Magnetic layer plasma thruster design and plasma parameter measurement

• Main Authors: Pei-Ci Li, 李培琦
• Other Authors: Bing-Hung Chen
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/28uk78

碩士 === 國立東華大學 === 電機工程學系 === 96 === Hall thrusters play the main role in the future aerospace propeller, but they usually need high power input, e.g. P5 and THT-III plasma thrusters having propulsive force 93mN and 20mN while their input power at 1.6kW and 1kW respectively. However, there have critical factors related thermal damages due to high power operation, hence it is necessary to design a high efficiency plasma thruster operating at lower power. Magnetic layer plasma thruster is one kind of Hall thruster and becomes a potential candidate because of its relatively higher thermal endurance and relatively longer accelerating channel length. Hall current is one kind of drifting current by the ExB force, occurred at exit where has maximum magnetic field to trap electrons to enrich gas ionization probability. Ion current is generated in plasma and accelerated along the channel. The decelerated electrons are emitted from cathode which can be a Hollow cathode. Based on the above description and design rules, we designed a magnetic layer plasma thruster which have inner radius 33mm, outer radius 42mm, 19mm accelerating channel length, and 9mm width. For the reason of suppressing second electron generation, a thin layer BN was coated on the channel wall. Magnetic field is therefore generated by the coils, one is inner with 550 turns, and 4 outer with 400 turns for each. The operation conditions are fixed at pressure 8x10-4 torr, gas flow rate 5mg/s, applied voltage 400V, inner current 3A, and outer coil current 2A. Then we can get a uniform magnetic field distribution along the accelerating channel having maximum value 650 Gauss at exit by measurement. This result compared with Maxwell software package simulation shows that 4% error exists between theoretical and experimental data, and 82% uniformity is distributed in the exit plane. Thrusting plasma is measured by Langmuir probe which is feed a scanning voltage ranging from -60V to 60V. Plasma parameters, such as plasma potent, plasma density, and electron temperature, can be derived from the collected current. From these measured I-V curves, we can get the thrusting plasma having 5eV electron temperature, and 3.4E11 cm-3 plasma density. After then, we can derive the propulsive force equal to 60mN which just use 400W power. This result shows that the lower power plasma thruster can be reached by using magnetic layer plasma thruster.