Dispersion of Acoustic Waves in Xenon Acoustoplasma in the Region of Non-Axial Acoustic Modes

An acoustoplasma discharge is experimentally investigated when low-intensity acoustic oscillations are far from the intensity region where shock waves exist. The frequency range of 20–50 kHz is considered, when non-axial modes, rather than a plane longitudinal wave, propagate in the discharge tube. The discharge trajectory in the tube is shown to take the form of a planar sinusoid. The calculated and experimentally measured spectra of acoustic oscillations arising during discharge current modulation and sound dispersion for non-axial modes are presented. The dispersion is found to be significant. The spectrum of non-axial modes has a band structure. In acoustoplasma, the transition from one frequency band to the next is characterized by a phase transition. Within each band, dispersion can be either normal or anomalous, depending on the frequency. When moving from one band to the next, dispersion becomes anomalous.