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Impurity flow velocity measurements have been conducted for different magnetic field configurations in a wide plasma parameter range in the divertor leg region of LHD for understanding of the edge impurity transport. In all cases (densities, magnetic configurations, hydrogen (H) & deuterium (D) discharges), flows of several tens of km/s are observed. It is found that the flow in thick stochastic layer is faster than in thin stochastic layer configuration by a factor of 3. Different velocities of different charge states of carbon impurity are observed. The simulation with EMC3-EIRENE code shows similar trend as the experiments, but only qualitatively: faster flow in H compared to D discharges due to the mass effect, faster flow in the case of thick stochastic layer. However, synthetic spectra show discrepancy with experiments in the absolute Doppler shift, where the impurity velocity in the experiments is one order faster compared to the simulations. Keywords: Spectroscopy, Hydrogen, Deuterium, Carbon, Impurity transport, Edge plasma

In magnetic field confinement plasma devices such as the International Thermonuclear Experimental Reactor (ITER), hydrogen atoms and molecules are emitted from plasma-facing materials by hydrogen recycling. The effect of the recycled hydrogen in edge plasma can be investigated by neutral transport analysis. In this paper, in order to obtain the boundary condition at the tungsten divertor for neutral transport simulation, a molecular dynamics simulation is performed to investigate the emission ratio of hydrogen atoms and molecules, the emission angle, the translational energy of emitted hydrogen atoms and molecules, and the vibrational and rotational energies of emitted hydrogen molecules. Moreover, from the simulation results, it is also found that the number of emitted hydrogen molecules increases as the ratio of the number of hydrogen and tungsten atoms (H/W) in the material increases, although the H/W dependence of the number of emitted hydrogen atoms is not significant in the range of our simulation, 0.49 ≤ H/W ≤ 1.37. The elementary process of the emission of hydrogen is also investigated by trajectory analysis. The analysis reveals that the hydrogen atom travels on the surface of the tungsten material and remains there for a while because it is trapped on the surface of the tungsten material.

When an ion or atom is injected into a target material, the incident energy increases the temperature around the injection point. Owing to the energy transfer to the surrounding atoms, the temperature of the material recovers to the initial temperature in the real system because heat is transferred to the bulk of material which consists of an almost infinite number of atoms. However, if we simulate the system by the molecular dynamics (MD) method, it is difficult to prepare a sufficiently large system to calculate the process of heat transfer to the bulk. Therefore, in this study, we develop an MD simulation model which includes the effect of heat transfer to the bulk by solving heat conduction equation. The simulation result shows that the process of heat removal proceeds on a time scale of approximately 1000 times slower than the time scale of the incident energy transfer from the incident atom to the target material.

This paper presents carbon impurity flow velocity and temperature measurements in the divertor region for a wide density range ne = (1 - 14) × 1019 m−3, central electron temperature Te = 1.5 - 3.5 keV, and with total neutral beam injection power of 9 - 12 MW. The isotope effect on the transport is studied in hydrogen (H) and deuterium (D) discharges. Flow velocities for D plasma are systematically slower, by the factor of 1.4 - 2, compared to H plasma. For all selected discharges, the carbon ions flow toward the divertor in both H and D plasmas. Different velocities are obtained depending on the charge states. For C+ and C2+ they are in the range of 10 - 30 km/s, and 5 - 20 km/s for C3+ ions. It is also found that there is no change of flow direction even in the lowest density, where the impurity transport model predicts flow toward upstream in the thermal force dominant regime. In H discharges velocities increase proportionally to the plasma density, while in D discharges this dependency is weaker. Possible mechanism to interpret these observations is discussed based on the parallel momentum balance of impurity transport.