formation of a laminar electron flow for 300GHz high-power pulsed gyrotron

This paper describes the design of a triode magnetron injection gun for use in a 200 kW, 300 GHz gyrotron. As power and frequency increase, the performance of the gyrotron becomes quite sensitive to the quality of the electron beam. Formation of a laminar electron flow is essential for the realization of a high quality beam with a small velocity spread. In this study, a new method is developed for a quantitative evaluation of the laminarity and is applied to optimize the electrode design. The laminarity depends not only on conventional design parameters such as the cathode slant angle but also on the spatial distribution of the electric field along the beam trajectory. In the optimized design, the velocity pitch factors, a, larger than 1.2 are obtained at 65 kV, 10A with spreads, Da, less than 5%

An emission model for the particle-in-cell method

The thesis ‘An Emission Model for the Particle-in-Cell Method‘, presents a comprehensive approach in simulating electron emission from a given electron source of any material type and geometrical shape. The model presented in this work is simple and computationally efficient. The shortcomings of the popular methods are circumvented and efficiency greatly enhanced in solving complex emission problems, which otherwise have remained un-addressed. In the beginning, the Theory of Electron Emission and the governing relations to model thermionic, field and photo emission are presented. The importance of having accurate field solutions on an arbitrary shaped emission surface is discussed. In this regard the Conformal Finite Integration Technique and its relevance in emission model is highlighted. The interaction of charged particles with external fields and the resulting dynamics is studied using the Particle-in-Cell method. A brief overview of this method and the time integration schemes of the particle equations of motion are presented. A vital component of the emission model is the initialization of the particle positions on the emitter. The initialization depends on the type of emission, the geometrical shape of the emitter and the initial conditions. To meet the requirements of any real time problem, we developed a Geometric Modeling tool that uses Constrained Delaunay Triangulation to generate a problem specific surface mesh necessary for initializing particles. In all practical problems, there is a limit to the current that can be drawn from the emitter. The limits can be classified as Space Charge Limited and Temperature Limited. The analytical solution to the space charge limited emission can be obtained using the 1D Child’s law. For practical problems, the Virtual Cathode method is widely used to obtain a 3D numerical solution of the Child’s law. There are obvious disadvantages in using this method which are highlighted. As an alternative, a Charge Conservation method is developed and its efficiency over the Virtual Cathode method is demonstrated. Finally the emission model is tested extensively in the case of planar, spherical and circular cylindrical diodes and a comparative study between the Virtual Cathode and Charge Conservation methods is presented. As an application problem, simulation of a Traveling Wave Tube Amplifier is performed at the end of the dissertation and the results are found to be in good agreement with the experiment

Gyrotron: The Most Suitable Millimeter-Wave Source for Heating of Plasma in Tokamak

In this chapter, brief outline is presented about gyro-devices. Gyro-devices comprise of a family of microwave devices and gyrotron is one among those. Various gyro devices, namely, gyrotron, gyro-klystron and gyro traveling-wave tubes (gyro-TWT) are discussed. Gyrotron is the only microwave source which can generate megawatt range of power at millimeter-wave and sub-millimeter-wave frequency. Gyrotron is the most suitable millimeter wave source for the heating of plasma in the Tokamak for the controlled thermoneuclear fusion reactors. This device is used both for the electron cyclotron resonance heating (ECRH) as well as for the electron cyclotron current drive (ECCD). In this chapter, the basic theory of gyrotron operation are presented with the explanation of various sub-systems of gyrotron. The applications of gyrotrons are also discussed. Also, the present state-of-the-art worldwide scenario of gyrotrons suitable for plasma heating applications are presented in details

Formation of Laminar Electron Flow for 300GHz High-Power Pulsed Gyrotron

This report describes the design of a magnetron-injection gun，which is intended for use 100 kW，30 0 GHz gyrotron. With increases in power and frequency，performance of the gyrotron becomes quite sensitive to the quality of the electron beam. Formation of a laminar electron flow is essential for the realization of a high qua1ity beam with small velocity spread .In th is study，a new method is developed for the evaluation of the laminarity，and applied to the design optimization of the electrodes. It is found that the laminarity depends not on1y on the conventional design parameter of the cathode slant angle，but also on the spatial distribution of the electric field inside the beam. In a well laminated beam， it is revealed that the pitch factor of each electon trajectory is modified to adjust the spatial separation between the neighboring trajectories around the cathode and first anode. An electron gun which is suitable for the new gyrotron has been successfully designed. In the future， we plan to clarify the relation between the laminarity and the profile of the electric field inside the electron beam