Gennadiy I. Zaginaylov

Novel approach to the theory of longitudinally inhomogeneous lossy waveguides

In this paper a new approach to the analysis of irregular lossy waveguides is proposed. It allows us to reduce the problem to the set of ordinary differential equations similar to lossless case. It is based on scalar expansions, which are more flexible and, as a rule, have better convergence compared to the vector ones. It takes into account local lossy boundary conditions in a rigorous manner. It can be applied for a lot of waveguide structures with different cross-sections, with non-uniform and anisotropic filling, and so on. A brief description of the approach is presented below for the case of a circular waveguide with an azimuthally symmetric radius variation.

Full wave simulation of the iter relevant coaxial cavity gyrotron operation

New generation of gyrotrons based on coaxial cavities with a corrugated inner conductor is able to reach the multi-megawatt output power in a continuous wave (CW) regime. The development of an industrial prototype of a coaxial cavity gyrotron with an RF output power of 2 MW in CW regime at 170 GHz is now in progress at the Centre de Recherches en Physique des Plasmas, Lausanne, Switzerland [1]. The pre-prototype tube (with the same main components) has been developed at the Karlsruhe Institute of Technology (KIT) (former Forschungszentrum Karlsruhe (FZK)) to verify the design of the most critical components of the prototype. The coaxial gyrotron cavity is higherly overmoded and is designed to operate on the TE34,19 mode. Usage of the corrugated inner conductor allows reducing problems of the mode competition and beam voltage depression. However the reliable design consideration of such a cavity becomes more complicated.

Theory of irregular impedance waveguides: Generalized method of separation of variables

Maxwells equations for longitudinally inhomogeneous (irregular) waveguides with impedance walls are equivalently reduced to an infinite set of ordinary differential equations (ODE) by applying transverse expansions. The resulting set of ODE is used for analysis of gyrotron cavities. In particular, the effects of mode conversion and ohmic losses on the operational frequency, quality factor, and field distribution in gyrotron cavities operating in the sub-millimeter range are investigated.

Improved theory of energy losses in corrugated inner conductor of coaxial gyrotron cavity

The improved theory of Ohmic losses which takes into account effects of a field increase near edges of corrugations is developed for a coaxial gyrotron cavity with a corrugated inner conductor. It is shown that for the ITER relevant TE34,19 coaxial gyrotron operating at the maximal output power (~2 MW) they do not lead to a notable increase of the total losses in the corrugated inner insert. However they can contribute substantially to the local density of losses near edges of corrugations especially in the shot pulse regimes when contribution of higher axial harmonics to the total field can be substantial.

Influence of Background Plasma on Operation Efficiency of High-Power CW Gyrotrons

A slow wave non-linear single mode stationary theory describing influence of background plasma which occurs in the gyrotron cavity on gyrotron operation has been developed. It is shown that the main effects of a low density background plasma on efficiency are concerned with decreasing the mismatch between operational and cyclotron frequencies and decreasing the beam-wave coupling coefficient. Numerical calculations are performed for the 140 GHz 1 MW CW gyrotron developed in Karlsruhe for fusion applications. Interpretation of some experimental effects which are not yet clearly understood is addressed.

Coupled mode theory for longitudinally inhomogeneous impedance waveguides

The well-known coupled mode theory is extended to the case of irregular waveguides with impedance boundary conditions on the walls. The developed theory is tested by calculating mode conversion and quality factors of a typical THz gyrotron cavity. High computational capabilities of the approach developed are found and a good agreement with earlier results is obtained.

Analysis and improvement of convergence of transverse expansions in excitation problems of irregular impedance waveguides

Efficiency of cross-section expansions based on the fields of waveguide with ideal walls as basis functions is investigated for impedance waveguides. The criterion of the uniform convergence with respect to the number of expansion terms is obtained. In addition, method of convergence improvement is suggested and illustrated by practical calculations.

Influence of mode conversion and ohmic losses on electromagnetic properties of THz gyrotron cavities

On the basis of a rigorous multimode approach it is shown that mode conversion and ohmic losses can notably influence quality factors of a THz gyrotron cavity. They also lead to the significant distortion of the field distribution inside the output section of the THz gyrotron cavity making it strongly multimode. Influence of these effects on the THz gyrotron operation is also discussed. Specific calculations were performed for the cavity of FU CW III gyrotron, designed in Fukui University to operate in sub-THz and THz ranges.

Cutoff frequencies of a waveguide filled with radially non-uniform magnetized plasma: an efficient computing method

An efficient computing method for cutoff frequencies of radially non-uniform plasma-filled waveguide in applied magnetic field is given. The plasma-filled waveguide is approximated by a multilayer structure and the computation is performed by using the recurrence relations between fields in different layers. The dispersion equations for TE and TM modes are obtained in the form independent of number of plasma layers. The equations are valid both for circular and coaxial plasma-filled waveguides with impedance boundaries and are examined numerically for some plasma density profiles.