Theory of the ion-channel laser

Technical Report · Sat Sep 01 00:00:00 EDT 1990

DOI:https://doi.org/10.2172/6295861· OSTI ID:6295861

Whittum, D H

A relativistic electron beam propagating through a plasma in the ion-focussed regime exhibits an electromagnetic instability with peak growth rate near a resonant frequency {omega}{approximately}2 {gamma}{sup 2} {omega}{beta}, where {gamma} is the Lorentz factor and {omega}{beta} is the betatron frequency. The physical basis for this instability is that an ensemble of relativistic simple harmonic oscillators, weakly driven by an electromagnetic wave, will lose energy to the wave through axial bunching. This bunching'' corresponds to the development of an rf component in the beam current, and a coherent centroid oscillation. The subject of this thesis is the theory of a laser capitalizing on this electromagnetic instability. A historical perspective is offered. The basic features of relativistic electron beam propagation in the ion-focussed regime are reviewed. The ion-channel laser (ICL) instability is explored theoretically through an eikonal formalism, analgous to the KMR'' formalism for the free-electron laser (FEL). The dispersion relation is derived, and the dependence of growth rate on three key parameters is explored. Finite temperature effects are assessed. From this work it is found that the typical gain length for amplification is longer than the Rayleigh length and we go on to consider three mechanisms which will tend to guide waveguide. First, we consider the effect of the ion channel as a dielectric waveguide. We consider next the use of a conducting waveguide, appropriate for a microwave amplifier. Finally, we examine a form of optical guiding'' analgous to that found in the FEL. The eikonal formalism is used to model numerically the instability through and beyond saturation. Results are compared with the numerical simulation of the full equations of motion, and with the analytic scalings. The analytical requirement on detuning spread is confirmed.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: DOE/ER
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 6295861
• Report Number(s): LBL-29720; ON: DE91007643; TRN: 91-004665
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

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EQUATIONS OF MOTION
NUMERICAL SOLUTION
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