Removal of helium, the ash from the D-T-fusion reaction, from a burning plasma flame, is one of the critical issues for future thermonuclear burning plasma. Even in plasmas driven by additional heating to large Q-values this is a severe problem. Recombination of fuel and ash ions at plasma exposed surfaces, re-emission as neutral particles and subsequent pumping (“recycling”) provides, at least in principle, the mechanism to flush the plasma from its ash. However, plasma surface interaction has to be limited in order to protect vessel components from excessive thermal load, often a conflicting requirement.