Berlin 2001 – scientific programme

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P: Plasmaphysik

P 1: Magnetic Confinement and Plasma Wall Interaction

P 1.6: Talk

Monday, April 2, 2001, 17:55–18:10, 2053

Electron Bernstein emission diagnostic of electron temperature profile at W7-AS Stellarator — •Francesco Volpe and Heinrich Peter Laqua — Max-Planck-Institut für Plasmaphysik, EURATOM Assoziation, 85748 Garching

We present an electron temperature profile diagnostic extending the operational regime of the electron cyclotron emission (ECE) beyond the cutoff density by detecting electron Bernstein waves (EBWs), that propagate without upper density limit and carry local temperature information, since the plasma acts as a blackbody emitter for them. The EBWs, otherwhise confined in the plasma core by the upper hybrid layers, access an external antenna after mode conversion into electromagnetic waves polarized in the extraordinary (X) and finally in the ordinary (O) mode (so called BXO process). Such O-mode polarized output can be detected along a special oblique sightline. An antenna has been designed with this scope, and optimised by means of EBWs ray tracing calculations in full stellarator geometry, in order to maximize the conversion efficiency and to minimize the Doppler broadening consequent to the oblique nature of the viewline itself. The elliptical polarization of the signal collected by the antenna is linearized by a broadband quarter wave phase-shifter, namely an elliptical waveguide, and finally spectrum-analysed in the 70GHz ECE heterodyne radiometer, added of 8 extra channels, for a total of 32. The spectra are converted in profiles by means of the above mentioned ray tracing code. The first profiles are presented, together with time- and space-resolved measurements of ELMs, L-H transitions and radiative collapse at high densities not accessible to conventional ECE.