High Power Helicon Antenna Design for DIII-D

Full text: A new current drive system is being designed and fabricated for the DIII-D tokamak to drive current in high-β discharges, using electromagnetic helicon waves. The high-power helicon antenna (HPHA) is expected to couple 1 MW of power into the DIII-D plasmas at a frequency of 476 MHz without degrading the plasma characteristics or introducing metal impurities. This high-power travelling wave antenna array is expected to have higher efficiency in driving current than other typical tokamak systems. The HPHA is a 30 CuCrZr module array mounted on a series of back plates. The modules inductively couple and resonate with the adjacent module. The two end modules are connected to a dual inner conductor strip-line transmitting RF power to and from four, 15 cm diameter vacuum coaxial feed-throughs located at the two DIII-D upper vessel ports. The modules, pitched 15° to follow the magnetic field lines of the tokamak, are bolted to six water cooled back-plates which are mounted on pedestals welded to the vessel wall. A description of the design and analyses of the HPHA and the RF strip-line feeds with anticipated overall antenna performance is presented. Work supported by the U.S. Department of Energy under DE-FC02-04ER54698. (author)