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Ann. Geophys., 17, 583-594, 1999
www.ann-geophys.net/17/583/1999/
© European Geosciences Union 1999
Injection and acceleration of H+ and He2+ at Earth's bow shock
M. Scholer1, H. Kucharek1, and K.-H. Trattner2
1Max-Planck-Institut für extraterrestrische Physik, 85740 Garching, Germany
2Lockheed Martin Missiles and Space, Palo Alto, CA 94304, USA
Abstract. We have performed a number of one-dimensional
hybrid simulations (particle ions, massless electron fluid) of quasi-parallel
collisionless shocks in order to investigate the injection and subsequent
acceleration of part of the solar wind ions at the Earth's bow shock. The shocks
propagate into a medium containing magnetic fluctuations, which are initially
superimposed on the background field, as well as generated or enhanced by the
electromagnetic ion/ion beam instability between the solar wind and
backstreaming ions. In order to study the mass (M) and charge (Q)
dependence of the acceleration process He2+ is included
self-consistently. The upstream differential intensity spectra of H+
and He2+ can be well represented by exponentials in energy. The
e-folding energy Ec is a function of time: Ec
increases with time. Furthermore the e-folding energy (normalized to the shock
ramming energy Ep) increases with increasing Alfvén Mach
number of the shock and with increasing fluctuation level of the initially
superimposed turbulence. When backstreaming ions leave the shock after their
first encounter they exhibit already a spectrum which extends to more than ten
times the shock ramming energy and which is ordered in energy per charge. From
the injection spectrum it is concluded that leakage of heated downstream
particles does not contribute to ion injection. Acceleration models that permit
thermal particles to scatter like the non-thermal population do not describe the
correct physics.
Key words. Interplanetary physics (planetary bow
shocks) · Space plasma physics (charged particle motion and acceleration;
numerical simulation studies)
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