V. A. Cherepenin

Magnetic induction tomography: experimental realization

Magnetic induction tomography (MIT) is a new non-contacting technique for visualization of the electrical impedance distribution inside inhomogeneous media. A measuring system for MIT has been developed. An oscillating magnetic field is applied in the system as a sounding agent. The system is designed mainly for biomedical applications. Experiments demonstrate that with proper selection of measurement conditions it is possible to use the phase shifts between inductor and detector signals for image reconstruction by filtered backprojection along magnetic lines. Measurements with saline filled phantoms having various spatial distributions of conductivity were carried out and images were reconstructed. The experiments have demonstrated the applicability of MIT for medical imaging and diagnostics.

A 3D electrical impedance tomography (EIT) system for breast cancer detection

A medical device which allows imaging of the distribution of conductivity in 3D in regions below the skin surface has been developed and tested. Its purpose is to enable early detection and preliminary diagnosis of breast tumours. Design of the measuring system and software are described. Results of clinical evaluation of the system are presented. EIT images of healthy and cancerous breasts are presented and discussed. The system is able to visualize various states of the breast and it may be possible to apply it to breast cancer detection.

Preliminary static EIT images of the thorax in health and disease

The results of a preliminary clinical evaluation of a one-frequency electrical impedance tomography (EIT) system enabling static in vivo imaging are presented. The design of the measuring system and image reconstruction software are described. Thirty-one subjects were examined and divided into four clinical groups. The first group consisted of 22 patients with clinical diagnosis of lung cancer with tumour localization in one lung. The second group consisted of seven healthy subjects. A patient after a one-sided pneumectomy and another with one-sided emphysema diagnosis were also examined. Static EIT images of a healthy human chest and a chest with various abnormalities are given and discussed. The evaluated system distinguishably visualizes various states of lungs and thorax including lung cancer. The average static conductivity of an affected lung in the first clinical group statistically differs from the average conductivity of a healthy lung. In spite of low spatial resolution, according to preliminary results, the method can be sensitive to cancer and other lung diseases in screening investigations.

Evolution of a high-density electron beam in the field of a super-intense laser pulse

The evolution of a high-density electron beam in the field of a super-intense laser pulse is considered. The one-dimensional (1D) theory for the description of interaction, taking into account the space-charge forces of the beam, is developed, and exact solutions for the equations of motion of the electrons are found. It was shown that the length of the high-density electron beam increases slowly in time after initial compression of the beam by the laser pulse as opposed to the low-density electron beam case, where the length is constant on average. Also, for the high-density electron beam, the sharp peak frozen into the density distribution can appear in addition to a microbunching, which is characteristic for a low-density electron beam in a super-intense laser field. Characteristic parameters for the evolution of the electron beam are calculated by an example of a step-like envelope of the laser pulse. Comparison with 1D particle-in-cell simulations shows adequacy of the derived theory. The considered issue is very important for a special two-pulse realization of a Thomson scattering scheme, where one high-intensity laser pulse is used for acceleration, compression and microbunching of the electron beam, and the other probe counter-streaming laser pulse is used for scattering with frequency up-shifting and amplitude enhancement.

Flying mirror model for interaction of a super-intense nonadiabatic laser pulse with a thin plasma layer: Dynamics of electrons in a linearly polarized external field

Interaction of a high-power laser pulse having a sharp front with a thin plasma layer is considered. General one-dimensional numerical-analytical model is elaborated, in which the plasma layer is represented as a large collection of electron sheets, and a radiation reaction force is derived analytically. Using this model, trajectories of the electrons of the plasma layer are calculated numerically and compared with the electron trajectories obtained in particle-in-cell simulations, and a good agreement is found. Two simplified analytical models are considered, in which only one electron sheet is used, and it moves transversely and longitudinally in the fields of an ion sheet and a laser pulse (longitudinal displacements along the laser beam axis can be considerably larger than the laser wavelength). In the model I, a radiation reaction is included self-consistently, while in the model II a radiation reaction force is omitted. For the two models, analytical solutions for the dynamical parameters of the ele...

Plasma Channels Formed by a Set of Filaments As a Guiding System for Microwave Radiation

The possibility of formation of a virtual guiding system from a bunch of plasma channels of the filaments of femtosecond laser pulses for transmission of microwave radiation in air is considered. The effective conductivity and the skin depth of the laser plasma of such filaments are calculated for the microwave band. Optimum spatial configurations of plasma channels corresponding to a single-wire transmission line and a hollow cylindrical waveguide are proposed. Estimates of the energy loss of microwave radiation in plasma waveguides of various configurations are obtained.

Compression and acceleration of dense electron bunches by ultraintense laser pulses with sharp rising edge

In this paper, the generation of a single ultrashort and coherent relativistic electron bunch (relativistic electron mirror) during interaction of an ultraintense femtosecond laser pulse having a sharp enough rising edge (nonadiabatic laser pulse) with a thin plasma layer is considered. It is shown that due to the action of the radiation reaction forces the Coulomb repulsion among the bunch electrons is partially compensated and the initial geometry of the bunch is supported in the acceleration process. Besides, the bunch can be compressed by many times in the longitudinal direction at the initial stage of interaction with the front of the nonadiabatic laser pulse. As a result, all of the bunch electrons can be synchronously accelerated to ultrarelativistic velocities during the first several half periods of the external electromagnetic field that can correspond to time intervals of hundreds of femtoseconds in the laboratory frame. The characteristics of the accelerated electron bunches for different lase...

Use of High-Power Electromagnetic Pulses in Processes of Disintegration and Opening of Rebellious Gold-Containing Raw Material

Possible mechanisms of mineral particle disintegration under the action of high-power electromagnetic pulses on gold-containing sulfides and enrichment products are described theoretically for the first time. The results of experimental investigations are presented, and the theoretical substantiation is given for the effect of synergetic influence of high-power electromagnetic pulses with a wide range of their parameters and pore moisture on the opening of rebellious gold-containing raw material of different type and subsequent gold extraction.

Acceleration of dense electron bunches at the front of a high-power electromagnetic wave

The acceleration of dense electron bunches (e.g., those produced by the ionization of thin films) at the front of a high-power electromagnetic wave in vacuum is considered. It is shown that the reaction force of the intrinsic radiation of a bunch can play a significant role in the acceleration process because it gives rise to an additional accelerating force acting on the bunch and to forces that compress the bunch in the longitudinal direction. As a result, all of the bunch electrons can be synchronously accelerated during the first several half-periods of the external electromagnetic field.

Development of the system for visualization of electric conductivity distribution in human brain and its activity by the magnetic induction tomography (MIT) method

Currently rapid development of functional activity researches of human brain sets the problem of reliable and non-invasive detection of mental processes and states. At present we know some traditional methods of rapid and contactless acquisition of brain activity characteristics, such as functional tomography (fMRI) and magnetoencephalography. But these methods have low temporal resolution, complicated and ambiguous association of measured values with information processes in brain. So possibility of MIT application is investigated. Estimation of possibility of such changes registration is performed. Investigations of magnetic field configuration, schematics of transmit-receive modules and numerical algorithms are in progress. It may allow us to register high speed conductivity changes in brain tissues.