Study On Fast Ion Distribution Measurement System Based On High Sensitivity Photomultiplier Materials In EAST

In the tokamak device,fast ions are produced by neutral beam injection,radio-frequency heating and fusion reactions,and they are the main source of plasma particles,momentum and energy in the device.So they determine the efficiency of heating or current drive.Fast ions also drive the instability,such as the Alfven eigenmodes.As a result,these instability results in a large amount of energy and particle loss,which reduces plasma quality.At the same time,the loss of fast ions will make the constraint properties of the plasma worse,and even destroy the first wall.Therefore,the study of fast ion diagnosis is an unavoidable problem.EAST tokamak is aimed at addressing physics and technology issues facing high power,long-pulse operation in high confinement regimes.Fast ions are mainly produced by auxiliary heating on EAST,As the auxiliary heating systems are being perfected gradually,high performance plasma has been achieved,but problems caused by fast ions get increasingly prominent.Therefore,it is necessary to develop the fast ion diagnostics on EAST to study fast ion behavior and related physical problems.A new filter-based fast ion D-alpha system f-FIDA has been recently developed on EAST to improve temporal resolution ability of the FIDA diagnostic and study relationship between fast-ion transport and plasma instabilities.This system equipped with band pass filters and photomultiplier tube modules measures integrated intensity evolution of the blue-shift part of Doppler shifted Da spectrum in the spectral region of 651-654 nm,and can detect high-frequency oscillations in FIDA signal benefiting from its high temporal resolution.The thesis is focused on design and development of the multi-channel f-FIDA diagnostic on EAST tokamak.An array-PMT is firstly used in the f-FIDA diagnostic.This PMT consists of a 4×4 multi-anode array,each of whose anodes has a size of 4.2×4.2 mm.As a result,diameter of the facula from the end of optical fiber should be limited within 4 mm in order to avoid interference between adjacent light spots,leading to that measured intensity does not satisfy requirements of the f-FIDA diagnostic well.Therefore,the f-FIDA diagnostic has been upgraded with single PMTs measuring independently to achieve high sampling rate and maximize light utilization efficiency.The system now consists of the optical part and the integrated part.While the former has no substantial change compared with the optical system of original f-FIDA diagnostic,the latter,by which the new f-FIDA diagnostic is featured,reduces noise and minimizes parasitic capacitance and leakage current by integrating the photomultiplier tube and current amplifier together.Benefiting from its high gain,broad bandwidth and low noise,good signals from f-FIDA diagnostic have been recorded as expected and experimental purpose has been achieved.Comparison of light parallelism,sampling rate and light utilization efficiency has been made between the two f-FIDA systems.It is observed in discharges that single-PMT f-FIDA has a much better signal-to-noise ratio than array-PMT system.Measurements show that parallelism of single-PMT f-FIDA is almost two times better than that of array-PMT system.The sampling rate of 2 MHz for f-FIDA with single-PMT is much higher than that of 150 kHz for f-FIDA with array-PMT.Moreover,light utilization efficiency of f-FIDA with single-PMT is 90%,while that of f-FIDA with array-PMT is only 60%.Therefore,as a result of its better signal-to-noise ratio,light parallelism,sampling rate and light utilization efficiency,multi-channel f-FIDA diagnostic equipped with single PMTs is preferred in EAST experiments.In EAST 2017 campaign,the f-FIDA diagnostic system with multi-array single PMT has been developed and put into the experiment.The signal of f-FIDA under neutral beam injection was analyzed.The f-FIDA signal under neutral beam injection was analyzed by combining with other fast ion diagnostic data.When the diagnostic beam NBI1L is injected,the f-FIDA signal increases significantly,and then decreases rapidly when the beam is closed.In addition,the consistency of FIDA signal was tested by integrating the net FIDA signal of corresponding wavelength interval of s-fida and the neutron rate of volume integral,and the obtained information was consistent with the variation trend of f-fida signal,further verifying the reliability of the device.