О. А. Gorshkov, I. P. Li, V. N. Shutov

At present the most broad spreading in cathode for hall and ion plasma thrusters have got the hollow tungsten-barium (W-Ba) and lanthanum-hexaboride (LaВ6) emitters. These cathodes function when presenting in emitters inert gas, usually Хe, in they are realized arc under it is enough high importances of the current ~ 1 - 20 А and high density of the current ~ 1 10 A/sm2 on surfaces of emitters. However each of these emitters has an essential defect. So the operating temperature of lanthanum-hexaboride (LaВ6) emitters is high ~ 1400 1600 С, that greatly above (approximately on 400 - 500 C), than beside tungsten-barium emitters. In turn tungsten-barium emitters noticeably sensitive to poisoning. In persisting article is undertaken attempt to research the possibility of the use of the other type emitters for cathode hall and ion plasma thruster, as follows, iridium-lanthanum emitters (Ir-La). This emitters, on the one hand, must differ greatly smaller aptitude to poisoning in contrast with tungsten-barium emitters, but, on the other hand, safely function under moderate temperature, noticeably more low, than the operating temperature of lanthanum-hexaboride (LaВ6) emitters. For study of the possibility of the use iridium-lanthanum emitters as main element cathode hall and ion plasma thruster was made two cathodes. Inwardly one of them was installed tungsten-barium) emitter, inwardly other - an iridium-lanthanum emitter. The cathodes were made absolutely identical. Constructive scheme cathode is in detail described in article. After fabrication each of cathode to be subjected to the serieses of the test. Autonomous fire test cathode were realized at vacuum chamber by volume ~ 1 m3, equiped by turbomolecular pump. The operating range current cathode was 1,5 - 5 A. Test were realized They are received volt-ampere feature (VAH) of the cathodes. VAH each cathode presents itself standard falling dependency of the voltage from current under fixed mass flow rate - gas He. With increase mass flow rate VAH is displaced downwards, in area of the smaller voltages. VAH for iridium-lanthanum cathode are situated several above corresponding to VAH for tungsten-barium cathode. However in the field of moderate cathode current~ 2,5 - 4 А, as well as for small mass flow rate 0,15 - 0,2 mg/s under greater current Iр > 5 А, VAH for both cathode begin to approach. Exist the states of the cathodes, under which difference in voltage is found at a rate of 1 V. The presented dependencies of the temperature of the emitter diaphragm from current. These temperature for iridium-lanthanum and tungsten-barium cathodes differ under alike current on ~ 120 - 180 C. Were researched also ignition modes of the cathode. What have shown the experimental studies of the different type cathodes, the main parameter, defining ignition of the cathode, is the emitter temperature. Presented importances of the cathodes ignition temperature. It is shown that emitter temperature of iridium-lanthanum cathode, required for ignition, must be on ~ 100 C more emitter temperature of tungsten-barium cathode. Big attention was spared also experimental check to stability iridium-lanthanum cathode to poisoning. For this purpose both cathodes were subjected to the alike climatic influence in current 4 hours at the temperature + 50 С and relative moisture ~ 60 %. Then, the autonomous fire test cathode were organized. They were defined emitter temperatures, required for the first (after climatic influence) ignition. The emitter temperatures under the first ignition was above earlier got temperature on ~ 30 C. That is to say given climatic influence has not brought about refusal of start ignition both cathodes. It was defined also track record of the change the cathode voltage on time of the work under fixed current and mass flow rate. The got results allow to draw a conclusion that poisoning of the iridium-lanthanum cathode though and exists, but it, first, several less are expressed, than poisoning tungsten-barium cathode, but, secondly, it does not bring about observable remaining effect. After climatic influence iridium-lanthanum cathode practically has completely restored their own initial features. On result of the called on studies was made conclusion that iridium-lanthanum emitters can be to advantage used in cathode for hall and ion plasma thrusters. For efficient work these emitters in composition cathodes is required increasing their operating temperatures in contrast with tungsten-barium эмиттерами emitters on 120 - 180 C.