from ICRF-accelerated fast ions interacting with plasma impurities; and the interpretation of sawtooth crash data. The profile monitor has also been used to measure bremsstrahlung from fast electrons generated using a lower hybrid current drive. The requirements which led to the upgrading of the prototype diagnostic are indicated and anticipated future applications are summarized.