Grill design and spectrum calculation of LHW antenna on HL-2M tokamak

The antenna for lower hybrid current driving on HL-2M tokamak is designed as 4x32 waveguide arrays. The width of grill is 9.9mm, the wall thickness is 3mm and the phase difference between two adjacent grills is 90 degree. The calculation shows that the reflectance R is 0.026 and the Nparallel, corresponding the peak value is 2.375. The gradient of edge electron density has nothing to do with the Nparallel, corresponding the peak value. But the larger electron density gradient of the plasma edge is, the smaller peak width is. When the phase difference between two adjacent grills is 81 degree and ∇ne=2 x 1012 cm-4, (1/Nparallel2) is optimum, 0.2010, R is minimum, 0.0223 and the Nparallel corresponding the peak value is 2.125. (authors)