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Contribution Poster

H– and D– sources for fusion, accelerators and other applications

Evaluation of the temperature dependance of the Cesium deposition on the plasma grid in the JT-60 negative ion source

Speakers

  • Dr. Masafumi YOSHIDA

Primary authors

Co-authors

Content

Modeling for a longer stable production of the negative ion beams in the JT-60 negative ion source is constructed, based on the experimentally obtained temperature dependace of the cesium (Cs) adsorption/desorption. In this model, a thickness of the Cs layer on a plasma grid (PG) in this source is evaulated, because the Cs layer loweres a work function of the PG to enhance the negative ion production. By using this model, slight degradation of the negative ion beams for a 100 s pulse operation in this source is understood. As a result, it is found that the thickness is deterimed by a balance of the adsorbed/desorbed amounts of Cs in the PG and a chamber wall and of the introduced/evacuated one. In addition, it is suggested that the origin of the degradation of the beams is an excessive depostion of the Cs on the PG, due to rising the temprature of the chamber wall and increasing the desorbed Cs from it. For suppression of the degradation and longer stable production of the negative ion beam, temperature dependance of the thickness of the Cs layer on the PG is examined by changing temperatures of the PG, chamber wall and Cs oven, and combination of the optimal temprature at them is preliminary proposed.