Development of high-frequency photomultiplier tube detector used for vacuum-ultraviolet spectroscopy in EAST tokamak

Abstract

In present tokamak experiments, radiative-divertor operation mode, achieved by injecting gaseous impurity in the divertor region, can effectively mitigate the erosion in divertor plates due to the huge heat load from main plasma. Precise measurement of injected impurity emissions is crucial to obtain the steady-state radiative-divertor operation mode. A space-resolved vacuum-ultraviolet (VUV) spectroscopy has been developed to observe impurity emissions of injected impurity from the divertor region on Experimental Advanced Superconducting Tokamak (EAST). However, high-frequency detector is still necessary for the vacuum-ultraviolet (VUV) spectroscopy to measure impurity emissions with sufficient sampling rate, e.g., ≥10kHz. Photomultiplier tube (PMT) is widely used in photon counting systems because of its high gain and low light sensing capability. Therefore, a high-frequency PMT-based detector system is developed for the existing VUV spectroscopy to measure the impurity emissions in EAST. The detector system composed by a Hamamatsu R8486 PMT, a 1MHz amplifier and a 1MHz data acquisition board (DAQ). The PMT has sufficient high quantum efficiency in the wavelength range of 115-320 nm, which satisfies the requirement of the VUV spectroscopy. The PMT is installed inside a vacuum chamber which is connected to the VUV spectrometer. The detector system has been preliminarily tested to verify the capability to measure high-frequency signals. The test results show that the performance of PMT detector satisfies the design requirement.