The locations of the q=2 and q=1.5 magnetic surfaces have been determined to within ±2 cm in TFTR using the emission from ablating deuterium pellets. As predicted theoretically, pronounced reductions in the average emission are found to occur when the pellet crosses these low order rational surfaces. Further, radial displacement of these surfaces is observed when the current distribution is modified. This modification has been accomplished by conditioning the graphite inner wall of TFTR so as to cause a higher effective pumping rate. The positions and radial displacements of these surfaces are predicted reasonably well by the transport analysis code TRANSP
Neutron and hard X-ray measurements during pellet deposition in TFTR