New initiatives for producing high current electron accelerators

New classes of compact electron accelerators able to deliver multi-kiloamperes of pulsed 10-50 MeV electron beams are being studied. One class is based upon rf linac technology with dielectric-filled cavities. For materials with {epsilon}/{epsilon}{sub o}>>1, the greatly increased energy storage permits high current operation. The second type is a high energy injected betatron. Circulating current limits scale as {Beta}{sup 2}{gamma}{sup 3}

Cross helicity and turbulent magnetic diffusivity in the solar convection zone

In a density-stratified turbulent medium the cross helicity is considered as a result of the interaction of the velocity fluctuations and a large-scale magnetic field. By means of a quasilinear theory and by numerical simulations we find the cross helicity and the mean vertical magnetic field anti-correlated. In the high-conductivity limit the ratio of the helicity and the mean magnetic field equals the ratio of the magnetic eddy diffusivity and the (known) density scale height. The result can be used to predict that the cross helicity at the solar surface exceeds the value of 1 Gauss km/s. Its sign is anti-correlated with that of the radial mean magnetic field. Alternatively, we can use our result to determine the value of the turbulent magnetic diffusivity from observations of the cross helicity.Comment: 9 pages, 2 figures, submitted to Solar Physic

A water-filled radio frequency accelerating cavity

This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The objective of this project was to study water-filled resonant cavities as a high-energy density source to drive high-current accelerator configurations. Basic considerations lead to the expectation that a dielectric-filled cavity should be able to store up to e/e{sub o} as much energy as a vacuum one with the same dimensions and thus be capable of accelerating a proportionately larger amount of charge before cavity depletion occurs. During this project, we confirmed that water-filled cavities with e/e{sub o} = 60-80 did indeed behave with the expected characteristics, in terms of resonant TM modes and cavity Q. We accomplished this result with numerical cavity eigenvalue codes; fully electromagnetic, two-dimensional, particle-in-cell codes; and, most significantly, with scaled experiments performed in water-filled aluminum cavities. The low-power experiments showed excellent agreement with the numerical results. Simulations of the high-field, high-current mode of operation indicated that charged-particle loss on the dielectric windows, which separate the cavity from the beamline, must be carefully controlled to avoid significant distortion of the axial fields

Cherenkov wakefield accelerators: Rippled waveguides

The properties of using periodically rippled waveguides as wakefield accelerators are investigated. An analysis is performed in the ultrarelativistic limit which accurately predicts the amplitude, wavelength of the wakefield, and their dependences on waveguide and drive beam parameters. These devices are found to have the properties that the synchronous transverse wake vanishes, and the accelerating field is independent of the radial position in the drift tube and independent of the radial profile of the drive beam current. The effects of the nonsynchronous wakefields are discussed. Also, particle-in-cell simulations are performed which agree with the analysis and reveal self-consistent and collective effects in particle acceleration. 20 refs., 2 figs

Catalogue des outils d'aide a la decision dans le domaine de l'energie pour les collectivites locales

Available from INIST (FR), Document Supply Service, under shelf-number : RP 400 (2202) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEAgence de l'Environnement et de la Maitrise de l'Energie (ADEME), 75 - Paris (France)FRFranc