Ion beam formation in a low-pressure geometrically expanding argon plasma

Abstract

Supersonic ion beam formation has been observed in a geometrically expanding low-pressure inductively coupled argon plasma. It is found that the ion beam is only observed below 3mTorr and only when the discharge is operated in inductive mode. The geometrical expansion of the plasma induces density and potential gradients leading to the ion beam formation. The ion beam energy increases with decreasing source tube radius. The results show that ion beam formation can be achieved by geometrical expansion alone and that the ion beam energy depends on the ratio of the cross-sectional area of the source and expansion region.

Supersonic Ion Beam Driven by Permanent-Magnets-Induced Double Layer in an Expanding Plasma

“…In magnetically expanding plasmas, supersonic ion beams accelerated by currentfree DLs are detected at the downstream side of the DLs, where a rapid potential drop with thickness of about several tens to several hundreds of Debye length is formed near the open end of the plasma sources [1]- [6]. On the other hand, the DL has not been observed in the series of experiments on a geometrically expanding plasma, but an ion beam accelerated by the Boltzmann electric field is detected [7], [8].…”

“…The condition that the PMs are set 0093-3813/$26.00 © 2009 IEEE around the source tube is labeled as "with PMs." When the PMs are not set, the source simply acts as an inductively coupled plasma (ICP) device, labeled as "without PMs," and basically the same as the geometrically expanding plasma machine [7].…”

Experimental studies on ion acceleration and stream line detachment in a diverging magnetic field

“…In plasma applications, a directed ion flux is used to obtain an efficient momentum exhaust for electric propulsion, e.g., variable specific impulse magnetoplasma rocket, 4 and to achieve high aspect ratios in material processing ͑plasma etching͒. [5][6][7] Diverging magnetic field configurations are often used to obtain a unidirectional flow, [8][9][10][11][12][13] where we may anticipate that the magnetization of ions breaks down in the low magnetic field region. For realizing and controlling the plasma flow, it is important to have the knowledge on flow structure in the low magnetic field region, in which the detachment of ion stream line from the magnetic field line takes place.…”

Observation of weakly and strongly diverging ion beams in a magnetically expanding plasma

“…by the RFEA facing radially is shifted to the low-energy side compared with one facing the source tube as reported in another experiments. 13 However, we can know the relative plasma potential structure by the RFEA facing radially and the beam energy by the RFEA facing the source tube. Figure 1͑b͒ shows the axial profiles of the plasma potential p measured by RFEA 1 on axis for 0.35 mTorr ͑open squares͒ and 1 mTorr ͑closed squares͒.…”

“…[1][2][3][4][5] Since the formation of an electric double layer ͑DL͒ and the subsequent ion acceleration in expanding helicon plasmas were recently reported, 6,7 much attention is focused on the magnetically and geometrically expanding plasmas [8][9][10][11][12][13] in the electric propulsion community because it would lead to the new type of electric thruster without any electrode. Typical subjects of interest to this community are the power consumption and the spatial distribution of the accelerated ion beam.…”