2-D Heat Load Distribution on the TFTR Bumper Limiter During High-Power Neutral Beam Injection

The plasma-facing wall in the Tokamak Fusion Test Reactor (TFTR) is covered in large part by a bumper limiter. The limiter extends the full 360° toroidally and ±60° with respect to the midplane on the small-majorradius side. The limiter is the primary power-handling surface of the first wall. The heat-distribution over the two-dimensional surface of the bumper limiter during high-power neutral-beam heated discharges is determined by using a large array of thermocouples distributed around the entire limiter. The heat distribution for normal high-power neutral-beam heated discharges is not very different from that for ohmic discharges. Large variations in heat loading are found, both poloidally and toroidally, even though the limiter was aligned, at the midplane, to within 0.5 mm of a true circle. The heat distribution for discharges which exhibited carbon blooms are compared to otherwise identical discharges which did not show blooms. The heat distribution of a particularly high-power disruptive discharge is examined to determine why recovery from this discharge was difficult.