Stabilisation of BGK modes by relativistic effects
Sircombe, N. J., Dieckmann, M. E., Shukla, P. K. and Arber, T. D.. (2006) Stabilisation of BGK modes by relativistic effects. Astronomy & Astrophysics, Vol.452 (No.2). pp. 371-381. ISSN 0004-6361
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Official URL: http://dx.doi.org/10.1051/0004-6361:20054074
Context. We examine plasma thermalisation processes in the foreshock region of astrophysical shocks within a fully kinetic and self-consistent treatment. We concentrate on proton beam driven electrostatic processes, which are thought to play a key role in the beam relaxation and the particle acceleration. Our results have implications for the eﬀectiveness of electron surfing acceleration and
the creation of the required energetic seed population for first order Fermi acceleration at the shock front.
Aims. We investigate the acceleration of electrons via their interaction with electrostatic waves, driven by the relativistic Buneman instability, in a system dominated by counter-propagating proton beams.
Methods. We adopt a kinetic Vlasov-Poisson description of the plasma on a fixed Eulerian grid and observe the growth and saturation of electrostatic waves for a range of proton beam velocities, from 0.15c to 0.9c.
Results. We can report a reduced stability of the electrostatic wave (ESW) with increasing non-relativistic beam velocities and an improved wave stability for increasing relativistic beam velocities, both in accordance with previous findings. At the highest beam speeds, we find the system to be stable again for a period of ≈160 plasma periods. Furthermore, the high phase space resolution
of the Eulerian Vlasov approach reveals processes that could not be seen previously with PIC simulations. We observe a, to our knowledge, previously unreported secondary electron acceleration mechanism at low beam speeds. We believe that it is the result of parametric couplings to produce high phase velocity ESW’s which then trap electrons, accelerating them to higher energies. This
allows electrons in our simulation study to achieve the injection energy required for Fermi acceleration, for beam speeds as low as 0.15c in unmagnetised plasma.
|Item Type:||Journal Article|
|Subjects:||Q Science > QB Astronomy|
|Divisions:||Faculty of Science > Physics|
|Library of Congress Subject Headings (LCSH):||Supernova remnants, Particle acceleration, Space plasmas, Proton beams|
|Journal or Publication Title:||Astronomy & Astrophysics|
|Official Date:||June 2006|
|Page Range:||pp. 371-381|
|Access rights to Published version:||Open Access|
|Funder:||European Commission (EC), Engineering and Physical Sciences Research Council (EPSRC), Deutsche Forschungsgemeinschaft (DFG), United Kingdom Atomic Energy Authority (UKAEA)|
|Grant number:||HPRN-CT-2001-00314 (EC)|
Aharonian, F. A., Akhperjanian, A. G., Aye, K.-M., et al. 2004, Nature, 432, 75
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