Collective scattering of gyrouon radiation and its potennal for plasma diapostics was investigated using the WFAS stellamor. The ion temperature was determined from thermal spectra in neuwd-beom-heated plasmas. The excitation of a n m w band plasma wave by a non.thermd ion component w a observed and the wave characteristics wece investigated experimentally. The results constitute an important step toward a-pmicle diagnostic via scattering of powerful microwave radiation.

Collective Thomson scattering (CTS) of electromagnetic radiation from thermal plasma fluctuations in principle 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.We have performed the first experiments at W7-AS with different scattering geometries to prove the applicability of gyrotrons for CTS. The experiments were performed with a 140 GHz gyrotron which is routinely used for ECRH, delivering a power of 0.45 MW. 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, we have measured a transversely propagating, non-thermal lower-hybrid turbulence, 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. The ion temperatures derived from these thermal spectra agree well with other diagnostics.A modified scattering geometry (90 • scattering) allows local measurements of the ion temperature and is considered a prototype for the design of a routine diagnostic for iontemperature measurements.

The principles of construction of millimeter wave detectors based on low-barrier Schottky diodes and planar antennas are discussed. The modified planar slot antenna with low beam spillover at the resonant frequency of 94 GHz has been developed. Experiments have been carried out to investigate detecting characteristics of the diodes with differential contact resistances R j ¼ 1 Ä 1000 kΩ at zero bias. Experimental data are well correspond to calculations in a simple model of detector. At R j ¼ 20 Ä 100 k Ω the maximum of rf-todc voltage sensitivity -more than 10000 V/W -is obtained. At lower values of R j ¼ 2 Ä 6 k Ω a better noise equivalent power (NEP), around 10 −12 W Hz −1/2 , is predicted.

We discuss the concept of developing a millimeter-wave multielement matrix receiver on the basis of planar antennas with directly coupled low-barrier Schottky diodes. Three main problems are considered which involve choosing and developing a design of the planar antenna coupled with the low-barrier Schottky diode, optimizing the parameters of the low-barrier Schottky diodes for obtaining maximum sensitivity, and ensuring compact arrangement with weak mutual influence of the planar detectors in a two-dimensional array. We propose a design of the slot antenna with an active resistance of about 800 Ω at a resonant frequency of 94 GHz. The detection characteristics of diodes with the differential Schottky-barrier resistance in the range R j = 0.4-1000 kΩ for a zero bias are studied experimentally. The mutual influence of the neighboring antennas is examined for developing the multielement radio-imaging system. The conditions of weak cross influence of the closely located planar detectors are determined.

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