Abstract
Bombardment of the keeper electrode by high-energy ions limits the lifetime of the ion thruster. To investigate its sputtering mechanism, this paper established a two-dimensional simulation model and applied the Particle-In-Cell method to simulating the generation process of the high-energy ions and their sputtering process on the keeper electrode surface. The Monte Carlo Collision method was used to address the collisions between particles. The results showed that the plasma potential downstream of the keeper electrode oscillated; therefore, ions in this area were accelerated and their energy was increased from 0.085 to 35 eV, which was enough to erode the keeper electrode’s surface. double charged xenon (Xe++) ions and charge exchange xenon (CEX) ions were the two kinds of high-energy ions. The most severe position was the center of the keeper electrode surface, and its erosion rate was about 2.0 × 10−4 m/1000 h, while the average erosion rate was about 10−5 m/1000 h when the frequency and the amplitude of the plasma potential were 50 Hz and 35 eV, respectively. Plasma potential oscillation greatly affected the sputtering mechanism of the keeper electrode.
Highlights
Compared with chemical propulsion, electric propulsion has significant advantages, such as high specific impulse, long lifetime, continuously and adjustable thrust,1 so that it can greatly reduce the mass requirement of the propellant and improve the payload ratio of the satellite
NASA completed a 2000 h wear test of the 30 cm ion thruster in 1995,6 and it showed that the hollow cathode was seriously eroded and the entire electron beam weld seam downstream of the orifice plate surface was removed from the orifice plate
The 8200 h wear test of the NSTAR ion thruster with the new hollow cathode was finished in 2001.8 The results showed that the keeper electrode was eroded and its diameter was slightly enlarged more than twice the original one
Summary
Electric propulsion has significant advantages, such as high specific impulse, long lifetime, continuously and adjustable thrust, so that it can greatly reduce the mass requirement of the propellant and improve the payload ratio of the satellite. The 8200 h wear test of the NSTAR ion thruster with the new hollow cathode was finished in 2001.8 The results showed that the keeper electrode was eroded and its diameter was slightly enlarged more than twice the original one. The experimental results showed that the keeper electrode was eroded away after the test and the orifice plate and the cathode tube were exposed to the plasma in the discharge chamber. A semi-empirical model was proposed by Gallimore, who calculated the keeper electrode’s erosion profile according to the results of the sputtering yield and counted the numbers of ions that entered into the cathode sheath, where the experimental plasma potential was treated as the model’s input. The Particle-In-Cell (PIC) method is used to track the particle’s trajectory, and the Monte Carlo Collision (MCC) method is used to handle the collision between particles
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