Conditioning of the plasma facing surfaces of a fusion device is a necessary prerequisite for the generaton of pure, hot and stable fusion plasmas. Thin layers of carbon or of boron containing carbon deposited plasmachemically on the entire inner surfaces of a tokamak have proven to be a very effective technique for wall prehandling.
Radiofrequency assisted dc glow discharges (RG‐discharges) in a throughflow of appropriate gases are a flexible tool to produce the reactive species for plasma assisted deposition of thin films. The presence of a well defined cathode sheath yields sufficient homogeneity of the deposits even in the complex geometry of fusion devices. The low operation pressure of RG‐discharges (≲10−3 mbar) leads to a high kinetic energy of the ionic species impinging on the surface, which is significant for film properties such as gas content, hardness, and adhesion to the substrate.
The carbonization technique, i.e. the deposition of amorphous hydrogenated carbon (a‐C:H)‐layers and the boronization which leads to boron containing a‐C/B:H films as they have been developed for the J̈ulich tokamak TEXTOR are shortly described. The specific properties of the RG‐discharges for film deposition are outlined and some material properties for plasma surface interaction are discussed. The reductioon in the impurity concentration of tokamak discharges following carbonization and boronization will be addressed.
- Plasma deposition
- Plasma materials processing
- Thin film deposition
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