Biomedical subjects

John G Wöhlbier

Publications and source records attributed to John G Wöhlbier.

3 recordsLinked to original sources

PubMed2004

Eulerian method for computing multivalued solutions of the Euler-Poisson equations and applications to wave breaking in klystrons.

We provide methods of computing multivalued solutions to the Euler-Poisson system and test them in the context of a klystron amplifier. An Eulerian formulation capable of computing multivalued solutions is derived from a kinetic description of the Euler-Poisson system and a moment closure. The system of the moment equations may be closed due to the special structure of the solution in phase space. The Eulerian moment equations are computed for a velocity modulated electron beam, which has been shown by prior Lagrangian theories to break in a finite time and form multivalued solutions. The results of the Eulerian moment equations are compared to direct computation of the kinetic equations and a Lagrangian method also developed in the paper. We use the Lagrangian formulation for the explicit computation of wave breaking time and location for typical velocity modulation boundary conditions.

Journal Article↗

PubMed2004

Mechanisms for phase distortion in a traveling wave tube.

We present a view of the physics of phase distortion in a traveling wave tube (TWT) based on unique insights afforded by the MUSE models of a TWT [IEEE Trans. Plasma Sci. 30, 1063 (2002)]]. The conclusion, supported by analytic theory and simulations, is that prior to gain compression phase distortion is due to harmonic frequencies in the electron beam and the resulting "intermodulation" frequency at the fundamental, and not the often cited "slowing down of electrons in the electron beam." We draw these conclusions based on MUSE simulations that allow explicit control of electron beam frequency content, an analytic solution to the S-MUSE model [IEEE Trans. Plasma Sci. 30, 1063 (2002)]] that reveals that phase distortion is due to the fact that the fundamental frequency is an intermodulation product of itself, and large signal LATTE [IEEE Trans. Plasma Sci. 30, 1063 (2002)]] simulations that are modified to remove the effect of the slowing down of electrons in the electron beam. As applications of the theory we compare S-MUSE simulations to an amplitude phase model using the analytic phase transfer curve, we study dependence of phase distortion on circuit dispersion and electron beam parameters at the second harmonic with large signal LATTE simulations for narrow and wide band TWT designs, and we consider the phase distortion theory in the context of TWT linearization.

Journal Article↗

PubMed2002

Generation and growth rates of nonlinear distortions in a traveling wave tube.

The structure of a steady state multifrequency model of a traveling wave tube amplifier is exploited to describe the generation of intermodulation frequencies and calculate their growth rates. The model describes the evolution of Fourier coefficients of circuit and electron beam quantities and has the form of differential equations with quadratic nonlinearities. Intermodulation frequencies are sequentially generated by the quadratic nonlinearities in a series solution of the differential equations. A formula for maximum intermodulation growth rates is derived and compared to simulation results.

Journal Article↗