Measurement of emitted power in the divertor region in PBX

Abstract

In strongly indented PBX plasmas, radiated power profiles are calculated by combining data obtained from two bolometer arrays in order to study poloidal asymmetries arising from plasma indentation and characterize emission from the divertor region. A compact, 15-channel bolometer array that views the plasma tangentially along the mid-plane complements a 19-channel array that scans the plasma vertically in a poloidal plane. Assuming that radiated power density is constant along a magnetic flux surface, the contribution to the irradiance viewed by the poloidal array from the region inside the separatrix can be calculated from the mid-plane measurements. The difference between this contribution and the measured poloidal distribution is assumed to originate in the expanded boundary divertor. In general, the total radiated power loss constitutes 40% of the total input power, and is independent of beam geometry. However, the radiation profiles in the main plasma and divertor region depend on operating conditions such as beam geometry and gas puffing rates. Radiation from the main plasma accounts for 20% of the input power and radiation from the divertor region accounts for 20%. Accumulation of impurities during neutral beam heated discharges can cause peak radiation levels to exceed 1 W/cm 3, leading to a thermal collapse of the plasma.