The JET soft x-ray diagnostic systems

Abstract

A new multicamera soft x-ray detector system has been constructed for the pumped divertor phase of JET to provide improved spatial and temporal resolution. It is based on 12 compact pinhole cameras each of which uses a 35 element PIN photodiode array. The cameras are housed in a secondary vacuum and view the plasma through beryllium windows 250-μm-thick which absorb x rays with energies below ∼2 keV. The front-end electronics, located up to 10 m away from the detectors, sample data at 250 kHz, with a 100 kHz passband. The diodes are operated at zero bias voltage. The system ran successfully during the 1995 phase of JET operation with poloidal mode numbers up to m=5 being successfully reconstructed. Detector noise levels (<1 nA) were small compared to signal statistical noise. Some deterioration in diode performance was observed after exposure to an integrated neutron fluence of ∼1013 n. cm−2. Tests have shown that operating with 3 V 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 which develop at lower energies near the plasma edge or in the divertor. Finally, a radiation hardened system is being developed for D-T operation.

ELM triggering by local pellet perturbations in type-I ELMy H-mode plasma at JET

“…In addition, the observation cone of the pellet monitor and the area covered by the vertical soft x-ray (SXR) cameras [13] 35 lines of sight are displayed. D α radiation mainly from the ablation zone optically accessed through a telescope and a quartz fibre was recorded by fast photomultipliers.…”

Extreme ultra-violet movie camera for imaging microsecond time scale magnetic reconnection

“…Time-resolved fast imaging of extreme ultra-violet (EUV) and soft x-ray radiation is useful to understand magnetic reconnection, magnetohydrodynamic (MHD) activity, particle and energy transport, plasma stability, and turbulence in laboratory plasmas such as tokamaks [1][2][3][4] spheromaks, 5 reversed field pinches, 6 and stellarators. 7 Since visible light technology does not work at EUV wavelengths, conventional optical schemes based on mirrors and lenses cannot be used to collect radiation and form images.…”

“…Various EUV imaging methods have been used previously, most particularly pinhole cameras 3,4,6,7 and diode arrays. 1,2,5 Pinhole cameras consist of a small pinhole to form an image, a micro-channel plate intensifier shutter that converts EUV into fast electrons, a scintillator/phosphor to convert the fast electrons into a visible light image, and a visible light camera to record the phosphor image. Pinhole cameras have the advantage of simplicity, but have extremely low sensitivity because of the necessarily small pinhole photon collection efficiency.…”

Preliminary design of the soft x-ray array tomographic diagnostic system for Korea Superconducting Tokamak Advanced Research (KSTAR) plasmas

“…Because the response of edge channels is known to be unsatisfactory in the case of a linear 32-channel detector due to the large incident angle, calibration depending on incident angle is required when the maximum incident angle on a detector element exceeds ±22.5°. 11,12 Because of the reason, a pair of AXUV-16EL detectors was decided to be arranged in the V-shape in order to avoid the large incident angle at the edge detector elements while maintaining a wide viewing angle.…”