Electron Bernstein wave electron temperature profile diagnostic (invited)

Electron cyclotron emission (ECE) has been employed as a standard electron temperature profile diagnostic on many tokamaks and stellarators, but most magnetically confined plasma devices cannot take advantage of standard ECE diagnostics to measure temperature. They are either "overdense," operating at high density relative to the magnetic field (e.g., omega (pe) much great er than Omega (ce) in a spherical torus) or they have insufficient density and temperature to reach the blackbody condition (tau >2). Electron Bernste in waves (EBWs) are electrostatic waves that can propagate in overdense pla smas and have a high optical thickness at the electron cyclotron resonance layers as a result of their large k(perp). In this article we report on mea surements of EBW emission on the CDX-U spherical torus, where B-0 similar t o 2 kG, [n(e)] similar to 10(13) cm(-3) and T-e approximate to 10-200 eV. R esults are presented for electromagnetic measurements of EBW emission, mode converted near the plasma edge. The EBW emission was absolutely calibrated and compared to the electron temperature profile measured by a multipoint Thomson scattering diagnostic. Depending on the plasma conditions, the mode -converted EBW radiation temperature was found to be less than or equal to T-e and the emission source was determined to be radially localized at the electron cyclotron resonance layer. A Langmuir triple probe and a 140 GHz i nterferometer were employed to measure changes in the edge density profile in the vicinity of the upper hybrid resonance where the mode conversion of the EBWs is expected to occur. Initial results suggest EBW emission and EBW heating are viable concepts for plasmas where omega (pe) much greater than Omega (ce). (C) 2001 American Institute of Physics.