Design and upgrades of the TCV fast ion loss detector

The Tokamak à Configuration Variable has a unique Fast Ion Loss Detector (FILD) that allows the simultaneous measurement of co- and counter-current fast-ion losses in forward or reverse magnetic field. Recently, multiple novel upgrades have been implemented that further extended its capabilities. The optical system throughput was improved by adding anti-reflective coatings to the internal components, in direct view of the camera, and installing a low wavelength filter to reduce unwanted stray light. The mechanical rigidity was increased by adding additional contact points closer to the heat shield, which significantly reduced the system vibration amplitude during operation. The entrance slit pinholes were reduced from 1 to 0.8 mm, obtaining an energy resolution improvement of over 40% for only an ∼20% signal level decrease. Finally, a rotary system now permits the FILD head angle to be scanned from ±30° on a shot-to-shot basis. These upgrades, described herein, greatly increase the functionality of the FILD diagnostic.