Control of antenna coupling in high-density plasma production by m=0 helicon waves

Antenna coupling has been controlled in high-density plasma production by m=0 helicon waves using multiple-loop antennas and varying the phase and the distance between antennas. When two single-loop antennas are connected in series with the phase between the two being zero, threshold power for the density jump Pth is reduced by a factor of 2–3 compared with that of the one-turn loop antenna. This reduction in Pth is caused by the increase in antenna coupling at the lower plasma density. The observed differences in antenna coupling among different antennas have been examined by using a two-dimensional wave code.