Development and Fabrication of Folded Waveguide Antenna for the Large Helical Device

We report a development and fabrication of an folded waveguide (FWG) antenna to produce and heat the plasma via ion Bernstein wave on the Large Helical Device (LHD) in the ion cyclotron range of frequency (ICRF). This antenna is 428 mm in height, 1050 mm in width and 3950 mm in length with 23 vanes and 24 folds. It will be installed to the horizontal vacuum port with an inclination angle of 38.9" for the RF electromagnetic field to be parallel to the magnetic field line at the last closed magnetic flux surface. It is housed in the LHD vacuum port with lm movable distance, when it is not used. It can launch an ion Bernstein wave from a lower magnetic field side. The resonant frequencies are determined from the previous experimental results using Type-III antenna on Compact Helical System (CHS). This antenna can deliver RF power in the wide frequency range of 25 to 64 MHz. It can produce and heat the plasma in the wide magnetic field operation on LHD. As an another feature, the wave number can be changed by replacing an array of polarization plates, which was experimentally demonstrated.