S-band Much Preliminary Studies Of Relativistic Klystron Amplifier

Multiple-Beam Relativistic Klystron Amplifier (MBRKA) uses multiple parallel beamlets that propagate in individual channels but interact in common RF regions such as in the cavity gaps. Multiple-Beam operation takes advantage of the low perveance of individual beamlet to avoid space-charge issues associated with beam transport and enable more efficient bunching and consequently higher efficiency. In the paper, a primary research is carried out on two kinds of MBRKAs with electron beams of different shapes;410MW of output power is produced in the experiment of Fan-shaped Multiple-Beam Relativistic Klystron Amplifier.The paper includes four parts:1. A general design methodology of MBRKA is developed by considering the characteristic of Intense Relativistic Electron Beams (IREBs) and the design methods of common klystron, which is of great importance to the design of MBRKA. In this paper, the design targets and their experiential ranges are given, the methods to design electron parameters are obtained, and the principles of designing the resonant cavities are described in detail.2. According to the design methodology, a Fan-shaped Multiple-Beam Relativistic Klystron Amplifier is designed via numerical simulation. The three dimensional computer codes are used for RF characteristics and beam-wave interaction studies, including:the RF parameters such as quality factors and characteristic impedance of operating modes for each cavity; the relationship between the absorbability of input power and the beam loading; the fundamental component of the bunching current downstream the input cavity and idler cavity; the electric field and RF breakdown problem in the gap of the single-gap output cavity; the output power with different drive frequencies and focusing magnetic fields. Making use of a 1MV/20kA electron beam, the device has a peak pulsed output power of4.73GW with a corresponding electronic efficiency of23.6%.3. Experimental investigations in FMBRKA are carried out with theoretical analysis and particle simulation. The experiments deal with RF parameters of the cavities, beam transport of FMBRKA. beam current modulation before the output cavity and the output power of the integration. Several aspects are studied:the RF parameters such as resonant frequency and quality factors of operating mode for each cavity; the relationship between the absorbability of input power and the beam loading; the fundamental component of the bunching current downstream the input cavity and idler cavity; the output power and its harmonic component. The problems of beam loss in the transport of electrons and the beam loading’s influence on the absorbability of input power are placed great emphasis. Making use of electron beams of670kV/11kA, input microwave of500kW and focus magnetic field of1T, the device generate a peak pulsed output power of410MW.4. A scheme for solving the problem of beam loss in FMBRKA is analyzed and verified by particle simulation. The mechanism for particle loss is worked out and the sectional shape of election beamlets and tunnels are meliorated, resulting in the development of Circular Multiple-Beam Relativistic Klystron Amplifier (CMBRKA). The influences of high frequency characteristics on beam-wave interaction are studied in the simulations, which also indicate that the circular-shaped Multiple-Beam employed in MBRKA requires less focusing magnetic field. Making use of electron beams of700kV/5.8kA, input microwave of65kW and focus magnetic field of0.4T. the device generates a peak pulsed output power of1.43GW by PIC simulation, The efficiency is36%.