Repetitive emissions of rising-tone chorus waves in the inner magnetosphere

Chorus waves are well known for their significant roles in the radiation belts of the Earth and other magnetized planets, including acceleration of electrons to relativistic energies, and precipitation of energetic electrons into the ionosphere to produce diffuse and pulsating aurora. They typically occur in the form of discrete and repetitive quasi-monochromatic emissions with a frequency chirping, which was discovered more than 50 years ago. However, until now there is still no satisfactory explanations for repetitive emissions of chorus waves. In this report, chorus emissions excited by energetic electrons with a temperature anisotropy are studied by both a one-dimensional \(\delta f\) simulation and theoretical model in a dipole magnetic field. The two models have unanimously demonstrated that a continuous injection of energetic electrons caused by an azimuthal drift is essential for the repetitive emissions of chorus waves. Consistent with satellite observations, both discrete and continuous spectra can be reproduced. An intense injection of energetic electrons will lead to a decrease of the time separation between the chorus elements, and the chorus emissions evolve from a discrete to a continuous spectrum when the injection is sufficiently strong.

Electron injection into laser wakefields by colliding circularly-polarized laser pulses

Electron injection into a laser wakefield by the colliding of two circularly polarized laser pulses is analyzed by the Hamiltonian approach and particle-in-cell simulations. If the pump pulse driving the laser wakefield is right-circularly-polarized, electron injection is found only when the counter-propagating injection pulse is left-circularly-polarized and vice versa. This holds when the injection pulse is at low intensity and has a frequency near the pump pulse frequency ω0. For a moderately intense injection pulse, even if the two pulses have the same polarization, electron injection is found but with less efficiency. It is also found that the injection pulse with the frequency within [0.5ω0,3ω0] can still create electron injection efficiently provided it has the opposite polarization with the pump pulse.