A self-consistent hybrid model of standing and moving striations was developed for low-current DC discharges in noble gases. We introduced the concept of surface diffusion in phase space (r,u) (where u denotes the electron kinetic energy) described by a tensor diffusion in the nonlocal Fokker-Planck kinetic equation for electrons in the collisional plasma. Electrons diffuse along surfaces of constant total energy ε=u-eφ(r) between energy jumps in inelastic collisions with atoms. Numerical solutions of the 1d1u kinetic equation for electrons were obtained by two methods and coupled to ion transport and Poisson solver. We studied the dynamics of striation formation in Townsend and glow discharges in Argon gas at low discharge currents using a two-level excitation-ionization model and a “full-chemistry” model, which includes stepwise and Penning ionization. Standing striations appeared in Townsend and glow discharges at low currents, and moving striations were obtained for the discharge currents exceeding a critical value. These waves originate at the anode and propagate towards the cathode. We have seen two types of moving striations with the 2-level and full-chemistry models, which resemble the s and p striations previously observed in the experiments. Simulations indicate that processes in the anode region could control moving striations in the positive column plasma. The developed model helps clarify the nature of standing and moving striations in DC discharges of noble gases at low discharge currents and low gas pressures.
<p>The Voyager space probes provided us with a global perspective on galactic cosmic ray transport through the heliosphere at low to moderate heliographic latitudes, as well as their behavior at the boundary with the very local interstellar medium (VLISM). There remain, however, multiple interesting region the Voyagers have not visited, including high latitudes and the distant flanks of the heliopause where long-term trapping of charged particles is though to take place. We attempt to fill the gaps in our understanding of the distant heliosphere using computer simulations. The Space Plasma and Energetic Charged particle TRansport on Unstructured Meshes (SPECTRUM) code is a versatile software platform to perform tracing of particle trajectories using multiple physics models and internal or externally provided MHD background data. We apply the model to the problem of galactic cosmic ray transport in the outer heliosphere and the surrounding very local interstellar medium (VLISM) using the MHD background provided on a adaptive block mesh from the Space Weather Modeling Framework (SWMF). We compare the guiding center and nearly isotropic (Parker) physics models and elucidate the role of perpendicular diffusion in cosmic-ray penetration through the heliospheric boundary.</p>
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