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

Highlights: • The electronic bandwidth of ME-SXR is consistent with the nominal value. • The relative gain errors for different channels were calibrated on the EAST tokamak. • A feedback loop was designed to automatically adjust the gains of the preamplifiers. • The dynamics of edge electron temperature evolution in different ELMs were compared. - 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 (T_e) profile was also uploaded automatically to the MDSplus server between discharges. Utilizing the fast temporal resolution of T_e (∼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 T_e profile collapsed during Type I ELMs, while for the HF-ELM regime, the edge T_e profile pedestal structure sustains stiffness.