The energy of ions accelerated by an intense electromagnetic wave in the radiation pressure dominated regime can be greatly enhanced due to a transverse expansion of a thin target. The expansion decreases the number of accelerated ions in the irradiated region resulting in an increase in the ion energy and in the ion longitudinal velocity. In the relativistic limit, the ions become phase locked with respect to the electromagnetic wave resulting in unlimited ion energy gain.

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The energy of the ions accelerated by an intense electromagnetic wave in the radiation pressure dominated regime can be greatly enhanced due to a transverse expansion of a thin target. The expansion decreases the number of accelerated ions in the irradiated region increasing the energy and the longitudinal velocity of remaining ions. In the relativistic limit, the ions become phase-locked with respect to the electromagnetic wave resulting in the unlimited ion energy gain. This effect and the use of optimal laser pulse shape provide a new approach for great enhancing the energy of laser accelerated ions.2

The nonlinear evolution of the two-dimensional collisionless magnetic field reconnection in a configuration with a null line and a strong perpendicular guide magnetic field is studied analytically and numerically by adopting a drift-kinetic description of the electron response. The foliation of the electron distribution function at fixed parallel canonical momentum allows us to establish a clear link between the fluid and the kinetic regimes of the collisionless reconnection instability in terms of the advection and mixing of Lagrangian invariants. (C) 2004 American Institute of Physics

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