Core electron temperature measurements have been performed in the large, high-current RFX reversed field pinch experiment (a = 0.46 m, R = 2 m, target plasma current = 2 MA) with the double filter technique. With this technique the soft x-ray emission is measured by two Si detectors, covered by different Be-filters, and viewing the same region of the plasma. By choosing the filters in such a way that only the emission from the continuum part of the spectrum is measured, the ratio of the two signals is a function of the highest electron temperature along the line of sight of the detectors. With this diagnostic, the electron temperature has been measured in RFX with a bandwidth of approximately 2 kHz. This allows the direct measurement, for the first time in a RFP on a single shot basis, of coherent oscillations, associated with relaxation events and showing under some conditions a sawtooth-like character. The measurements of electron temperature obtained with this method are in good agreement with those performed with other diagnostics.
Electron temperature diagnostics in the RFX reversed fieldpinch experiment