Low Pressure RF Plasmas in Modecular Gases for Aerospace Applications.
Abstract
There is a need to use molecular gas propellants in plasma thrusters due to the limited global production capabilities of xenon and krypton and their relative scarcity in the atmosphere. Molecular gases such as nitrogen, oxygen, hydrogen, as well as air, carbon dioxide and methane are abundant and could also be used for chemical propulsion, enabling the implementation of multimode hybrid propulsion combining both plasma and chemical thrusters. The main challenges are- 1) achieving efficient ionization of molecular gases and 2) sustaining plasma generation in chemically reactive gas environments where metal surfaces of direct current (DC) electrodes may be etched away, acquire non-conducting deposits and coatings or lose properties required for supporting DC current. In order to sustain an efficient ionization of molecular gases at low pressures, it is also important to confine, and multiply energetic electrons induced by SEE from RF plasma boundaries (walls or electrodes). Building on the success of our previous studies of SEE effects in Hall thrusters and recent experiments with e-beam generated DC-RF plasma source for materials processing, in which by varying bias of plasma boundaries we enhanced the confinement of energetic electrons and increased plasma density in the source, we also propose to explore the effects of RF frequency powering RF inductively-coupled plasma (ICP) and also duty cycle, and waveform shape of the RF bias or DC pulse of plasma boundaries with the goal to maximize the plasma density at low pressures. Moreover, we will investigate the effect of a weak magnetic field on the confinement of energetic electrons in these hybrid DC pulsed-RF and RF-RF plasmas. Some of the above-mentioned effects have been studied for RF plasmas to various degrees at kW power levels and pressures above a few mtorr. Our focus will be on the lower pressures and lower RF power with focus on SEE-induced effects and molecular gases relevant to in-space power propulsion technologies.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 06, 2025
- Source ID
- FA95502510071
Entities
People
- Yevgeny Raitses
Organizations
- Air Force Office of Scientific Research
- Trustees of Princeton University
- United States Air Force