Abstract
Magnetoplasma thruster is one of the attractive plasma engines for space propulsion in future manned deep space exploration. Usually two helical antennas are equipped to produce and heat plasmas with separate radio frequency sources. It is presented in this paper that a helical antenna, which is used to launch one wave mode in one direction so far, exhibits bi-directional nature, where the waves with different mode numbers are launched and couple with electrons and ions selectively in opposite directions. A two-dimensional numerical calculation is performed to predict wave propagation and power absorption in a non-uniform hydrogen plasma immersed in a non-uniform external static magnetic field, based on the hot plasma theory. It is confirmed that appropriate choice of the excitation condition of the antenna can select axial propagation direction of specific wave modes and consequently select a species that absorbs power from generated waves. A small-scale experiment is performed to confirm the prediction of the calculation. By measuring a change in electron and ion temperatures due to the wave launch from the helical antenna, it is found that both the production and heating at different axial positions are accomplished simultaneously by one antenna showing that another type of the radio frequency driven magnetoplasma thruster would be achieved.
Highlights
Radio frequency (RF) driven magnetoplasma thruster is one of the electric propulsion systems, in which high density plasmas, produced by helicon waves (HW) launched from one RF system at a frequency ω such that ω Ωi 1 with Ωi being the local ion cyclotron frequency, flow downward to the ion cyclotron range of frequencies (ICRF) heating section where the other RF system is used to excite ion cyclotron waves (ICW) at ω Ωi ∼ 1
A collection of appropriately phased circular antennas might be employed in the real magnetoplasma thruster design
We have performed a two-dimensional numerical calculation of wave propagation and power absorption in a non-uniform plasma immersed in a non-uniform external static magnetic field, based on the hot plasma theory
Summary
Radio frequency (RF) driven magnetoplasma thruster is one of the electric propulsion systems, in which high density plasmas, produced by helicon waves (HW) launched from one RF system at a frequency ω such that ω Ωi 1 with Ωi being the local ion cyclotron frequency, flow downward to the ion cyclotron range of frequencies (ICRF) heating section where the other RF system is used to excite ion cyclotron waves (ICW) at ω Ωi ∼ 1. It is expected that when the helical antenna launches the right-rotating RF field in the positive axial direction, the left-rotating RF field is launched in the negative axial direction and vice versa This bi-directional simultaneous launching of different fields is attractive for simplifying the RF systems toward a compact magnetoplasma thruster. We present the experimental evidence of bi-directional characteristics of the helical antenna that the RF fields of different kinds are launched in opposite directions through the measurements of plasma production and ion heating As a result both the production and heating are accomplished simultaneously by one antenna showing that another type of the radio frequency driven magnetoplasma thruster would be achieved
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