Abstract
A transient TRansport Analysis method for Modulation (t-TRAM) has been developed. This method consists of two methods. One is an instantaneous modulation analysis method using the Hilbert transform (HT) with the analytical mode decomposition (AMD). In the modulation experiments, plasma transport can be changed periodically by modulated external input. Profiles of the modulation amplitude and phase change in time due to the change in the plasma transport. The HT with AMD method can evaluate an instantaneous analytic signal in the presence of changes in the modulation amplitude and phase in time. The other is a transport analysis method to evaluate the diffusion coefficient and the convection velocity from the analytic signal. The t-TRAM has enabled us to evaluate a momentum diffusion coefficient and momentum convection velocity in the presence of a momentum source. The t-TRAM is applied to momentum modulation experiments in JT-60U. The evaluation reveals that a normalized momentum flux has a linear dependence on a normalized momentum gradient during a half cycle of the modulation.
Highlights
Modulation experiments are commonly used to evaluate the diffusion coefficient and the convection velocity of magnetically confined plasmas experimentally.1–8 In the experiments, the plasma transport changes periodically by the modulated external input, e.g., gas puff injection, electron cyclotron resonant heating, and neutral beam injection (NBI)
The diffusion coefficient and the convection velocity are evaluated from the modulation amplitude and phase, which are commonly evaluated by the fast Fourier Transform (FFT)
This paper presents the transient transport analysis method for modulation (t-TRAM), using the Hilbert transform (HT) with analytical mode decomposition (AMD) method, and the diffusion coefficient and the convection velocity calculated from the analytic signal
Summary
Modulation experiments are commonly used to evaluate the diffusion coefficient and the convection velocity of magnetically confined plasmas experimentally. In the experiments, the plasma transport changes periodically by the modulated external input, e.g., gas puff injection, electron cyclotron resonant heating, and neutral beam injection (NBI). Modulation experiments are commonly used to evaluate the diffusion coefficient and the convection velocity of magnetically confined plasmas experimentally.. The diffusion coefficient and the convection velocity are evaluated from the modulation amplitude and phase, which are commonly evaluated by the fast Fourier Transform (FFT). In order to apply the FFT to the modulation experiments, the FFT requires one or more modulation periods in which the plasma condition is kept constant. These plasma operations are generally difficult and time-consuming, and they limit the experimental condition. The FFT cannot evaluate these changes of the plasma transport in time
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