Study on the influence of three-grid assembly thermal deformation on breakdown times and an ion extraction process

In order to study the influence of three-grid assembly thermal deformation caused by heat accumulation on breakdown times and an ion extraction process,a hot gap test and a breakdown time test are carried out to obtain thermal deformation of the grids when the thruster is in 5 k W operation mode.Meanwhile,the fluid simulation method and particle-in-cell-Monte Carlo collision(PICMCC) method are adopted to simulate the ion extraction process according to the previous test results.The numerical calculation results are verified by the ion thruster performance test.The results show that after about 1.2 h operation,the hot gap between the screen grid and the accelerator grid reduce to 0.25–0.3 mm,while the hot gap between the accelerator grid and the decelerator grid increase from 1 mm to about 1.4 mm when the grids reach thermal equilibrium,and the hot gap is almost unchanged.In addition,the breakdown times experiment shows that 0.26 mm is the minimal safe hot gap for the grid assembly as the breakdown times improves significantly when the gap is smaller than this value.Fluid simulation results show that the plasma density of the screen grid is in the range 6?×10~(17)–6?×?10~(18) m~(13) and displays a parabolic characteristic,while the electron temperature gradually increases along the axial direction.The PIC-MCC results show that the current falling of an ion beam through a single aperture is significant.Meanwhile,the intercepted current of the accelerator grid and the decelerator grid both increase with the change in the hot gap.The ion beam current has optimal perveance status without thermal deformation,and the intercepted current of the accelerator grid and the decelerator grid are 3.65 m A and 6.26 m A,respectively.Furthermore,under the effect of thermal deformation,the ion beam current has over-perveance status,and the intercepted current of the accelerator grid and the decelerator grid are 10.46 m A and 18.24 m A,respectively.Performance test results indicate that the breakdown times increase obviously.The intercepted current of the accelerator grid and the decelerator grid increases to 13 m A and 16.5 m A,respectively,due to the change in the hot gap after 1.5 h operation.The numerical calculation results are well consistent with performance test results,and the error comes mainly from the test uncertainty of the hot gap.     

如何搞好计量工作的几点思考

计量工作关系国计民生,搞好计量工作要做到:以服务为本,帮企业节能降耗;加强学习,提高计量工作人员素质;关注民生计量工作,维护大众利益;锐意创新,促进计量工作再上台阶。     

低浓度硼对锆合金缓蚀作用研究

采用动电位极化和电化学阻抗谱法（EIS）研究了核电厂包壳材料锆合金在3种pH值相同的正常硼锂水质中的高温电化学腐蚀行为；采用高压釜腐蚀增重和微观分析等手段研究了锆合金在2种锂浓缩水质中的均匀腐蚀行为。高温电化学腐蚀试验表明:在3种pH值相同的正常硼锂水质中，随着硼浓度的增加， 锆合金的钝化电流密度减少而交流阻抗值增大，硼对减缓锆合金的腐蚀有利。均匀腐蚀试验表明:相对于无硼的锂浓缩水质而言，加硼显著降低了锆合金的腐蚀增重量，减少了氧化膜厚度，并使氧化膜更为致密，对提高锆合金的耐锂浓缩加速腐蚀有明显作用。      

Study of the key factors affecting the triple grid lifetime of the LIPS-300 ion thruster

