The effects of downstream magnetic field on current-free double layers and beam formation in the Njord helicon plasma device

Fredriksen, Åshild; Mishra, Lekha Nath; Byhring, Hanne Sigrun

doi:10.1088/0963-0252/19/3/034009

Cited by 25 publications

(33 citation statements)

References 24 publications

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“…Several groups have observed accelerated ion populations in these sources, particularly with a physical and=or magnetic field expansion region. [1][2][3][4][5][6][7][8][9][10][11][12] Double layers (DLs) are narrow (tens of Debye lengths) regions of positive and negative charge separated in space. They provide a transition region between two quasi-neutral plasmas with different properties, such as density or temperature.…”

Section: Introductionmentioning

confidence: 99%

Experimental observation of ion beams in the Madison Helicon eXperiment

2011

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Argon ion beams up to E b ¼ 165 eV at P rf ¼ 500 W are observed in the Madison Helicon eXperiment (MadHeX) helicon source with a magnetic nozzle. A two-grid retarding potential analyzer (RPA) is used to measure the ion energy distribution, and emissive and rf-filtered Langmuir probes measure the plasma potential, electron density, and temperature. The supersonic ion beam (M ¼ v i =c s up to 5) forms over tens of Debye lengths and extends spatially for a few ion-neutral charge-exchange mean free paths. The parametric variation of the ion beam energy is explored, including flow rate, rf power, and magnetic field dependence. The beam energy is equal to the difference in plasma potentials in the Pyrex chamber and the grounded expansion chamber. The plasma potential in the expansion chamber remains near the predicted eV p $ 5kT e for argon, but the upstream potential is much higher, likely due to wall charging, resulting in accelerated ion beam energies E b ¼ e[V beam À V plasma ] > 10kT e .

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Section: Introductionmentioning

confidence: 99%

Experimental observation of ion beams in the Madison Helicon eXperiment

2011

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“…The rapid potential change of this ''low-collisional'' CFDL near the expanding magnetic field (with an associated acceleration of the ions by the DL electric field) is now being employed in the development of a plasma thruster, for studies on plasma instabilities [13] and for solar plasma physics [14]. The ion energy distribution functions in the ''Hairapetian and Stenzel'' CFDL in vacuum and in the low-collisional CFDL are not dissimilar.…”

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confidence: 99%

Electron Energy Distribution of a Current-Free Double Layer: Druyvesteyn Theory and Experiments

et al. 2011

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Electron energy distributions upstream of a current-free double layer (CFDL) contained in a lowcollisional plasma are modeled and compared with experimental results. The experimentally observed electron energy probability functions (EEPFs) with a depleted tail above the energy corresponding to the potential drop of the CFDL can be well approximated by a Druyvesteyn distribution function. Theoretical effective electron temperatures for the Druyvesteyn distribution are in good agreement with the values obtained from the experimental EEPFs over the range of pressure where the CFDL is observed.

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“…3, No. 1 which is due to the background ion population as 50 V and that of beam potential as 77 V. Consequently, one can be estimated the double layer potential drop as f dl = V beam -V p = 27 V. In more detail, it could be found in Byhring et al [2008] and Fredriksen et al [2010]. Figure 5 shows the typical profiles of plasma potentials as function of guiding coil current obtained with RFEA facing towards the side wall.…”

Section: Resultsmentioning

confidence: 99%