Abstract
We have proposed Rotating Magnetic Field (RMF) acceleration method as one of electrodeless plasma accelerations. In our experimental scheme, plasma generated by an rf (radio frequency) antenna, is accelerated by RMF antennas, which consist of two-pair, opposed, facing coils, and these antennas are outside of a discharge tube. Therefore, there is no wear of electrodes, degrading the propulsion performance. Here, we will introduce our RMF acceleration system developed, including the experimental device, e.g., external antennas, a tapered quartz tube, a vacuum chamber, external magnets, and a pumping system. In addition, we can change RMF operation parameters (RMF applied current IRMF and RMF current phase difference ϕ, focusing on RMF current frequency fRMF) by adjusting matching conditions of RMF, and investigate the dependencies on plasma parameters (electron density ne and ion velocity vi); e.g., higher increases of ne and vi (∼360 % and 55 %, respectively) than previous experimental results were obtained by decreasing fRMF from 5 MHz to 0.7 MHz, whose RMF penetration condition was better according to Milroy’s expression. Moreover, time-varying component of RMF has been measured directly to survey the penetration condition experimentally.
Highlights
In the field of a space propulsion, electric propulsion systems have been studied due to an advantage of the higher fuel efficiency than that of chemical ones
The present results show that the maximum ∆vi/vi and ∆ne/ne were ∼ 55 % and ∼ 360 % with fRMF = 1 MHz (IRMF = 46 App), respectively, and these results showed that decreasing fRMF with an increment of IRMF can enhance the thermal thrust, which is represented as surface integrals of a static pressure ne kB T e and a dynamic pressure ni mi vi,[2] where ni is ion density (= ne), kB is Boltzmann constant, T e is electron temperature, ni is ion density, and mi is ion mass
We have utilized two pairs of 5 turns, opposed facing coils as Rotating Magnetic Field (RMF) acceleration antennas with Large Mirror Device (LMD), and changed RMF operation conditions including to fRMF, IRMF, and φ, in addition to target plasma conditions
Summary
In the field of a space propulsion, electric propulsion systems have been studied due to an advantage of the higher fuel efficiency than that of chemical ones. Conventional electric thrusters, e.g., gridded ion thruster,[1] Hall thruster,[2] and Magneto-Plasma-Dynamics (MPD) thruster,[3] have electrodes, which contact with plasma directly, and this interaction makes an operating time limited and a long space exploration difficult because of the erosion of the electrodes. In order to accomplish a longer operating time, which is in proportion to a specific impulse (exhaust velocity divided by gravitational acceleration), and high thrust performance for a generation space propulsion scheme, some electrodeless plasma thrusters have been proposed and studied on, e.g., Electron Cyclotron Resonance (ECR) plasma thruster,[4] Variable Specific Impulse Magnetoplasma Rocket (VASIMR),[5] ratio frequency (rf) plasma thruster.[6] In these acceleration schemes, the plasma production and heating are conducted by external rf antennas, employing microwave ECR, Ion Cyclotron Heating (ICH), and a magnetic expansion scheme (so-called a magnetic nozzle). Helicon electrodeless plasma acceleration,[6,7,8] using a helicon wave[9] excitation to generate plasmas (electron density ne is up to ∼ 1013 cm-3) with additional acceleration methods have been studied under the Helicon Electrodeless Advanced Thruster (HEAT)[7,8] project.
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