Recently achieved high intensities of short laser pulses open new prospects in their application to hole boring in inhomogeneous overdense plasmas and for ignition in precompressed DT fusion targets. A simple analytical model and numerical simulations demonstrate that pulses with intensities exceeding 10;{22} W/cm;{2} may penetrate deeply into the plasma as a result of efficient ponderomotive acceleration of ions in the forward direction. The penetration depth as big as hundreds of microns depends on the laser fluence, which has to exceed a few tens of GJ/cm;{2}. The fast ions, accelerated at the bottom of the channel with an efficiency of more than 20%, show a high directionality and may heat the precompressed target core to fusion conditions.
A high-efficiency overmoded klystron-like relativistic backward wave oscillator with low guiding magnetic field Phys. Plasmas 19, 093102 (2012) Relativistic plasmas in uniform magnetic fields. I. General off-axis coupling methods J. Math. Phys. 53, 083302 (2012) Derivation of nonlinear Schrödinger equation for electrostatic and electromagnetic waves in fully relativistic twofluid plasmas by the reductive perturbation method Phys. Plasmas 19, 082303 (2012) Parametric decays in relativistic magnetized electron-positron plasmas with relativistic temperatures Laser ponderomotive force at superhigh intensities provides an efficient ion acceleration in bulk dense targets and evacuates a channel enabling further laser beam propagation. The developed quasistationary model of a laser piston-a double layer structure supported by the radiation pressure-predicts the general parameters of the acceleration process in homogeneous and inhomogeneous overdense plasmas. Particle-in-cell simulations confirm the estimated characteristics in a wide range of laser intensities and ion densities and show advantages of circularly polarized laser pulses. Two nonstationary effects are identified in the simulations. First, oscillations of the piston velocity and of the thickness of the ion charge separation layer broaden the energy spectrum of accelerated ions. Second, the electrons accelerated toward the incoming laser wave emit strong high-frequency radiation, enabling a cooling effect, which helps to sustain high charge neutrality in the piston and to maintain an efficient ion acceleration.
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