Nonlinear Development of Streaming Instabilities In Strongly Magnetized Plasmas

The nonlinear development of streaming instabilities in the current layers formed during magnetic reconnection with a guide field is explored. Theory and 3-D particle-in-cell simulations reveal two distinct phases. First, the parallel Buneman instability grows and traps low velocity electrons. The remaining electrons then drive two forms of turbulence: the parallel electron-electron two-stream instability and the nearly-perpendicular lower hybrid instability. The high velocity electrons resonate with the turbulence and transfer momentum to the ions and low velocity electrons.Comment: Accepted by PR

Second harmonic electromagnetic emission of a turbulent magnetized plasma driven by a powerful electron beam

The power of second harmonic electromagnetic emission is calculated for the case when strong plasma turbulence is excited by a powerful electron beam in a magnetized plasma. It is shown that the simple analytical model of strong plasma turbulence with the assumption of a constant pump power is able to explain experimentally observed bursts of electromagnetic radiation as a consequence of separate collapse events. It is also found that the electromagnetic emission power calculated for three-wave interaction processes occurring in the long-wavelength part of turbulent spectrum is in order-of-magnitude agreement with experimental results

The Orientation of the Reconnection X-line

We propose a criterion for identifying the orientation of the X-line when two regions of plasma with arbitrary densities, temperatures, and magnetic fields undergo reconnection. The X-line points in the direction that maximizes the (suitably-defined) Alfv\'en speed characterizing the reconnection outflow. For many situations a good approximation is that the X-line bisects the angle formed by the magnetic fields

Cosmic-ray electron injection from the ionization of nuclei

We show that the secondary electrons ejected from the ionization of heavy ions can be injected into the acceleration process that occurs at supernova remnant shocks. This electron injection mechanism works since ions are ionized during the acceleration when they move already with relativistic speed, just like ejected electrons do. Using the abundances of heavy nuclei measured in cosmic rays at Earth, we estimate the electron/proton ratio at the source to be ~10^-4, big enough to account for the nonthermal synchrotron emission observed in young SNRs. We also show that the ionization process can limit the maximum energy that heavy ions can reach.Comment: 4 pages, 1 figure, accepted for publication in Physical Review Letter

Resonance Broadening Induced Nonlinear Saturation of Kinetic Alfven Turbulence in the Interplanetary Plasma

The saturation of ion cyclotron Alfven turbulence excited by beam particles is investigated using resonance broadening theory. The stochastic scattering which decorrelates particles, includes both random acceleration by electric fields and a turbulent magnetic mirroring effect. Turbulent mirroring is shown to yield non-Gaussian corrections to the orbits even if the random electric and magnetic fields are Gaussian. The predicted steady-state turbulence level exhibits a peaked anglular distribution, with a maximum near Theta ~ 60 degrees.Comment: 5 pages (including 2 figures

Ionizing wave via high-power HF acceleration

Recent ionospheric modification experiments with the 3.6 MW transmitter at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska led to discovery of artificial ionization descending from the nominal interaction altitude in the background F-region ionosphere by ~60 km. This paper presents a physical model of an ionizing wavefront created by suprathermal electrons accelerated by the HF-excited plasma turbulence

Artificial ionospheric layers driven by high-frequency radiowaves : an assessment

High-power ordinary mode radio waves produce artificial ionization in the F-region ionosphere at the European Incoherent Scatter (EISCAT at Tromsø, Norway) and High-frequency Active Auroral Research Program (HAARP at Gakona, Alaska, USA) facilities. We have summarized the features of the excited plasma turbulence and descending layers of freshly-ionized (“artificial”) plasma. The concept of an ionizing wavefront created by accelerated suprathermal electrons appears to be in accordance with the data. The strong Langmuir turbulence (SLT) regime is revealed by the specific spectral features of incoherent radar backscatter and stimulated electromagnetic emissions. Theory predicts that the SLT acceleration is facilitated in the presence of photoelectrons. This agrees with the intensified artificial plasma production and the greater speeds of descent but weaker incoherent radar backscatter in the sunlit ionosphere. Numerical investigation of propagation of O-mode waves and the development of SLT and descending layers have been performed. The greater extent of the SLT region at the magnetic zenith than at vertical appears to make magnetic zenith injections more efficient for electron acceleration and descending layers. At high powers, anomalous absorption is suppressed, leading to the Langmuir and upper hybrid processes during the whole heater-on period. The data suggest that parametric UH interactions mitigate anomalous absorption at heating frequencies far from electron gyroharmonics and also generate SLT in the upper hybrid layer. The persistence of artificial plasma at the terminal altitude depends on how close the heating frequency is to the local gyroharmonic