The monitoring system of a high performance fusion neutron spectrometer

Neutron emission spectroscopy (NES) diagnosis of high-power fusion plasma has been performed with the magnetic proton recoil (MPR) spectrometer installed at the Joint European Torus tokamak. The MPR is a high performance instrument where the setting of working points to prescribed calibration values is essential. This includes the MPR focal plane detector whose photomultipliers must be monitored for gain stability with respect to short- and long-term drifts as well as transient changes. A special monitoring system was developed for the MPR including a light pulser in the form of light emitting diodes. The monitoring system as part of the MPR focal plane detector is described here as well as the monitoring procedures and applications. Results from the use of the monitoring system are presented illustrating its present capabilities and possibilities for further developments in next step NES diagnostics.