A Compact Permanent-Magnet Helicon Thruster
Summary (1 min read)
I. DISCHARGE CONFIGURATION
- NORMAL spacecraft thrusters eject a fast ion beam, whichhas to be neutralized by electrons from an auxiliary source to prevent the spacecraft from charging up negatively.
- Helicon discharges require less power to generate a given plasma density than other ambipolar sources, but they require a dc magnetic field B.
- As a result, a smaller system using a commercially available magnet was designed and tested.
- The discharge tube is of 2-in ID and 2-in height, topped by a grounded aluminum plate (to reflect the back wave).
- The single loop antenna is located near the exit to minimize plasma loss to the walls.
- As plasma exits the source, the electron density decreases, following the diverging field lines.
- Thus, there is an electric field that accelerates the ions along B. Using a retarding-field ion analyzer (RFIA) made by Impedans, Ltd. of Ireland, the authors have measured the ion energy distribution function Manuscript received February 11, 2014; revised March 7, 2014; accepted September 16, 2014.
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- Fig. 6 shows how the RFIA is mounted in the experimental chamber.
III. APPLICATION TO THRUSTERS
- At their normal operating pressure of 15 mTorr, Fig. 8 shows that the peak ion energy is only ∼10 eV; but at pressures in thrusters, the ion energy is much larger, as seen in Fig.
- The question is whether this energy can be increased even further by biasing the top plate of the discharge relative to the spacecraft ground.
- Because of the severe RF environment, an electronic power supply can be used only with filtering by large electrolytic capacitors.
- Instead, the authors used two 12-V lead-acid batteries in series to supply ±24 V to the top plate.
- Compared with these, a helicon thruster can provide a much denser ion beam with automatic electron neutralization.
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Cites background from "A Compact Permanent-Magnet Helicon ..."
...Mini-Helicon thrusters are a sub-type of micro-plasma thruster with high plasma densities, with expected performance of around 1 mN and 1000 s for less than 50 W power input [25,39]....
...4 15-20 5-20  Mini-Helicon Xenon 1 1000 50 20  Argon 1200 50  Resistojet Hydrazine 300-400 100-1000 65-90 [1, 26] Water 0....
"A Compact Permanent-Magnet Helicon ..." refers background in this paper
...More importantly, it blocks the position where the double-layer studied in  would normally occur (Fig....
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Q1. What contributions have the authors mentioned in the paper "A compact permanent-magnet helicon thruster" ?
In this paper, a small helicon source using a permanent magnet has been tested for possible application as a spacecraft thruster.