Ion Acceleration by the Radiation Pressure of Slow Electromagnetic Wave

When the ions are accelerated by the radiation pressure of the laser pulse, their velocity can not exceed the laser group velocity, in the case when it is less than the speed of light in vacuum. This is demonstrated in two cases corresponding to the thin foil target irradiated by a high intensity laser light and to the hole boring by the laser pulse in the extended plasma accompanied by the collisionless shock wave formation. It is found that the beams of accelerated at the collisionless shock wave front ions are unstable against the Buneman-lke and the Weibel-like instabilities which result in the ion energy spectrum broadening.Comment: 22 pages, 9 figure

The quasiparallel collisionless shock wave: A simulation study

Thesis (Ph.D.) University of Alaska Fairbanks, 1988The structure of the quasi-parallel collisionless shock wave is studied via a numerical simulation model. The model is compared to observations and theoretical predictions and within its limitations appears to reproduce the true shock structure reasonably well. Three electron equations of state and their effects on the simulation are examined. It is found that only the isotropic-adiabatic electron equation of state yields acceptable results in the simulation at high Mach numbers. The scale lengths of the shock are measured, normalized by the natural scale lengths of the plasma, and plotted as a function of the Alfven Mach number. It is found that the wavelength of the upstream waves follows that predicted for a phase standing whistler quite well and the scalelength of the jump in the magnitude of the magnetic field is generally greater than, but approximately equal to this wavelength. For Alfven Mach numbers M\sb{A} > 2.5, waves are generated in the downstream region. Their wavelength and the scale length of the plasma transition are larger than the natural scale lengths of the plasma. The ion heating is seen to occur in two stages. In the first stage which occurs upstream of the principal shock ramp, the heating can be characterized by a polytropic power law equation of state with an exponent much greater than the isentropic-adiabatic rate of $\gamma$ = 5/3. The second stage of heating which occurs from the principal shock ramp to the downstream region is characterized by an exponent on the order of the isentropic-adiabatic rate. The results show that the ion heating occurs mainly around the principle density jump near the center of the shock transition region, while the increase in entropy takes place mainly in the upstream side of the shock transition region. It is suggested that the ion heating is a consequence of the non-adiabatic scattering of the ions through the magnetic field of the shock and its upstream precursor wave

A collisionless shock wave experiment

Collisionless shock waves are a very important heating mechanism for plasmas and are commonly found in space and astrophysical environments. Collisionless shocks were studied in the laboratory more than 20 years ago, and more recently in space via in situ satellite measurements. The authors propose a new laboratory shock wave experiment to address unresolved issues related to the differences in the partition of plasma heating between electrons and ions in space and laboratory plasmas, which can have important implications for a number of physical systems

Generation of Collisionless Shocks by Laser-Plasma Piston in Magnetised Background: Experiment “BUW”

Theoretical basis and main results of the first successful large-scale, Laser-Plasma experiment “BUW”, on generation of Collisionless Shock Wave in magnetised Background Plasma, are presented. Our classic approach is based on the action of so called Magnetic Laminar Mechanism (or Larmor coupling) for collisionless interaction between interpenetrating super-Alfvenic plasma flows of Laser-Plasma and Background in transverse magnetic field

On The Possible Mechanism Of Energy Dissipation In Shock-Wave Fronts Driven Ahead Of Coronal Mass Ejections

Analysis of Mark 4 and LASCO C2, C3 coronagraph data shows that, at the distance $R \leq 6$ R$_\odot$ from the center of the Sun, the thickness of a CME-generated shock-wave front ($\delta_F$) may be of order of the proton mean free path. This means that the energy dissipation mechanism in the shock front at these distances is collisional. A new discontinuity (thickness $\delta_F^* \ll \delta_F$) is observed to appear in the anterior part of the front at $R \geq 10$ R$_\odot$. Within the limits of experimental error, the thickness $\delta_F^* \approx$ 0.1-0.2 R$_\odot$ does not vary with distance and is determined by the spatial resolution of the LASCO C3 instrument. At the initial stage of formation, the discontinuity on the scale of $\delta_F^*$ has rather small amplitude and exists simultaneously with the front having thickness $\delta_F$. The relative amplitude of the discontinuity gradually increases with distance, and the brightness profile behind it becomes even. Such transformations may be associated with the transition from a collisional shock wave to a collisionless one.Comment: 3 figure

Collisionless plasma expansion in the presence of a dipole magnetic field

The collisionless interaction of an expanding high-energy plasma cloud with a magnetized background plasma in the presence of a dipole magnetic field is examined in the framework of a 2D3V hybrid (kinetic ions and massless fluid electrons) model. The retardation of the plasma cloud and the dynamics of the perturbed electromagnetic fields and the background plasma are studied for high Alfven-Mach numbers using the particle-in-cell method. It is shown that the plasma cloud expands excluding the ambient magnetic field and the background plasma to form a diamagnetic cavity which is accompanied by the generation of a collisionless shock wave. The energy exchange between the plasma cloud and the background plasma is also studied and qualitative agreement with the analytical model suggested previously is obtained.Comment: 10 pages, 4 figure

Resolved shock structure of the Balmer-dominated filaments in Tycho's supernova remnant: Cosmic-ray precursor?

We report on the results from H{\alpha} imaging observations of the eastern limb of Tycho's supernova remnant (SN1572) using the Wide Field Planetary Camera 2 on the Hubble Space Telescope. We resolve the detailed structure of the fast, collisionless shock wave into a delicate structure of nearly edge-on filaments. We find a gradual increase of H{\alpha} intensity just ahead of the shock front, which we interpret as emission from the thin (~1") shock precursor. We find that a significant amount of the H{\alpha} emission comes from the precursor and that this could affect the amount of temperature equilibration derived from the observed flux ratio of the broad and narrow H{\alpha} components. The observed H{\alpha} emission profiles are fit using simple precursor models, and we discuss the relevant parameters. We suggest that the precursor is likely due to cosmic rays and discuss the efficiency of cosmic-ray acceleration at this position.Comment: Prepared with emulateapj.sty (5 pages, 4 figures). Published in ApJL

Relativistic Laser-Matter Interaction and Relativistic Laboratory Astrophysics

The paper is devoted to the prospects of using the laser radiation interaction with plasmas in the laboratory relativistic astrophysics context. We discuss the dimensionless parameters characterizing the processes in the laser and astrophysical plasmas and emphasize a similarity between the laser and astrophysical plasmas in the ultrarelativistic energy limit. In particular, we address basic mechanisms of the charged particle acceleration, the collisionless shock wave and magnetic reconnection and vortex dynamics properties relevant to the problem of ultrarelativistic particle acceleration.Comment: 58 pages, 19 figure