Fast ion ignition with ultra-intense laser pulses

Fast ignition by laser-driven ion beams benefits from the strong collisional interaction of energetic ions with the imploded fuel. However, conditions for an efficient transformation of the laser pulse energy into ion kinetic energy and for the transport of these ions from the acceleration region to the fusion pellet core without significant temporal and angular spread have to be clarified. The laser ponderomotive force may provide efficient ion acceleration in bulk dense targets such as a precompressed DT capsule and evacuate a channel for further laser beam propagation. The main characteristics of ponderomotive ion acceleration and channel formation inferred from analytical theory and confirmed by particle-in-cell simulations are applied for the design of a new scheme of ion fast ignition. Contrary to schemes based on the mechanism of target normal sheath ion acceleration, at least two laser pulses are used in our proposal. The first pulse (or a sequence of several pulses) creates a channel with a diameter of similar to 20 mu m through the plasma corona up to a fuel density of similar to 1 g cm(-3). The second pulse with a higher intensity of similar to 10(22) W cm(-2) accelerates the deuterium and tritium ions at the head of this channel to energies 5-25 MeV on a time scale less than 1-3 ps. The overall ignition energy in this proposal is relatively high, greater than or similar to 100 kJ, but no additional target arrangements will be required. This feature makes the scheme attractive for a high repetition rate operation.