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63Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2016
LASER ION ACCELERATION FROM MASS-LIMITED TARGETS WITH PREPLASMA
K. V. Lezhnin1,2, F. F. Kamenets2, T. Zh. Esirkepov3, S. V. Bulanov3,4, O. Klimo1,5, S. Weber1,
and G. Korn1
institute of Physics of the ASCR, ELI-Beamlines, Prague, Czech Republic 2Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, Russia 3Kansai Photon Science Center, Japan Atomic Energy Agency, Kyoto, Japan 4A. M. Prokhorov GeneralPhys. Inst., Moscow, Russia
5Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic
High-energy ion generation in the interaction of intense laser pulses with mass-limited targets is promising for applications in a wide range, from the development of ion sources for medicine and the fast ignition of controlled thermonuclear fusion to the investigation of warm dense matter, high energy density phenomena, and laboratory astrophysics. Mass-limited targets have a finite transverse size comparable with the laser focal spot diameter. Their principal advantage is that an intense laser pulse can remove much more electrons from it than from a wide and thick target. This generates a greater electrostatic potential thus enhancing the ion acceleration. In wider targets, electrons from the periphery additionally reduce the ion acceleration quickly smoothing out the electric potential, while in thick targets, the laser radiation cannot reach deeper layers. The advantage of mass-limited targets is best seen with isolated clusters, from which an intense laser sweeps all the electrons. Then the Coulomb explosion occurs: the ions are accelerated under the repulsion force of uncompensated electric charge. A pure Coulomb explosion provides an isotropic ion acceleration with very characteristic energy spectrum, where a large number of ions acquire a high energy.
In general, a laser system produces a high-intensity short-duration (main) pulse on top of a relatively low intensity nanosecond (background) amplified spontaneous emission (ASE), possibly with a few prepulses. When a laser pulse with a finite contrast irradiates a solid target, preplasma is created before the main pulse arrival. Preplasma created around structured snow-targets irradiated by intense laser pulses facilitates the efficient ion acceleration via the edge field intensification effect. The main pulse interacting first with preplasma exhibits regimes typical to gaseous targets, especially when the plasma density is near-critical. While the main pulse loses its energy in preplasma it can also self-focus due to relativistic effects, thus an optimized preplasma can crucially enhance the ion acceleration.
Here we investigate how ion acceleration mechanisms reveals itself depending on the geometry of a mass-limited target and a plasma corona around it. We carry out two-dimensional (2D) Particle-in-Cell (PIC) simulations using the REMP code based on the density decomposition scheme. We describe the effects occurring in the presence of a plasma corona around a mass-limited target: the enhancement of the Coulomb explosion of the ion core of the target due to the density squeezing by the quasistatic magnetic field, formation of a density hole near the tip of the target due to plasma resonance, etc [1].
References
[1] Lezhnin, K. V., Kamenets, F. F., Esirkepov, T. Zh., Bulanov, S. V., Klimo, O., Weber, S., and Korn, G., arxiv:1603.04232
