Electrical potentials at probes in supersonic plasma flow

Decay of the electron number density in the nitrogen afterglow using a hairpin resonator probe A diagnostic method for real-time measurements of the density of nitrogen atoms in the postglow of an Ar -N 2 discharge using a catalytic probe This paper examines the propagation of spark-generated shockwaves ͑1.0Ͻ MachϽ 2.0͒ into argon and nitrogen glow discharges and their afterglow. Diagnostic methods were employed and expanded in order to capture the dynamics of the shock front in these weakly-ionized, nonmagnetized, collisional plasmas. We used a microwave hairpin resonator to measure the electron number density, and, for all cases, we measured an increase in the electron number density at the shock front. By comparing the increase in electron number density at the shock front in the active discharge and in the afterglow, we conclude that electrons with a temperature much greater than room temperature can be compressed at the shock front. The ratio of electron number density before and after the shock front can be approximately predicted using the Rankine-Hugoniot relationship. The large gradient in electron density, and hence a large gradient in the flux of charged species, created a region of space-charge separation, i.e., a double layer, at the shock front. The double layer balances the flux of charged particles on both sides of the shock front. The double layer voltage drop was measured in the current-carrying discharge using floating probes and compared with previous models. As well, we measured argon 1s 5 metastable-state density and demonstrate that metastable-state neutral species can be compressed across a shock front and approximately predicted using the Rankine-Hugoniot relationship.

show abstract

The dynamic sheath: Objects coupling to plasmas on electron-plasma-frequency time scales

Borovsky

1988

The Physics of Fluids

View full text Add to dashboard Cite

The time-dependent interaction between solid objects and the unmagnetized plasmas in which they are immersed is investigated. To this end over 1900 high-resolution, one-dimensional particle-in-cell simulations of the plasmas surrounding cylindrical and planar objects are statistically analyzed. Numerical shot noise produces an electron-plasma-frequency ringing in the simulations, the amplitude of which is related to the plasma temperature and to the numerical system temperature. Whenever the potential of an object is rapidly biased, the surrounding plasma rings with a large amplitude at the electron-plasma frequency. During this ringing, a depletion layer forms around the object on ion-acoustic time scales. Positively charged objects discharge via plasma currents in about τpe /4 and negatively charged objects discharge in about τpi . Owing to charge separations in the plasmas, for the first few ion-plasma periods after a perturbation, the potential of an object is not directly related to the charge on it. The electron-plasma-frequency ringing drives large-amplitude Langmuir waves, which energize electrons and drive cavitation in the plasma. The fluxes of electrons reaching the objects are bursty at ωpe, and the energies of the ions striking the object slowly and systematically vary with time.

show abstract

Electrical potentials at probes in supersonic plasma flow

Cited by 4 publications

References 11 publications

Atomic Interactions in Weakly Ionized Gas: Ionizing Shock Waves in Neon

Atomic Interactions in Weakly Ionized Gas: Ionizing Shock Waves in Neon

Electrical double layers at shock fronts in glow discharges and afterglows

The dynamic sheath: Objects coupling to plasmas on electron-plasma-frequency time scales

Contact Info

Product

Resources

About