Particle balance and wall pumping in tokamaks

The properties of carbon, with respect to its ability to absorb and release hydrogen, are reviewed and applied to the interpretation of density behaviour in Ohmic-, NBI- and ICRF-heated tokamak discharges. Based on the experimental observations, improvement of H-mode parameters in JET due to reduced hydrogen re-emission from the walls is predicted with a numerical model. The particle removal rates required for Q = 1 in JET are estimated.