A grid lifetime model is proposed for the lifetime estimation of a 3-grid ion engine system. Grid life is assumed to be determined by electron backstreaming caused by the decreased negative voltage due to the enlargement of accel grid hole radius by charge exchange ion erosion. The model is based on the following grid life scenario: 1) the charge exchange ion erosion enlarges the accel grid hole radius, 2) the enlarged accel grid hole radius decreases the extended effective acceleration length between the screen and accel grids, and 3) the decreased extended effective acceleration length decreases the negative voltage to satisfy the space-charge limited current density law. The characteristic of the model is that lifetime exhibits very strong dependence on beam current and accel grid voltage. A computer program was used to validate the model and it was shown that the model agrees fairly well with the simulations in high NP/H conditions.
2001 The Japan Society for Aeronautical and Space Sciences