Abstract
Abstract. The primary process occurring at a collisionless shock is the redistribution of the bulk upstream energy into other degrees of freedom. One part of this process results in the acceleration of electrons at the shock front. Accelerated electrons are observed at the terrestrial and other planetary shocks, comets, and their effects are observed in astrophysical phenomena such as supernova remnants and jets in the form of X-ray bremsstrahlung radiation. One of the physical models for electron acceleration at supercritical shocks is based on low-hybrid turbulence due to the presence of reflected ions in the foot region. Since lower hybrid waves propagate almost perpendicular to the magnetic field they can be simultaneously in resonance with both the unmagnetised ions (ω=Vik⊥) and magnetised electrons (ω=Vek||). In this paper, Cluster observations of the electric field are used to study the occurrence of lower hybrid waves in the front of the terrestrial bow shock. It is shown that the lower hybrid waves exist as isolated wave packets. However, the very low level of the observed lower hybrid turbulence is too small to impart significant energisation to the electron population.
Highlights
The energisation of electrons within a collisionless shock requires the transfer of a portion of the energy associated with the incoming upstream plasma flow to the electron population
Waves with characteristics consistent with the lower hybrid mode were observed from the results shown in the previous section not all wave packets that occur just above the lower hybrid resonance frequency are propagating in the lower hybrid wave mode
This article has presented observations and analysis of waves observed in the frequency range 10–40 Hz in the foot region of a set of quasiperpendicular shocks
Summary
The energisation of electrons within a collisionless shock requires the transfer of a portion of the energy associated with the incoming upstream plasma flow to the electron population. In order for this energy transfer to occur, there has to be some media that can channel energy from the incoming ion population to the electrons. One mechanism that has commonly been proposed, both for solar systems and for astrophysical applications is based on excitation of lowerhybrid waves (Laming, 2001). The wave has linear polarisation and propagates almost perpendicular with respect to the magnetic. The maximum growth rate γMAX occurs when k||/k∼ωpi /ωpe
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