Hydrogen retention in gallium samples exposed to ISTTOK plasmas

The use of liquid metals such as lithium and gallium have been pointed out as a suitable solution to solve problems related to the use of solid walls submitted to high power loads. A proper use of liquid materials in fusion reactors depends, among others, on their affinity to retain hydrogenic isotopes. While retention in lithium has been studied in detail, less is known for gallium. Taking into account the deep influence of this property on plasma behaviour it is deemed relevant to perform such studies in tokamak plasmas. An experimental setup has been developed to produce high purity gallium samples which were exposed to ISTTOK plasmas on both liquid and solid phases. Hydrogen retention and in-depth profiles were simultaneously measured by ERDA and RBS analytical techniques. Experimental data proved that most of the retention takes place in a thin layer near the surface. Liquid samples present higher retention values which may be understood if higher hydrogen diffusivity is assumed. Retained fraction (Hretained/Hincident) around 0.3 and 1% were obtained for solid and liquid samples, respectively.