Collective Thomson scattering at W7-AS
Collective Thomson scattering (CTS) of electromagnetic radiation from thermal plasma fluctuations allows the velocity distribution of plasma ions and its composition in the plasma to be measured. The use of powerful microwave radiation from gyrotrons opens new perspectives for the application of CTS, which is considered to be a promising candidate for alpha-particle diagnostics in reactor-size tokamaks with D/T operation. This paper describes the first experiments performed at W7-AS with different scattering geometries to prove the applicability of gyrotrons for CTS. The receiver antenna and detection system for the registration of CTS spectra were especially designed for the scattering experiment. In backscattering experiments, which have inherently no spatial resolution, a transversely propagating, non-thermal lower-hybrid turbulence has been measured, which is driven by perpendicularly injected fast particles from a diagnostic neutral beam. The instability is excited by the beam ions under double-resonance conditions, where the LH frequency coincides with some harmonic of the beam ion gyrofrequency. For scattering geometries with the scattering wavevector not perpendicular to the magnetic field, thermal density fluctuations in the plasma were experimentally detected.
Bibliographic Reference: Article: Plasma Physics and Controlled Fusion, Vol. 39 (1997) pp. B337-B351
Record Number: 199810304 / Last updated on: 1998-03-09
Original language: en
Available languages: en