Convective Plasma Loss Caused by an Ion-Cyclotron rf Field and Its Elimination by Mode Control

This paper reports experimental evidence that a convective loss occurs in a low-density plasma subjected to the ion-cyclotron rf field of $m=\pm 1$ azimuthal mode which is conventionally employed. By utilization of an $m=+1\mathrm{}$ circularly polarized rf field produced with a multiphase rf source, the convective plasma loss is eliminated, which results in an improvement in heating efficiency by more than 70%.