Development Of The Multi-channel Analyzer For X-ray Spectrometer On J-TEXT Tokamak

Plasma disruption is a severe event during tokamak operation,several damages can be caused including heat loading to the plasma facing components(PFCs),the large electromagnetic force and the high energy runaway electrons(REs).Due to the high energy of the REs(~100MeV in some large tokamaks),heavy damages will be caused when they are lost control and impinge on the PFCs.Thus,the disruption mitigation and the behavior of the REs are the hot research topic in the fusion field.For the study of REs,several methods can be used such as hard X-ray(HXR)diagnostic,measurement of synchrotron radiation from IR camera and the photoneutron diagnostic.As one of the conventional diagnostic methods,HXR diagnostic can provide the basic physical information for the study of disruption and REs,which has been widely used in tokamak device.The HXR diagnostic system on J-TEXT mainly consists of the toroidal and space detector arrays around of the device.However,they are all HXR flux diagnostic,can not provide energy evolution of the HXR,but only the HXR radiation intensity.In this paper,A dedicated multi-channel analyzer(MCA)has been designed and the existing HXR detector arrays have been used to develop the HXR spectrometer system on J-TEXT.The spectrometer system can resolve the HXR energy by digitizing the signals of the detectors and provide the distribution of REs by the specific particles inversion algorithm,which provides the detail information for the study of REs.The core content of this paper is the designing of MCA for HXR spectrometer on the J-TEXT tokamak.In the multi-channel analyzer,the digital signal processor(DSP)and dedicated pulse peak detection circuit based on phase compensation have been used to achieve the requirements of high throughput rate(1.2 Mcps),high temporal resolution(0.5ms)and high accuracy(1%).We use mathematical calculation and qualitative analysis methods to design the underlying hardware system circuit and the signal acquisition printed circuit board(PCB).Special mathematical model has been used to analyze the characteristic of the analog signal processing circuit,and the Multisim simulation software was used to verify the circuit.The C language was used to design the underlying hardware system control procedure and the C# language was applied for the designing of acquisition control software.Some particular optimizing was also processed for the software system to meet the needs of high time resolution and stability.Now,the multi-channel analyzer has been used on J-TEXT tokamak for the HXR spectrometer,the energy evolution of REs during the initial phase of discharge and during the runaway current plateau phase have been monitored,the transport behavior of REs during the sawtooth activities has been studied.It was found that the MCA of the HXR spectrometer performed very well in throughput rate,time & energy resolution and stability during experiments.