Effect of impurities on radiation loss in the RPI tokamak

A pyroelectric detector has been used to study the power flux on the Rentor tokamak. In particular, we have observed gross changes in the impurity radiation as it relates to vacuum and plasma conditions. Pyroelectric detectors are a potential improvement over bolometers, however, they are more sensitive making them susceptible to electrical, magnetic and plasma noise. Because of this sensitivity, it is important to have separate grounds for the detector-amplifier assembly and the chamber which houses them to keep noise currents in the detector chamber from flowing through the electronics. In addition, the top electrode of the detector must be grounded and the bottom electrode isolated to prevent contact of the plasma with the high impedance signal line. We studied plasmas during the conditioning period after a major vacuum opening when high impurity conditions were present. These plasmas then evolved into lower impurity density discharges as the machine base pressure dropped