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Astron. Astrophys. 330, 381-388 (1998)


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Motion of ions reflected off quasi-parallel shock waves in the presence of large-amplitude magnetic field fluctuations

H.-T. Claßen and G. Mann

Astrophysikalisches Institut Potsdam, Observatorium für solare Radioastronomie, Telegrafenberg A31, D-14473 Potsdam, Germany

Received 10 February 1997 / Accepted 17 September 1997

Abstract

We analyse the behaviour of protons reflected off supercritcal, quasi-parallel shock waves in the presence of large amplitude magnetic field fluctuations with a magnetic field compression larger than the background magnetic field ([FORMULA]). These so-called SLAMS (short large-amplitude magnetic field structures) have originally been observed in the quasi-parallel region of the earth's bow shock. In general, the characteristics of the particle motion depend on the amplitude, the phase and the propagation direction of the SLAMS convected back to the shock front. Numerically calculated test particle trajectories show that in case of small gyroradii these dependencies reduce to pure geometrical conditions. In this case the computations can be simplified using results from adiabatic theory. Furthermore, it can be seen that the presence of SLAMS prevents the reflected ions from escaping into the upstream region of the shock. Although the shock geometry is quasi-parallel, some of the upstream moving ions return back to the shock front and subsequently penetrate into the downstream region. Because of their reflection at the incoming SLAMS these ions have a larger energy than their starting energy and can thus contribute to downstream heating and thermalisation. As a possible application we present an interpretation of cold ion bunches observed in connection with supercritical, quasi-parallel shock waves.

Key words: shock waves – acceleration of particles – magnetic fields – interplanetary medium

Send offprint requests to: H.-T. Claßen

© European Southern Observatory (ESO) 1998

Online publication: January 8, 1998
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