Double layer formation in a magnetised laboratory plasma

Andersson, Dag

doi:10.1088/0022-3727/14/8/008

Cited by 36 publications

(17 citation statements)

References 10 publications

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“…Previous work had suggested that an instability was needed for spot onset. 16 The model presented here suggests a significantly different picture that does not include instability as a feature of spot onset.…”

Section: Introductionmentioning

confidence: 75%

“…Thus, quasineutrality must first be established on the high potential side, creating a region with E ≈ 0, before an imbalance in the static Langmuir condition implies expansion of the double layer. Previous attempts to model spot onset solved an integral form of Poisson's equation 16,28,29 . In these models, the integral of the charge density within the sheath, including contributions from electron impact ionization, were formulated as a function of the sheath electric field…”

Section: A Anode Spot Onsetmentioning

confidence: 99%

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Theory and simulation of anode spots in low pressure plasmas

et al. 2017

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When electrodes are biased above the plasma potential, electrons accelerated through the associated electron sheath can dramatically increase the ionization rate of neutrals near the electrode surface. It has previously been observed that if the ionization rate is great enough, a double layer separates a luminous high-potential plasma attached to the electrode surface (called an anode spot or fireball) from the bulk plasma. Here, results of the first 2D particle-in-cell simulations of anode spot formation are presented along with a theoretical model describing the formation process. It is found that ionization leads to the buildup of an ion-rich layer adjacent to the electrode, forming a narrow potential well near the electrode surface that traps electrons born from ionization. Anode spot onset occurs when a quasineutral region is established in the potential well and the density in this region becomes large enough to violate the steady-state Langmuir condition, which is a balance between electron and ion fluxes across the double layer. A model for steady-state properties of the anode spot is also presented, which predicts values for the anode spot size, double layer potential drop, and form of the sheath at the electrode by considering particle, power, and current balance. These predictions are found to be consistent with the presented simulation and previous experiments.Comment: Submitted to Phys. Plasma

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Section: Introductionmentioning

confidence: 75%

Section: A Anode Spot Onsetmentioning

confidence: 99%

Theory and simulation of anode spots in low pressure plasmas

et al. 2017

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“…Actually, Knight theory does not deal with the reaction of the plasma on the electric field. Experimental [6] and theoretical [7,8,9,10] works showed that when an electric potential drop appears in a plasma, it tends to concentrate over a region of small extent (a few Debye lengths). It forms a coherent electrostatic structure, called double layer (DL) which is said to be strong when the potential drop exceeds the plasma thermal energy, and weak otherwise.…”

Section: Time Independent J : Quasi-static Acceleration Regionmentioning

confidence: 99%

The role Alfvén waves in the generation of Earth polar auroras

Mottez¹

2012

AIP Conference Proceedings

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The acceleration of electrons at 1-10 keV energies is the cause of the polar aurora displays, and an important factor of magnetic energy transfer from the solar wind to the Earth. Two main families of acceleration processes are observed: those based on coherent quasi-static structures called double layers, and those based of the propagation of Alfvén Waves (AW). This paper is a review of the Alfvénic acceleration processes, and of their role in the global dynamics of the auroral zone. FIGURE 1. Left: Schematic view of the magnetosphere, the main currents and the auroral zone, evidenced on this figure through the auroral currents. Right: Solar wind/magnetosphere energy flowchart Reprinted with permission from [2]. Copyright [1984], Springer.addresses the very important role of quasi-static electrostatic structures in the generation of the discrete auroral arcs. Then, the role of the Alfvén waves on auroral acceleration is considered, paying attention to the frequency range.Most of the energy directed from the magnetotail towards the Earth is conveyed through the field aligned currents (FAC), also called Birkeland currents, which are electric currents in the auroral zone propagating along the magnetic field lines. According to Stern, the energy flux along the FAC is 1.4 × 10 11 W during quiet times, and 2.7 × 10 11 W during substorms.He considers 4 processes connecting the FAC and the ionosphere 1. Some of the FAC are connected to the ring current and can provide energy to it. This energy is lost for the ionosphere. (The ring current is a vast electric current flowing in the magnetosphere at a distance ∼ 8 Earth radii all around the Earth.) 2. In the auroral zone, some plasma is accelerated towards the Earth. The acceleration results form parallel electric fields E . These processes are very sensitive to the magnetospheric activity. Auroral plasma acceleration involves energy fluxes in the range 1 − 5 × 10 10 W, the highest values being reached during substorms. 3. The same parallel electric field can accelerate a part of the plasma out of the ionosphere. Stern argues that the involved flux of energy are negligible in comparison to the others. (Some recent observations and theories put this assertion into question as will be shown later in this review.) 4. The FAC reach the ionosphere. Then, the current system is closed in the ionosphere, mainly with horizontal currents propagating in a medium of finite (Pedersen and Hall) conductivities. Then, 2 − 16 × 10 10 W come into Joule dissipation.The sum of all these energy fluxes is, again, comparable to those transiting through the internal layer of the magnetotail current sheet. Therefore, the auroral region is the region where most of the energy flowing Earthward from the magnetotail is dissipated.

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“…In the present paper we report our investigations of the properties of EIC waves associated with a strong (eck/kTe 5-15), three-dimensional, magnetized double layer. The double layers are of the "anode type" as described by Torv•n and Andersson [1979] and Andersson [1981] in which a low rate of volume ionization provides the trapped electron species required to maintain the potential structures. These potential structures are produced in the diverging magnetic field region of a cylindrical argon discharge device, thus giving rise to V-shaped equipotentials.…”

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confidence: 99%

Laboratory observations of ion cyclotron waves associated with a double layer in an inhomogeneous magnetic field

Alport¹,

Cartier²,

Merlino³

1986

J. Geophys. Res.

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Observations of coherent electrostatic ion cyclotron (EIC) waves associated with a strong, magnetized double layer are presented. The double layers are produced in a weakly ionized argon plasma by applying a positive potential to an electrode plate located in the diverging magnetic field region of a cylindrical plasma column. Ionization within the electrode sheath is essential to the formation of these double layers. The resulting V‐shaped potential structures have extended parallel, oblique and perpendicular (to B) electric field components. The frequency of the ion cyclotron instability is dependent upon the magnetic field strength at the position of the parallel potential structure. The properties of EIC waves in the presence of the double layer are discussed in relation to the possible excitation mechanisms (field‐aligned currents, ion and electron beams, and perpendicular E fields).

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Double layer formation in a magnetised laboratory plasma

Cited by 36 publications

References 10 publications

Theory and simulation of anode spots in low pressure plasmas

Theory and simulation of anode spots in low pressure plasmas

The role Alfvén waves in the generation of Earth polar auroras

Laboratory observations of ion cyclotron waves associated with a double layer in an inhomogeneous magnetic field

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