Laser-driven Plasma-based Accelerator Research Articles

Self-focusing of a Bessel–Gaussian laser beam in plasma under density transition

The model given by Patil et al., for the self-focusing of lowest-order Bessel–Gaussian laser beam, is revisited by introducing the exponential plasma density ramp in this paper. Plasma density changes due to combined effect of the relativistic and ponderomotive nonlinearities, which arise due to the nonuniform spatial profile of the laser beam leading to stronger self-focusing. Under paraxial ray approximation, the expression for the evolution of laser-beam width parameter is obtained and solved numerically in order to achieve self-focusing. We have observed that as Bessel beam propagates through the plasma, it does not diffract and spread out, which is in contrast to the usual behavior of light that spreads out after being focused down to the small spot. Laser spot size decreases considerably under the presence of exponential density ramp. This study will be useful for better understanding the self-focusing mechanism of lasers as it becomes effective for the optimized parameters under the proposed situation. Bessel laser beams play an important role in enhancing the energy gain in laser-driven accelerators. In addition, for all laser-driven plasma-based accelerators, it appears possible to guide a laser beam over large distances using a plasma density channel, thus enhancing the acceleration length and the energy gain.

Beam dynamics challenges in linear colliders based on laser-plasma accelerators

In this paper we discuss design considerations and beam dynamics challenges associated with laser-driven plasma-based accelerators as applied to multi-TeV-scale linear colliders. Plasma accelerators provide ultra-high gradients and ultra-short bunches, offering the potential for compact linacs and reduced power requirements. We show that stable, efficient acceleration with beam quality preservation is possible in the nonlinear bubble regime of laser-plasma accelerators using beam shaping. Ion motion, naturally occuring for dense beams (i.e., low emittance and high energy) severely damps transverse beam instabilities. Coulomb scattering by the background ions is considered and it is shown that the strong focusing in the plasma strongly suppresses scattering-induced emittance growth. Betatron radiation emission from the transverse motion of the beam in the plasma will result in beam power loss and energy spread growth; however for sub-100 nm emittances, the beam power loss and energy spread growth will be sub-percent for multi-TeV-class plasma linacs.

Laser-driven electron beam and radiation sources for basic, medical and industrial sciences.

To date active research on laser-driven plasma-based accelerators have achieved great progress on production of high-energy, high-quality electron and photon beams in a compact scale. Such laser plasma accelerators have been envisaged bringing a wide range of applications in basic, medical and industrial sciences. Here inheriting the groundbreaker’s review article on “Laser Acceleration and its future” [Toshiki Tajima, (2010)],1) we would like to review recent progress of producing such electron beams due to relativistic laser-plasma interactions followed by laser wakefield acceleration and lead to the scaling formulas that are useful to design laser plasma accelerators with controllability of beam energy and charge. Lastly specific examples of such laser-driven electron/photon beam sources are illustrated.

Scaling and design of high-energy laser plasma electron acceleration

Recently there has been great progress in laser-driven plasma-based accelerators by exploiting high-power lasers, where electron beams can be accelerated to multi-GeV energy in a centimeter-scale plasma due to the laser wakefield acceleration mechanism. While, to date, worldwide research on laser plasma accelerators has been focused on the creation of compact particle and radiation sources for basic sciences, medical and industrial applications, there is great interest in applications for high-energy physics and astrophysics, exploring unprecedented high-energy frontier phenomena. In this context, we present an overview of experimental achievements in laser plasma acceleration from the perspective of the production of GeV-level electron beams, and deduce the scaling formulas capable of predicting experimental results self-consistently, taking into account the propagation of a relativistic laser pulse through plasma and the accelerating field reduction due to beam loading. Finally, we present design examples for 10-GeV-level laser plasma acceleration, which is expected in near-term experiments by means of petawatt-class lasers.

