ITER ECE: PLANS AND CHALLENGES

Measuring ECE in ITER plasmas will present several difficulties in both hardware and physics that will impede efforts to determine T_c(r,t) and characteristics of the electron distribution function. Recent work on the diagnostic systems and techniques to be employed on ITER has clarified some of these issues and found some solutions. Studies show that even with the greater relativistic broadening due to the high electron temperature, T_e measurements with spatial resolution of 6-10 cm are still possible especially with properly designed front-end optics and instruments. ECE will still be able to provide high resolution T_c profiles in both core and edge regions and even follow oscillations of high m, n TAE modes. Of greater concern is the possibility and effects of non-Maxwellian electron distributions created by intense auxiliary heating. In these cases modeling will have to be used to correct and define the valid limits of T_e from ECE and a special oblique viewing antenna is recommended. The planned ECE instruments, heterodyne radiometer and Michelson interferometer, will provide complementary measurement capabilities. A viable in-port-plug calibration source for these instruments is a concern; progress on work being done to develop a prototype is reported.