G.V. Sotnikov

Space charge limiting current of an electron beam transported in a coaxial drift chamber

An expression for the space charge limiting current of an electron beam in a vacuum coaxial drift chamber is obtained in the strong field approximation. The expression is an analogue of the Bogdankevich-Rukhadze interpolation formula for a cylindrical drift chamber. The space charge limiting currents in the coaxial and cylindrical chambers are compared. The space charge limiting current in the vacuum coaxial chamber is numerically calculated and compared to analytical predictions.

Removal of asphalt-paraffin deposits in oil pipelines by a moving source of high-frequency electromagnetic radiation

A new method for removing asphalt-paraffin and gasohydrate plugs in oil pipelines with a movable source of electromagnetic radiation, electromagnetic pig, is suggested. The pig melts the plug when the latter absorbs intense electromagnetic radiation and heats up. Effective melting of the dielectric plug is achieved with the source moving along the pipeline as the solid-liquid interface propagates. The time of paraffin plug removal and the dependence of this time on the radiation frequency are found with the model suggested. The efficiency of the method is estimated.

Space-charge limited current of relativistic charged-particle beam in coaxial drift tube of finite length

The analytical estimate of space-charge limited (SCL) current of axisymmetric relativistic charged-particle beam in coaxial drift tube bounded in the longitudinal direction is obtained. We compare numerical nonlinear and analytical estimates of the SCL current in the finite drift tube. A simple correspondence between the analytical estimate of the SCL current in unbounded and bounded coaxial drift tubes is demonstrated.

Wakefield excitation in dielectric wavguides by a sequence of relativistic electron bunches

At the elaboration of the concept of the multi-bunch dielectric wakefield accelerator1 the investigations of the three issues - multi-bunch, multimode, and resonator schemes, on which the concept is based to enhance the acceleration rate, should be carried out. This presentation gives the results of theoretical and experimental studies of the first scheme, namely, wakefield excitation in dielectric structures by a long sequence of relativistic electron bunches in order to increase the amplitude of the wakefield at summing coherent fields of separate bunches when the bunch repetition frequency coincides with the excited field frequency. It is theoretically shown that in the dielectric waveguide of length L the excited wakefield, consisting of Cerenkov and transition radiation goes out from waveguide with the group velocity νg, so that the summation of fields, leading to an increase the total field amplitude, occurs only for the number of bunches Nmax=(1-νg/ν0)L/d, ν0 - velocity of the bunch, d - distance between the bunches. For experimental verification of this result the facility has been created, in which to excite the wakefield in a tubular dielectric waveguide (inner and outer diameters are 2.1cm 8.5cm, the permittivity is 2.1) with a copper jacket, a sequence 6×103 of electron bunches (charge 0.32nC, energy 4.5MeV, length 1.7cm, diameter 1.0cm, each), produced by linear resonance accelerator “Almaz”, has been used. In accordance with the theory linearly increasing dependence of the wakefield amplitude upon the dielectric waveguide length is obtained. Stepwise dependence of Cherenkov radiation is smoothed by the inevitable transition radiation occurring at the entrance. For a waveguide with reflections (SWR=2–3) on the increasing dependence the resonant peaks take place corresponding to the waveguide length multiple to the excited wave length.

Limiting current of axisymmetric relativistic charged-particle beam in coaxial drift tube

Summary form only given. On the basis of numerical modeling, we discuss in the strong axial magnetic field approximation limiting current definitions of a charged-particle beam in finite and infinitely long coaxial drift tubes. A method of successive approximations in the bias voltage applied to the inner conductor of drift tube that allows one in the strong axial magnetic field approximation to obtain analytical estimates of the limiting current of axisymmetric charged-particle beam of finite thickness propagating in an infinitely long coaxial drift tube, which outer conductor is lined with a finite-width dielectric insert, is put forward. The proposed technique takes into account that the radial position of the extremal value of scalar potential inside the beam even in the strong magnetic field approximation depends on the geometry of infinitely long coaxial drift tube, transverse dimensions of the charged-particle beam and dielectric liner insert of the outer conductor of drift tube, as well as on the permittivity of the insert. Using this technique, it is not difficult to obtain analogous analytical estimates if the inner conductor of drift tube is in addition lined with a finite-width dielectric insert. In the strong magnetic field approximation, we also derive corresponding analytical generalizations to the infinitely long coaxial drift tubes of the limiting current of tenuous charged-particle beam. A comparison of proposed analytical expressions and limiting current definitions with results of numerical simulations is fulfilled.

High-power coaxial microwave ubitron : Simulation by the particle-in-cell method

Results of complete numerical simulation of a high-power coaxial microwave ubitron are reported. The simulation uses a 2.5-dimensional numerical electromagnetic code based on the particle-in-cell method and is performed for the amplification and oscillation operating modes. The results of our numerical simulation are compared with analytical results and results following from the nonlinear theory that are obtained by partial computer simulation.

PIC simulation of powerful microwave coaxial ubitron

Results of numerical simulation of a powerful coaxial UHF-ubitron are given. We received these results using the numerical 2.5-dimensional electromagnetic code, which we developed. This code is based on the PIC method. In the work the algorithm adapted to the coaxial ubitron geometry is described. The numerical analysis of ubitron operation in amplification and in generation regimes is given.

Nonlinear regimes of coaxial gyro-BWO

Nonlinear generation regimes of coaxial gyro-BWO were investigated. The results allow determination of necessary parameters of gyro-BWO (beam current, system length) for reception of required modes of generation (stationary, self-modulation and stochastic modes).

Theory of high power coaxial ubitron

Strong focusing of high current relativistic electron beam (REB) has been investigated in spatially periodic magnetic field of coaxial magnetic ondulator (CMO). Theory of the amplification of the intensive microwaves in coaxial ubitron has been developed.

Starting currents in coaxial gyro-BWO

In this paper, we conducted theoretical investigation of coaxial BWO, operating at resonance of relativistic electron beam (REB) with back wave on the normal Doppler effect (gyro-BWO). Linear theory of exciting process is presented. The dependence of starting current values upon the coaxial waveguide length and the electron beam energy is investigated.