[en] A magnetic field has been applied to the 800 MHz four-waveguide lower-hybrid heating grill on the Versator II tokamak to suppress plasma formation and RF breakdown in the evacuated waveguides during tokamak operation. Without an auxiliary magnetic field, the incident power density is limited typically to 0.13 kW/cm². When the imposed magnetic field in the antenna is above the electron-cyclotron resonance value, the grill operates without RF breakdown or plasma formation at an incident power level of 0.42 kW/cm², limited only by the available RF power. A power density of 0.94 kW/cm² has been achieved when all the RF power was injected into one waveguide, again with no evidence of plasma formation