We investigate particle acceleration by strong lower-hybrid turbulence produced by the relaxation of an energetic perpendicular ion ring distribution. Ion ring distributions are associated with counterstreaming plasma flows in a magnetic field, and are found at perpendicular shocks as a result of ion reflection from the shock surface. Using a 2½D particle-in-cell (PIC) code that is fully electromagnetic and relativistic, we show that the ion ring is unstable to the generation of strong plasma turbulence at the lower-hybrid resonant frequency. The lower-hybrid wave turbulence collapses in configuration space, producing density cavities. The collapse of the cavities is halted by particle acceleration, producing energetic electron and ion tails. For solar flare plasmas with temperatures of 1 keV and a ratio of the plasma frequency to the electron cyclotron frequency of ½, we demonstrate electron acceleration to energies up to MeV, while the ions are accelerated to energies in the region of several MeV.

We present two findings: (i) in the absence of compressibility of (cold) neutrals, the instability triggered by neutral drift due to gradients in plasma density and magnetic field and (ii) the equilibrium pressure-gradient- (PG-) driven instabilities with and without neutral dynamics. The results of detailed analysis suggest that on account of neutral dynamics the growth of these instabilities is suppressed by a neutral perturbational effect. Suppression of PG-driven instabilities is highlighted and the critical wavelength for sustainable growth is found. The physics involved in the mechanism of instabilities is discussed. The endeavour in these investigations is justifiable in its usefulness for understanding the phenomena pertinent to partially ionized plasma (PIP). The stability analysis presented here may be useful for understanding the plasma processes in ‘deep’ coma (very near to the nucleus of coma), at the edges of a plasma column, near a divertor region and in the case of sublimating gas from a cloud.

Using linear kinetic plasma theory the relation between electron density and magnetic field fluctuations for low-frequency plasma waves for Maxwellian background distribution functions of arbitrary temperatures in a uniform magnetic field is derived. By taking the non-relativistic temperature limit this ratio is calculated for the diffuse intercloud medium in our Galaxy. The diffuse intercloud medium is the dominant phase of the interstellar medium with respect to radio wave propagation, dispersion and rotation measure studies. The differences between the relation of electron density and magnetic field fluctuations from the linear kinetic theory compared with the classical magnetohydrodynamics theory are established and discussed.

Experimental line profiles can be altered by so-called spectral interference that appears due to different causes. One of the most commonly appearing sources of interference is random noise due to the detector used for measuring the spectra in the laboratory. In this work, the noise is studied using a simulation procedure. This study helps to pinpoint the changes that the noise produces in the parameters of the experimental profiles and, consequently, in the information provided by them.

Energy gain by an electron during its motion in the fields of the fundamental TE10 mode excited by microwave radiation in a rectangular waveguide is analysed. Expressions have been obtained for the fields of the mode, the angle of deflection and the acceleration gradient of the electron when it is injected along the direction of mode propagation. An electron of energy 25 keV gains 120.44 keV when a microwave of intensity 1010 Wm−2 at frequency 6 GHz is employed to excite the mode in a waveguide of width 0.03 m and height 0.02 m. The effects of the microwave frequency and the width of the waveguide are to decrease the electron energy gain for fixed microwave intensity. However, higher acceleration gradients are obtained when the electron is injected with greater initial energy.

A technique is developed for analysing the linear collapse properties of spatially linear two-dimensional null points with open boundary conditions. A treatment is given of the collapse of nulls which have current and flow so that they are initially in a steady-state balance between a magnetic force, a pressure force and a centrifugal force. This extends the previous results for initially current-free X-type nulls with no flow. It is found that all X-points, regardless of the current and flow tend to collapse. Also, O-points collapse in the absence of a plasma flow, but O-points with a large current and possessing a highly super-Alfvénic plasma flow can be stable against linear collapse.