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Simulation of Laser Particle Acceleration

Particle Acceleration

Short pulse, high-intensity lasers can be used to accelerate particles by creating large-amplitude electric field structures within gaseous or solid-density plasmas. The field strengths reached can be thousands to millions of times higher than possible with conventional RF technology, opening up the prospect of cheap, compact desktop accelerators for a wide range of industrial and medical applications. Laser-electron acceleration at the GeV level has been achieved by a number of labs worldwide and is now being seriously considered by CERN as a potential future collider technology.

Because of their higher inertia, ions are much harder to accelerate, and require a somewhat different approach, relying on laser-maintained charge separation as a way of supplying a 'DC' accelerating field. Our work on this concept has focussed on so-called 'mass-limited' targetry, such as nanoclusters or thin foils, in which the entire structure is pushed by radiation pressure to relativistic velocities (see figure). The advantage of this scheme compared to the more conventional 'sheath' acceleration from the rear side of micron-thick foils is that the proton spectrum is quasi-monoenergetic, or beam-like rather than exhibiting a broad thermal spread.

Result from a PIC simulationResult from a PIC simulation: shown on the left are the laser field and proton density, the right shows the particle spectrum.

Further reading:

B. Qiao et al., Phys. Rev. Lett. 105, 155002 (2010); DOI:10.1103/PhysRevLett.105.155002

B. Qiao et al., Phys. Rev. Lett. 108, 115002 (2012); DOI:10.1103/PhysRevLett.108.115002

Leaky Light Sail Route to High-Quality Proton Beams

Relativisitc Attosecond Electron Emission

Recent investigations in ultrashort electron bunches created by the interaction of high-intensity, femtosecond laser pulses with plasma targets have shown their potential as a powerful source of attosecond X-ray pulses. The latter can be produced in X-ray tube fashion by bombarding a secondary target with the electron bunches, and have an immediate application in ultrafast X-ray microscopy and atomic dynamics studies. One of the most promising schemes for the development of such a device makes use of laser-illuminated solid nanometer-sized droplets. At Plasma SimLab at JSC we have performed detailed 3D simulations in order to determine the dynamics of the attosecond bunches emissionin spherical geometry, and additional 2D simulations to study the propagation of such bunches in the laser wave plane. The movies below show the physics of the phenomenon: the angular pattern of the bunches starts to depart for usual Mie emission for relativistic laser intensities. A model has been built which explains such emission in terms of relativistic ponderomotive scattering and further interaction of the emitted electrons with the laser ponderomotive force in vacuum. An empirical criterion has been found, which allows to determine the range of droplet and laser parameters corresponding to this new acceleration regime.