New electron cyclotron emission diagnostic for measurement of temperature based upon the electron Bernstein wave

Most magnetically confined plasma devices cannot take advantage of standard electron cyclotron emission (ECE) diagnostics to measure temperature. They either operate at high density relative to their magnetic field (e.g., omega(p)much greater than Omega(c) in spherical tokamaks) or they do not have sufficient density and temperature to reach the blackbody condition (tau > 2). The standard ECE technique measures the electromagnetic waves emanating from the plasma. Here we propose to measure electron Bernstein waves (EBW) to ascertain the local electron temperature in these plasmas. The optical thickness of EBW is extremely high because it is an electrostatic wave with a large k(i). For example, the National Spherical Torus Experiment (NSTX) will have an optical thickness tau approximate to 3000 and CDX-U will have tau approximate to 300. One can reach the blackbody condition with a plasma density approximate to 10(11) cm(-3) and T-e approximate to 1 eV. This makes it attractive to most plasma devices. The serious issue with using EBW is the wave accessibility for the emission measurement. Simple accessibility arguments indicate the wave may be accessible by either direct coupling or mode conversion through an extremely narrow layer (approximate to 1-2 mm). EBW experiments on the Current Drive Experiment-Upgrade (CDXU) will test the accessibility properties of the spherical tokamak configuration. (C) 1999 American Institute of Physics. [S0034-6748(99)74201-2].