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The interaction between neutrals outside tokamak plasmas and fast ions that are generated by neutral beam injection and pass outside the plasma is studied. It is shown that at beam energies up to ~100 keV fast-ion losses are significant, up to 20% in the studied case, because of charge exchange reactions between the neutrals and the fast ions. About half of the fast ions that neutralize outside the plasma get lost to the wall while the other half re-enters the plasma and ionizes again, often on better confined orbits, which is visible as an enhanced beam power deposition in the plasma core (). As a result, the plasma performance as measured from beam-plasma fusion reactions is hardly changed despite the significant fast-ion losses toward the plasma edge. [ABSTRACT FROM AUTHOR]

The installation of a new poloidal charge exchange recombination spectroscopy (CXRS) diagnostic at ASDEX Upgrade (AUG) has enabled the determination of the radial electric field, Er, using the radial force balance of impurity ions. Er has been derived from charge exchange (CX) spectra measured on different impurity species, such as He2+, B5+, C6+ and Ne10+. The resulting Er profiles are found to be identical within the uncertainties regardless of the impurity species used, thus, demonstrating the validity of the diagnostic technique. The Er profile has been compared to the main ion pressure gradient term, which is found to be the dominant contribution at the plasma edge, thus, supporting that the Er well is created by the main ion species. The Er profile has been measured in different confinement regimes including L-, I- and H-mode. The depth of the Er well and the magnitude of the Er shear are correlated with the ion pressure at the pedestal top. The temporal evolution of the measured CX profiles and the resulting Er have been studied during an edge-localized mode (ELM) cycle. At the ELM crash, the Er minimum is less deep resulting in a reduction of the E × B shear. Within 2ms after the ELM crash, the edge kinetic profiles have nearly recovered and the Er well is observed to recover simultaneously. In high density type-I ELM mitigated H-mode plasmas, obtained via externally applied magnetic perturbations (MPs) with toroidal mode number n = 2, no clear effect on Er due to the MPs has been observed. [ABSTRACT FROM AUTHOR]

Hot atoms with chaotically directed velocities are generated by charge-exchange with plasma ions of neutrals recycling from the vessel wall of a fusion reactor. Some of them flee into openings in the vessel made for ducts guiding to diagnostic installations; in particular, to first mirrors for optical observations. On the one hand, hot atoms, hitting the mirror directly, can erode its surface. On the other hand, impurity species, released from the walls of the vessel and of the diagnostic duct, migrate to the mirror and can be deposited there. Both the erosion of and impurity deposition on the mirror decline its reflection properties. Models elaborated to describe processes above are outlined, including a 2D kinetic description for neutral species in the vicinity of the duct opening, an assessment for the erosion of the duct walls and mirror surface by hot atoms, estimates for influxes of the wall material into the duct and a consideration of the migration of impurity atoms along the duct. Calculations are done for the conditions predicted for a fusion reactor like DEMO. The rates for erosion of and impurity deposition on first mirrors of Mo are assessed versus input parameters such as the duct radius, the distance from the opening to the mirror, the density ng of the working gas in the duct, the probabilities for impurity sticking to the duct wall and mirror surface. It is demonstrated that, by ng exceeding a level of m−3, the mirror sputtering can be reduced to the target level of 1 nm per full power year. Moreover, for long enough ducts the erosion rate of impurities deposited onto the mirror exceeds their deposition one and no formation of impurity precipitations on the mirror surface has to be expected. [ABSTRACT FROM AUTHOR]

The effective ionic charge, , is determined through the integration of soft x-ray tomography and charge exchange recombination spectroscopy impurity density measurements in the Madison Symmetric Torus. is found is be 2.3  ±  0.1 in the core of high temperature, high current, improved confinement discharges, with a slightly hollow profile peaking near mid-radius. A Bayesian probability framework, developed as part of an on-going effort in Integrated Data Analysis, was used to incorporate these two measurements. This framework provides a method to address different systematic and statistical uncertainties associated with each diagnostic and to test hypothetical contributions to against the existing data set. The combined analysis provides much higher confidence in the result than previous single-diagnostic attempts to characterize using near-infrared bremsstrahlung or x-ray spectroscopy. [ABSTRACT FROM AUTHOR]