Electric fields in high-frequency parallel-plate helium discharges

Spatially and temporally resolved electric fields in the sheath region of a 13.56-MHz, parallel-plate helium discharge have been measured as a function of voltage, pressure, phase, bias, and electrode drive configuration. The electric field was determined from laser-induced fluorescence measurements of the Stark structure of the n=11 singlet Rydberg manifold. Two-dimensional maps of the electric field indicate that the field is uniform across a large fraction of the electrode diameter. Measured values of the sheath electric field are compared with the results of a hybrid Boltzmann-equation–average-equation simulation.