Ion acceleration driven by superintense laser pulses is attracting an impressive and steadily increasing effort. Motivations can be found in the applicative potential and in the perspective to investigate novel regimes as available laser intensities will be increasing. Experiments have demonstrated, over a wide range of laser and target parameters, the generation of multi-MeV proton and ion beams with unique properties such as ultrashort duration, high brilliance, and low emittance. An overview is given of the state of the art of ion acceleration by laser pulses as well as an outlook on its future development and perspectives. The main features observed in the experiments, the observed scaling with laser and plasma parameters, and the main models used both to interpret experimental data and to suggest new research directions are described.

/pdf/ion-acceleration-by-superintense-laser-plasma-interaction-2jqzeizem7.pdf

Ion acceleration by superintense laser-plasma interaction

For many years, laser-driven ion acceleration, mainly proton acceleration, has been proposed and a number of proof-of-principle experiments have been carried out with lasers whose pulse duration was in the nanosecond range. In the 1990s, ion acceleration in a relativistic plasma was demonstrated with ultra-short pulse lasers based on the chirped pulse amplification technique which can provide not only picosecond or femtosecond laser pulse duration, but simultaneously ultra-high peak power of terawatt to petawatt levels. Starting from the year 2000, several groups demonstrated low transverse emittance, tens of MeV proton beams with a conversion efficiency of up to several percent. The laser-accelerated particle beams have a duration of the order of a few picoseconds at the source, an ultra-high peak current and a broad energy spectrum, which make them suitable for many, including several unique, applications. This paper reviews, firstly, the historical background including the early laser-matter interaction studies on energetic ion acceleration relevant to inertial confinement fusion. Secondly, we describe several implemented and proposed mechanisms of proton and/or ion acceleration driven by ultra-short high-intensity lasers. We pay special attention to relatively simple models of several acceleration regimes. The models connect the laser, plasma and proton/ion beam parameters, predicting important features, such as energy spectral shape, optimum conditions and scalings under these conditions for maximum ion energy, conversion efficiency, etc. The models also suggest possible ways to manipulate the proton/ion beams by tailoring the target and irradiation conditions. Thirdly, we review experimental results on proton/ion acceleration, starting with the description of driving lasers. We list experimental results and show general trends of parameter dependences and compare them with the theoretical predictions and simulations. The fourth topic includes a review of scientific, industrial and medical applications of laser-driven proton or ion sources, some of which have already been established, while the others are yet to be demonstrated. In most applications, the laser-driven ion sources are complementary to the conventional accelerators, exhibiting significantly different properties. Finally, we summarize the paper.

https://iopscience.iop.org/article/10.1088/0034-4885/75/5/056401/pdf

Review of laser-driven ion sources and their applications.

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

We present measurements of a magnetic reconnection in a plasma created by two laser beams (1 ns pulse duration, 1 x 10(15) W cm(-2)) focused in close proximity on a planar solid target. Simultaneous optical probing and proton grid deflectometry reveal two high velocity, collimated outflowing jets and 0.7-1.3 MG magnetic fields at the focal spot edges. Thomson scattering measurements from the reconnection layer are consistent with high electron temperatures in this region.

https://www.lle.rochester.edu/media/publications/presentations/documents/APS06/Nilson_APS06.pdf

Magnetic Reconnection and Plasma Dynamics in Two-Beam Laser-Solid Interactions

Electromagnetic ($E/B$) fields generated by the interaction with plasmas of long-pulse, low-intensity laser beams relevant to inertial confinement fusion have been measured for the first time using novel monoenergetic proton radiography methods. High-resolution, time-gated radiography images of a plastic foil driven by a ${10}^{14}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$ laser implied $B$ fields of $\ensuremath{\sim}0.5\text{ }\text{ }\mathrm{MG}$ and $E$ fields of $\ensuremath{\sim}1.5\ifmmode\times\else\texttimes\fi{}{10}^{8}\text{ }\text{ }\mathrm{V}/\mathrm{m}$. Simulations of these experiments with $\mathrm{LASNEX}+\mathrm{LSP}$ have been performed and are in overall (though not exact) agreement with the data both for field strengths and for spatial distributions; this is the first direct experimental test of the laser-generated $B$-field package in LASNEX. The experiments also demonstrated that laser phase plates substantially reduce medium-scale chaotic field structure.

/pdf/measuring-e-and-b-fields-in-laser-produced-plasmas-with-5diog6p3da.pdf

Measuring E and B fields in laser-produced plasmas with monoenergetic proton radiography.

Laser driven proton beams have been used to diagnose transient fields and density perturbations in laser produced plasmas. Grid deflectometry techniques have been applied to proton radiography to obtain precise measurements of proton beam angles caused by electromagnetic fields in laser produced plasmas. Application of proton radiography to laser driven implosions has demonstrated that density conditions in compressed media can be diagnosed with million electron volt protons. This data has shown that proton radiography can provide unique insight into transient electromagnetic fields in super critical density plasmas and provide a density perturbation diagnostics in compressed matter.

/pdf/proton-radiography-as-an-electromagnetic-field-and-density-304qyvcakt.pdf

S. C. Lerner

Papers

Proton radiography as an electromagnetic field and density perturbation diagnostic (invited)