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Effects of the critical breakdown path on the ignition performance in heaterless hollow cathodes

Plasma Science and Technology 2020年第6期22卷 164-179页

作者： Bo YU Yanda LEE Xiaolu KANG Qing ZHAO Center for Information Geoscience School of Resources and EnvironmentUniversity of Electronic Science and Technology of ChinaChengdu 611731People's Republic of China Shanghai Institute of Space Propulsion Shanghai 201112People's Republic of China

The critical breakdown path(CBP)has a significant impact on the breakdown voltage curve and the ignition time of heaterless hollow cathodes(HHCs).To determine the pattern of the variation in the CBP position and its impact on ignition performance,a numerical model named the CBP evaluation(CBPE)was established in this paper to calculate the CBP of a *** CBPE model can be used to screen various potential breakdown paths to identify those that are most likely to satisfy the Townsend breakdown conditions,which are denoted as *** verify the calculation accuracy of the CBPE model,4.5 A-level HHC ignition tests were conducted on HHCs with three different *** comparing the test results and the calculated results of the breakdown voltage,the calculation errors of the CBPE under three HHC conditions ranged from 1.6%to 5.8%,and the trends of the calculated results were consistent with those of the test *** ignition test also showed the characteristics of the breakdown voltage curve and the ignition time for the three *** on the CBPE model,an in-depth analysis was conducted on the mechanism of the patterns revealed by the *** main conclusions are presented as follows:(1)the CBP always shifts from the long path to the short path in the HHCs with an increasing gas flow rate;and(2)the ignition time of the HHCs depends on the position of the CBP because different CBP positions can cause different mechanisms of heat transfer from the plasma to the *** study can guide the optimization of the CBP position and the corresponding ignition times of HHCs.

关键词： breakdown path heaterless hollow cathode breakdown voltage ignition time numerical calculation

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IGNITING SHS BY LASER AND ITS APPLICATION TO SELECTIVE LASER SINTERING OF METALLIC POWDER MATERIAL

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Acta Metallurgica Sinica(English Letters) 2004年第5期17卷 694-704页

作者： Y.S.Shi S.C.Chen X.L.Lu S.H.Huang StateKeyLaboratoryofPlasticFormingSimulationandDie＆MouldTechnology SchoolofMaterialScienceandEngineeringHuazhongUniversityofScienceandTechnologyWuhan430074China

How to directly fabricate metallic functional parts with selective laser sintering (SLS) process is a potential technique that scientists are researching. Existent problems during directly fabricating metal part by use of SLS are analyzed. For the sake of solving the problems, a new idea of adding self-propagating high-temperature synthesis (SHS) material into metallic powder material to form new type of SLS metallic powder material is put forward. This powder material can release controllable amount of heat during its interaction with the laser beam energy to reduce the requirement to laser power during directly sintering metallic part, to prolong the time of metallic liquid phase existing, and to improve the intensity and accuracy of SLS part. For this reason, SHS material′s interaction with the CO2 laser beam energy is researched, which proves that CO2 laser beam energy may instantly ignite SHS reaction. On the basis of the above-mentioned researches, the effect of sintering the metal powder material mixing SHS material with CO2 laser is also researched, which shows: there is an optimal blending ratio of various material in the new metallic powder material. Under the optimal blending ratio and SLS process parameters, this new metallic powder material can indeed release amount of heat and SHS reaction may be controlled within the laser sintering. This research result makes it possible that the metallic part is directly sintered with small CO2 laser (less than 50W), which may greatly reduce the volume, cost and running expenditure of SLS machine, be propitious to application.

关键词： selective laser sintering (SLS) self-propagating high-temperaturesynthesis (SHS) ignition time metallic powder material,metallic part

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Experimental Study on Igniting Self-propagating High-temperature Synthesis by Laser

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Chinese Journal of Lasers 2002年第1期11卷 67-73页

作者： CHEN Senchang SHI Yusheng HUANG Shuhuai (College of Material Science and Engineering of Huazhong University of Sci. & Tech., Wuhan 430074, China) College of Material Science and Engineering of Huazhong University of Set. & Tech. Wuhan 430074

An applied range of self-propagating high-temperature synthesis (SHS) is extended under igniting by laser, but there is no study in detail on its ignition process. The ignition time of SHS by laser is studied in detail in this paper for searching igniting law. A laser beam produced by CO 2 laser scans back and forth along a straight line on the surface of a sample, and an ignition time is measured under different testing conditions. The results show that the ignition time is the shortest at certain mixing time, the ignition time is longer with decreasing of the density and increasing of the sample density, and the ignition time becomes shorter when pre-heat temperature rises, but the ignition time has no relation with the area and the thickness of samples when the thickness is thicker, and it has no close relation with shield gas of N 2.

关键词： SHS laser ignition time

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