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Froese, A.*; Takizuka, Tomonori; Yagi, Masatoshi
Journal of Plasma and Fusion Research SERIES, Vol.9, p.557 - 562, 2010/08
Heat flux parallell to the magnetic field in scrape-off layer is studied using the particle code PARASOL. In order to evaluate the heat load on the divertor plate, the velocity distribution functions of ions and electrons, as well as heat fluxes, and their flux limiting factors are investigated in detail, mainly about the effects of collisionality and recycling. It is found that the flux limiting factors are basically about 0.1 but varied widely from 0.001 to about 1 depending on plasma parameters.
Froese, A.*; Takizuka, Tomonori; Yagi, Masatoshi
Plasma and Fusion Research (Internet), 5, p.026_1 - 026_15, 2010/08
Fluid models are not generally applicable to fusion edge plasmas without external provision of kinetic factors: closure parameters and boundary conditions inside the sheath region. We explain the PARASOL-1D simulation, a particle-in-cell code with a binary collision Monte-Carlo model, and use it to determine four kinetic factors commonly needed in fluid codes. These are the electron and ion heat flux limiting factors, the ion adiabatic index, and the electron and ion temperature anisotropy. We survey these factors over a wide range of collisionalities and find that, as predicted, the conductive heat flux is accurately described by the Spitzer-Harm expression in the collisional limit and asymptotes to a constant value in the collisionless limit. The effects of electron energy radiation and Langevin heating are explored. Finally, the strong deviations of the energy distribution function from Maxwellian in the weakly collisional and collisionless regimes are explained.
Froese, A.*; Takizuka, Tomonori; Yagi, Masatoshi
Contributions to Plasma Physics, 50(3-5), p.273 - 278, 2010/05
Times Cited Count：8 Percentile：31.2(Physics, Fluids & Plasmas)Electron heat transport parallel to magnetic field in the SOL is studied via fully kinetic simulations using the one-dimensional particle code PARASOL. The heat flux in fluid model is usually approximated with the Spitzer-Harm value in the collisional case, and the free-streaming value adjusted by a limiting factor in the collisionless case. While typically taken to be a constant 0.1, we survey the dependence of the limiting factor with respect to plasma parameters (collisionality, type of source and sink etc). It is found that the limiting factor is strongly affected by the collisionality, covering magnitude from 0.01 to 10. A high-energy tail plays an important role for this large variation. Langevin heating source maintains a Maxwellian electron energy distribution, and the limiting factor remains between 0.05 and 0.3. It is also found that the radiation loss is essential to increase the limiting factor.
Froese, A.*; Takizuka, Tomonori; Yagi, Masatoshi
Plasma and Fusion Research (Internet), 5, p.S1017_1 - S1017_4, 2010/03
Electron heat transport parallel to the magnetic field in the scrape-off layer plasma is investigated with the use of the particle-in-cell code PARASOL. Coulomb collisions are simulated correctly by a binary collision model. The heat flux is lost by radiation cooling, in addition to convection/conduction to the divertor plates. It is confirmed for the collisional case that the conductive heat flux is given by the Spitzer-Harm expression. For the long mean free path case, the conductive heat flux is limited to a factor 
of the free streaming value. It is found that is small (
0.1 of the sheath-limited value) for the low radiation condition, but becomes large (1.0) for the high radiation condition.
