High-Pressure Helium Plasma Produced in the Local Electric Fields of a Piezoelectric Transformer

A millimeter-scale confined helium plasma was produced at 177 kPa by placing a piezoelectric transformer (PT) in the vicinity of the quartz tube and stimulating the transformer into an electromechanical resonance. The resulting plasma occurred at twice the electromechanical resonance frequency of the transformer. Time-resolved high-speed measurements of luminous emissions and simultaneous measurements of the proximity electric fields near the PT were used to demonstrate a strongly biperiodic behavior. Optical emission spectra, recorded using a synchronized spectrograph, were too weak to elucidate any tendencies toward a biperiodic spectral emission characteristic; however, time-integrated spectra over a broad range of wavelengths demonstrated the characteristic lines of nitrogen. The band of nitrogen emission lines associated with the 377-nm band head was used in conjunction with a spectrum-fitting routine to determine that the ions were essentially cold (rotation temperature on the order of 28 meV).