Assessment of the impact of kinetic effect of ion parallel heat conduction on DEMO relevant SOL plasma using integrated SOL-divertor code SONIC

In plasmas of relatively lower collisionality, such as scrape-off layer (SOL) of fusion tokamak device, parallel heat conductivity of plasma ion becomes smaller than expected by the classical Spitzer-Harm model due to nonlocal kinetic effect. We have assessed, by simulation, impact and role of such kinetic effect of ion heat conductivity (abbreviated by ion KE in this paper) on DEMO relevant tokamak SOL plasma, supposing Japanese demonstration tokamak reactor concept JA DEMO. A series of test simulation, where the ion KE is modeled by a widely used Free-streaming energy (FSE) limited model, has demonstrated the following significant impact of the ion KE on JA DEMO SOL plasma at the baseline operation scenario: (1) the ion KE decreases the ion parallel heat flux density around X-point and further upstream of low field side (LFS) area along the separatrix, where the parallel collisionality tends to decrease due to combination of higher temperature, lower density (i.e. longer mean free path of ion collisions) and higher temperature gradient (shorter characteristic length). Up to 40-60 % of decrease, compared to the case w/o ion KE, is observed among the tested cases where the ion KE level, specified by parameter αi in the FSE-limited model, is scanned over the possible range 0.2 < αi < 2.0. (2) The ion KE leads to significant increase in the ion temperature Ti (up to 600 % of increase among the tested cases) and significant decrease in the ion density ni (up to -80 % of decrease among the tested cases), widely over SOL upstream. By energy balance analysis, it has been suggested that the ion KE affects the upstream ni and Ti, respectively by power of 0.4 and -0.4 of the flux limiting factor, around the separatrix upstream as far as spatial change in plasma parameters are moderate. The results of this study serve as a fundamental assessment of the ion KE for DEMO relevant SOL plasma, clarifying the need of further sophistication of the modeling toward quantitaive prediction.

Evolution of Heavy Ion Beam Probing from the Origins to Study of Symmetric Structures in Fusion Plasmas

The overview discusses development of the unique fusion plasma diagnostics—Heavy Ion Beam Probing (HIBP) in application to toroidal magnetic plasma devices. The basis of the HIBP measurements of the plasma electric potential and processing of experimental data are considered. Diagnostic systems for probing plasma in tokamaks TM-4, TJ-1, TUMAN-3M and T-10, stellarators WEGA, TJ-II and Uragan-2M are presented. Promising results of the HIBP projects for various existing modern machines, such as TCV, TCABR, MAST, COMPASS, GLOBUS-M2, T-15 MD and W7-X and the international fusion tokamak reactor ITER are given. Results from two machines with similar size and plasma parameters, but with different types of the magnetic con-figuration: axisymmetric tokamak T-10 and helically symmetric stellarator TJ-II are compared. The results of studies of stationary potential profiles and oscillations in the form of quasimonochromatic and broadband fluctuations, turbulent particle flux, fluctuations of density and poloidal magnetic field are presented. The properties of symmetric structures—zonal flows and geodesic acoustic modes of plasma oscillations as well as Alfvén Eigenmodes excited by fast particles from neutral beam injection heating are described. General trends in the behavior of electric potential and turbulence in magnetized fusion plasmas are revealed.

Моделирование ионного облучения кристаллических и аморфных мишеней --- материалов первой стенки токамака-реактора

An overview of results concerning simulation of various processes which occur due to atomic bombardment of crystalline and amorphous solids is presented. With the use of original computational codes, the following data were obtained: reflection coefficients, projected energy losses and ranges of ions in solids, channeling data as well as sputtering yield and its dependence on incident angle of bombarding particles for Be-W and Ne-W combinations. Be, C and W targets were studied as these are among the plasma-facing materials in tokamaks, including ITER. The emphasis was made on atom-target combinations which lack reliable experimental data. Experimental data on other materials were used to verify calculations. A significant influence of the interaction potential used on the simulation results is shown. The reviewed results are tied by a common subject – a study of interaction of plasma ions and first-wall materials of a tokamak-reactor – and also by a common method of study – the use of an original computational code.

Ядерные тормозные способности изотопов водорода и гелия в бериллии, углероде и вольфраме

The nuclear stopping power of hydrogen isotopes and helium in Be, C, W materials, which are promising for use as the first wall of a tokamak-reactor, are calculated. It is shown that the presence of an attractive well in the potential significantly affects the dependence of nuclear stopping power on the collision energy. The use of potentials calculated in the density functional theory with an attractive well allowed us to obtain more accurate values of the nuclear stopping power for hydrogen isotopes, which at low energies differ by 27-60% from the reference data. The results for different hydrogen isotopes are well described by a universal curve.