On Fermi acceleration and MHD-instabilities at ultra-relativistic magnetized shock waves TeX Export

@misc{citeulike:3036023, abstract = {Fermi acceleration can take place at ultra-relativistic shock waves if the upstream or downstream magnetic field has been remodeled so that most of the magnetic power lies on short spatial scales. The relevant conditions under which Fermi acceleration become efficient in the presence of both a coherent and a short scale turbulent magnetic field are addressed. Within the MHD approximation, this paper then studies the amplification of a pre-existing magnetic field through the streaming of cosmic rays upstream of a relativistic shock wave. The magnetic field is assumed to be perpendicular in the shock front frame, as generally expected in the limit of large shock Lorentz factor. In the MHD regime, compressive instabilities seeded by the net cosmic-ray charge in the shock precursor (as seen in the shock front frame) develop on the shortest spatial scales but saturate at a moderate level \$\delta B/B \sim 1\$, which is not sufficient for Fermi acceleration. As we argue, it is possible that other instabilities outside the MHD range provide enough amplification to allow successful Fermi acceleration.}, archivePrefix = {arXiv}, author = {Pelletier, Guy and Lemoine, Martin and Marcowith, Alexandre}, citeulike-article-id = {3036023}, citeulike-linkout-0 = {http://arxiv.org/abs/0807.3459}, citeulike-linkout-1 = {http://arxiv.org/pdf/0807.3459}, day = {23}, eprint = {0807.3459}, keywords = {and, instablity, perpendicular, shock, upstream}, month = {Jul}, posted-at = {2008-11-14 19:27:34}, priority = {4}, title = {On Fermi acceleration and MHD-instabilities at ultra-relativistic magnetized shock waves}, url = {http://arxiv.org/abs/0807.3459}, year = {2008} }

TY - ELEC ID - citeulike:3036023 L3 - citeulike-article-id:3036023 N2 - Fermi acceleration can take place at ultra-relativistic shock waves if the upstream or downstream magnetic field has been remodeled so that most of the magnetic power lies on short spatial scales. The relevant conditions under which Fermi acceleration become efficient in the presence of both a coherent and a short scale turbulent magnetic field are addressed. Within the MHD approximation, this paper then studies the amplification of a pre-existing magnetic field through the streaming of cosmic rays upstream of a relativistic shock wave. The magnetic field is assumed to be perpendicular in the shock front frame, as generally expected in the limit of large shock Lorentz factor. In the MHD regime, compressive instabilities seeded by the net cosmic-ray charge in the shock precursor (as seen in the shock front frame) develop on the shortest spatial scales but saturate at a moderate level $\delta B/B \sim 1$, which is not sufficient for Fermi acceleration. As we argue, it is possible that other instabilities outside the MHD range provide enough amplification to allow successful Fermi acceleration. TI - On Fermi acceleration and MHD-instabilities at ultra-relativistic magnetized shock waves KW - and KW - instablity KW - perpendicular KW - shock KW - upstream AU - Pelletier, Guy AU - Lemoine, Martin AU - Marcowith, Alexandre PY - 2008/Jul/23/ UR - http://arxiv.org/abs/0807.3459 ER -