Measurement of the momentum accommodation coefficient for the interactions between electric thruster plume and a solid surface

Abstract

When the plume of electric thrusters, which is the plasma flow, collides with a surface of spacecraft, a force is exerted on the surface, causing the spacecraft to be flipped or deorbited. The force is generated by the plasma–surface interactions, which can be described using the momentum accommodation coefficient (MAC). As far as we know, only the MAC where the plasma flow is assumed as the combination of singly charged ions, electrons, and neutral gases has been studied. However, the plasma flow of electric thrusters contains not only singly charged ions but also multiply charged ions. In addition, the plasma–surface interactions are usually accompanied by the charged-exchange (CEX), sputtering, and plasma sheath, all of which influence the momentum transfer. Therefore, in this study, the MAC in plasma–surface interactions is developed by quantifying the effect of the multiply charged ions, CEX, sputtering, and plasma sheath. The formulas of the normal momentum accommodation coefficient (NMAC) and tangential momentum accommodation coefficient are derived, respectively, and then, a measurement method of the MAC is proposed with the derived formulas. Moreover, a NMAC was measured when the plasma flow, which was jetted by an ion thruster with an acceleration voltage of 1000 V, impacted an immersed surface vertically, and the measured NMAC is approximated as 1.0. The effect degree and mechanism of the aforementioned factors on the MAC were discussed. Finally, the force exerted on the immersed surface was simulated using the measured NMAC, and the results are in good agreement with the experimental results.