Theoretical and experimental investigation of the phase-runaway in microwave reflectometry

Abstract

Runaway of the reflectometer output phase can be produced by transversely propagating density fluctuations if the antenna system is operated in the tilt-mode, i.e. away from perpendicular incidence. The observed characteristics of the phase runaway are explained with an analytical model. The two-dimensional (2D) effects resulting from poloidally propagating density fluctuations are calculated using a time-independent full-wave 2D code. Numerical simulations for both monochromatic and turbulent density fluctuations are presented. Good agreement with the characteristics of phase runaway measured with reflectometry in the W7-AS stellarator is obtained. The potential of a reflectometer in the tilt-mode to measure the radially resolved poloidal propagation velocity of density fluctuations is analysed.

Polarizer design for millimeter-wave plasma diagnostics

“…The replacement of grooved mirrors by birefringent windows simplifies the quasi-optics and is principally applicable to other low power microwave systems such as ECE or correlated ECE detection, [16][17][18] polarimetry, reflectometry 19 or Doppler back scattering, where probing and receiving beam penetrates or leaves the plasma under an oblique angle. [20][21][22] While a power absorption of less than 1% in sapphire is still too large for high power application such as ECRH or ECCD, it is easily acceptable for low power millimeter wave diagnostics.…”

Three Dimensional Measurements Of Radially Sheared Zonal Flows By Correlation Doppler Reflectometry

“…There are artificial higher frequency components (30 − 50kHz) in the spectrum from phase derivative method, which could be induced by the zero order of the reflected signal as discussed in Ref. [16]. A coherent peak of 12kHz is observed from the spectra.…”

Chapter 3: Microwave Diagnostics

“…instabilities. 162 The complex interplay of all the parameters have led to the development of comprehensive simulation codes 161,163 as well as analytical developments. 164,165 On the experimental side, different antenna configurations monostatic versus bi-static antennas, normal horns versus Gaussian focused beams, symmetrical launchers, etc.!…”

“…have been used. Of particular interest are the devoted experiments carried out in the W7-AS device, 160,161,166,167 using several antennas at different tilt One of the added features was the use of two symmetrical launchers in order to separate phenomena~possible effects of "tilted" structure of the turbulence, as in a "blazed" diffraction grating! and also to improve the determination of the actual tilt angle.…”