Large Amplitude Plasma Oscillations Research Articles

Quasimonoenergetic Proton Acceleration via Quantum Radiative Compression

Dense high-energy monoenergetic proton beams are vital for wide applications, thus modern laser-plasma-based ion-acceleration methods are aiming to obtain high-energy proton beams with energy spread as low as possible. In this work, we put forward a quantum radiative compression method to postcompress a highly accelerated proton beam and convert it to a dense quasimonoenergetic one. We find that when the relativistic plasma produced by radiation-pressure acceleration collides head on with an ultraintense laser beam, large-amplitude plasma oscillations are excited due to quantum radiation reaction and the ponderomotive force, which induce compression of the phase space of protons located in its acceleration phase with negative gradient. Our three-dimensional spin-resolved quantum electrodynamics (QED) particle-in-cell simulations show that hollow-structure proton beams with a peak energy approximately $\mathrm{GeV}$, relative energy spread of few percents, and number ${N}_{p}\ensuremath{\sim}{10}^{10}$ (or ${N}_{p}\ensuremath{\sim}{10}^{9}$ with a $1\mathrm{%}$ energy spread) can be produced in near-future laser facilities, which may fulfill the requirements of alternative applications, such as, for radiography of ultrathick dense materials, or as injectors of hadron colliders.

Observation of anomalous side-scattering in laser wakefield accelerators

AbstractHigh-intensity femtosecond laser–plasma interaction experiments were performed to investigate laser–plasma wakefield acceleration in the “bubble” regime. Using a 15 TW laser pulse, the emission of side-scattered radiation was spectrally and spatially resolved and was consequently used to diagnose the evolution of the laser pulse during the acceleration process. Side-scattered emission was observed immediately before wavebreaking at a frequency of ωL + 1.7ωp (where ωL is the laser frequency and ωp is the background plasma frequency). This emission may result from scattering of laser light by large amplitude plasma oscillations generated in the shell of the wakefield “bubble” and which occurs immediately prior to the wavebreaking/injection process. The observed variation of the frequency of scattered light with electron density agrees with theoretical estimates.

Residual Bernstein-Greene-Kruskal-like waves after one-dimensional electron wave breaking in a cold plasma

A one-dimensional particle in cell simulation of large amplitude plasma oscillations is carried out to explore the physics beyond wave breaking in a cold homogeneous unmagnetized plasma. It is shown that after wave breaking, all energy of the plasma oscillation does not end up as random kinetic energy of particles, but some fraction, which is decided by Coffey's wave breaking limit in warm plasma, always remains with two oppositely propagating coherent Bernstein-Greene-Kruskal like modes with supporting trapped particle distributions. The randomized energy distribution of untrapped particles is found to be characteristically non-Maxwellian with a preponderance of energetic particles.

On the maximum longitudinal electric field of a large amplitude electron plasma wave excited by a short electromagnetic radiation pulse

The excitation of large amplitude plasma oscillations by the ponderomotive force exerted by a short electromagnetic (e.m.) radiation pulse on the electrons, is described within a one-dimensional, relativistic, cold plasma model. The quasistatic approximation, which assumes that the fluid variables follow adiabatically the temporal evolution of the field variables, is assumed to be valid. For a fixed rectangular profile of the e.m. wavepacket, travelling with group velocity v g< c, the analytical solution of the problem is obtained. It is shown that, after the transit of the pulse, the coherent longitudinal electric field (travelling with phase velocity v φ = v g) can reach values higher than E MAX st =√2(m e cω pe /e)(γ φ−1) 1 2 , where γ φ=(1−v 2 φ/c 2) -1 2 , up to E MAX =√2(m e cω pe /e)(γ 2 φv φ/c) (3−v 2 φ/c 2−√5−2v 2 φ/c 2+v 4 φ/c 4) 1 2 . However, this is only a transient dynamics which leads inevitably to the wavebreaking at a distance of approximately one wavelength from the beginning of the pulse. Actually, only for E< E MAX st stationary plasma oscillations can be sustained.

Scattering of electromagnetic waves into plasma oscillations via plasma particles

A plasma subjected to an intense electromagnetic wave can exhibit a large number of parametric instabilities. An interesting example which has received little attention is the decay of the electromagnetic wave into a plasma oscillation with the excess energy and momentum being carried off by electrons. This process has been simulated on a one−and−two−halves dimensional electromagnetic code. The incident electromagnetic wave had a frequency near the plasma frequency so that decay into a plasma oscillation and a backscattered electromagnetic wave was excluded. As expected, the threshold for this instability was very large , so it is unlikely that this instability is competitive in most laser plasmas. Nevertheless, the physical mechanism involved provides a means for absorption of laser light and acceleration of particles in a plasma containing large amplitude plasma oscillations.

Alternating Current Instability Produced by the Two-Stream Instability

Theory and numerical experiments show that large amplitude plasma oscillations are unstable when the mobility of the ions is taken into account. This instability can lead to an anomalously rapid damping of the plasma oscillations. It is expected that large amplitude plasma oscillations produced by the electron two-stream instability would be subject to this instability and the associated damping. Numerical experiments have been performed which indicate that this is so and that there is good correspondence to theory.

Fast Beam-Switching Electron Gun for Transient Beam-Plasma Interaction Study

An electron gun and deflection system used to study transient beam-plasma interactions is described. The gun produces a 1 or 2 mm diam beam which can be switched off or on in ∼0.5 nsec. Two such guns used in a two beam device can easily excite large amplitude plasma oscillations. Measurements of damping in the time domain were made by measuring the damping rate of these oscillations following beam cutoff.