Correlation analysis of 110 GHz ECH modulation experiments on the DIII-D tokamak

Abstract

Experiments on electron cyclotron heating (ECH) power modulation have been carried out on the DIII-D tokamak with a gyrotron generating about 900 kW and operating at the second cyclotron harmonic, to investigate the power deposition in the plasma, to characterize the microwave beam and to study electron thermal transport. To this end the 110 GHz Gycom Centaur gyrotron output has been modulated in the range 50-300 Hz. The ECH power deposition, beam propagation and the plasma thermal diffusivity have been investigated by using the cross-correlation between the incident ECH power and the electron temperature reaction.

Turbulence at the transition to the high density H-mode in Wendelstein 7-AS plasmas

“…This means that for positive lags, density fluctuations occur first, while for negative lags, they are delayed with respect to the other series. We will denote the lag where the correlation has a maximum the 'toplag', τ 0 [12]. The cross correlation will be calculated for several density fluctuation frequency bands and represented in contour plots; in these plots we define a global maximum correlation position in (τ, ν)-space:…”

Experimental Measurement of ECH Deposition Broadening: Beyond Anomalous Transport

“…EC deposition has been treated by 1D ray tracing and more complex full-wave calculations [3] and benchmarked against experimental deposition measurements [4]. Still, unresolved questions with significance for ITER remain.…”

“…ECCD and ECH experimental profile measurements are made through modulation, perturbing a discharge with a known input, and analyzing its effect on plasma parameters [4]. ECCD measurements can be made by Motional Stark Effect(MSE) [6].…”

Finding evidence for density fluctuation effects on electron cyclotron heating deposition profiles on DIII-D

“…WMECH analysis, which includes a relativistic correction, finds good agreement between TORAY and experimental deposition centres, which were modestly disparate in past studies [6], but experimental deposition profiles remain wider, and higher FFT harmonics do not asymptote to the TORAY values. Transport coefficients for saturation have been fit to BIS profiles, and work is underway to fit diffusive and convective fluxes to data derived from FFT.…”

“…makes higher frequency modulations and higher harmonics within the same modulation successively less susceptible to transport and saturation effects. Unfortunately, as the case of direct derivatives, high frequency measurements are subject to considerable error [6], and in available DIII-D data, frequencies above ~1 kHz are below the noise level of the diagnostics (See Section 3). Equation 2 can be rearranged, defining !"!"…”