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A cosmic acceleration mechanism is introduced which is based on the wakefields excited by the Alfven shocks in a relativistically flowing plasma. We show that there exists a threshold condition for transparency below which the accelerating particle is collision-free and suffers little energy loss in the plasma medium. The stochastic encounters of the random accelerating-decelerating phases results in a power-law energy spectrum: ƒ(ε) ∝ 1/ε[SUP2]. As an example, we discuss the possible production of super-GZK ultra high energy cosmic rays (UHECR) in the atmosphere of gamma ray bursts. The estimated event rate in our model agrees with that from UHECR observations. [ABSTRACT FROM AUTHOR]

Recent years have seen growing interests in the laboratory investigation of astrophysical phenomena that can be addressed by ultra intense electromagnetic fields. Such fields are becoming available through the advancement of technologies in lasers as well as high-energy particle beams. History has shown that the symbiosis between direct observations and laboratory studies is instrumental in the progress of astrophysics. We believe that a dedicated facility for laboratory astrophysics using high intensity particle and photon beams can help to significantly advance our knowledge in some critical aspects of astrophysical phenomena. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The physics of energy transfer between the laser and the plasma in laser wakefield accelerators is studied. We find that wake excitation by arbitrary laser shapes can be parameterized using the total pulse energy and pulse depletion length. A technique for determining laser profiles that produce the required plasma excitation is developed. We show that by properly shaping the longitudinal profile of the driving laser pulse, it is possible to maximize both the transformer ratio and the wake amplitude, achieving optimal laser-plasma coupling. The corresponding family of laser pulse shapes is derived in the nonlinear regime of laser-plasma interaction. Such shapes provide theoretical upper limit on the magnitude of the wakefield and efficiency of the accelerating stage by allowing for uniform photon deceleration inside the laser pulse. We also construct realistic optimal pulse shapes that can be produced in finite-bandwidth laser systems and propose a two-pulse wake amplification scheme using the optimal solution. [ABSTRACT FROM AUTHOR]