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In the first part of this paper, the status of the 140-GHz continuously operated gyrotrons with an output power of 1 MW or the stellarator Wendelstein 7-X will be described. With the first series tube, an output power of 1000 kW has been achieved in short pulse operation (milliseconds) with an electron beam current of 40 A, and of 1150 kW at 50 A. With a pulse length of 3 min limted by the available high-voltage (HV) power supply, an output power of 920 kW at an electron beam current of about 40 A with an efficiency of 45% and a mode purity of 97.5% has been obained. At a reduced beam current of 29 A, an output power of 570 kW was measured with a pulse length of 1893 s without significant increase in tube pressure. The energy content of this pulse is almost 1.1 GJ. For the next fusion plasma device, International Thermonuclear Experimental Reactor (ITER), gyrotrons with a higher output power of about 2 MW are desirable. In short-pulse experiments, the feasibility of the fabrication of coaxial cavity gyrotrons with an output power up to 2-MW, continuous wave (CW), has been demonstrated, and the information necessary for a technical design has been obtained. The development of a long-pulse 2-MW coaxial cavity gyrotron started within a European coopera tion. In parallel to the design and fabrication of an industrial prototype gyrotron, a short-pulse preprototype gyrotron has been operated to verify the design of critical components. An output power of 1.2 MW with an efficiency of 20% has been achieved. The development of frequency tunable gyrotrons operating in the range from 105 to 140 GHz for stabilization of current driven plasma instabilities in fusion plasma devices (neoclassical tearing modes) is another task in the development of gyrotrons at the Forschungszentrum Karlsruhe. Index Terms--Coaxial gyrotron, diamond window, frequency tuning, gyrotron, high-power microwaves, quasi-optical mode converter, single-stage depressed collector, step tunability, stray radiation.

The feasibility of fabrication of coaxial cavity gyrotrons with an output power up to 2 MW, CW is demonstrated in a short pulse experiments and obtained information necessary for a technical design. The status of the development of the 140-GHz continuously operating gyrotrons with an output power of 1MW for the stellarator Wendelstein 7-X is described.

This paper describes a mathematical model enabling the calculation of the effective permeability tensor of heterogeneous magnetic materials set in various magnetization states. The theoretical approach we propose permits to predict the microwave behavior of unsaturated magnetic loaded composites as well as those of unsaturated polycrystalline ferrites. The model gives all the complex components of the permeability tensor in a single calculation phase whatever the magnetization state of the material is. This is useful for the computer-aided design of microwave magnetic devices. The calculation of the effective permeability tensor is carried out from a limited number of parameters: saturation magnetization, anisotropy field, damping factor, external dc field strength, concentration, and shape of the magnetic particles or domains. The model is predictive in the way that the magnetization state of the material is determined from the strength of the external dc magnetic field applied on the material. Index Terms--Magnetic anisotropy, magnetic hysteresis, nonhomogeneous media, permeability.

A theory is developed which is intended to give an expression for the gyroresonance frequency of magnetic composites in their unsaturated magnetic state. The proposed relation, which is an extension of the Kittel's expression for the resonance frequency of a saturated body, points out a noteworthy close link between the concept of reciprocity and the one of demagnetization.

Development overview and test results of a multibeam inductive output tube that produces over 1.2 MW peak power at 704 MHz with over 65% efficiency are presented. This is a collaborative effort between Thales Electron Devices and Communications & Power Industries to design and fabricate a new RF source for the European Spallation Source. The first prototype unit has been designed and built. Initial test at CERN demonstrated output power of 1.2 MW peak, efficiency of 69.8%, and gain of 21.4 dB at 1-ms operation. When the pulselength was increased to 4 ms, instability in the RF output pulse developed as the result of a mechanical contact issue in the output window. The prototype is in the process of being repaired and the unit will be returned to CERN for full characterization and final testing in early 2018. [ABSTRACT FROM AUTHOR]

Presents a physical model of the properties of polycrystalline ferrites below magnetic saturation. Characterization of properties through permeability tensor as functions of magnetization states, anisotropy field and frequency; Homogeneity of medium through medium approximation; Comparison of results for different states with empirical formulations of permeability tensor components.