Plasma-material boundary conditions for discontinuous Galerkin continuum-kinetic simulations, with a focus on secondary electron emission

Cagas, Petr; Hakim, Ammar; Srinivasan, Bhuvana

doi:10.1016/j.jcp.2019.109215

Cited by 8 publications

(5 citation statements)

References 44 publications

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“…The ghost cells are a set of cells place outside the edge of the domain which are set by the boundary condition in the previous time step, and are used in the RHS update of the interior cell layer bordering the domain edge (the 'skin' cells) during the DG update. In most cases dealing with particle emission, the ghost cell distribution calculated by the boundary condition will depend on the incoming distribution in the skin cells [30].…”

Section: The Kinetic Equationsmentioning

confidence: 99%

“…More complete low-temperature emission measurements by Cimino et al [40][41][42] suggest that the reflection function may actually go to unity at E ′ = 0 and present an alternate model based on the quantum mechanical probability for the reflection of a plane-wave that fits well to their data. For dielectric materials, the work of Bronold and Fehske gives accurate fits to reflection and rediffusion data at low energies [43]; numerical implementation of this model has been described by Cagas et al [30].…”

Section: Elastic Modelmentioning

confidence: 99%

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Energy-dependent implementation of secondary electron emission models in continuum kinetic sheath simulations

Bradshaw,

Srinivasan

2024

Plasma Sources Sci. Technol.

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The plasma-material interactions present in multiple fusion and propulsion concepts between the flow of plasma through a channel and a material wall drive the emission of secondary electrons. This emission is capable of altering the fundamental structure of the sheath region, significantly changing the expected particle fluxes to the wall. The emission spectrum is separated into two major energy regimes, a peak of elastically backscattered primary electrons at the incoming energy, and cold secondary electrons inelastically emitted directly from the material. The ability of continuum kinetic simulations to accurately represent the secondary electron emission is limited by relevant models being formulated in terms of monoenergetic particle interactions which cannot be applied directly to the discrete distribution function. As a result, rigorous implementation of energy-dependent physics is often neglected in favor of simplified, constant models. We present here a novel implementation of semi-empirical models in the boundary of continuum kinetic simulations which allows the full range of this emission to be accurately captured in physically-relevant regimes.

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Section: The Kinetic Equationsmentioning

confidence: 99%

Section: Elastic Modelmentioning

confidence: 99%

Energy-dependent implementation of secondary electron emission models in continuum kinetic sheath simulations

Bradshaw,

Srinivasan

2024

Plasma Sources Sci. Technol.

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“…The code KISSES2D simulates non-magnetized plasmas bounded by surfaces in a 2D-2V Cartesian geometry. We choose the continuum kinetic method [15,[28][29][30][31][32] over particle-in-cell in order to avoid numerical noise and ensure that the simulation data shows clear sheath structures and distribution functions. The computational domain has a rectangular outer boundary consisting of absorbing and sometimes emitting surfaces, see figure 1.…”

Section: Overview Of 2d Kinetic Sheath Simulation With Emitting Surfa...mentioning

confidence: 99%

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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“…Plasma sheaths have been simulated using particlein-cell (PIC) methods, [20][21][22] fluid methods, 23,24 and con-tinuum kinetic methods. [24][25][26] In this paper, we use the continuum kinetic approach for the following reasons. Firstly, much of the physics of sheath formation lie at kinetic scales which fluid models cannot resolve.…”

Section: Introductionmentioning

confidence: 99%

Continuum kinetic investigation of the impact of bias potentials in the current saturation regime on sheath formation

Rathod¹,

Bradshaw²,

Juno³

et al. 2022

Preprint

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Plasma-material boundary conditions for discontinuous Galerkin continuum-kinetic simulations, with a focus on secondary electron emission

Cited by 8 publications

References 44 publications

Energy-dependent implementation of secondary electron emission models in continuum kinetic sheath simulations

Energy-dependent implementation of secondary electron emission models in continuum kinetic sheath simulations

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

Continuum kinetic investigation of the impact of bias potentials in the current saturation regime on sheath formation

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