Analysis of the Transition Time between the Space-Charge-Limited and Inverse Regimes

Johnson, Grant; Campanell, Michael

doi:10.1134/s1063780x19010033

Cited by 4 publications

(3 citation statements)

References 33 publications

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“…Already, we see an outcome in 2D that differs from previous results in 1D planar geometry [10,11,13]. An SCL equilibrium with a trapped ion cloud was not seen in planar 1D.…”

Section: Plasma Bounded By a Surface With An Emitting Segmentcontrasting

confidence: 75%

“…In this paper, we studied electron-emitting surface sheath effects in multidimensional plasmas. The unmagnetized 1D-1V kinetic continuum code from references [10,11,13] was extended to 2D-2V. Using the 2D-2V code, we simulated a plasma bounded by a surface that strongly emits from a segment of its length, and simulated small emissive surfaces in the interior of a large bounded plasma.…”

Section: Discussionmentioning

confidence: 99%

“…More recent 1D planar sheath theories have demonstrated the existence of an inverse sheath solution where the emitting surface is above the plasma potential and the ions are confined [5][6][7][8][9]. Time-dependent 1D simulations with chargeexchange (CX) collisions show that SCL sheaths break down due to ion trapping in the VC potential well, leading to the formation of an inverse regime [10][11][12][13]. Since collisions are always present in practice, one might conclude from the 1D Figure 1.…”

Section: Introductionmentioning

confidence: 99%

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Effects of emitting surfaces and trapped ions on the sheath physics and current flow in multidimensional plasma systems

Johnson¹,

Campanell²

2021

Plasma Sources Sci. Technol.

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Recent one-dimensional simulations of planar sheaths with strong electron emission have shown that trapping of charge-exchange ions causes transitions from space-charge limited (SCL) to inverse sheaths. However, multidimensional emitting sheath phenomena with collisions remained unexplored, due in part to high computational cost. We developed a novel continuum kinetic code to study the sheath physics, current flow and potential distributions in two-dimensional unmagnetized configurations with emitting surfaces. For small negatively biased thermionic cathodes in a plasma, the cathode sheath can exist in an equilibrium SCL state. The SCL sheath carries an immense density of trapped ions, neutralized by thermoelectrons, within the potential well of the virtual cathode. For further increases of emitted flux, the trapped ion cloud expands in space. The trapped ion space charge causes an increase of thermionic current far beyond the saturation limit predicted by conventional collisionless SCL sheath models without ion trapping. For sufficiently strong emission, the trapped ion cloud consumes the entire 2D plasma domain, forming a mode with globally confined ions and an inverse sheath at the cathode. In situations where the emitted flux is fixed and the bias is swept (e.g. emissive probe), the trapped ions cause a large thermionic current to escape for all biases below the plasma potential. Strong suppression of the thermionic emission, required for the probe to float, only occurs when the probe is above the plasma potential.

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“…Already, we see an outcome in 2D that differs from previous results in 1D planar geometry [10,11,13]. An SCL equilibrium with a trapped ion cloud was not seen in planar 1D.…”

Section: Plasma Bounded By a Surface With An Emitting Segmentcontrasting

confidence: 75%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effects of emitting surfaces and trapped ions on the sheath physics and current flow in multidimensional plasma systems

Johnson¹,

Campanell²

2021

Plasma Sources Sci. Technol.

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Latest progress in Hall thrusters plasma modelling

Taccogna

Garrigues

2019

Rev. Mod. Plasma Phys.

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In the last thirty years, numerical models have revealed different physical mechanisms involved in the Hall thruster functioning leading to a bridge between analytical prediction / empirical intuition and experiments. For this reason, modeling effort is continuously increasing in the domain of Hall Thrusters. Two basic approaches exist: one based on fluid/hybrid simulation where the distribution of electrons is assumed Maxwellian and the plasma inside the thruster, considered as quasineutral, is described with macroscopic quantities (density, velocity and energy); the second approach is based on kinetic description for charged particles where no approximation is made for the distribution of particles. Fluid or hybrid approaches offer the advantage of demanding low run times and computational resources. They are very useful to perform parametric studies but actually the anomalous phenomena responsible for electron transport across the magnetic field barrier have not been selfconsistently modeled. Kinetic approach is able to better capture phenomena originating on the Debye scale length like the lateral sheaths, ExB electron drift instability, important to explain the anomalous electron transport, but it requires very long run times. For this latter, the progress in computer science offers the advantage to describe conditions more and more close to the thruster operation. In this review, we will present the two approaches emphasizing on numerical schemes used with assumptions and approximations and on main results obtained. Future directions on the Hall thruster modeling will finally outlined.

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A study of SCL sheath in presence of two dust species in a photoemissive environment

Deka

Bora

2020

Physics of Plasmas

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We have presented a basic model for a one dimensional collisionless space charge limited (SCL) plasma sheath consisting of electrons, ions, and two kinds of dust populations—a nano-dust population and a micrometer sized dust population. We have assumed that the nano-dust particles, plasma electrons, photoelectrons, and ions are the constituents of the plasma fluid and the micrometer sized dust particles behave as suspended impurities in the plasma without affecting the plasma dynamics. We have assumed that the charges of the micrometer-dusts are determined from the current balance on them and the charges on the nano-dusts are fixed. Due to photoemission, like the lunar surface charges to a positive potential, so the nano-dust and micrometer-dust particles charge to a positive potential. The electron densities have been derived by assuming both the electrons and photoelectrons to be Maxwellian, whereas the ion and nano-dust densities are derived from energy conservation of the ions and nano-dust particles and the continuity equations. Being a constituent of plasma, the nano-dusts do affect the sheath dynamics through the Poisson equation, which determines the plasma potential in the sheath region. The typical conditions for the levitation of dust particles in an SCL sheath including the maximum height and maximum size of the particles are calculated.

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Analysis of the Transition Time between the Space-Charge-Limited and Inverse Regimes

Cited by 4 publications

References 33 publications

Effects of emitting surfaces and trapped ions on the sheath physics and current flow in multidimensional plasma systems

Effects of emitting surfaces and trapped ions on the sheath physics and current flow in multidimensional plasma systems

Latest progress in Hall thrusters plasma modelling

A study of SCL sheath in presence of two dust species in a photoemissive environment

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