Theoretical Study of a Plasma-Filled Relativistic Cerenkov Generator With Coaxial Slow-Wave Structure
The linear and nonlinear theory of a plasma-filled relativistic Cherenkov generator with coaxial slow-wave structure (SWS) is developed. Linear analysis includes the space-charge limiting current, dispersion relations, dispersion curves, and coupling impedance. In nonlinear theory, the electron beam space-charge effect, nonsynchronous interaction, and complex reflection coefficients of the electromagnetic wave at the boundaries of the SWS are taken into account. With the assumption of quasi steady state, the self-consistent equations are numerically calculated using the fourth-order Runge-Kutta method. The effects of the relative phase between inner and outer corrugations, phase and amplitude of the complex reflection coefficient at the boundaries of the SWS, and plasma density on device efficiency are discussed. Efficiencies of up to 37% without plasma and about 50% with plasma density of np = 3-7 times 1011 cm-3 are obtained.
Analytic theory of relativistic high power microwave generator with coaxial slow wave structure
In this paper,a linear theory is presented of a relativistic high power microwave generator with coaxial slow wave structure.The space-charge-limiting current of a coaxial cylindrical waveguide is derived,which is larger than that of a hollow cylindrical waveguide.Thus,the electron beam in the former has more kinetic energy than that in the latter when the cathode potential and the current are the same and the coaxial device might obtain higher beam-wave conversion efficiency.Also derived is the dispersion relation for a coaxial cylindrical waveguide with sinusoidally varying wall radii.For the case of dispersion relation without considering the beam space charge effect,the theoretical results agree very well with the simulation results with Superfish.According to the numerical solutions to the dispersion equation considering the beam space charge effect,the operating mode of the generator is π point of quasi-TEM mode and the frequency is 7.67 GHz in which the high peak growth rate correspondingly occurs and the energy conversion efficiency is 34%.These results calculated by the analytic theory are close to those obtained by PIC simulation and reveal the advantages of high efficiency and short microwave pulse risetime for the generator.
Continuous calibration of a vacuum ultraviolet system from 65 to 125 nm by a cascade arc and comparison with the calibrated line radiation of a hollow cathode.
A high-power stationary helium cascade arc has been developed as a standard source for continuum radiation in the VUV spectral range from 65 to 125 nm. The calibration of the VUV system response was based on the calculated and measured continuum radiation of a 2-mmphi pure He arc. Diagnostics of the arc plasma in partial thermal equilibrium yielded the electron density and the temperature that were inserted in the calculations of the continuous radiation. The results were compared with the helium, argon, and krypton radiation lines of a high-current hollow cathode lamp. This lamp was built according to the construction drawings of a hollow cathode, which was calibrated by means of the electron synchrotron radiation at the Physikalisch Technische Bundesanstalt Berlin.