IMPURITY BEHAVIOR IN REAL AND SIMULATED TOKAMAK PLASMAS

A fusion reactor based upon the tokamak principle will only be possible if methods can be developed for controlling the impurity influx so as to maintain an extremely low level of radiating impurity in the plasma. The last few years have seen remarkable experimental progress in this area, so that whereas, even three years ago it was difficult to find a hot tokamak plasma with an effective Z value less than 4 or 5, many tokamaks now routinely produce Zeff close to one. Over a similar period, work with numerical simulation codes has shown that, even for a fixed transport model, the accumulation of impurities in central or in edge regions is determined by density and temperature profiles, which in turn are determined by a complicated interplay of transport, radiation and power deposition. Some calculations have shown that in these circumstances profiles can be manipulated by controlling the power and particle deposition and that as a result the impurity influx can be limited. The present paper presents a review of recent progress in the field. © 1978.