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75EFFECT OF ELECTROMAGNETIC PULSE TRANSVERSE INHOMOGENEITY ON THE ION ACCELERATION BY RADIATION
PRESSURE
1 1 14 2 2
K.V. Lezhnin , F.F. Kamenets , V.S. Beskin ' , M. Kando , T. Zh. Esirkepov and
S.V. Bulanov1'2'3
Moscow Institute of Physics and Technology, Institutskiy per. 9, Dolgoprudny,
Moscow Region, Russia Kansai Photon Science Center, Japan Atomic Energy Agency, Kyoto, Japan A. M. Prokhorov General Phys. Inst., Vavilov Str. 38, Moscow, Russia 4Russian Acad. Sci., P. N. Lebedev Phys. Inst., Leninskii Prosp 53, Moscow, Russia
Studies of the high energy ion generation in the interaction between an ultraintense laser pulse and a small overdense targets, are of fundamental importance for various research fields ranging from the developing the ion sources for thermonuclear fusion and medical applications to the investigation of high energy density phenomena in relativistic astrophysics. Depending on the laser and target parameters different regimes of acceleration appear - from acceleration at the target surface called the Target Normal Sheath Acceleration (TNSA) through the Coulomb explosion to radiation pressure dominance acceleration (RPDA) regime. In the present paper, we discuss the RPDA regime under the conditions when a transverse inhomogeneous laser pulse irradiates a MLT positioned not precisely at the laser pulse axis. This situation naturally occurs due to a finite pointing stability of the laser systems. As a result the transverse component of the radiation pressure leads to the displacement of the irradiated target in the off-axis direction. Apparently, after a finite interval of time the target leaves the laser pulse preventing from the further ion acceleration. On the ground of a theoretical model of relativistic mirror we calculate the acceleration time and hence the achieved ion energy dependence on the laser pulse amplitude and transverse size and on the initial displacement of the target from the laser axis. According to recently published papers, various instabilities of the target plasma appear in the RPDA regime, for instance, the Rayleigh-Taylor-like instability leads to the target modulation forming the low density bubbles and high density clumps resulting in the broadening of the accelerated ion energy spectrum.
In order to elucidate the kinetic, nonlinear and instability effects we carry out the PIC simulations of the finite waist laser pulse interaction with the MLT by using the REMP code. Phase and polarization properties of high harmonics generated in elliptically polarized laser field.
