Tritium retention of plasma facing components in tokamaks

Abstract

The areal distribution of tritium retention in tiles from TEXTOR, TFTR, JT-60U and JET has been measured via the imaging plate technique and the results are discussed from the perspective of carbon–hydrogen chemistry. It is found that the observed tritium distribution clearly shows asymmetries in poloidal and toroidal directions and also reflects the local temperature history of the analyzed tiles. We show the first clear evidence of the loss of high energy tritons by toroidal magnetic field ripple. We distinguish three different contributions to tritium retention in tokamaks with carbon plasma facing components: high energy tritons escaping from the core plasma, low energy ions and neutrals from the edge plasma, and molecular tritium from gas fueling. These components are retained at different depths and with different concentrations. Tritium from the edge plasma dominates the retained inventory but could be reduced if the surface temperature was higher. We propose tokamak operation with plasma facing components above 1000 K as a possible way to reduce the tritium inventory.