Beginnings of Developing Kinetic Scenarios of Plasma Evolution Due to Coulomb Collisions

A new logic of reducing the two-time formalism to a highly informative scenario of redistribution of plasma particles in momentum due to Coulomb collisions is reported. Based on objective plasma evolution equations following from a properly reduced full plasma description, it has a more sound foundation than that presented in the previous report on increasing the informativeness of scenarios of the phenomenon. The possibilities of adapting the approach to the further development of more informative scenarios of plasma collisional relaxation and the modelling of transport phenomena are discussed.

Collisional Relaxation of Fast Electrons Energy in Gas

We present results of theoretical and experimental study of collisional relaxation of fast electrons energy in gas. The dependence on the gas pressure p and electron energy ε of the mean pass Λ of fast electrons injected into a gas being sufficient to spend on ionization all their initial energy ε has been calculated. It was found that Λ is directly proportional to ε2 and inversely proportional to the gas pressure. To sustain glow discharge with electrostatic confinement of fast electrons, Λ should be less than the mean way to the anode of emitted by the cathode electrons.

Anomalous Humidity Dependence in Photoacoustic Spectroscopy of CO Explained by Kinetic Cooling

Water affects the amplitude of photoacoustic signals from many gas phase molecules. In quartz-enhanced photoacoustic (QEPAS) measurements of CO excited at the fundamental vibrational resonance of CO, the photoacoustic signal decreases with increasing humidity, reaches a pronounced minimum at ~0.19%V, and increases with humidity for higher water contents. This peculiar trend is explained by competing endothermal and exothermal pathways of the vibrational relaxation of CO in N2 and H2O. Near-resonant vibrational–vibrational transfer from CO to N2, whose vibrational frequency is 188 cm−1 higher than in CO, consumes thermal energy, yielding a kinetic cooling effect. In contrast, vibrational relaxation via H2O is fast and exothermal, and hence counteracts kinetic cooling, explaining the observed trend. A detailed kinetic model for collisional relaxation of CO in N2 and H2O is presented. Simulations using rate constants obtained from literature were performed and compared to humidity dependent QEPAS experiments at varying pressure. Agreement between the experiments and simulations confirmed the validity of the model. The kinetic model can be used to identify optimized experimental conditions for sensing CO and can be readily adapted to include further collision partners.

Observing collisions beyond the secular approximation limit

Quantum coherence plays an essential role in diverse natural phenomena and technological applications. The unavoidable coupling of the quantum system to an uncontrolled environment incurs dissipation that is often described using the secular approximation. Here we probe the limit of this approximation in the rotational relaxation of molecules due to thermal collisions by using the laser-kicked molecular rotor as a model system. Specifically, rotational coherences in N2O gas (diluted in He) are created by two successive nonresonant short and intense laser pulses and probed by studying the change of amplitude of the rotational alignment echo with the gas density. By interrogating the system at the early stage of its collisional relaxation, we observe a significant variation of the dissipative influence of collisions with the time of appearance of the echo, featuring a decoherence process that is well reproduced by the nonsecular quantum master equation for modeling molecular collisions.

N-body chaos, phase-space transport and relaxation in numerical simulations

Using direct N-body simulations of self-gravitating systems we study the dependence of dynamical chaos on the system size N. We find that the N-body chaos quantified in terms of the largest Lyapunov exponent Λmax decreases with N. The values of its inverse (the so-called Lyapunov time tλ) are found to be smaller than the two-body collisional relaxation time but larger than the typical violent relaxation time, thus suggesting the existence of another collective time scale connected to many-body chaos.

Cужение линии поглощения легких атомов щелочных металлов в атмосфере тяжелых инертных газов при росте интенсивности излучения

The effect of narrowing of the absorption line of light alkali metal ^7Li and ^23Na atoms present in an atmosphere of heavy inert gas (xenon) with an increase in the external radiation intensity has been investigated. For ^7Li atoms at temperature T = 300 K and buffer gas (Xe) pressure $${{p}_{{{\text{Xe}}}}} = 0.002$$ Torr, the linewidth at half maximum decreases by a factor of 1.20 with an increase in the radiation intensity from 1 µW/cm^2 to 2.5 mW/cm^2. For ^23Na atoms at T = 600 K and $${{p}_{{{\text{Xe}}}}} = 0.01$$ Torr, the linewidth at half maximum decreases by a factor of 1.29 with an increase in the radiation intensity from 1 µW/cm^2 to 6 mW/cm^2. The effect of field narrowing of the absorption line is due to the following factors. First, the collisional relaxation of the velocities of light resonance particles in an atmosphere of heavy buffer particles is divided into two stages with significantly different durations: relaxation in the velocity direction (fast stage) and relaxation in the velocity magnitude (slow stage). Second, there are no collisional transitions between hyperfine components of the ground state.