: This publication is a listing of journal articles and conference papers by Naval Research Laboratory authors for 1994. The bibliographic information is taken, primarily, from the Institute of Scientific Information database, Science Citation Index Expanded. Additional citations are generated from reprints of publications which are received in the Laboratory's Ruth H. Hooker Research Library. All references are unclassified. Citations are arranged alphabetically by author. An author index is included at the end of the citation listing. An HTML version of this publication is mounted on the Website of the Ruth H. Hooker Research Library - http://infoweb.nrl.navy.mil.

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1994 Bibliography of NRL Journal Articles and Conference Papers

A time‐dependent nonlinear analysis of a helix traveling wave tube (TWT) is presented for a configuration where an electron beam propagates through a sheath helix surrounded by a conducting wall. The effects of dielectric and vane loading are included in the formulation as is efficiency enhancement by tapering the helix pitch. Dielectric loading is described under the assumption that the gap between the helix and the wall is uniformly filled by a dielectric material. The vane‐loading model describes the insertion of an arbitrary number of vanes running the length of the helix, and the polarization of the field between the vanes is assumed to be an azimuthally symmetric transverse‐electric mode. The field is represented as a superposition of azimuthally symmetric waves in a vacuum sheath helix. An overall explicit sinusoidal variation of the form exp(ikz−iωt) is assumed (where ω denotes the angular frequency corresponding to the wave number k in the vacuum sheath helix), and the polarization and radial variation of each wave is determined by the boundary conditions in a vacuum sheath helix. The propagation of each wave in vacuo as well as the interaction of each wave with the electron beam is included by allowing the amplitudes of the waves to vary in z and t. A dynamical equation for the field amplitudes is derived analogously to Poynting’s equation, and solved in conjunction with the three‐dimensional Lorentz force equations for an ensemble of electrons. Electron beams with a both a continuous and emission‐gated pulse format are analyzed, and the model is compared with linear theory of the interaction as well as with the performance of a TWTs operated at the Naval Research Laboratory and at Northrop–Grumman Corporation.

http://oscillet.com/Articles_Files/Freund_1996.pdf

Theory of helix traveling wave tubes with dielectric and vane loading

An advanced incremental scheme for generating tunable coherent radiation in a free-electron laser has been presented: the basic concept is the use of a relativistic electron beam propagating through a magnetized dusty plasma channel where dust helicon, dust Alfven and coupled dust cyclotron-Alfven waves can play a role as a low-frequency wiggler, triggering coherent emissions. The wiggler wavelength at the sub-mm level allows one to reach the wavelength range from a few nm down to a few A with moderately relativistic electrons of kinetic energies of a few tens/hundreds of MeV. The laser gain and the effects of beam self-electric and self-magnetic fields on the gain have been estimated and compared with findings of the helical magnetic and electromagnetic wigglers in vacuum. To study the chaotic regions of the electron motion in the dusty plasma wave wiggler, a time independent Hamiltonian has been obtained. The Poincare surface of a section map has been used numerically to analyze the nonintegrable system where chaotic regions in phase-space emerge. This concept opens a path toward a new generation of synchrotron sources based on compact plasma structures.

https://iopscience.iop.org/article/10.1088/1612-2011/12/7/075002/pdf

Low-frequency wiggler modes in the free-electron laser with a dusty magnetoplasma medium

Propagation of the equilibrium electron beam in a free-electron laser with an axial guide magnetic field

A theory of self-fields in a free-electron laser with electromagnetic-wave wiggler and ion-channel guiding is presented. The equations of motion for an electron have been analyzed. This equation together with its numerical solutions shows that the first part of group I and II trajectories is unstable. The effects of self-fields on the gain for groups I and II orbits have also been investigated by deriving the gain formula and numerical calculation. A gain decrement is found due to the effects of self-fields for group I orbits, and the gain enhancement for group II orbits. The gain decrement (enhancement) arises from diamagnetic (paramagnetic) generated by the self-fields. The gain decrement (enhancement) increases by increasing the beam density.

Self-fields in a free-electron laser with electromagnetic-wave wiggler and ion-channel guiding

A model of the self‐fields associated with the charge density and current of the electron beam is incorporated into three‐dimensional nonlinear formulations of the interaction in free‐electron lasers for both planar and helical wiggler configurations. The model assumes the existence of a cylindrically symmetric electron beam with a flat‐top density profile and a uniform axial velocity, and the self‐electric and self‐magnetic fields are determined from Poisson’s equation and Ampere’s law. Diamagnetic and paramagnetic effects due the electron beam interaction with the wiggler field are neglected; hence, the model breaks down when the wiggler‐induced transverse displacement is comparable to the beam radius. The nonlinear formulations are based upon the arachne and wigglin codes, which represent slow‐time‐scale formulations for the evolution of the amplitudes and phases of a multimode superposition of vacuum waveguide modes. The electron dynamics in these codes are treated by means of the complete three‐dimen...

The nonlinear analysis of self‐field effects in free‐electron lasers

A model of the DC self-fields associated with the electron beam is incorporated into 3-dimensional nonlinear formulations of free-electron lasers. The nonlinear formulations are based upon the ARACHNE and WIGGLIN codes which are slow-time-scale formulations for the evolution of the amplitudes and phases of a multi-mode superposition of vacuum waveguide modes. The electron dynamics in these codes are treated by means of the complete 3-dimensional Lorentz force equations, and the representations for the self-fields are incorporated directly into this formulation. Results of the simulations are compared with experiments at LLNL using a planar wiggler, and at MIT and NRL which used helical wigglers. These experiments exhibited comparable space-charge depressions of Δγ self γ 0 ≈ 0.53–0.78% across the beam. The simulations are in reasonable agreement with the experiments.

H. P. Freund

Papers

The nonlinear analysis of self‐field effects in free‐electron lasers

The nonlinear analysis of self-field effects in free-electron lasers