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.