Bi-Directional Excitation of Radio Frequency Waves Using a Helical Antenna in Non-Uniform Plasmas towards a Compact Magnetoplasma Thruster

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.

Effect of antenna helicity on discharge characteristics of helicon plasma under a divergent magnetic field

“…Shinohara et al [4] reported that the diameter and extent of the blue core depend on the magnetic field structure as well as the RF power and observed a blue core with a diameter of 10-20 cm and axial length of more than 1 m in a large-diameter helicon plasma source. Soltani and Habibi [12] demonstrated the appearance of a blue core from the change from purple color in the magnetized plasma as the RF power increased to 300 W in the low-pressure regime (i.e. p = 0.7 mTorr).…”

Numerical Design of RF Antennas for Ion Cyclotron Resonance Heating in ECRIS Environment

“…Hereinafter, we present the numerical simulation of three selected types of strap antennas (simple-loop, Nagoya III and helical) employed for ICRH and working inside a plasma chamber, that is in Electron Cyclotron Resonance (ECR) environment. The slow ion cyclotron wave excitation is radiated by left-handed circular polarization (LHCP) by the strap antennas [4,5] or, more in general, by induction coils generating long-wavelength ion-cyclotron waves that propagates along the magnetic field lines from high-to-low magnetic field. Near the ICR region [6] (where ω RF = ω ci = 2πf ci = QeB/m i , ion charge Qe, mass m i , and ion cyclotron frequency f ci ), wavelength becomes shorter, wave energy is damped and transferred to ions.…”