Numerical Simulation of HiPEP Ion Optics

Abstract

The ffx code was used to investigate the lifetime and propellant throughput capability of the High Power Electric Propulsion (HiPEP) thruster ion optics as part of NASA's Project Prometheus. Erosion predictions are presented as a function of beamlet current, accel grid voltage, and propellant utilization efficiency. These predictions were then compared to the lifetime goals of the thruster, and for nominal operating conditions, the ffx code indicates that the HiPEP thruster will have propellant throughput capability of 100 kg/kW and lifetimes in excess of 135 khrs. In addition to lifetime assessment, a detailed study was completed where grid design parameters were varied in a systematic manner to determine their effects on beamlet current limitations and electron backstreaming margins. The parameters that were varied included the net and total accelerating voltage, grid spacing, aperture center-to-center distance, accel grid thickness, screen grid thickness, discharge voltage, and accel grid aperture diameter.

Whole Ion Optics Gridlet Simulations Using a Hybrid-Grid Immersed-Finite-Element Particle-in-Cell Code

“…Specifically, in the upstream region, the electron density is given by n e n e0 exp e 0 kT e0 (13) where 0 , n e0 , and T e0 are, respectively, the potential, electron density, and electron temperature of the discharge plasma. The downstream electron density is given by n e n e1 exp e 1 kT e1 (14) where 1 , n e1 , and T e1 are, respectively, the potential, electron density and electron temperature of the downstream neutralized plasma.…”

“…The nature of plasma flow in ion optics renders particle-in-cell (PIC) [1] based models, which simulate a collisionless plasma by solving plasma particle trajectories, space charge, and the electric field self-consistently as the most appropriate approach for ion optics modeling. Numerous PIC-based ion optics simulation codes have been developed (see, for example, [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and references therein). Whereas earlier studies have focused on the physics of a single beamlet, recent studies have also begun to use ion optics models to predict the behavior of entire ion optics.…”

Electric Propulsion Technology Development for the Jupiter Icy Moon Orbiter Project

“…6 Specific aspects of the HiPEP program are described more thoroughly elsewhere. 6,7,9,10,11,12,13,14,15 This year the JIMO-HiPEP team explored various plasma production options including DC hollow cathode and AC microwave discharge options. 7 Both were used with the HiPEP thruster, demonstrating the applicability of either discharge approach to the rectangular concept.…”

“…9 This grid material and geometry is projected to provide the 100 kg/kW xenon throughput at both 8000 and 6000 seconds. 9,10,11,12,13 Analysis by Aerojet has projected that such flat grids, with the proper flight designed thruster, can survive launch with margin. 14 Two different neutralizer concepts were also investigated by HiPEP this year; one using conventional hollow cathodes and two using microwave sources.…”

Sputtering Yield of Carbon-Carbon Composite Due to Xenon Ion Bombardment in Ion Engines

“…Yamamura's sputtering yield formula is a well-known semi-empirical formula in the field of electric propulsion, 18,19) and it has been used widely to evaluate the erosion of molybdenum grids of ion engines. [20][21][22] In the case of sputtering carbon by xenon bombardment, Yamamura's formula is not accurate at and below the threshold energy of 160.84 eV because it does not account for sputtering. However, experimental evidence indicates that the amount of sputtering cannot be neglected.…”