Oblique Double Layers: A Comparison between Terrestrial and Auroral Measurements

Charles, Christine; Boswell, Roderick; Hawkins, Rhys

doi:10.1103/physrevlett.103.095001

Cited by 31 publications

(44 citation statements)

References 15 publications

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“…25 Recent experiments demonstrated that the DL extends across a wide swath of the divergent field lines and that the resultant U-shaped potential structure is consistent with Fast Auroral SnapshoT satellite measurements of naturally occurring DL structures in the auroral zone. 26 However, certain aspects of the observed ion acceleration process are inconsistent with expectations for a "classic" DL, e.g., in the LIF measurements the ion acceleration extends over many tens to hundreds of Debye lengths 19 instead of the 10-50 D lengths 15 expected in a classic DL. In addition, although the mean free paths of the plasma constituents has been shown to play a critical role in triggering the formation of the DL ͑through the experimental observations of a critical neutral pressure for DL formation͒, 19,[27][28][29][30] only recently has a first-principles theoretical explanation for DL formation been proposed.…”

Section: Introductionmentioning

confidence: 87%

Time-resolved measurements of double layer evolution in expanding plasma

et al. 2010

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Observations in steady-state plasmas confirm predictions that formation of a current-free double layer in a plasma expanding into a chamber of larger diameter is accompanied by an increase in ionization upstream of the double layer. The upstream plasma density increases sharply at the same driving frequency at which a double layer appears. For driving frequencies at which no double layer appears, large electrostatic instabilities are observed. Time-resolved measurements in pulsed discharges indicate that the double layer initially forms for all driving frequencies. However, for particularly strong double layers, instabilities appear early in the discharge and the double layer collapses.

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Section: Introductionmentioning

confidence: 87%

Time-resolved measurements of double layer evolution in expanding plasma

et al. 2010

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“…Later, others [14][15][16][17] have pointed out the 2D nature of the CFDL, in that the electrons follow the magnetic field lines and escape toward the side walls, while the non-magnetized ions follow a straight path from the source into the expansion chamber [18]. A curved 2D CFDL potential structure [19,20] and the conics of enhanced plasma density along the outermost magnetic fields emerging from the source region [21] has been observed.…”

Section: Introductionmentioning

confidence: 97%

RFEA Measurements of High-Energy Electrons in a Helicon Plasma Device with Expanding Magnetic Field

Gulbrandsen

Fredriksen

2017

Front. Phys.

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In the inductively coupled plasma of the Njord helicon device we have, for the same parameters as for which an ion beam exists, measured a downstream population of high-energy electrons emerging from the source. Separated measurements of energetic tail electrons was carried out by Retarding Field Energy Analyzer (RFEA) with a grounded entrance grid, operated in an electron collection mode. In a radial scan with the RFEA pointed toward the source, we found a significant population of high-energy electrons just inside the magnetic field line mapping to the edge of the source. A second peak in high-energy electrons density was observed in a radial position corresponding to the radius of the source. Also, throughout the main column a small contribution of high-energy electrons was observed. In a radial scan with a RFEA biased to collect ions a localized increase in the plasma ion density near the magnetic field line emerging from the plasma near the wall of the source was observed. This is interpreted as a signature of high-energy electrons ionizing the neutral gas. Also, a dip in the floating potential of a Langmuir probe is evident in this region where high-energy electrons is observed.

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“…These studies have led to the application of HPD-CFDLs in electrodeless plasma thrusters for propulsion in space. 7 Boswell et al 84 and Charles et al 73 proposed possible applications of HPDCFDLs for acceleration of ions in space and astrophysical 85 plasmas. More recently, Singh 86 proposed the acceleration of ions by TET-CFDLs in the expansion of solar chromospheric plasma with electrons heated by reconnection in the chromospheric magnetic networks.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, the high magnetic field in the source tube abruptly diverges in the diffusion tube. Following these studies, motivated by the possible applications of CFDLs in HPD for plasma propulsion, there are a series of studies consisting of laboratory work, [59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75] theory, [76][77][78] and simulations 79-83 on such CFDLs. These studies have led to the application of HPD-CFDLs in electrodeless plasma thrusters for propulsion in space.…”

Section: Introductionmentioning

confidence: 99%

Current-free double layers: A review

Singh

2011

Physics of Plasmas

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During the last decade, there has been an upsurge in the research on current-free DLs (CFDLs). Research includes theory, laboratory measurements, and various applications of CFDLs ranging from plasma thrusters to acceleration of charged particles in space and astrophysical plasmas. The purpose of this review is to present a unified understanding of the basic plasma processes, which lead to the formation of CFDLs. The review starts with the discussion on early research on electric fields and double layers (DLs) and ion acceleration in planar plasma expansion. The review continues with the formation of DLs and rarefaction shocks (RFS) in expanding plasma with two electron populations with different temperatures. The basic theory mitigating the formation of a CFDL by two-electron temperature population is reviewed; we refer to such CFDLs as double layers structures formation by two-temperature electron populations (TET-CFDLs). Application of TET-CFDLS to ion acceleration in laboratory and space plasmas was discussed including the formation of stationary steady-state DLs. A quite different type of CFDLs forms in a helicon plasma device (HPD), in which plasma abruptly expands from a narrow plasma source tube into a wide diffusion tube with abruptly diverging magnetic fields. The formation mechanism of the CFDL in HPD, referred here as current free double layer structure in helicon plasma device (HPD-CFDL), and its applications are reviewed. The formation of a TET-CFDL is due to the self-consistent separation of the two electron populations parallel to the ambient magnetic field. In contrast, a HPD-CFDL forms due to self-consistent separation of electrons and ion perpendicular to the abruptly diverging magnetic field in conjunction with the conducting wall of the expansion chamber in the HPD. One-dimensional theoretical models of CFDLs based on steady-state solution of Vlasov-Poisson system of equations are briefly discussed. Applications of CFDLs ranging from helicon double-layer thrusters (HDLTs) to the accelerations of ions in space and astrophysical plasmas are summarized.

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Oblique Double Layers: A Comparison between Terrestrial and Auroral Measurements

Cited by 31 publications

References 15 publications

Time-resolved measurements of double layer evolution in expanding plasma

Time-resolved measurements of double layer evolution in expanding plasma

RFEA Measurements of High-Energy Electrons in a Helicon Plasma Device with Expanding Magnetic Field

Current-free double layers: A review

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