HR: 0830h
AN: SH11C-1108    [PDF]
TI: Ion acceleration in quasi-perpendicular PIC simulations of a reforming heliospheric termination shock
AU: * Lee, R E
EM: r.e.lee@warwick.ac.uk
AF: Space and Astrophysics Group, Department of Physics University of Warwick, Coventry, CV4 7AL United Kingdom
AU: Chapman, S C
EM: S.C.Chapman@warwick.ac.uk
AF: Space and Astrophysics Group, Department of Physics University of Warwick, Coventry, CV4 7AL United Kingdom
AU: Dendy, R O
EM: richard.dendy@ukaea.org.uk
AF: UKAEA Culham Division, Culham Scienece Centre Abingdon, Oxfordshire, OX14 3DB United Kingdom
AB: Recent Particle-in-cell (PIC) simulations have revealed time-dependent shock solutions for parameters relevant to astrophysical and heliospheric shocks [1,2,3]. These solutions are characterised by a shock which cyclically reforms on the spatio-temporal scales of the incoming protons. Whether a shock solution is stationary or reforming depends not only upon the correct treatment of the electrons, but also on the plasma parameters, the upstream $\beta$ in particular. In the case of the heliospheric termination shock these parameters are not well determined, however, some estimates suggest that the termination shock may be in a parameter regime such that it is time-dependent. It has been pointed out [3] that this will switch off some acceleration mechanisms, for example shock surfing, which has been proposed previously for time-stationary shock solutions. The introduction of time-dependent electromagnetic fields intrinsic to the shock does however introduce the possibility of new mechanisms for the acceleration of protons. Here we present for the first time one such process as revealed by high phase space resolution 1.5D PIC simulations in which all vector quantities are three dimensional, the solution then varying with the spatial coordinate and time. We find that a subset of the protons that reflect off the reforming shock front are accelerated by subsequent interaction with the shock to form a suprathermal population which then propagates into the downstream region with energies of order six times the upstream inflow energy. These may provide an injection population for further acceleration to cosmic ray energies. [1] Shimada, N., and M. Hoshino, {\it Astrophys. J, 543}, L67, 2000.\\ [2] Schmitz, H., S.C. Chapman and R.O. Dendy, {\it Astrophys. J, 570}, 637, 2002\\ [3] Scholer, M., I. Shinohara and S. Matsukiyo, {\it J. Geophys. Res., 108}, 1014, 2003
DE: 2104 Cosmic rays
DE: 2114 Energetic particles, heliospheric (7514)
DE: 2124 Heliopause and solar wind termination
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting