Ultrahigh intensity lasers can potentially be used in conjunction with conventional fusion lasers to ignite inertial confinement fusion (ICF) capsules with a total energy of a few tens of kilojoules of laser light, and can possibly lead to high gain with as little as 100 kJ. A scheme is proposed with three phases. First, a capsule is imploded as in the conventional approach to inertial fusion to assemble a high‐density fuel configuration. Second, a hole is bored through the capsule corona composed of ablated material, as the critical density is pushed close to the high‐density core of the capsule by the ponderomotive force associated with high‐intensity laser light. Finally, the fuel is ignited by suprathermal electrons, produced in the high‐intensity laser–plasma interactions, which then propagate from critical density to this high‐density core. This new scheme also drastically reduces the difficulty of the implosion, and thereby allows lower quality fabrication and less stringent beam quality and symmet...

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Ignition and high gain with ultrapowerful lasers

Femtosecond filamentation in transparent media

Particle accelerators are used in a wide variety of fields, ranging from medicine and biology to high-energy physics. The accelerating fields in conventional accelerators are limited to a few tens of MeV m(-1), owing to material breakdown at the walls of the structure. Thus, the production of energetic particle beams currently requires large-scale accelerators and expensive infrastructures. Laser-plasma accelerators have been proposed as a next generation of compact accelerators because of the huge electric fields they can sustain (>100 GeV m(-1)). However, it has been difficult to use them efficiently for applications because they have produced poor-quality particle beams with large energy spreads, owing to a randomization of electrons in phase space. Here we demonstrate that this randomization can be suppressed and that the quality of the electron beams can be dramatically enhanced. Within a length of 3 mm, the laser drives a plasma bubble that traps and accelerates plasma electrons. The resulting electron beam is extremely collimated and quasi-monoenergetic, with a high charge of 0.5 nC at 170 MeV.

A laser-plasma accelerator producing monoenergetic electron beams

Laser-driven accelerators, in which particles are accelerated by the electric field of a plasma wave (the wakefield) driven by an intense laser, have demonstrated accelerating electric fields of hundreds of GV m-1 (refs 1–3) These fields are thousands of times greater than those achievable in conventional radio-frequency accelerators, spurring interest in laser accelerators4,5 as compact next-generation sources of energetic electrons and radiation To date, however, acceleration distances have been severely limited by the lack of a controllable method for extending the propagation distance of the focused laser pulse The ensuing short acceleration distance results in low-energy beams with 100 per cent electron energy spread1,2,3, which limits potential applications Here we demonstrate a laser accelerator that produces electron beams with an energy spread of a few per cent, low emittance and increased energy (more than 109 electrons above 80 MeV) Our technique involves the use of a preformed plasma density channel to guide a relativistically intense laser, resulting in a longer propagation distance The results open the way for compact and tunable high-brightness sources of electrons and radiation

https://escholarship.org/content/qt9c55r46s/qt9c55r46s.pdf?t=lnras5

High-quality electron beams from a laser wakefield accelerator using plasma-channel guiding

High-power lasers that fit into a university-scale laboratory can now reach focused intensities of more than 10(19) W cm(-2) at high repetition rates. Such lasers are capable of producing beams of energetic electrons, protons and gamma-rays. Relativistic electrons are generated through the breaking of large-amplitude relativistic plasma waves created in the wake of the laser pulse as it propagates through a plasma, or through a direct interaction between the laser field and the electrons in the plasma. However, the electron beams produced from previous laser-plasma experiments have a large energy spread, limiting their use for potential applications. Here we report high-resolution energy measurements of the electron beams produced from intense laser-plasma interactions, showing that--under particular plasma conditions--it is possible to generate beams of relativistic electrons with low divergence and a small energy spread (less than three per cent). The monoenergetic features were observed in the electron energy spectrum for plasma densities just above a threshold required for breaking of the plasma wave. These features were observed consistently in the electron spectrum, although the energy of the beam was observed to vary from shot to shot. If the issue of energy reproducibility can be addressed, it should be possible to generate ultrashort monoenergetic electron bunches of tunable energy, holding great promise for the future development of 'table-top' particle accelerators.

Monoenergetic beams of relativistic electrons from intense laser–plasma interactions

The charge separation effects in the collisionless plasma expansion into a vacuum are studied in great detail. Accurate results are obtained concerning the structure of the ion front, the resultant ion energy spectrum, and more specifically the maximum ion energy. These are of crucial importance for the interpretation of recent experiments, where high-energy ion jets were produced from short pulse interaction with solid targets.

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Plasma Expansion into a Vacuum

The past few years have seen remarkable progress in the development of laser-based particle accelerators. The ability to produce ultrabright beams of multi-megaelectronvolt protons routinely has many potential uses from engineering to medicine, but for this potential to be realized substantial improvements in the performances of these devices must be made. Here we show that in the laser-driven accelerator that has been demonstrated experimentally to produce the highest energy protons, scaling laws derived from fluid models and supported by numerical simulations can be used to accurately describe the acceleration of proton beams for a large range of laser and target parameters. This enables us to evaluate the laser parameters needed to produce high-energy and high-quality proton beams of interest for radiography of dense objects or proton therapy of deep-seated tumours.

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Laser-driven proton scaling laws and new paths towards energy increase

Fast time averaged equations are derived for the motion of particles and the generation of electromagnetic wake fields under the action of the ponderomotive potential of an ultraintense laser pulse propagating through a tenuous plasma. Based on these averaged equations, a new particle code is designed which calculates the particle trajectories on the plasma period time scale. The regime of total cavitation of the plasma is investigated. It is found that stable propagation over a long distance is possible in this regime, and that energetic electrons are produced with a simple characteristic dependence of their angle of deflection on energy. This new code allows for computationally efficient modeling of pulse propagation over great distances.

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Kinetic modeling of intense, short laser pulses propagating in tenuous plasmas

By comparison with fully kinetic Fokker-Planck calculations, a nonlocal macroscopic formula has been derived for the thermal heat flux. This formula leads in a physically relevant way to the saturation and the delocalization of the heat flux. Its introduction in a fluid code is straightforward and gives to some extent results comparable with classical flux-limited transport calculations with $f=0.1$. However, it also describes a significant level of preheating.

Nonlocal heat transport due to steep temperature gradients

In order to investigate ponderomotive force in the relativistic regime, the interaction of ultraintense laser pulses with free electrons in vacuum is studied both theoretically and numerically. Various expressions for the electromagnetic field of the laser in the case of a Gaussian transverse profile are given, which take into account corrections to the monochromatic paraxial approximation, and the effects of finite pulse duration. A detailed demonstration of relativistic ponderomotive force (RPF) is established which makes apparent the domain of validity of this concept. Computer simulations are carried out using a three-dimensional test-particle code. They show the importance of the correct description of the fields, and confirm the domain of validity of the RPF which is $1\ensuremath{-}{v}_{z}/c\ensuremath{\gg}{1/kw}_{0}$, where ${v}_{z}$ is the component of the electron velocity parallel to the laser propagation direction, $c$ is the velocity of light, $k$ is the laser wave vector, and ${w}_{0}$ the beam waist at focus. Outside of this domain, the electron motion is more complicated, with a high sensitivity on the initial distance from the laser propagation axis and a relatively low energy gain.

Patrick Mora

Papers

Plasma Expansion into a Vacuum

Laser-driven proton scaling laws and new paths towards energy increase

Kinetic modeling of intense, short laser pulses propagating in tenuous plasmas

Nonlocal heat transport due to steep temperature gradients

Theory and simulation of the interaction of ultraintense laser pulses with electrons in vacuum