Development of a prototype of ECH system without window for vacuum seal

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A window for vacuum seal is one of the most serious problems in the development of high power ECH system in fusion research. In this project, we tested an ECH system without windows for vacuum seal.A prototype of 48 GH_z demountable gyrotron operating at the 2nd electron cyclotron harmonics was designed , built and tested. Then the window for vacuum seal of the gyrotron was removed and the gyrotron was directry connected to the vacuum chamber of the WT-3 tokamak with a 4m long circular waveguide.The pressure in the gyrotron tube attains the maximum value when a tokamak plasma is disrupted. After the interval of tokamak discharge, the pressure in the tube is restored at the initial value which is no problem in operating the gyrotron.We confirmed that there is no problem in synchronized operation of the gyrotron and the tokamak.It can be cocluded that the ECH system without windows for vacuum seal can be applicable to fusion research.The problems about maitenance of the system are not clear. They will be clear in use for ECH experiments on the WT-3 tokamak.In a big facility something like ITER, there will be different kind of problems from small facilties. Further investigation will be required.