Mechanical and Total Pressure Statistics in Vlasov-Maxwell Plasmas

Abstract

Pressure is an important parameter in plasma turbulence. Historically, pressure fluctuations have been studied extensively via density in the nearly incompressible (NI) magnetohydrodynamic (MHD) framework1-3. However, the statistics of mechanical and total pressure in kinetic plasmas have not been explored much. In this study, we examine the statistics of mechanical and total pressure using a 2.5D particle-in-cell (PIC) simulation of plasma turbulence4. As turbulence is fully developed in the system, it is found that the magnetic and thermal pressure display a negative correlation keeping the total pressure about constant, consistent with MHD behavior. This negative correlation is observed locally in regions near the current sheets and justified by the nature of the joint probability distribution of the two5. Further, pressure spectra are calculated for magnetic, thermal and total pressure. The thermal and magnetic pressure spectra exhibit a slope of -5/3 in the inertial range, while the total pressure spectrum exhibits a slope of -7/3 in agreement with hydrodynamic scaling, influenced by the cross-spectral contribution of the individual pressures. Finally, the implications of the local structures of pressure to intermittency are discussed using probability distribution functions and scale dependent kurtosis.1. Montgomery, D., Brown M. R., and Matthaeus W. H. "Density fluctuation spectra in magnetohydrodynamic turbulence"JGR: Space Physics A1 (1987): 282-284.2. Matthaeus, W. H., Brown M. R., "Nearly incompressible magnetohydrodynamics at low Mach number"The Physics of Fluids 12 (1988): 3634-3644.3. Matthaeus, W. H., et al. "Nearly incompressible magnetohydrodynamics, pseudosound, and solar wind fluctuations" JGR: Space Physics A4 (1991): 5421-5435.4. Adhikari, S., et al. "Energy transfer in reconnection and turbulence" Physical Review E 6 (2021): 065206.5. Adhikari S., et al. “Statistics of Total Pressure in Kinetic Plasma Turbulence" ESS Open Archive (2023).