Hollow cathode life-time prediction from low work function surface coverage evolution

摘要

In this paper a procedure to update the plasma parameters relatively to changes of the hollow cathode surface work function has been developed. This procedure has been validated with experimental results and then coupled with the deposition/desorption model already developed by the authors. The evolution of the surface of the cathode tested for 28,000 hours by Sarver-Verhey has been simulated and from the data obtained an end of life criterion has been developed. Then using this criterion the ELT NSTAR discharge cathode has been simulated for various throttle conditions deriving the lifetime at TH0 (200,000 h), TH8 (100,000 h) and TH15 (25,000 h). The lifetimes found are in agreement with the theoretical expectation. The lifetime of the ELT NSTAR cathode under the throttling conditions used during the Deep Space 1 Spare Ion Engine life test has been found to be in excess of 30,000 hours and in particular 100,000 or more if the cathode is run at TH8 or lower from 30,000 hours onward.