Synergetic Effects of Runaway and Disruption Induced by VDE on the First Wall Damage in HL-2A

The plasma facing component in HL-2A has been damaged seriously after disruption,and for this reason its operation is suspended for maintenance.The experimental phenomena and plasma configurations,calculated by the current filament code(CF-code) using the plasma parameters measured by diagnostics and the signals of the magnetic probes,confirm that the first wall is damaged by the synergetic effects of runaway electrons and disruption induced by a vertical displacement event(VDE).When the plasma column is displaced upward/downward,the strong runaway electrons normally hit the baffle plate of the MP 3 or MP 1 coil in the upper and lower divertor during the disruption,causing the baffle plates to be holed and wrinkled by the energetic runaway current,and water(for cooling or heating the baffle plates) to leak into the vacuum vessel.Another disastrous consequence is that bellows underlying the baffle plate and outside the coil of MP 3 for connecting two segments of the jacket casing pipe are punctured by arcing.The arc may be part of the halo current that forms a complete circuit.The experimental phenomena are indirect but compelling evidence for the existence of a halo current during the disruption and VDE,though the halo current has not been measured by the diagnostics in the HL-2A tokamak.     

硅漂移探测器电子温度测量系统研制

在2005年HL-2A实验中,我们首次采用两通道硅漂移探测器(Silicon Drift Detector,SDD)软X射线能谱系统对等离子体电子温度进行了测量。文章详细地介绍了SDD软X射线能谱测量系统的原理、设计和初次运行,给出了HL-2A电子温度的测量结果。结果表明,SDD非常适合于HL-2A电子温度测量,为在HL-2A上建立多通道SDD阵列测量电子温度分布奠定了坚实的基础。     

硅漂移(SDD)阵列探测器X射线能谱测量诊断

采用最新的SDD探测器阵列测量HL-2A托卡马克等离子体软X射线(1～20keV)辐射的能谱,获得电子温度、Zeff、重金属杂质含量绝对值及其时、空分布。由于SDD探测器较之传统的Si(Li)探测器有体积小、计数率高(≥10^6／S),能量分辨和量子效率高,不需液氮冷却的特点,并采用高速ADC和海量缓存器,电子温度测量的时、空分辨能力接近汤姆逊散射和ECE等方法．而测量精确度、使用寿命、造价、抗干扰能力、适应性等方面优于后者．且信息获取量大,可获得多种等离子体参数而备受重视,是一种最先进的诊断手段。     

Development of Prototype Neutron Flux Monitor for ITER

The prototype neutron flux monitor consists of a high purity 235U fission chamber detector and a “blank” detector, which is a fissile material free detector with the same dimension as the fission chamber detector to identify noise issues such as noise coming from gamma rays. The main parameters of the fission chamber assembly that have been measured in the laboratory are confirmed to approach the technological level of the International Thermonuclear Experimental Reactor (ITER) in the near future. This prototype neutron flux monitor will be further developed to become a neutron flux monitor suitable for the operation phase of D-D fusion on the ITER.     

Fusion Neutron Flux Detector for the ITER

Two fission chambers with different amounts of fissile material （enriched 90% uranium-235） have been manufactured for neutron flux detection in a thermonuclear fusion device. The characteristics of neutron signal and its discrimination from other signals, and a plateau of high voltage between the anode and cathode have been validated in a thermal neutron source. The energy responses of the two fission chambers at seven energy levels have been calibrated in an accelerator fast neutron source and the results agree well with the simulations.