Spatial evolution of an ion beam created by a geometrically expanding low-pressure argon plasma

Applied Physics Letters

2009

The spatial distribution of an ion beam created in a magnetically expanding plasma using permanent magnets is experimentally investigated for 0.35 and 1 mTorr, where the magnetic-field strength is about 100 G in the plasma source and is decreasing into a few gauss in the diffusion chamber. The beam profile for 0.35 mTorr is weakly divergent. On the other hand, the strongly diverging beam is detected for 1 mTorr. The results are discussed from the viewpoint of the plasma-potential structures and imply the beam divergence caused by the radial electric fields in the ion acceleration region and the diffusion chamber.

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confidence: 72%

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confidence: 99%

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

Applied Physics Letters

2009

“…5(b) also shows the accelerated group of the beam ions at V c ∼ 25 V corresponding to the upstream plasma potential in Fig. 4(b), in addition to the background ions at V c ∼ 12 V. The ion acceleration by the Boltzmann electric field has been observed in many experiments on simple ICP devices; these showed two types of the IEDF having the beam ions and the hot-tail ions [7], [8], [16]- [19]. The shape of the IEDF is relevant to the charge-exchange process, which is discussed here qualitatively because we have now no information on the spatial variation of the neutral pressure.…”

Section: Resultsmentioning

confidence: 99%

“…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].…”

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confidence: 97%

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

Shida

IEEE Trans. Plasma Sci.

et al. 2009

Abstract-Plasma potential structures and ion-energy distribution functions are measured in a magnetically expanding radiofrequency plasma using permanent magnets (PMs) and in a geometrically expanding one, where the radio-frequency power and the argon-gas pressure are maintained at 250 W and 1 mtorr, respectively. In the magnetically expanding plasma, a rapid potential drop like a double-layer structure and a subsequent supersonic ion beam are detected by retarding field energy analyzers. On the other hand, a plasma potential structure following Boltzmann relation accelerates the ions in the geometrically expanding plasma. The comparison between the results in both cases indicates that the existence of the PMs is effective for the generation of the high-speed ion beam, where the mach number of the ion beam is increased to about 3.5 by using the PMs compared with the mach number of 2.3 in the operation mode of the geometrically expanding plasma.Index Terms-Double layer (DL), expanding plasma, ion acceleration, permanent magnets (PMs), plasma potential structures.

“…19 In contrast with the magnetically expanding plasmas, the hemispherical expansion in the "geometrically" expanding plasma has shown the generation of the strongly divergent ion beam, which is guessed to be due to the hemispherical plasma-potential structures. 20,21 In the present letter, we report a variation in the plasmapotential structure from a plane shape to a hemispherical shape when increasing the gas pressure in the magnetically expanding plasma, which is directly associated with the divergence of the ion beam. The results demonstrate the trajectory of the ions accelerated by the potential drop is dominated by the potential structure while it is found the electrons overcoming the potential drop move along the magnetic-field lines.…”

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confidence: 98%

Plane and hemispherical potential structures in magnetically expanding plasmas

Igarashi

Applied Physics Letters

2010

Two-dimensional potential structures are measured for different gas pressure in expanding argon plasma using permanent magnets, where the magnetic field is about 100 G in the source and several gauss in the diffusion chamber. The plane potential drop is observed near the source exit for 0.35 mTorr, while the potential structure becomes hemispherical when increasing up to 1 mTorr; the hemispherical structure results in the radial divergence of the ion beam. It is found that the trajectories of the accelerated ions and the electrons overcoming the potential drop are dominated by the potential structure and magnetic-field lines, respectively. © 2010 American Institute of Physics. ͓doi:10.1063/1.3467857͔Expansion of low-pressure radiofrequency plasmas operated in inductively coupled or helicon wave mode along divergent magnetic-field lines has recently attracted a great deal of interests in communities of space and laboratory plasmas and electric propulsion because a nonlinear potential structure called an electric double layer ͑DL͒ spontaneously forms near the source exit and ions are subsequently accelerated by the potential drop.