Laser electron acceleration beyond 100 GeV

Nowadays there is great progress on laser-driven plasma-based accelerators by exploiting petawatt-class lasers, where for one aspect electron beams can be accelerated to multi-GeV energy in a centimeter-scale plasma due to laser wakefield acceleration mechanism. While to date, worldwide researches on laser-plasma accelerators are focused to create compact particle and radiation sources for applications in a wide range of sciences, including basic, medical and industrial sciences, there are great interests in applications for high energy physics and astrophysics that explore unprecedented high-energy frontier phenomena, for which laser plasma accelerator concepts provide us with promising tools. Here, our endeavors toward “extreme light” in the IZEST are envisaged for the next 30 years perspective and issues on laser plasma electron acceleration beyond 100 GeV and furthermore toward the TeV regime, aiming at high energy physics applications.

Physics of laser-driven plasma-based electron accelerators

Laser-driven plasma-based accelerators, which are capable of supporting fields in excess of 100 GV/m, are reviewed. This includes the laser wakefield accelerator, the plasma beat wave accelerator, the self-modulated laser wakefield accelerator, plasma waves driven by multiple laser pulses, and highly nonlinear regimes. The properties of linear and nonlinear plasma waves are discussed, as well as electron acceleration in plasma waves. Methods for injecting and trapping plasma electrons in plasma waves are also discussed. Limits to the electron energy gain are summarized, including laser pulse diffraction, electron dephasing, laser pulse energy depletion, and beam loading limitations. The basic physics of laser pulse evolution in underdense plasmas is also reviewed. This includes the propagation, self-focusing, and guiding of laser pulses in uniform plasmas and with preformed density channels. Instabilities relevant to intense short-pulse laser-plasma interactions, such as Raman, self-modulation, and hose instabilities, are discussed. Experiments demonstrating key physics, such as the production of high-quality electron bunches at energies of 0.1-1 GeV, are summarized.

Measurement of stability of electron beam generated by laser-driven plasma-based accelerator

Quasi-monoenergetic electron beams with the energy of 30-80 MeV and large number of electrons more than 108 were produced by focusing a 8TW, 50 fs Ti:sapphire laser pulse onto 1.6−1.9 × 1019 cm−3 plasmas. Stability of the quasi-monoenergetic electron beam generation was evaluated using an in-situ observation system for the electron beam diagnostics.

Terahertz radiation as a bunch diagnostic for laser-wakefield-accelerated electron bunches

Experimental results are reported from two measurement techniques (semiconductor switching and electro-optic sampling) that allow temporal characterization of electron bunches produced by a laser-driven plasma-based accelerator. As femtosecond electron bunches exit the plasma-vacuum interface, coherent transition radiation (at THz frequencies) is emitted. Measuring the properties of this radiation allows characterization of the electron bunches. Theoretical work on the emission mechanism is presented, including a model that calculates the THz wave form from a given bunch profile. It is found that the spectrum of the THz pulse is coherent up to the 200 μm thick crystal (ZnTe) detection limit of 4THz, which corresponds to the production of sub-50fs (rms) electron bunch structure. The measurements demonstrate both the shot-to-shot stability of bunch parameters that are critical to THz emission (such as total charge and bunch length), as well as femtosecond synchronization among bunch, THz pulse, and laser beam.

Laser-driven plasma-based accelerators: Wakefield excitation, channel guiding, and laser triggered particle injection

Plasma-based accelerators are discussed in which high-power short pulse lasers are the power source, suitably tailored plasma structures provide guiding of the laser beam and support large accelerating gradients, and an optical scheme is used to produce time-synchronized ultrashort electron bunches. From scaling laws laser requirements are obtained for development of compact high-energy accelerators. Simulation results of laser guiding and wakefield excitation in plasma channels, as well as laser-based injection of particles into a plasma wake, are presented. Details of the experimental program at Lawrence Berkeley National Laboratory on laser guiding, laser wakefield-based accelerators, and laser triggered injection are given.