Modelling of isotope exchange experiments in JET

Isotope exchange experiments from hydrogen to deuterium in JET are theoretically described by employing a simple global isotope exchange model. Experimental results for discharges with limiter temperature around 2500C can be approximated by this model if an additional slow diffusion process of hydrogen in the limiter bulk is assumed. In discharges where thermal desorption occurs due to higher limiter temperatures (> or approx. 10000C) (post carbonisation discharges) the change over process seems to be predominantly governed by thermal processes. (orig.)