Calculations of Wall-Material Washout by Plasma in MAGO Chamber

Abstract

An issue important for the magnetic compression/magnetized target fusion (MAGO/MTF) approach is the impurity transport into plasma from the walls in the turbulent motion of the plasma, as the impurity-plasma radiation makes a significant contribution to cooling. For the axisymmetric magnetohydrodynamic flows in the azimuthal magnetic field that exist in the MAGO plasma, the appearing turbulence can be two-dimensional (2-D), as the magnetic field impedes the magnetic-field line bending. This paper estimates the adsorbed gas and copper washout from the walls by the moving plasma using one-dimensional (1-D) model equations of a turbulent impurity diffusion. The amount of desorbed gas impurities, which is composed of light elements (C, O), entered to plasma for 0.5-1 mus after the heated plasma generation is found to be insufficient to explain the X-ray diode signals in the experiment. However, a significant gas amount has been entered at later times, which agrees with the gas inflows obtained after shots in stationary facility experiments. It is found that, a given copper wall surface vaporization, the copper-impurity amount entered to plasma for 0.5-1 mus can in general explain the diode signals. Thus, the copper impurity entering can be an important or even determining effect influencing energy losses due to impurities in the chamber