J. T. Mendonça

Plasma based charged-particle accelerators

Studies of charged-particle acceleration processes remain one of the most important areas of research in laboratory, space and astrophysical plasmas. In this paper, we present the underlying physics and the present status of high gradient and high energy plasma accelerators. We will focus on the acceleration of charged particles to relativistic energies by plasma waves that are created by intense laser and particle beams. The generation of relativistic plasma waves by intense lasers or electron beams in plasmas is important in the quest for producing ultra-high acceleration gradients for accelerators. With the development of compact short pulse high brightness lasers and electron positron beams, new areas of studies for laser/particle beam-matter interactions is opening up. A number of methods are being pursued vigorously to achieve ultra-high acceleration gradients. These include the plasma beat wave accelerator mechanism, which uses conventional long pulse (~100 ps) modest intensity lasers (I ~ 1014–1016 W cm−2), the laser wakefield accelerator (LWFA), which uses the new breed of compact high brightness lasers ( 1018 W cm−2, the self-modulated LWFA concept, which combines elements of stimulated Raman forward scattering, and electron acceleration by nonlinear plasma waves excited by relativistic electron and positron bunches. In the ultra-high intensity regime, laser/particle beam–plasma interactions are highly nonlinear and relativistic, leading to new phenomena such as the plasma wakefield excitation for particle acceleration, relativistic self-focusing and guiding of laser beams, high-harmonic generation, acceleration of electrons, positrons, protons and photons. Fields greater than 1 GV cm−1 have been generated with particles being accelerated to 200 MeV over a distance of millimetre. Plasma wakefields driven by positron beams at the Stanford Linear Accelerator Center facility have accelerated the tail of the positron beam. In the near future, laser plasma accelerators will be producing GeV particles.

Using high-power lasers for detection of elastic photon-photon scattering

The properties of four-wave interaction via the nonlinear quantum vacuum is investigated. The effect of the quantum vacuum is to generate photons with new frequencies and wave vectors, due to elastic photon-photon scattering. An expression for the number of generated photons is derived, and using state-of-the-art laser data it is found that the number of photons can reach detectable levels. In particular, the prospect of using the high-repetition Astra Gemini system at the Rutherford Appleton Laboratory is discussed. The problem of noise sources is reviewed, and it is found that the noise level can be reduced well below the signal level. Thus, detection of elastic photon-photon scattering may for the first time be achieved.

Formation of dusty plasma molecules

Abstract The electrostatic interaction potential energy for two Debye shielded macroscopic grains or impurities is obtained for all values of intergrain separation both in the plasma as well as in the plasma sheath. The predicted cohesive energy assumes a form familiar from molecular physics but with no ad hoc assumptions regarding the form of the repulsive and attractive regions and no phenomenological adjustable parameters. The result is significant as a molecular model and constitutes an important element for understanding the interaction forces responsible for the formation of the novel Coulomb or plasma crystal systems.

Proton and neutron sources using terawatt lasers

We review the production of high-energy protons and neutrons in the interaction of intense lasers with gases, clusters and solid targets. Some potential applications are briefly discussed.

The neutrino electron accelerator

It is shown that a wake of electron plasma oscillations can be created by the nonlinear ponderomotive force of an intense neutrino flux. The electrons trapped in the plasma wakefield will be accelerated to high energies. Such processes may be important in supernovas and pulsars.

Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering

Twisted Laguerre–Gaussian lasers, with orbital angular momentum and characterized by doughnut-shaped intensity profiles, provide a transformative set of tools and research directions in a growing range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high-gradient positron acceleration. The production of ultra-high-intensity twisted laser pulses could then also have a broad influence on relativistic laser–matter interactions. Here we show theoretically and with ab initio three-dimensional particle-in-cell simulations that stimulated Raman backscattering can generate and amplify twisted lasers to petawatt intensities in plasmas. This work may open new research directions in nonlinear optics and high–energy-density science, compact plasma-based accelerators and light sources.

Interaction of ultrashort high-intensity laser pulses with atomic clusters

A fully relativistic particle-in-cell code is used to simulate atomic clusterexplosions following the interaction with ultrashort high-intensity laser pulses, investigating the dynamics of a 1 μm hydrogen cluster explosion and providing information about the time-resolved position, momentum, and energy of electrons and ions, for different laser intensities. The results indicate that the mechanism responsible for cluster expansion is Coulombic explosion producing MeV ions and electrons.

Cyclotron maser radiation from astrophysical shocks

One of the most popular coherent radio emission mechanisms is electron cyclotron maser instability. In this article we demonstrate that electron cyclotron maser emission is directly associated with particular types of charged particle acceleration such as turbulence and shocks commonly inferred in astrophysical plasmas.

Equivalent charge of photons and neutrinos in a plasma

It is suggested that it is possible to define an equivalent electric charge for an intense laser pulse (which can be described as a photon bunch) propagating in a plasma. It is also shown that this equivalent charge can be a source of new radiation processes in an inhomogeneous plasma. The results are extended to the case of a neutrino bunch, which is coupled to the plasma by weak nuclear forces.

Analysis of four-wave mixing of high-power lasers for the detection of elastic photon-photon scattering

We derive expressions for the coupling coefficients for electromagnetic four-wave mixing in the nonlinear quantum vacuum. An experimental setup for detection of elastic photon-photon scattering is suggested, where three incoming laser pulses collide and generate a fourth wave with a new frequency and direction of propagation. An expression for the number of scattered photons is derived and, using beam parameters for the Astra Gemini system at the Rutherford Appleton Laboratory, it is found that the signal can reach detectable levels. Problems with shot-to-shot reproducibility are reviewed, and the magnitude of the noise arising from competing scattering processes is estimated. It is found that detection of elastic photon-photon scattering may be achieved.