Characterization of internal MHD modes in Princeton beta experiment modification by ECE fluctuation radiometry

Localized measurements of internal magnetohydrodynamic (MHD) activity in th e Princeton Beta Experiment-Modification (PBX-M) have been made using a het erodyne radiometer. The radiometer measures third harmonic optically gray e lectron cyclotron emission (ECE) from the center to the outer edge of the p lasma on eight radially localized frequency channels from 112-128 GHz. The radiometer uses a focusing Gaussian optics system, which provides a vertica l resolution of approximately 6 cm throughout the plasma. The radial resolu tion of the diagnostics is limited by the relativistic broadening to approx imately 2-3 cm. Long wavelength (k <0.5 cm(-1)) temperature and density flu ctuations can therefore be detected using this diagnostic. A MHD mode's cha racteristics such as pressure fluctuations and mode amplitude can be derive d from the coherent fluctuations it causes in the ECE signal using an analy tical theory developed by Luckhardt (MIT Plasma Fusion Center Report No. PF C-JA/91-16, 1991). Using this analysis, pressure fluctuations (deltaP/P) ha ve been calculated for high n-number MHD modes in high-beta (p) PBX-M plasm as. (C) 2001 American Institute of Physics.