The JET Soft X-Ray Diagnostic Systems

摘要

A 250 channel soft X-ray detector system has been constructed for the pumped divertor phase of JET. It is based on 12 compact pinhole cameras each of which uses a 35 element PIN photodiode, providing six independent poloidal views of the plasma at one toroidal location. The cameras are housed in a secondary vacuum and view the plasma through beryllium windows 250μm thick. The front-end electronics, located up to 10m away from the detectors, sample data at 250kHz, with a 100kHz pass-band. With the diodes at zero bias voltage, the diagnostic operated successfully during the 1995 phase of JET operation with noise levels below lnA. Some deterioration in diode performance was observed after exposure to an integrated neutron fluence of ~10~(13) n.cm~(-2). Tests have shown that operating with 3V reverse bias can offset much of the fall in performance from radiation damage. Using a similar 16 element PIN photodiode, a windowless camera has been developed for installation in the JET primary vacuum, to investigate fast XUV/X-ray events in the divertor. Finally, a radiation hardened system is being developed for D-T operation.