Upgrade of the multi-energy soft x-ray diagnostic system for studies of ELM dynamics in the EAST tokamak

Abstract

The multi-energy soft x-ray (ME-SXR) diagnostic system has been calibrated to study the evolution of the edge electron temperature profile during the edge localized mode (ELM) events. The electronic bandwidth of the Mazet MTi04 multi-channel variable gain trans-impedance amplifier measured in the laboratory is consistent with the nominal value. As the gain of the preamplifier is increased from 105 to 2 × 107, the bandwidth is decreased from 100 kHz to 10 kHz. The relative gain errors for different channels (5 arrays ×20 channels) were also calibrated in situ after the system was installed on the EAST tokamak. The results showed that the relative gain error (RGE) in each array was less than 10% compared to the reference channel of the array, and was insensitive to the preamplifier gains. A feedback loop was designed to automatically adjust the programmable gains of the preamplifiers based on the signal amplitudes measured in the previous discharge. The reconstructed edge electron temperature (Te) profile was also uploaded automatically to the MDSplus server between discharges. Utilizing the fast temporal resolution of Te (∼5 kHz), the dynamics of edge electron temperature evolution during Type I and high frequency ELM (HF-ELM) events were compared. The results showed that the edge Te profile collapsed during Type I ELMs, while for the HF-ELM regime, the edge Te profile pedestal structure sustains stiffness.