ICRF antenna design in Large Helical Device

Design of the ICRF (ion cyclotron range of frequencies) fast-wave heating antenna in the Large Helical Device is discussed. From the physics viewpoint, the optimization of the deposition profiles and the suppression of the loss cone and parasitic heating at the peripheral region are studied. From the engineering viewpoint, long pulse operation and high power coupling are discussed. Cooling system design for the operation time of over 30 min with a several-MW power level is studied. As a result, loss cone problems for the ICRF heating in the helical device are solved or largely improved in the new antenna design. Calculations of plasma loading resistance and maximum voltage on the transmission line show that the optimum antenna position is at a moderate distance from the plasma surfaces. This is due to the relatively large space between the plasma and vacuum wall at the antenna setting point