Control of ion temperature anisotropy in a helicon plasma

Scime, Earl; Keiter, P. A.; Zintl, M. W.; Balkey, M. M.; Kline, J. L.; Koepke, M. E.

doi:10.1088/0963-0252/7/2/013

Cited by 64 publications

(82 citation statements)

References 6 publications

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“…2 Laboratory helicon experiments typically produce plasmas of density 10 10 − 10 13 cm −3 with electron temperatures in the range 3-10 eV 3 and ion temperatures below 0.5 eV. 4 Tenuous electron beams with energies up to ∼ 100 eV have also been documented. 5 This paper reports on energetic ion beams formed during the expansion of a helicon plasma from a magnetic nozzle.…”

Section: Introductionmentioning

confidence: 99%

Ion acceleration in plasmas emerging from a helicon-heated magnetic-mirror device

et al. 2003

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Using laser-induced fluorescence, measurements have been made of metastable argon-ion, Ar + * (3d 4 F 7/2 ), velocity distributions on the major axis of an axisymmetric magnetic-mirror device whose plasma is sustained by helicon wave absorption. Within the mirror, these ions have sub-eV temperature and, at most, a subthermal axial drift. In the region outside the mirror coils, conditions are found where these ions have a field-parallel velocity above the acoustic speed, to an axial energy of ∼ 30 eV, while the field-parallel ion temperature remains low. The supersonic Ar + * (3d 4 F 7/2 ) are accelerated to one-third of their final energy within a short region in the plasma column, ≤ 1 cm, and continue to accelerate over the next 5 cm. Neutralgas density strongly affects the supersonic Ar + * (3d 4 F 7/2 ) density.

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Section: Introductionmentioning

confidence: 99%

Ion acceleration in plasmas emerging from a helicon-heated magnetic-mirror device

et al. 2003

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“…However, naturally occurring double layers have been identified in nonuniform magnetized plasma. [29][30][31] Representative experimental double layers in which trapped and free particles are provided at plasma boundaries are shown in Fig. 17 ͑Ref.…”

Section: -6mentioning

confidence: 99%

Sheaths: More complicated than you think

Hershkowitz¹

2005

Physics of Plasmas

184

162

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Sheaths in low temperature collisionless and weakly collisional plasmas are often viewed as simple examples of nonlinear physics. How well do we understand them? Closer examination indicates that they are far from simple. Moreover, many predicted sheath properties have not been experimentally verified and even the appropriate "Bohm velocity" for often encountered two-ion species plasma is unknown. In addition, a variety of sheathlike structures, e.g., double layers, can exist, and many two-and three-dimensional sheath effects have not been considered. Experimental studies of sheaths and presheaths in weakly collisional plasmas are described. A key diagnostic is emissive probes operated in the "limit of zero emission." Emissive probes provide a sensitive diagnostic of plasma potential with a resolution approaching 0.1 V and a spatial resolution of 0.1 cm. Combined with planar Langmuir probes and laser-induced fluorescence, they have been used to investigate a wide variety of sheath, presheath, and sheathlike structures. Our experiments have provided some answers but have also raised more questions.

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“…Measuring the intensity of the emitted photons as a function of laser frequency constitutes a LIF measurement. Originally employing an argon-ion laser to pump a coherent 899-21 ring dye laser (Scime et al 1998), the current LIF laser system consists of a 10 W Spectra-Physics Millennium Pro diode laser that pumps a Sirah Matisse-DR tunable ring dye laser running rhodamine-6G dye. The dye laser is tuned to 611.6616 nm (vacuum wavelength) to pump the Ar-II 3d 2 G 9/2 metastable state to the 4p2F 7/2 state, which then decays to the 4s 2 D 5/2 state by emitting 461.086 nm (vacuum wavelength) photons.…”

Section: Diagnosticsmentioning

confidence: 99%

The hot hELicon eXperiment (HELIX) and the large experiment on instabilities and anisotropy (LEIA)

et al. 2014

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The West Virginia University Hot hELIcon eXperiment (HELIX) provides variable density and ion temperature plasmas, with controllable levels of thermal anisotropy, for space relevant laboratory experiments in the Large Experiment on Instabilities and Anisotropy (LEIA) as well as fundamental studies of helicon source physics in HELIX. Through auxiliary ion heating, the ion temperature anisotropy (T ⊥ /T || ) is variable from 1 to 20 for parallel plasma beta (β = 8πnkT i /B 2 ) values that span the range of 0.0001 to 0.01 in LEIA. The ion velocity distribution function is measured throughout the discharge volume in steady-state and pulsed plasmas with laser induced fluorescence (LIF). The wavelengths of very short wavelength electrostatic fluctuations are measured with a coherent microwave scattering system. Operating at low neutral pressures triggers spontaneous formation of a current-free electric double layer. Ion acceleration through the double layer is detected through LIF. LIF-based velocity space tomography of the accelerated beam provides a twodimensional mapping of the bulk and beam ion distribution functions. The driving frequency for the m = 1 helical antenna is continuously variable from 8.5 to 16 MHz and frequency dependent variations of the RF coupling to the plasma allow the spontaneously appearing double layers to be turned on and off without modifying the plasma collisionality or magnetic field geometry. Single and multi-species plasmas are created with argon, helium, nitrogen, krypton, and xenon. The noble gas plasmas have steep neutral density gradients, with ionization levels reaching 100% in the core of the plasma source. The large plasma density in the source enables the study of Aflvén waves in the HELIX device. † Email address for correspondence: escime@wvu.edu 2 E. E. Scime et al.

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Control of ion temperature anisotropy in a helicon plasma

Cited by 64 publications

References 6 publications

Ion acceleration in plasmas emerging from a helicon-heated magnetic-mirror device

Ion acceleration in plasmas emerging from a helicon-heated magnetic-mirror device

Sheaths: More complicated than you think

The hot hELicon eXperiment (HELIX) and the large experiment on instabilities and anisotropy (LEIA)

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