A Temperature Programmed Desorption Diagnostic for SPIDER Cs Operations

Cesium evaporation, aimed at enhancing the production of negative ions, has recently started during the last experimental campaigns in Source for the Production of Ions of Deuterium Extracted from a Radio frequency plasma (SPIDER). In view of the full-scale ITER heating neutral beam injector (HNBI) future operations, Megavolt ITER Injector and Concept Advancement (MITICA), understanding the behavior of cesium during plasma operation is necessary to optimize the generation of negative hydrogen ions. Determining the contribution of the different mechanisms affecting the cesium distribution in the source requires a characterization of the desorption energies of the cesium compounds deposited over the source walls. The temperature programed desorption (TPD) diagnostic allows to estimate these energies using a pair of tungsten filaments, and can also be used as a Langmuir–Taylor detector. Two identical versions of the diagnostic have been assembled, giving the possibility to perform tests and characterizations on one of the copies, while having the second copy installed and operational in SPIDER. This work presents the design and development of the device, as well as experimental results in a testing vacuum chamber and in SPIDER. Finally, first estimations of the desorption energies of cesium compounds are carried out to support the plasma-Cs models for SPIDER.