Particle simulations of collisional transport in a high recycling, diverted tokamak scrape-off layer

Procassini, R.J.; Birdsall, C.K.; Cohen, B. I.

doi:10.1088/0029-5515/30/11/010

Cited by 45 publications

(33 citation statements)

References 25 publications

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“…For the same secondary emission coefficient, the normalized potential drop e(I~//rcll in Fig. 4(a) shows an increase with collisionality, which is consistent with the results of PIC simulations [9,10] where the secondary emission is not included. To understand the increase of eq~/r~ll with collisionality, it is helpful to compare the parallel electron distribution function in collisionless case (see Fig.…”

Section: Simulation Resultssupporting

confidence: 83%

Nonlinear collisional monte carlo simulations for high-temperature SOL plasma

et al. 1998

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A nonlinear Monte Carlo collisional model is applied to to investigate scrape-off layer (SOL) plasmas with high temperatures. In the proposed SOL modeling, A steady state SOL plasma, which satisfies the particle and energy balances and neutrality constraint, is determined in terms of total particle and heat fluxes across the separatrix, the edge plasma temperature, the secondary electron emission coefficient, and the SOL size. A conductive heat flux into the SOL is effectively modeled via random exchange of source particles and the SOL plasma particles. It is found that the potential drop and the electron transmission factor in the collisional SOL plasma are in good agreement with the theoretical prediction. The cooling effect of secondary electrons in the high temperature divertor operation is investigated. In such a collisionless plasma, the present nonlinear collision model is useful because the electron distribution function deviates far from a Maxwellian distribution. In the presence of strong secondary electron emission, the electron sheath energy transmission factor in the collisionless regime is found to be significantly smaller than that in the collisional regime. This fact suggests that a high-temperature divertor operation can be possible.

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Section: Simulation Resultssupporting

confidence: 83%

Nonlinear collisional monte carlo simulations for high-temperature SOL plasma

et al. 1998

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“…A numerical simulation using the particle-in-ceU method of a diverted tokamak scrape-off layer taking account of recycling was carried out in [37]. The particle-in-cell method was used in combination with the BC-MC algorithm to model Coulomb collisions of charged particles (v" = 1) and the MC method for computing the charged particle-neutral interaction (charged recharging; ionization by electron collision).…”

Section: Ivo(~(t))dt the Inversion Of This Formula Presentsmentioning

confidence: 99%

Application of the particle-in-cell method for numerical simulation of sheath plasma

Filippychev¹

1998

Comput Math Model

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We give a survey of papers on the numerical simulation of the sheath plasma using the particle-in-cell method. We study the problem of the behavior of a plasma bounded in the longitudinal direction of an absorbing wall. The model studied contains charged particles (electrons and ions) 1. Introduction. Under laboratory conditions a plasma is always bounded by surfaces of a suitable device. The study of the processes in the sheath layer occupies a significant place in the studies of plasma physics. The importance of this problem is due to the large number of different applications among which one may mention electrostatic probes, divertor and limiter tokamak plates, thermoemission energy transformers, plasma electrons, and ion particle sources, plasma technology processes, and so forth.In the present paper we study a one-dimensional plasma model consisting of electrons and single-charge ions. In the longitudinal direction the system is bounded by absorbing walls. Due to their greater mobility the electron flux across any section of plasma is so much larger than the ion flux that the condition of approximately equal exit of electrons and ions from the plasma region (the condition of steady state of the system) leads to a plasma potential that is positive relative to the walls. The electrostatic potential varies only weakly in the plasma region, where the ion and electron densities are approximately equal (quasi-neutrality of the plasma). Near the absorbing surface a region approximately several Debye lengths in extent forms, in which the quasi-neutrality of the plasma is significantly violated, and in which a sharp potential drop occurs. The electric field is significantly different from null in this sheath region, which is called the Langmuir (or Debye) region.The basic problem in the theoretical study of a plasma with bounding walls is the study of the very complicated structure of the sheath regions, which to a significant degree is determined (in the absence of an external magnetic field) by the Knudsen number Kn -L/L and the Debye number De =-~.JL. Here ~. is the effective length of free travel of particles, ~-o is the Debye length, and L is the characteristic macroscopic dimension of the problem (the length of the region). A case of practical interest is the case Kn << 1, De << 1. Here the region containing the charged particles can be divided into a quasi-neutral hydrodynamic part and a thin sheath layer of bulk charge. Usually in a gas-discharge plasma the inequalities L >> L >> L D hold. In this case a collisionless protective layer forms around the absorbing wall, to which the strongly nonequilibrium quasi-neutral Knudsen layer is adjacent. Depending on the problem in question we use different models for describing the plasma. Far away from the wall (at distances that exceed several free travel lengths) the plasma is quasi-neutral and collisional, and the distribution function of the velocities of the particles is nearly Maxwell. In this region we use hydrodynamic models or the diffusion approximation to...

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“…Nevertheless, the study of weakly collisional plasmas has motivated the development of several techniques, which utilize Monte Carlo binary scattering algorithms for modeling Coulomb collisions in PIC simulations. [35][36][37][38][39][40] These algorithms are based on the random pairing of nearby particles and pairwise scattering such as to conserve both energy and momentum. An alternative approach to modeling Coulomb collisions in PIC codes is based on the re-expression of the Fokker-Planck collision operator as a corresponding Langevin operator.…”

Section: Introductionmentioning

confidence: 99%

Influence of binary Coulomb collisions on nonlinear stimulated Raman backscatter in the kinetic regime

et al. 2011

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The influence of binary Coulomb collisions on trapped particle nonlinearities related to stimulated Raman scatter ͑SRS͒ in a single laser speckle is examined using one-dimensional particle-in-cell simulations. Binary Coulomb collisions are incorporated using a numerical particle-pairing algorithm that reproduces a collision integral of the Landau form. The onset of nonlinearly enhanced levels of SRS reflectivity is shown to coincide with electron trapping in the daughter plasma wave and is sensitive to the collisional scattering rate. Relaxation of trapping-induced perturbations to the electron velocity distribution via collisional velocity space diffusion is predicted to have the largest effect on the onset of SRS when the amplitude of the daughter plasma wave is smallest, and trapping-induced perturbations to the electron velocity distribution function are also small. In the absence of higher dimensional detrapping mechanisms ͑e.g., electron side-loss͒, it is shown that the onset threshold for enhanced SRS reflectivity is determined predominantly by the parallel diffusion of trapped electrons scattering from bulk thermal electrons, and that for the conditions studied here, the contribution to detrapping from perpendicular diffusion is non-negligible. Additionally, inverse bremsstrahlung heating of the bulk electrons is shown to shift the daughter plasma wave spectrum upward along the Stoke's resonance to larger wave frequency and smaller wave number, changing the linear parametric coupling conditions to SRS backscatter as a function of time. The reduction in SRS reflectivity from binary Coulomb collisions is greatest for laser intensities near the collisionless onset threshold, ulimately leading to an increase in the onset threshold laser intensity for enhanced SRS reflectivity in the kinetic regime.

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Particle simulations of collisional transport in a high recycling, diverted tokamak scrape-off layer

Cited by 45 publications

References 25 publications

Nonlinear collisional monte carlo simulations for high-temperature SOL plasma

Nonlinear collisional monte carlo simulations for high-temperature SOL plasma

Application of the particle-in-cell method for numerical simulation of sheath plasma

Influence of binary Coulomb collisions on nonlinear stimulated Raman backscatter in the kinetic regime

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