Relativistic particle acceleration in a developing turbulence

An efficient particle acceleration process in the course of parametric instabilities of large amplitude Alfven waves in a relativistic pair plasma is investigated by utilizing one dimensional full particle-in-cell (PIC) code. Although MHD turbulence is ubiquitous in space and astrophysical environments, particle acceleration processes in turbulent MHD waves such as diffusive shock acceleration often assume fully developed, or incoherent, turbulence. However, at least in the vicinity of a source region which may not be small compared with whole acceleration site, an MHD turbulence may have not fully developed but be rather coherent. Such a developing MHD turbulence is reproduced in PIC simulation as parametric instabilities of large amplitude Alfven waves. When amplitude of a parent Alfven wave is large as same as an ambient magnetic field, successive decay instabilities result in rapid spectral cascade. In such a developing turbulence coherent wave-particle interactions lead to strong particle acceleration. The acceleration process is analyzed in detail and it is shown that relativistic effects in wave-particle interactions play decisive roles in the process. (author)