A study of grid failure mode drivers and methods for accelerated life testing of a 30cm diameter ion thruster

In view of the high cost caused by the 1:1 lifetime verification test of ion thrusters,the lifetime acceleration test should be considered.This work uses the PIC-MCC(Particle-in-Cell MonteCarlo Collision)method to analyze the five failure factors that lead to the failure of the accelerator grid of a 30 cm diameter ion thruster under the working mode of 5 k W.Meanwhile,the acceleration stress levels corresponding to different failure factors are obtained.The results show that background pressure has the highest stress level on the grid's erosion.The accelerator grid aperture's mass sputtering rate under the rated vacuum degree(1×10^(-4)Pa)of 5 k W work mode is 8.78 times that of the baseline vacuum degree(1×10^(-6)Pa),and the mass sputtering rate under worse vacuum degree(5×10^(-3)Pa)is 5.08 times that of 1×10^(-4)Pa.Under the influence of the other four failure factors,namely,the voltage of the accelerator grid,upstream plasma density,the screen grid voltage and mass utilization efficiency,the mass sputtering rates of the accelerator grid hole are 2.32,2.67,1.98 and 2.51 times those of the accelerator grid hole under baseline condition,respectively.The ion sputtering results of two 30 cm diameter ion thrusters(both installed with new grids assembly)after working for 1000 h show that the mass sputtering rate of the accelerator grid hole under vacuum conditions of 5×10^(-3)Pa is 4.54 times that under the condition of 1×10^(-4)Pa,and the comparison error between simulation results and test results of acceleration stress is about 10%.In the subsequent ion thruster lifetime verification,the working vacuum degree can be adjusted according to the acceleration stress level of background pressure,so as to shorten the test time and reduce the test cost.

A realistic expectation of sea level rise in the Mexican Caribbean

This paper provides a realistic estimation of the sea level rise by 2050 and by 2100 in the Mexican Caribbean,and more specifically in the North-East side of the Yucatan peninsula,in between Cancun and Playa del Carmen,where the most part of the touristic developments of the Yucatan is located.The forecast is based on the relative sea level result for Key West,the closest long-term trend(LTT)tide gauge,the relative sea level results for all the other LTT tide gauge records of the world,and the absolute velocity of GPS domes located close to the Key West tide gauge,and in between Cancun and Playa del Carmen.The likely change of the sea level is 67-76 mm higher by 2050,and 201-223 mm higher by 2100,with reference to the values of 2018.

The global mean sea level rise,still accelerated

Subject Code:D06A collaborative study partly sponsored by the National Natural Science Foundation of China indicates that the global mean sea level is still accelerated rising,with much of the increase from the accelerated Greenland ice sheet melting during 1993—2014.The work is coauthored by Prof.Chen Xianyao(陈显尧)

Coastal life is not under threat by the carbon dioxide emissions

The near future of coastal life is threated by the claim of global warming alarmist that sea levels will rise by one to seven metres by 2100,destroying many coastal cities and habitats.This paper shows that sea levels will more likely rise no more than just a few centimetres during this century as the Earth defrosts from the Little Ice Age 500 years ago with a mild warming.