Dust in Plasma I. Particle Size and Ion‐Neutral Collision Effects

Abstract

A fully kinetic self-consistent model of an absorbing particle immersed in stationary isotropic weakly collisional plasma has been developed. The combined effects of particle size and ion-neutral charge exchange collisions have been investigated for intermediate regimes, where no analytic theories are available. It is shown that collisional effects related to the ion orbital destruction (presence of extrema in ion flux collected on the particle surface and in particle potential and charge) are important for small particles, while they are totally absent for large particles. The potential distribution around the particle is quite well represented by a Yukawa form, but with an effective screening length that shows different dependences from the gas pressure for small and large particle size. Analytical fitting formulas of particle charge and potential and screening length depending on the particle radius parameter and on the Knudsen number have been obtained.

Dust in Plasma II. Effects of Secondary Electrons: Ionization and Surface Emission

“…This work represents the continuation of the previous paper I [1] where effects of grain size and ion-neutral collisions have been studied in relation to grain charge and plasma parameters. The driving mechanism of plasmaparticle interaction is the process of particle charging in an electrically floating condition, that is no net current is drawn from the plasma on the dust surface:…”

“…In addition to the previous collisionless PIC model [1], electron-atom collisions (elastic scattering, excitation and ionization) have been added using a null-collision MCC technique [12]. The 3D-3V spherical problem can be reduced to 1D-2V since all the quantities are uniform in the polar and azimuthal angular directions and the macroparticles lie on different orbits around the dust grain that are all equivalent limiting in this way the number of velocity components to the radial and tangential ones.…”

“…Under conditions where the emission from the dust is negligible, the grain acquires a negative charge and a negative potential relative to the plasma [2] (red line in Fig. However, it has been recently demonstrated that electron-induced ionization (EII) events (see 2.1) in the vicinity of a grain can increase the ion flux by a ΔΓ i,EII (analogous to ion-neutral resonant charge exchange CX collisions studied in paper I [1]) by creating slow ions falling onto its surface and leading to a significant reduction of charge and surface potential. However, it has been recently demonstrated that electron-induced ionization (EII) events (see 2.1) in the vicinity of a grain can increase the ion flux by a ΔΓ i,EII (analogous to ion-neutral resonant charge exchange CX collisions studied in paper I [1]) by creating slow ions falling onto its surface and leading to a significant reduction of charge and surface potential.…”

“…The reflected flux of secondaries Γ (1) see,b in turn can induce an additional flux of secondaries with an emission coefficient δ s : Γ The potential well has in this case a dual function: it not only reflects back to the dust part of the flux of secondaries, but it reduces also the flux of primaries towards the dust surface which is the cause of secondary emission (space-charge-limited (SCL) regime).…”

Particle Methods for Nonequilibrium Hypersonic and Plasma Flows

“…We have implemented a one-dimensional Particle-in-Cell (PIC) code [18][19][20][21][22][23]. Electrons and ions are tracked in the radial domain (motion in a central field of forces) using the electric field generating from their dynamics.…”