Paper

Paper of any type conference or journal

Laser reflection as a catalyst for direct laser acceleration in multipicosecond laser-plasma interaction

Publication type
Citation

K. Weichman, A. P. L. Robinson, F. N. Beg, and A. V. Arefiev, "Laser reflection as a catalyst for direct laser acceleration in multipicosecond laser-plasma interaction", Phys. Plasmas 27, 013106 (2020).

Abstract

We demonstrate that laser reflection acts as a catalyst for superponderomotive electron production in the preplasma formed by relativistic multipicosecond lasers incident on solid density targets. In 1D particle-in-cell simulations, high energy electron production proceeds via two stages of direct laser acceleration: an initial stochastic backward stage and a final nonstochastic forward stage. The initial stochastic stage, driven by the reflected laser pulse, provides the preacceleration needed to enable the final stage to be nonstochastic. Energy gain in the electrostatic potential, which has been frequently considered to enhance stochastic heating, is only of secondary importance. The mechanism underlying the production of high energy electrons by laser pulses incident on solid density targets is of direct relevance to applications involving multipicosecond laser-plasma interactions.

Energy gain by laser-irradiated electrons in a strong magnetic field

Publication type
Citation

A. Arefiev, Z. Gong, A. P. L. Robinson, "Energy gain by laser-irradiated electrons in a strong magnetic field", Phys. Rev. E 101043201 (2020).

Abstract

This paper deals with electron acceleration by a laser pulse in a plasma with a static uniform magnetic field B∗. The laser pulse propagates perpendicular to the magnetic field lines with the polarization chosen such that (Elaser⋅B)=0. The focus of the work is on the electrons with an appreciable initial transverse momentum that are unable to gain significant energy from the laser in the absence of the magnetic field due to strong dephasing. It is shown that the magnetic field can initiate an energy increase by rotating such an electron, so that its momentum becomes directed forward. The energy gain continues well beyond this turning point where the dephasing drops to a very small value. In contrast to the case of purely vacuum acceleration, the electron experiences a rapid energy increases with the analytically derived maximum energy gain dependent on the strength of the magnetic field and the phase velocity of the wave. The energy enhancement by the magnetic field can be useful at high laser amplitudes, a0≫1, where the acceleration similar to that in the vacuum is unable to produce energetic electrons over just tens of microns. A strong magnetic field helps leverage an increase in a0 without a significant increase in the interaction length.

Net energy gain in direct laser acceleration due to enhanced dephasing induced by an applied magnetic field

Publication type
Citation

A. P. L. Robinson and A. Arefiev, "Net energy gain in direct laser acceleration due to enhanced dephasing induced by an applied magnetic field", Phys. Plasmas 27, 023110 (2020).

Abstract

Even in the situation where an electron interacts with a single plane wave, the well-known dynamical adiabaticity can be broken when an applied magnetic field is present, which will act to increase the dephasing rate of the electron during the interaction. Here we demonstrate this for the case where there is a uniform static magnetic field which is oriented either parallel or perpendicular to the electric field of the incident plane wave, and perpendicular to the direction of its propagation. The described energy gain phenomenon has direct relevance to laser-plasma interactions that involve external magnetic fields generated by laser-driven capacitor coils.

Radiation reaction as an energy enhancement mechanism for laser-irradiated electrons in a strong plasma magnetic field

Publication type
Citation

Z. Gong, F. Mackenroth, X. Q. Yan, and A. Arefiev, "Radiation reaction as an energy enhancement mechanism for laser-irradiated electrons in a strong plasma magnetic field", Scientific Reports 9, 17181 (2019).

Abstract

Conventionally, friction is understood as a mechanism depleting a physical system of energy and as an unavoidable feature of any realistic device involving moving parts. In this work, we demonstrate that this intuitive picture loses validity in nonlinear quantum electrodynamics, exemplified in a scenario where spatially random friction counter-intuitively results in a highly directional energy flow. This peculiar behavior is caused by radiation friction, i.e., the energy loss of an accelerated charge due to the emission of radiation. We demonstrate analytically and numerically how radiation friction can dramatically enhance the energy gain by electrons from a laser pulse in a strong magnetic field that naturally arises in dense laser-irradiated plasma. We find the directional energy boost to be due to the transverse electron momentum being reduced through friction whence the driving laser can accelerate the electron more efficiently. In the considered example, the energy of the laser-accelerated electrons is enhanced by orders of magnitude, which then leads to highly directional emission of gamma-rays induced by the plasma magnetic field.

Extreme nonlinear dynamics in vacuum laser acceleration with a crossed beam configuration

Publication type
Citation

A. P. L. Robinson, K. Tangtartharakul, K. Weichman, and A. V. Arefiev, "Extreme nonlinear dynamics in vacuum laser acceleration with a crossed beam configuration", Phys. Plasmas 26, 093110 (2019).

Abstract

A relatively simple model problem where a single electron moves in two relativistically strong obliquely intersecting plane wave-packets is studied using a number of different numerical solvers. It is shown that, in general, even the most advanced solvers are unable to obtain converged solutions for more than about 100 fs in contrast to the single plane wave problem, and that some basic metrics of the orbit show enormous sensitivity to the initial conditions. At a bare minimum, this indicates an unusual degree of nonlinearity, and may well indicate that the dynamics of this system are chaotic.

