DEVELOPMENT OF CARBON COATING BY PLASMA CVD

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A CARBON COATING TECHNIQUE, WHICH HAS BEEN EXPECTED AS A NEW IMPURITY CONTROL IN NUCLEAR FUSION, IS BASICALLY STUDIED. A PRESENT URGENT SUBJECT IN FUSION DEVICE COATING IS HOW TO REDUCE A LARGE AMOUNT OF HYDROGEN DESORBED FROM THE COATED WALLS. SO, WE SYSTEMATICALLY STUDIED THE COATING CONDITIONS TO MINIMIZE THE HYDROGEN CONTENT OF CARBON FILMS.A HOT-CATHODE DISCHARGE IN A TOROIDAL MAGNETIC FIELD AND A COLD-CATHODE GLOW DISCHARGE WITHOUT MAGNETIC FIELDS WERE USED FOR COATING. BESIDE THESE, WE DEVELOPED A NEW COATING METHOD CALLED A DOUBLE PLASMA. FROM THESE COATING EXPERIMENTS, WE OBTAINED A GUIDING PRINCIPLE OF REDUCING THE HYDROGEN CONTENT OF FILMS AS FOLLOWS:(1) COATING THE WALLS AT TEMPERATURES HIGHER THAN 400゜C. (2) COATING WITH SEVERE ION BOMBARDMENT ON THE WALLS. (3)ACETYLENE DISCHARGES REDUCE THE HYDROGEN CONTENT BY HALF, COMPARED WITH METHANE DISCHARGES.IN ADDITION, THE HYDROGEN CONTENT TURNED OUT TO BE ALMOST INDEPENDENT OF ADMIXING HYDROGEN OR HELIUM GASES, WHILE THE CARBON DENSITY OF FILMS IS DECREASED BY ADMIXED HYDROGEN. ON THE OTHER HAND, WE FOUND THAT THE HYDROGENS CAN BE DESORBED FROM THE CARBON FILMS BY HELIUM DISCHARGES. THIS HELIUM-DISCHARGE TREATMENT LOWERS THE HYDROGEN RECYCLING RATE LESS THAN 1. THUS, THE HELIUM GLOW DISCHARGE CAN BE USED AS A NEW RECYCLING CONTROL TECHNIQUE.BESIDES THE FUSION ORIENTED STUDIES CITED ABOVE, WE DEVELOPED AN ORIGINAL COATING METHOD, i.e., A DOUBLE PLASMA METHOD WHICH ENABLES US TO FORM DIAMOND-LIKE FILMS WITH HIGH QUALITY AND CONTROLLABILITY.