Two-Electrode Ion-Extraction System of a Radio-Frequency Ion Source: Numerical and Experimental Studies of Erosion of the Accelerating Electrode

Abstract

The results of numerical and experimental studies of the erosion rate of the accelerating electrode of an ion thruster are presented. When the ion beam propagates beyond the edge of the thruster, the process of resonant charge-exchange leads to the formation of slow ions in the engine volume. Under the action of negative electric potential of the accelerating electrode, ions bombard the electrode surface which faces the outgoing beam. Erosion due to the bombardment of the accelerating electrode by charge-exchange ions is the main factor limiting the ion-thruster lifetime. A 25-layer coating of optically contrasting copper and chromium layers, which is applied to the outer electrode surface, is used to diagnose the sputtering rate. The total time of exposure is 14 h. The time dependence of the growing cavity depth is obtained by recording the cavity profile every 3–5 hours. The results obtained in the experiment are used as the initial data for the numerical 3D modeling of multilayer-coating erosion under conditions corresponding to the experiment. Based on the results, the lifetime of the test thruster is estimated at 13 800 hours in respect to the wear of the titanium electrode at its potential of –500 V.