Speaker
Mr
Vladimir Popov
(Budker Institute of Nuclear Physics SB RAS)
Description
According to modern concepts in a fusion reactor with magnetic confinement first wall will be exposed to continuous and pulsed plasma flows, neutrons, and so on, leading to damage of the materials. So the continuous heat load to divertor plates in the experimental fusion reactor ITER is supposed to be about 10 MW/m$^2$ and a pulsed heat loads up to 10 GW/m$^2$ during few milliseconds [1]. Such pulsed heat loads on a material can be experimentally simulated by electron beams, lasers and plasma fluxes [2,3]. This work is focused on the numerical modeling of the heating and shielding effect in the interaction of the electron beam and the plasma flow with materials. The shielding of electron beam is supposed to be reduced in comparison with the plasma flow due to larger stopping range for electrons. The simulation was performed for the tungsten as a promising material for divertor plates. The parameters close to GOL-3 electron beam (duration 100 µs, surface power 2$~$GW/m$^2$, electron energy 55 KeV, exposed area 4 cm$^2$) were taken for numerical modelling. The same values of the power flux and the duration were used for plasma flow modeling. The heat release was supposed to be surface at the case.
The one-dimensional thermal conductivity equation was solved for calculation of temperature propagation into material. Special conductivity and capacity of tungsten were taken as function of temperature because of its significant dependence, especially near melting point. One-dimensional approximation is acceptable, because depth of heating at least an order of magnitude less than the typical radius of the exposed area. The shielding effect also was assumed to be one-dimensional. The approach is valid if the evaporated material does not move along the material surface to the typical size of exposed area. So the energy flow reached surface depends only on the amount of the vaporized material. Rate of vaporization into vacuum is supposed to depends on surface temperature. For shielding of plasma were used model of energy scattering on nuclei [4]. Shielding of free electrons is based on its stopping range.
The discussed model was used to calculate the power fluxes and the durations at which the shielding effect become significant for heating of the material. Roughly it happens if the thickness of the evaporated layer becomes close to heating particle penetration depth. Calculations show that electron beam heats surface more effective than plasma flow with similar initial power flux and duration. At the certain power flux and heating duration, the calculated surface temperature of the tungsten heated by the electron beam was a 2000 K higher than by plasma flow.
[1] Loarte A et al 2007 Phys. Scr. T128 222
[2] A. Huber et al., 2014 Phys. Scr., T159
[3] V.M. Safronov et al., 2008 PROBL ATOM SCI TECH. №6. Series: Plasma Physics (14), p.52-54
[4] D. I. Skovorodin et al., 2016 Phys. Plasmas 23, 022501
Primary author
Mr
Vladimir Popov
(Budker Institute of Nuclear Physics SB RAS)
Co-authors
Dr
Aleksey Arakcheev
(Budker Institute of Nuclear Physics SB RAS)
Mr
Alexander Vasilyev
(Budker Institute of Nuclear Physics SB RAS, Novosibirsk State University)
Mr
Alexandr Kasatov
(Budker Institute of Nuclear Physics SB RAS)
Dr
Leonid Vyacheslavov
(Budker Institute of Nuclear Physics SB RAS)
