Turbulent microwave plasma thermodynamics for fundamental fluctuation modes

Abstract

Microwave plasmas are generated in helium, neon, argon, krypton, and xenon at a range of microwave powers from 300 to 1800 W. A floating Langmuir double probe is employed to determine plasma electron density and temperature for all five species. The standard turbulence analysis is carried out by using time resolved neutral line emission data form these gases at a sampling rate of 100 MHz. From the Fourier power spectrum of the data, the strongest fluctuation frequency is found to be consistently the fundamental or a second harmonic of a turbulence characteristic frequency in the spectra. In all five species the strongest frequency is not influenced by increased microwave power even though other thermodynamic parameters are changed. The low chaotic dimension for all species seems independent of microwave power and of turbulent fluctuation energy. The phase space trajectories show simplicity and periodicities are consistent with the low chaotic dimension and with the peak frequencies obtained from the fluctuation spectra. The deterministic cyclic evolution of the phase space trajectories with low chaotic dimension for our plasma suggests underlying simplicity in the local turbulence physics. The average value of the strongest fluctuation frequency decreases with increasing atomic weight suggesting that the fundamental frequency is a characterizing parameter for the turbulent system.