Permanent Magnet Helicon Source for Ion Propulsion

Abstract

Helicon sources have been proposed by at least two groups for generating ions for space propulsion: the HDLT concept at the Australian National University (ANU), and the VASIMR concept at the Johnson Space Center in Houston. These sources normally require a large electromagnet and power supply to produce the magnetic field. At this stage of research, emphasis has been on the plasma density and ion current that can be produced, but not much on the weight, size, impulse, and gas efficiency of the thruster. This paper concerns the source itself and shows that great savings in size and weight can be obtained by using specially designed permanent magnets (PMs). This PM helicon design, originally developed for plasma processing of large substrates, is extended here for ion thrusters of both the HDLT and VASIMR types. Measured downstream densities are of order 10 12 cm -3 , which should yield much higher ion currents than reported so far. The design principles have been checked experimentally, showing that the predictions of the theory and computations are reliable. The details of two new designs are given here to serve as examples to stimulate further research on the use of such sources as thrusters.

Performance of a permanent-magnet helicon source at 27 and 13 MHz

“…For this, the HELIC code by D. Arnush 9 was used. The use of this code was illustrated in a previous paper 10 . The code computes the plasma resistance R (or R p ), which is proportional to the deposition of RF energy for a given antenna current.…”

Direct thrust measurement of a permanent magnet helicon double layer thruster

“…The recent discovery of current-free double layers ͑DLs͒ in rf plasmas, 1,2 together with the formation of ion beams in such systems, 2 has stimulated a renewed interest in plasma expansion studies, especially within a propulsion context, [3][4][5] since such systems can, in principle, be used to provide thrust for spacecraft. In contrast to more familiar electrostatic acceleration thrusters, such as ion engines and hall thrusters, 6 plasma thrusters make use of ambipolar electric fields or DLs to accelerate ions to supersonic speeds.…”

“…5,9 Performance estimations with regard to propulsion applications are only now starting to be considered. 7 Initial theoretical and thruster performance modeling has been performed, 4 notably by Fruchtman,14,15 but these predictions have not yet been tested experimentally due to the lack of explicit experimental thrust measurements. In this letter we present thrust measurements of a permanent magnet helicon DL thruster ͑PM-HDLT͒, and analyze the results in the context of some of these recent models.…”

Direct thrust measurements and modelling of a radio-frequency expanding plasma thruster

“…The measured thrusts are in good agreement with the maximum upstream electron pressure found from measurements of the plasma parameters and in fair agreement with a simple global approach used to model the thruster. Expanding plasma and double layer (DL) thrusters [1][2][3][4] are receiving increasing interest due to their potential advantages over conventional systems such as ion or hall thrusters. Such advantages include the lack of an explicit neutralizer, high power and thrust densities, and the absence of biased electrodes.…”