Numerical simulation of high-current ion linear induction accelerator with additional electron beam injection

title: Numerical investigation of high-current ion beam acceleration and charge compensation in two accelerating gaps of induction linac
abstract: The numerical investigation of the hollow high-current ion beam (HHCIB) dynamics in two magnet-isolated accelerating gaps of induction linac are presented. It has been shown that the applied electric field destroys partially the charge and current compensations, and impairs the brightness of the ion beam when the electron beam energy is not sufficient to overcome the potential difference. The acceleration, the charge and current compensations, and the stability of the high-brightness ion beam can be achieved under the optimum parameters choice.<<ETX>>

title: Kinetic simulation of fields excitation and particle acceleration by laser beat wave in non-homogeneous plasmas
abstract: Resonance excitation of longitudinal plasma electrostatic wave by double-frequency laser radiation is investigated numerically to study in detail conditions of particle beat wave acceleration. The computer simulation is based on the highly specialized code SUR, using splitting technique. Both the space uniform and slightly non-uniform cases are investigated. Maintaining of phase synchronism between accelerated particles and excited longitudinal wave is provided by a choice of density plasma profile.

title: 2,5-dimensional numerical simulation of propagation of the finite sequence of relativistic electron bunches (REB) in tenuous and dense plasmas
abstract: Particle simulation results on the wake-field excitation with the programmed finite sequence of REB in tenuous and dense plasmas are presented. The REB/background plasma configuration is described by full set of 2D3V relativistic Vlasov equations for each plasma species and nonlinear Maxwell equations for self-consistent electromagnetic field. The physical parameters in runs carried out are close to those used in laboratory experiment at Kharkov IPT (Ya. Fainberg et al., 1994). The simulation points to the fact that the reached value of electric field depends on charge distribution and choice of intervals between bunches in programmed sequence.

title: 2.5D numerical simulation of relativistic electron bunches (REB) interaction with underdense and overdense plasmas
abstract: The results of REB-plasma interaction numerical simulation by means of our relativistic particle EM code-are presented. Nonlinear evolution of a single REB injected into underdense and overdense plasmas is studied in detail for cylindrical geometry. It is found that in case of comparable bunch and plasma densities an instantaneous amplitude of excited longitudinal electric field substantially depends on density ratio, relativistic factor and space density distribution of REB. Transversal electric field can considerably exceed the longitudinal one, causing more severe restrictions to initial phase and radial position of particles to be accelerated.<<ETX>>

title: Numerical modelling of time-space behavior of high-current relativistic electron beam in plasma waveguide
abstract: The physical processes in a magnetized plasma waveguide, in which a high-current relativistic electron beam (Sudan parameter S>1) is injected, are investigated by the developed 2.5-D relativistic electromagnetic code. The computer study has shown that the charge and current compensations of the high-current beam are considerably different from those of the low-current beam. In addition the self-consistent electromagnetic fields generated by a beam at the initial state radically alter both the linear and the nonlinear instability stages.<<ETX>>

title: The Galactic centre mini-spiral in the mm-regime
abstract: The mini-spiral is a feature of the interstellar medium in the central ∼2 pc of the Galactic center. It is composed of several streamers of dust and ionised and atomic gas with temperatures between a few 100 K to 10 4 K. There is evidence that these streamers are related to the so-called circumnuclear disk of molecular gas and are ionized by photons from massive, hot stars in the central parsec.  We attempt to constrain the emission mechanisms and physical properties of the ionized gas and dust of the mini-spiral region with the help of our multiwavelength data sets.  Our observations were carried out at 1.3 mm and 3 mm with the mm interferometric array CARMA in California in March and April 2009, with the MIR instrument VISIR at ESO’s VLT in June 2006, and the NIR Brγ with VLT NACO in August 2009.  We present high resolution maps of the mini-spiral, and obtain a spectral index of 0.5 ± 0.25 for Sgr A*, indicating an inverted synchrotron spectrum. We find electron densities within the range 0.8–1.5 × 10 4 cm −3 for the mini-spiral from the radio continuum

title: Modeling the X-ray fractional variability spectrum of Active Galactic Nuclei using multiple flares
abstract: Using Monte-Carlo simulations of X-ray flare distributions across the accretion disk of active galactic nuclei (AGN), we obtain modeling results for the energy-dependent fractional variability amplitude. Referring to previous results of this model, we illustrate the relation between the shape of the point-to-point fractional variability spectrum, F_pp, and the time-integrated spectral energy distribution, F_E. The results confirm that the spectral shape and variability of the iron Kalpha line are dominated by the flares closest to the disk center.

title: 2.5-Dimension Numerical Simulation Of Selfmodulation of Relativistic Electron Bunches in a Plasma.

title: Charge compensation and acceleration of a thick-walled high-current ion beam in induction linac
abstract: The authors carried out systematic investigations of the dynamics of relativistic electron and nonrelativistic ion beam propagation in both an electric field and an axisymmetric nonuniform magnetic field. In previous papers, the investigation results of the acceleration, and the charge and current compensation of HHCIBs in one and two linac cusps are reported. These results have shown that both in the presence and in the absence of an accelerating electric field, the following effects take place: (1) charge and current compensation of HHCIB in the accelerating gaps, (2) stability of the ion beam during times that substantially exceed the inverse ion Langmuir and Larmor frequencies. The performed numerical simulations have also shown that a required charge neutralization of the ion beam is only achieved within accelerating gaps of linac. This investigation is directed towards: (1) reaching of the optimal relation between the external electric field parameters and the compensating electron beam parameters; (2) defining of the optimal thickness of annular beam at which the ion beam is effectively accelerated and at a time is remaining compensated and not losing a stability.

title: Influence of frame-dragging on magnetic null points near rotating black holes
abstract: Understanding the mechanisms of particle acceleration from the vicinity of black holes poses a challenge. Electromagnetic effects are thought to be a prime suspect, but details still need an explanation. To this end, we study a three-dimensional structure of oblique magnetic fields near a rotating black hole in vacuum. It has been proposed that such a setup can lead to efficient acceleration when plasma is injected near a magnetic null point. We focus our attention especially on the magnetic field in the immediate neighborhood of the magnetic null point, which was previously shown to occur in the equatorial plane. By employing the line integral convolution method, we visualize the magnetic field lines and explore the electric lines rising out of the equatorial plane. We show the magnetic field structure near the boundary of ergosphere, depending on the spin of the black hole. Electric field develops a non-vanishing component passing through the magnetic null point and ensuring efficient acceleration of charged particles from this particular location near the horizon. We also examine the effect of translatory boost on the field lines. Similarly to the frame-dragging by rotation, the linear motion carries field lines along with the black hole. The position of the magnetic null point recedes from the black hole horizon as the spin parameter increases. For the extreme value of a = 1, the null point can occur outside the ergosphere.