The acceleration of high-energy ion beams (up to several tens of mega-electron-volts per nucleon) following the interaction of short (t 1018 W˙cm-2˙μm-2) laser pulses w...

Fast ion generation by high-intensity laser irradiation of solid targets and applications

A scheme for collimating fast electrons in a specially engineered solid target is proposed. Unlike previous approaches, the collimation is achieved by generating an azimuthal magnetic field as opposed to a radial electric field. The target is engineered such that it consists of a fiber surrounded by material of a lower resistivity than that of the fiber. The fast electrons are collimated along the fiber. Hybrid Vlasov-Fokker-Planck simulations supported by analytic calculations show that this concept is viable.

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Magnetic collimation of fast electrons produced by ultraintense laser irradiation by structuring the target composition

We present hybrid PIC simulations of fast electron transport and energy deposition in pre-compressed fusion targets, taking full account of collective magnetic effects and the hydrodynamic response of the background plasma. Results on actual ignition of an imploded fast ignition configuration are shown accounting for the increased beam divergence found in recent experiments (Green et al 2008 Phys. Rev. Lett. 100 015003) and the reduction in the electron kinetic energy due to profile steepening predicted by advanced PIC simulations (Chrisman et al 2008 Phys. Plasmas 15 056309). Target ignition is studied as a function of injected electron energy, distance of cone tip to dense core, initial divergence and kinetic energy of the relativistic electron beam. We found that beam collimation reduces substantially the ignition energies of the cone-guided fuel configuration assumed here.

https://iopscience.iop.org/article/10.1088/0741-3335/51/1/014008/pdf

Fast ignition of fusion targets by laser-driven electrons

In solid targets irradiated by short pulse high intensity lasers, fast electrons have collision times longer than the laser pulse duration and mean free paths much larger than the radius of the laser spot. In these conditions, fast electron transport is dominated by electric and magnetic field. Although the fast electrons are collisionless, collisions of background electrons determine the ability of the background plasma to carry the return current which balances the fast electron current. Hence collisions are important even in this regime. A successful numerical simulation has to be able to model a plasma in which some electrons are collisionless and others are strongly collisional. An expansion of the electron distribution in spherical harmonics in momentum space is well suited to this, and we describe the formulation of the Vlasov?Fokker?Planck equation in terms of spherical harmonics and its solution in our KALOS code. We review the physics that must be modelled in a numerical simulation of fast electron transport and then describe KALOS.

https://iopscience.iop.org/article/10.1088/0741-3335/48/3/R01/pdf

Fast electron transport in laser-produced plasmas and the KALOS code for solution of the Vlasov–Fokker–Planck equation

Since their discovery, laser accelerated ion beams have been the subject of great interest. The ion beam peak power and beam emittance is unmatched by any conventionally accelerated ion beam. Due to the unique quality, a wealth of applications has been proposed, and the first experiments confirmed their prospects. Laser ion acceleration is strongly linked to the generation and transport of hot electrons by the interaction of ultra-intense laser light with matter. Comparing ion acceleration experiments at laser systems with different beam parameters and using targets of varying thickness, material and temperature, some insight on the underlying physics can be obtained. The paper will present experimental results obtained at different laser systems, first beam quality measurement on laser accelerated heavy ions, and ion beam source size measurements at different laser parameters. Using structured targets, we compare information obtained from micro patterned ion beams about the accelerating electron sheath, and the influence of magnetic fields on the electron transport inside conducting targets.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0263034605050160

D. Moreno

Papers

Hybrid simulations of fast electron transport in conducting media