The longer life and high performance of lithium containing coatings developed by ICRF in the HT-7 superconducting tokamak

A new wall conditioning method, lithium containing silicon coatings (α-C:H/Li-Si) in situ realized by means of ion cyclotron range of frequency plasma assisted chemical vapor deposition, has been successfully developed in the HT-7 superconducting tokamak, which leads to not only the effective suppression of carbon and oxygen impurities, but also lower hydrogen recycling than siliconization. After the wall conditioning, the impurity level in the vacuum vessel of HT-7 device measured by QMS and spectroscopy was largely reduced and obviously lower than siliconization and even approaches lithium in situ coatings. The depth profile of deposition was investigated by Auger surface analysis. The decreases of edge plasma temperature and electron density showed that the plasma confinement has been significantly improved comparing with siliconization, and is sustained for nearly 350 shots.