Kostyantyn Ilyenko

The sub-THz clinotron-multiplier

We outline an experimental set-up for the sub- terahertz CW clinotron (a BWO with a comb-type slow- wave structure and an inclined beam) frequency multiplier oscillator. The clinotron-multiplier operation is expected to quadruple fb ~ 146.5 GHz (2.04 mm) microwave signal, which is generated in the buncher section of the device, to obtain fc ~ 586 GHz (0.51 mm) signal in the catcher section. Some results of preliminary experimental tests with a prototype sub-THz clinotron-multiplier are presented and discussed.

Scalar potential calculations for relativistic charged-particle beam in unbounded coaxial drift tube

We receive the first order analytical expression for the scalar potential transversal distribution of finite width uniform density axisymmetric relativistic charged-particle beam propagating in the unbounded in the longitudinal direction coaxial drift tube in the strong guide magnetic field, which exhibits nonlinear dependence on the beam injection current. Ranges of the injection current values that show non-uniqueness of the solutions to the nonlinear ordinary differential equation describing the transverse distribution of the scalar potential in unbounded coaxial drift tube are also found numerically.

Permanent magnet focusing system optimization for SubMM-waveband clinotrons

We propose to use composite permanent magnet and iron insert focusing system for modern compact submm-waveband vacuum electron devices of the clinotron type that has the potential of improving by at least a quarter on the mass of the current in-house design while preserving the required values of guide magnetic field, simplifying the system assembly, and reducing the overall system dimensions.

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.

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.

3-D Green's function modeling for moderately relativistic chargedparticle beams in cylindrical geometry

Recently, utilization of integral (Greens function) methods has gained a substantial attention in modeling intense (i.e. space-charge dominated) relativistic charged-particle beams [1,2,3]. Such applications range from dynamics simulations of axially-symmetric charged-particle beams in grounded regular drift tubes [2,3] to modeling space-charge effects in free-electron lasers [1,4]. However, there are many situations, which require totally three-dimensional (3-D) treatment (see [5] and references therein, where the corresponding approach has been published for the non-relativistic (υ/c ≤ 0.3) case).

FEL dispersion equation with account for relativistic space-charge effects

We give a qualitative derivation of a free-electron laser (FEL) dispersion equation, which takes into account not only non-relativistic (potential) but also relativistic (rotational) space-charge effects. The derivation is based on a generalisation of a dispersion equation for a Compton FEL obtained by us earlier, a certain weakly-relativistic quasistatic approximation of the space-charge field (the Darwin model), and uses an analogy between FEL and a travel wave tube (TWT). An analysis of the obtained linear growth rates is presented.

Numerical simulation of amplification in hybrid planar ubitron

We accomplish numerical simulation of microwave amplification in a hybrid planar ubitron (free electron maser). Results are compared to those obtained in the linear theory.

Dynamical chaos and magnetoresonant gain in hybrid planar ubitron

We study the magnetoresonant amplification regime, formulate a criterion of chaotic dynamics and find the maximal gain under the undulator synchronism for a weakly-relativistic hybrid planar ubitron/ free-electron maser.

Free-electron laser with resonant pumping

We find the boundaries of regular and chaotic dynamics zones around the magnetoresonance for a hybrid planar free-electron laser amplifier. For the zones of regular dynamics the maximal magnetoresonant gain is calculated analytically and is shown to be in a good agreement with non-linear numerical simulations. It is also analytically demonstrated that in the vicinity of magnetoresonance the gain is independent of the spatial amplitude of undulator magnetic field. Moreover, we find that in the zone of regular dynamics above the magnetoresonance the efficiency of amplification achieves its maximal value and is less prone to the influence of space-charge effects.