Laser-driven acceleration of quasi-monoenergetic, near-collimated titanium ions via a transparency-enhanced acceleration scheme

Publication type
Citation

J. Li, P. Forestier-Colleoni, M. Bailly-Grandvaux, C. McGuffey, A. Arefiev, S. S. Bulanov, J. Peebles, C. Krauland, A. E. Hussein, T. Batson, J. C. Fernandez, R. P. Johnson, G. Petrov, and F. Beg, "Laser-driven acceleration of quasi-monoenergetic, near-collimated titanium ions via a transparency-enhanced acceleration scheme", New J. Phys. 21 103005 (2019).

Abstract

Laser-driven ion acceleration has been an active research area in the past two decades with the prospects of designing novel and compact ion accelerators. Many potential applications in science and industry require high-quality, energetic ion beams with low divergence and narrow energy spread. Intense laser ion acceleration research strives to meet these challenges and may provide high charge state beams, with some successes for carbon and lighter ions. Here we demonstrate the generation of well collimated, quasi-monoenergetic titanium ions with energies ~145 and 180 MeV in experiments using the high-contrast (<10−9) and high-intensity (6 x 1020 W cm-2) Trident laser and ultra-thin (~100 nm) titanium foil targets. Numerical simulations show that the foils become transparent to the laser pulses, undergoing relativistically induced transparency (RIT), resulting in a two-stage acceleration process which lasts until ~2 ps after the onset of RIT. Such long acceleration time in the self-generated electric fields in the expanding plasma enables the formation of the quasi-monoenergetic peaks. This work contributes to the better understanding of the acceleration of heavier ions in the RIT regime, towards the development of next generation laser-based ion accelerators for various applications.

Direct laser acceleration of electrons in the plasma bubble by tightly focused laser pulses

Publication type
Citation

T. Wang, V. Khudik, A. Arefiev, and G. Shvets, "Direct laser acceleration of electrons in the plasma bubble by tightly focused laser pulses", Phys. Plasmas 26, 083101 (2019).

Abstract

We present an analytical theory that reveals the importance of the longitudinal laser electric field in the course of the resonant acceleration of relativistic electrons by a tightly confined laser beam. It is shown that this laser field component always counteracts the transverse one and effectively decreases the final energy gain of electrons via the direct laser acceleration (DLA) mechanism. This effect is demonstrated by carrying out particle-in-cell simulations of the DLA of the electrons injected into the accelerating phase of the plasma wake. It is shown that the electron energy gain from the wakefield is substantially compensated by the quasiresonant energy loss to the longitudinal laser field component. The analytically obtained scalings and estimates are in good agreement with the results of the numerical simulations.

Probing and possible application of the QED vacuum with micro-bubble implosions induced by ultra-intense laser pulses

Publication type
Citation

J. K. Koga, M. Murakami, A. Arefiev, and Y. Nakamiya, "Probing and possible application of the QED vacuum with micro-bubble implosions induced by ultra-intense laser pulses", Matter Radiat. Extremes 4, 034401 (2019).

Abstract

The interaction of micro-bubbles with ultra-intense laser pulses has been shown to generate ultra-high proton densities and correspondingly high electric fields. We investigate the possibility of using such a combination to study the fundamental physical phenomenon of vacuum polarization. With current or near-future laser systems, measurement of vacuum polarization via the bending of gamma rays that pass near imploded micro-bubbles may be possible. Since it is independent of photon energy to within the leading-order solution of the Heisenberg–Euler Lagrangian and the geometric optics approximation, the corresponding index of refraction can dominate the indices of refraction due to other effects at sufficiently high photon energies. We consider the possibility of its application to a transient gamma-ray lens.

Relativistic proton emission from ultrahigh-energy-density nanosphere generated by microbubble implosion

Publication type
Citation

M. Murakami, A. Arefiev, M. A. Zosa, J. K. Koga, and Y. Nakamiya, "Relativistic proton emission from ultrahigh-energy-density nanosphere generated by microbubble implosion", Phys. Plasmas 26 043112 (2019).

Abstract

Laser intensity scalings are investigated for accelerated proton energy and attainable electrostatic field using microbubble implosion (MBI). In MBI, the bubble wall protons are subject to volumetric acceleration toward the center due to the spherically symmetric electrostatic force generated by hot electrons filling the bubble. Such an implosion can generate an ultrahigh density proton core of nanometer size on the collapse, which results in an ultrahigh electrostatic field to emit energetic protons in the relativistic regime. Three-dimensional particle-in-cell and molecular dynamics simulations are conducted in a complementary manner. As a result, underlying physics of MBI are revealed such as bubble-pulsation and ultrahigh energy densities, which are higher by orders of magnitude than, for example, those expected in a fusion-igniting core of inertially confined plasma. MBI has potential as a plasma-optical device, which optimally amplifies an applied laser intensity by a factor of two orders of magnitude; thus, MBI is proposed to be a novel approach to the Schwinger limit.