To solve a problem of a short lifetime due to a wear of the electrodes, we have been studying a completely electrodeless electric propulsion system. High-density (∼10 13 cm −3 ) helicon plasmas are being used for a dense source of our proposed system. Plasmas are accelerated by the Lorentz force in the axial direction, which is generated by the azimuthal current j θ induced in the plasma and the radial component of the external magnetic field B r . Here, this j θ can be generated by a Rotating Magnetic Field (RMF) scheme proposed. As an initial try of the plasma acceleration, we have measured electron density n e and ion velocity v i using the RMF method, and found that n e (v i ) increased by a maximum of ∼ 15% (16%) compared to those without RMF. These results were the first step that shows experimentally the effectiveness of RMF acceleration scheme in the electrodeless electric propulsion system.
In order to establish a completely electrodeless electric thruster, we have been studying the proposed electromagnetic acceleration methods, and estimating plasma performance using various diagnostics. Plasma thrust is the most important feature of the thruster; therefore estimation of the plasma thrust is necessary. In this study, we have developed a pendulum-target-type plasma thrust stand. Our experiment uses a Large Mirror Device and a high-power radiofrequency source (7 MHz, ∼5 kW) to produce high-density helicon plasma. The thruster uses both permanent magnets and electromagnets for generating magnetic field with a large radial component to increase electromagnetic acceleration by the proposed method of including an azimuthal current. In this paper, details of the developed thrust stand and experimental results for thrust, thrust efficiency and specific impulse are presented.
In our proposed method of the completely electrodeless electric propulsion system, a high-density (∼ 10 13 cm −3) helicon plasma is accelerated by the Lorentz force, i.e., the product of the azimuthal current j θ and the radial component of magnetic field B r. In order to promote the plasma acceleration scheme, we used permanent magnets (PMs) designed to increase B r in comparison to the present electromagnets (EMs). As an initial try of the plasma acceleration by our system, electron density n e and ion velocity v i of generated plasma using PMs' magnetic field were measured, and we have obtained the maximum value of n e = 2.5 × 10 12 cm −3 and v i = 2.2 km/s. In addition, we have also introduced a combined, flexible operation of using PMs and EMs leading to better plasma performance.
To establish electrodeless electric propulsion, we have been developing a new electrodeless plasma acceleration thruster using high-density helicon plasmas and permanent magnets, and characterizing them by, e.g., electrostatic and magnetic probes, a high-resolution spectrometer (measuring argon line intensity and line intensity ratio to derive plasma parameters), and a high-speed camera measurements (deriving radial distribution of electron density), in addition to a laser induced fluorescence (LIF) method to measure plasma flow velocity, where they are under development. Here, we will present preliminary acceleration methods using such as Rotating Magnetic Field coil and m = 0 coil along with results of various measurements mentioned above to estimate the plasma performance.
We have been studying long-lifetime helicon plasma thrusters as the Helicon Electrodeless Advanced Thruster (HEAT) project. Two important elements of the proposed helicon plasma thruster are a generation of a dense source plasma using a helicon wave, and an acceleration of the plasma by the Lorentz force using the product of the induced azimuthal current and static radial magnetic field. Here, in order to eliminate damage of electrodes, both generation and acceleration schemes are operated in non-contact condition between the plasma and electrodes. Acceleration schemes use two type of coils: rotating magnetic field coils and azimuthal mode number m = 0 ones. These studies have been carried out on the Large Mirror Device (LMD), which has two types the magnetic field source, permanent magnets and electromagnets, and the Small Helicon Device (SHD), which has small diameter discharge tubes. In this paper, current performances of acceleration schemes are reported.
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