Performance of the LH antenna with carbon grill in JT-60U

A multijunction-type LH antenna in JT-60U had been damaged through excessive heat loads owing to a direct plasma bombardment or an RF breakdown during 10-years operation. To repair the antenna and also enhance the injected power, thin carbon grills are firstly installed on the LH antenna mouth. The reason for selecting a carbon material is its high heat load resistance power and low Z number in order to have less influence on the plasma performance. The carbon grill consists of a base frame, an RF contact and a carbon mouth. The RF contact made of a very thin copper plate is used to improve electrical contact between the base frame and the carbon mouth. construction of the newly developed LH antenna, conditioning of the LH antenna has favorably been done with and without plasmas. RF energy of ∼5 MJ, so far, has been successfully injected into plasma. Good coupling property was obtained and sufficient plasma current was driven by LH injection of ∼1 MW. Therefore it is concluded that the application of carbon grill to the LH antenna has been successful.