A novel scanning method for tokamak spectroscopy

This paper discusses the problem of optical access for spectroscopic diagnostics to all poloidal regions of a plasma in a current generation tokamak which has become severe. Window sizes are limited and plasmas have grown; as a result, one must scan a large angle through a small window in a high (over 5 Tesla) field, often at elevated temperatures. No prudent person wants to put a moving system in such an environment. A system has been designed which uses only a mirror at the window. The rest of the elements (field lenses, a small, easily shielded mirror scanner, and the spectrometer) are several meters away behind a wall. The details of a design for TFTR are presented. All components are catalog items. Scan angles of ±40 degrees are achieved, and the scan angle in the plasma is linearly proportional to the ramp voltage applied to the scanner. Access to tokamak is through a 15 cm hole in the floor, and the optics of the spectrometer are filled