Evolution of the radiated power profile and thermal collapse in ATF

Thermal plasma collapses have been observed in the Advanced Toroidal Facility (ATF) and in some cases these collapses limit the plasma performance. A 15-channel bolometer array has been used to measure the radiated power profile. It has been found that thermal collapses, defined by a drop in the plasma stored energy, occur when the local radiated power exceeds the local power input to the electrons. The local radiated power at the collapse first increases at the edge and then begins to propagate inward, leading to a peaking of the radiated power profile. This finding indicates that additional central heating would be effective in preventing the thermal collapse.