Victor A. Tarasov

Dynamics of electron bunches in subpicosecond streak tubes

Abstract The dynamics of electron bunches in subpicosecond streak tubes is studied numerically taking into account space-charge effects and various initial photoelectron energy distributions. Three computing and analytical models (aberrational-Lorentz model, the model describing the limiting case of zero initial energy and simplified analytical model) are used.

Computer modeling of a subfemtosecond photoelectron gun with time-dependent electric field for TRED experiments

In the paper, theoretical and numerical studies on temporal focusing of photoelectron bunch in time-dependent fields are continued. Presented are the results of computer modeling on electron-optical system with combined time-dependent electric and static magnetic fields to ensure both spatial focusing and temporal compressing of photoelectron bunch down to sub-femtosecond level. The peculiarity of space charge effect contribution to the bunch broadening in the case of time-dependent electric field is discussed.

Theoretical and computer study on the possibility of sub- femtosecond (attosecond) temporal focusing of photoelectron probing bunches with quasi-stationary electromagnetic fields

The problem of ideal first-order temporal focusing of photoelectron bunches with quasi-stationary electromagnetic fields is discussed on the basis of theoretical electron optics and computer modelling.

Computer studies on dynamics of ultrashort electron packets in streak tubes and diffractometers

Computer techniques and software are developed to study the dynamics of electron packets on a subpicosecond time scale in streak image tubes and photoelectron diffractometers. It is shown that the Coulomb spread of an electron packet substantially increases for a sufficiently narrow energy distribution of photoelectrons, due to disinte- grative space charge effects inside the packet.

Perturbation techniques in the problems of computational charged particle optics

Basing on perturbation technique, discussed are some urgent problems of computational charged particle optics including numerical evaluation of fringe fields and field perturbations caused by small deviation of the shape of electrodes from rotational or planar symmetry as well as aberrational analysis of charged particle beams in the most general tensor form. It is shown that perturbation technique, being combined with other numerical approaches such as the tau- variations method and generalized method of initial parameters variation, proves to be most promising for evaluation of mechanical tolerances and simulation of Coulomb repulsion effects and charged particles scattering upon a fine-structure grid.

The results of computer and experimental studies on compressing the ultrashort photoelectron bunches with time-dependent electric fields

Some theoretical milestones, in definite sense summarizing our studies on temporal compressing of photoelectron bunch with time-depending electric fields, are elucidated. The recent experimental results on dynamic compression of photoelectron bunches of picosecond duration, gained with the use of a newly designed photoelectron gun employing the electric field ramp of about 1.5 kV/ns, are presented and compared with the results of computer simulation.

Formation of subfemtosecond photoelectron bunches in time-dependent electric fields

In the paper new theoretical aspects of temporal focusing of photoelectron bunch in time-dependent fields are elucidated. The results of computer modeling on electron-optical system with combined time-dependent eletric and static magnetic fields which ensure both spatial focusing of the bunch and its temporal compressing up to the sub-femtosecond level are presented.

A grid photocathode free of the first-order temporal chromatic aberration

The paper is devoted to the problem of temporal resolution in electron-optical streak tubes intended for ultrafast processes investigation. The temporal threshold of about 150-200 femtoseconds can be hardly overcome without a principally new approach to the design of electron-optical scheme of such tubes. One of the possibilities, namely the use of a photocathode having rather fine grid structure, is numerically analyzed on the basis of 3D field calculations.

Computer modeling of image intensifiers and photoelectron guns for time-resolved electron diffraction experiments

The first part of the work is devoted to the problem of computer simulation of static image intensifiers and streak image tubes. The most peculiar and sensible points of the simulation, such as image curvature surface, aberration coefficients, spatial and temporal resolution along the work area, are illustrated on typical examples. The problem of image curvature correction is discussed as well. The second part of the work outlines the theoretical grounds and results of computer-aided design of a principally new photoelectron-optical system with time-depending fields capable of essential compressing of electron bunches for the needs of time-resolved electron diffraction (TRED) experiments. Some recent experimental results on the bunch compressing obtained with the newly designed and manufactured photoelectron gun are presented.

Comparative analysis of two approaches to image tube computation

Two different approaches to image tube computation, numerical optimization and design being developed in GPI (Russia) and BIT (China) are presented and comparatively discussed as applied to a Russian-made streak image tube.