Current-free double-layer formation in a high-density helicon discharge

Charles, Christine; Boswell, Rod

doi:10.1063/1.1557319

Cited by 281 publications

(292 citation statements)

References 24 publications

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“…Understanding the spatial damping of the ion beam is important if this device is to be used as a space thruster as was proposed earlier [2,3]. Further investigations on the 3-D profile of the double layer is needed and optical diagnostics could provide useful informations if the experiment could be reproduced in a device with full optical access to the source tube.…”

Section: A Existence Of a Double Layer And Spatial Dependenciesmentioning

confidence: 99%

“…In these experiments, a plasma expansion was forced by a strong divergence of a high magnitude magnetic field at very low pressure. Detailed investigations of these currentfree DLs have been performed using electrical measurements [2,[6][7][8][9][10][11], laser induced fluorescence [12][13][14][15][16] and numerical simulations [17,18]. An upstream ionization instability has recently been observed in one of the experimental systems [19].…”

Section: Introductionmentioning

confidence: 99%

“…Due to the electrical bias, a current is flowing through these current-driven DLs. Since the work of Charles and Boswell [2], there has been considerable interest in static current free double layers that are selfconsistently created in low-pressure expanding plasmas. These DLs have applications in space propulsion [3,4] and in modeling of astrophysical processes [5].…”

Section: Introductionmentioning

confidence: 99%

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Experimental investigation of double layers in expanding plasmas

2007

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Double layers (DLs) have been observed in a plasma reactor composed of a source chamber attached to a larger expanding chamber. Positive ion beams generated across the DL were characterized in the low plasma potential region using retarding field energy analyzers. In electropositive gases, DLs were formed at very low pressures (between 0.1 and 1 mTorr) with the plasma expansion forced by a strongly diverging magnetic field. The DL remains static, robust to changes in boundary conditions, and its position is related to the magnetic field lines. The voltage drop across the DL increases with decreasing pressure, i.e. with increasing electron temperature (around 20 V at 0.17 mTorr). DLs were also observed in electronegative gases without a magnetic field over a greater range of pressure (0.5 to 10 mTorr). The actual profile of the electronegative DL is very sensitive to external parameters and intrusive elements, and they propagate at high negative ion fraction. Electrostatic probes measurements and laser induced photodetachment show discontinuities in all plasma parameters (electron density, electron temperature, negative ion fraction) at the DL position. The voltage drop across the electronegative DL is about 8 V, is independent of the gas pressure and therefore of the electron temperature.

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Section: A Existence Of a Double Layer And Spatial Dependenciesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Experimental investigation of double layers in expanding plasmas

2007

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“…While the first scheme could be obtained with only one plasma source, the second one requires two independent sources. Note that in this configuration, axial flows could be driven from the magnetic expansion of the plasma (Charles and Boswell 2004;Plihon et al 2007). Alternative schemes such as single grid acceleration of the plasma (Dudin and Rafalskyi 2009) may also be implemented to independently control the ratio of the poloidal (s) and toroidal (t) flows.…”

Section: Machine Description and Capabilitiesmentioning

confidence: 99%

Flow dynamics and magnetic induction in the von-Kármán plasma experiment

et al. 2014

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The von-Kármán plasma experiment is a novel versatile experimental device designed to explore the dynamics of basic magnetic induction processes and the dynamics of flows driven in weakly magnetized plasmas. A high-density plasma column (10 16 -10 19 particles. m −3 ) is created by two radio-frequency plasma sources located at each end of a 1 m long linear device. Flows are driven through J × B azimuthal torques created from independently controlled emissive cathodes. The device has been designed such that magnetic induction processes and turbulent plasma dynamics can be studied from a variety of time-averaged axisymmetric flows in a cylinder. MHD simulations implementing volume-penalization support the experimental development to design the most efficient flow-driving schemes and understand the flow dynamics. Preliminary experimental results show that a rotating motion of up to nearly 1 km/s is controlled by the J × B azimuthal torque.

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“…Several helicon plasma devices [1][2][3][4], used in studies of warm low-β plasma flow along expanding magnetic fields, have shown the acceleration of plasma to supersonic speeds occurring in short distances, i.e., ∼ 50 Debye lengths, λ D,e , after the field has expanded 10−20%. Theoretical analysis of these results [5][6][7][8] have attributed the ion acceleration to electrostatic layers, single or double, generated by the expanding magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Particle-in-cell modeling of magnetized argon plasma flow through small mechanical apertures

Sefkow

Cohen

2009

Physics of Plasmas

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Motivated by observations of supersonic argon-ion flow generated by linear helicon-heated plasma devices, a three-dimensional particle-in-cell (PIC) code is used to study whether stationary electrostatic layers form near mechanical apertures intersecting the flow of magnetized plasma. By self-consistently evaluating the temporal evolution of the plasma in the vicinity of the aperture, the PIC simulations characterize the roles of the imposed aperture and applied magnetic field on ion acceleration. The PIC model includes ionization of a background neutral-argon population by thermal and superthermal electrons, the latter found upstream of the aperture. Near the aperture, a transition from a collisional to a collisionless regime occurs. Perturbations of density and potential, with mm wavelengths and consistent with ion acoustic waves, propagate axially. An ion acceleration region of length ∼ 200 − 300 λD,e forms at the location of the aperture and is found to be an electrostatic double layer, with axially-separated regions of net positive and negative charge. Reducing the aperture diameter or increasing its length increases the double layer strength.

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Current-free double-layer formation in a high-density helicon discharge

Cited by 281 publications

References 24 publications

Experimental investigation of double layers in expanding plasmas

Experimental investigation of double layers in expanding plasmas

Flow dynamics and magnetic induction in the von-Kármán plasma experiment

Particle-in-cell modeling of magnetized argon plasma flow through small mechanical apertures

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