Practical limitations to plasma edge electron temperature measurements by radiometry of electron cyclotron emission
Various types of limitations to electron temperature measurements by radiometry of electron cyclotron emission (ECE) are reviewed with respect to their practical relevance for T(e) diagnostics at the edge of fusion plasmas. Low and high density limits exist due to finite optical depth and right-hand wave cut-off, respectively. The spatial resolution is limited by Doppler and relativistic broadening. A new effect is the observation of enhanced ECE at frequencies resonant at plasma edge, obtained at high T(e) gradients and low density. Experimental results are presented to characterize this phenomenon and its dependence on plasma parameters. The distortion of the electron distribution function near the plasma edge necessary is estimated using Fokker-Planck simulations. It is found that the measured ECE spectra can be reproduced if enhanced diffusion of fast particles is assumed. Neo-classical transport, taking into account mirror and ripple trapped particle losses, cannot account for this transport enhancement.
Bibliographic Reference: Report: IPP 1/306 EN (1996) 26pp.
Availability: Available from the Max-Planck-Institut für Plasmaphysik, 85748 Garching bei München (DE)
Record Number: 199710185 / Last updated on: 1997-04-01
Original language: en
Available languages: en