Measurement of Time Delay between Magnetic Diagnostic Coils in Tokamak Using Cross-Spectral Analysis

Abstract

Delay in detecting the position and boundaries of the plasma confined by a tokamak increases plasma instability and decreases the accuracy of plasma control in tokamak. In this article, two techniques called ‘‘periodogram’’ and ‘‘cross-spectral analysis’’ are used to provide a quantitative approach for computing the time delay between data received by two diversity coils from one source (plasma fluctuations) in IR-T1 tokamak. To analysis the achieved data after performing the Fourier transform on the data, the periodogram, square-coherency and spectrum phase diagram of the data were plotted in terms of frequency at three different time intervals. In the time interval, $29000<t<3000$ $\mu$s, when the plasma current is almost constant, the average phase shift between the $\omega$-frequencies components of the data was obtained by using the phase-spectrum analysis. At the frequency of the highest coherency the time delay ($\tau_{d}=1.831$ $\mu$s) between the data of the Rogowski and Mirnov coils was calculated by considering the average phase shift between them.