• Energy Research

We elaborate a hybrid fluid-kinetic model for neutral particles in the plasma edge. A macro/fluid model with kinetic corrections in the closure terms of the fluid moment equations is solved in the entire domain. The kinetic corrections follow from a Monte Carlo simulation of the micro/kinetic part. We compare two hybrid models with different underlying fluid approximations: (i) a pure pressure-diffusion equation; and (ii) a continuity and parallel momentum equation with pressure-diffusion transport only retained in the directions perpendicular to the magnetic field lines. We asses their performance for a high recycling slab case with fixed background plasma. Compared to a Monte Carlo simulation of the full kinetic equation, the statistical error on the particle source is reduced with 40% and 47% for respectively the hybrid model without and with the parallel momentum equation for the same computational time. For the parallel momentum source there is only a reduction for the model with parallel momentum equation (about 69%). Unfortunately, the statistical error on the ion energy source slightly increases for both hybrid models. Keywords: Fluid approximations, Kinetic model, Neutrals, Plasma edge modeling

We elaborate a hybrid fluid-kinetic model for neutral particles in the plasma edge. A macro/fluid model with kinetic corrections in the closure terms of the fluid moment equations is solved in the entire domain. The kinetic corrections follow from a Monte Carlo simulation of the micro/kinetic part. We compare two hybrid models with different underlying fluid approximations: (i) a pure pressure-diffusion equation; and (ii) a continuity and parallel momentum equation with pressure-diffusion transport only retained in the directions perpendicular to the magnetic field lines. We asses their performance for a high recycling slab case with fixed background plasma. Compared to a Monte Carlo simulation of the full kinetic equation, the statistical error on the particle source is reduced with 40% and 47% for respectively the hybrid model without and with the parallel momentum equation for the same computational time. For the parallel momentum source there is only a reduction for the model with parallel momentum equation (about 69%). Unfortunately, the statistical error on the ion energy source slightly increases for both hybrid models. Keywords: Fluid approximations, Kinetic model, Neutrals, Plasma edge modeling

AbstractWe compare the plasma sources (particle, parallel momentum and ion energy) due to plasma-neutral interactions computed with different fluid neutral models with the sources from a Monte Carlo simulation of the kinetic neutral equation. This is done for a fixed background plasma, which is representative for an ITER detached case. We illustrate that the reaction data from the AMJUEL-HYDHEL databases can be incorporated in the fluid models. A pure pressure-diffusion equation gives already accurate results for the particle source, but it is inaccurate for the momentum and energy source. A parallel momentum equation has to be added to achieve predictions of the momentum and energy source within 30% of accuracy. Newly developed boundary conditions, based on the diffusion approximation for incident neutrals, show to be crucial for accurate results of the fluid models close to the divertor target. The slight overestimation of the momentum and energy sources can be further reduced by adding a separate neutral energy equation.

AbstractWe compare the plasma sources (particle, parallel momentum and ion energy) due to plasma-neutral interactions computed with different fluid neutral models with the sources from a Monte Carlo simulation of the kinetic neutral equation. This is done for a fixed background plasma, which is representative for an ITER detached case. We illustrate that the reaction data from the AMJUEL-HYDHEL databases can be incorporated in the fluid models. A pure pressure-diffusion equation gives already accurate results for the particle source, but it is inaccurate for the momentum and energy source. A parallel momentum equation has to be added to achieve predictions of the momentum and energy source within 30% of accuracy. Newly developed boundary conditions, based on the diffusion approximation for incident neutrals, show to be crucial for accurate results of the fluid models close to the divertor target. The slight overestimation of the momentum and energy sources can be further reduced by adding a separate neutral energy equation.

AbstractPlasma edge simulation codes are crucial for the interpretation of present experiments as well as for the assessment of new concepts and next generation nuclear fusion devices. These codes are most often based on a combined Finite Volume (FV) / Monte Carlo (MC) numerical approach to simulate coupled plasma and neutral particle transport. In this paper we apply recently derived error reduction analysis to assess numerical errors in a partially detached ITER case. We show that also for this strongly coupled FV/MC simulation case, statistical averaging over iterations provides an accurate means to achieve well reproducible and statistically accurate results. Moreover, the error reduction analysis with respect to numerical parameters provide a framework to achieve increased accuracy for a given computational cost. We also show how significant code speed-up can be achieved for a desirable accuracy compared to presently used simulation strategies.

AbstractPlasma edge simulation codes are crucial for the interpretation of present experiments as well as for the assessment of new concepts and next generation nuclear fusion devices. These codes are most often based on a combined Finite Volume (FV) / Monte Carlo (MC) numerical approach to simulate coupled plasma and neutral particle transport. In this paper we apply recently derived error reduction analysis to assess numerical errors in a partially detached ITER case. We show that also for this strongly coupled FV/MC simulation case, statistical averaging over iterations provides an accurate means to achieve well reproducible and statistically accurate results. Moreover, the error reduction analysis with respect to numerical parameters provide a framework to achieve increased accuracy for a given computational cost. We also show how significant code speed-up can be achieved for a desirable accuracy compared to presently used simulation strategies.