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Multimachine Data–Based Prediction of High-Frequency Sensor Signal Noise for Resistive Wall Mode Control in ITER

Yueqiang Liu, S. A. Sabbagh, I. T. Chapman, S. Gerasimov, Y. Gribov, T. C. Hender, V. Igochine, M. Maraschek, G. Matsunaga, M. Okabayashi, E. J. Strait

Fusion Science and Technology / Volume 70 / Number 3 / November 2016 / Pages 387-405

Technical Paper / dx.doi.org/10.13182/FST15-207

First Online Publication:August 12, 2016
Updated:November 2, 2016

The high-frequency noise measured by magnetic sensors, at levels above the typical frequency of resistive wall modes, is analyzed across a range of present tokamak devices including DIII-D, JET, MAST, ASDEX Upgrade, JT-60U, and NSTX. A high-pass filter enables identification of the noise component with Gaussian-like statistics that shares certain common characteristics in all devices considered. A conservative prediction is made for ITER plasma operation of the high-frequency noise component of the sensor signals, to be used for resistive wall mode feedback stabilization, based on the multimachine database. The predicted root-mean-square n = 1 (n is the toroidal mode number) noise level is 104 to 105 G/s for the voltage signal, and 0.1 to 1 G for the perturbed magnetic field signal. The lower cutoff frequency of the Gaussian pickup noise scales linearly with the sampling frequency, with a scaling coefficient of about 0.1. These basic noise characteristics should be useful for the modeling-based design of the feedback control system for the resistive wall mode in ITER.

 
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