In situ measurement of hydrogen retention in JET carbon tiles

The retention of hydrogen isotopes, particularly tritium, in the plasma-facing walls of fusion devices presents a serious difficulty for the exploitation of future machines. Investigation of techniques to reduce this effect is hampered by the difficulty in making measurements. Current methods rely on analysis of samples removed from machines after venting to atmosphere (J.P. Coad, et al., J. Nucl. Mater. 226 (1995) 156). Conclusions have, therefore, been drawn on a global basis, since it is not possible to assess the effects of individual plasma configurations. Detailed studies require a more prompt means of measuring the hydrogen content of samples, ideally on a shot-by-shot basis and without the necessity of breaking the machine vacuum (A. Huber, et al., this Conference). A new technique is described that meets these criteria and has been demonstrated at JET.