In order to ascertain the key factors affecting the lifetime of the triple grids in the LIPS-300 ion thruster,the thermal deformation,upstream ion density and component lifetime of the grids are simulated with finite element analysis,fluid simulation and charged-particle tracing simulation methods on the basis of a 1500 h short lifetime test.The key factor affecting the lifetime of the triple grids in the LIPS-300 ion thruster is obtained and analyzed through the test results.The results show that ion sputtering erosion of the grids in 5 kW operation mode is greater than in the case of 3 kW.In 5 kW mode,the decelerator grid shows the most serious corrosion,the accelerator grid shows moderate corrosion,and the screen grid shows the least amount of corrosion.With the serious corrosion of the grids in 5 kW operation mode,the intercept current of the acceleration and deceleration grids increases substantially.Meanwhile,the cold gap between the accelerator grid and the screen grid decreases from 1 mm to 0.7 mm,while the cold gap between the accelerator grid and the decelerator grid increases from 1 mm to 1.25 mm after 1500 h of thruster operation.At equilibrium temperature with 5 k W power,the finite element method(FEM)simulation results show that the hot gap between the screen grid and the accelerator grid reduces to 0.2 mm.Accordingly,the hot gap between the accelerator grid and the decelerator grid increases to 1.5 mm.According to the fluid method,the plasma density simulated in most regions of the discharge chamber is 1?×?10~(18)-8?×?10~(18)m~(-3).The upstream plasma density of the screen grid is in the range 6?×?10~(17)-6?×?10~(18)m~(-3)and displays a parabolic characteristic.The charged particle tracing simulation method results show that the ion beam current without the thermal deformation of triple grids has optimal perveance status.The ion sputtering rates of the accelerator grid hole and the decelerator hole are 5.5?×?10~(-14)kg s~(-1)and 4.28?×?10~(-14)kg s~(-1),respectively,while after the thermal deformation of the triple grids,the ion beam current has over-perveance status.The ion sputtering rates of the accelerator grid hole and the decelerator hole are 1.41?×?10~(-13)kg s~(-1)and 4.1?×?10~(-13)kg s~(-1),respectively.The anode current is a key factor for the triple grid lifetime in situations where the structural strength of the grids does not change with temperature variation.The average sputtering rates of the accelerator grid and the decelerator grid,which were measured during the 1500 h lifetime test in5 k W operating conditions,are 2.2?×?10~(-13)kg s~(-1)and 7.3?×?10~(-13)kg s~(-1),respectively.These results are in accordance with the simulation,and the error comes mainly from the calculation distribution of the upstream plasma density of the grids.     

分压电流对7.62 cm光电倍增管性能的影响

7.62 cm(3英寸)光电倍增管(Photomultiplier Tube,PMT)是江门中微子实验(Jiangmen Underground Neutrino Observatory,JUNO)巨型探测器的重要组成部分,以此构成的一套独立探测系统,承担着独立物理测量、与50.8 cm(20英寸)PMT探测系统相互检验等重要任务。为提高探测系统的可靠性,使每个7.62 cm PMT供电高压的单通道电流不超过10?A,研究了不同高压电流对7.62 cm PMT探测性能的影响。采用三种高压电流的分压器,对海南展创生产的型号为XP72B20(样管编号为70069)的7.62 cm PMT的性能进行实验测试,包括增益、能量分辨率、峰谷比和阳极输出信号的非线性。结果表明:不同分压电流对7.62 cm PMT性能的影响较小。这个结果为该7.62 cm PMT在JUNO探测器中使用小分压电流的方案提供了重要的实验依据。     

国际新趋势 超市中的餐饮

正在超市中开餐饮店?国内好像还少有,但是,在美国和加拿大等地,却方兴未艾,经营红火。混合型食品超市在美国加州,有一家较大型的混合型食品超市,销售着某些类型的海鲜、酒类、饮品、芝士、餐具、酒具等,主要以销售生蚝为多。所谓混合型,就是既有像超市一样自助选取商品,也有柜台式的销售。整个市场少说也有4000平方米。笔者与家人来到了其中一个蚝档。此档长约七八米,宽约3米多,团团围绕着档口的是吧台式光滑的石板,石板前是高高的吧椅,供食客坐着享用美味。堆     

丙硫菌唑中间体的合成优化

作为一种新型的三唑硫酮类杀菌剂,丙硫菌唑凭借其广谱的杀菌活性及低毒、安全、环保特性,目前已跃居全球第三大杀菌剂。但是,丙硫菌唑关键中间体的合成阻碍了原药的大量生产,主要对α-乙酰基-α-氯-γ-丁内酯和3,5-二氯-2-戊酮的合成进行了研究和优化,为原药的合成与生产做好铺垫。