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[en] Beyond the 12 GeV upgrade at the Jefferson Lab a Medium Energy Electron-Ion Collider (MEIC) has been considered. In order to achieve the desired high luminosities at the Interaction Points (IP), the use of crabbing cavities is under study. In this work, we will present to-date designs of superconducting cavities, considered for crabbing both ion and electron bunches. A discussion of properties such as peak surface fields and higher-order mode separation will be presented. Keywords: super conducting, deflecting cavity, crab cavity.
[en] It is studied the penetration of an electron beam in an ionizable medium by means of a generalized kinetic equation. This equation is related to elastic collisions, processes of creation and destruction of particles. By integrating numerically the transport equation, it can be evaluated the relative effects of all the processes involved in the evolution of the system. (A.C.A.S.)
[pt]Estuda-se a penetracao de um feixe de eletron em um meio ionizavel, atraves da equacao cinetica generalizada. Esta equacao abrange as condicoes elasticas e os processos de formacao e destruicao de particulas. Integra-se numericamente a equacao de transporte, avaliando o efeito relativo dos processos envolvidos com a evolucao do sistema. (C.G.C.)
[en] The present work has contributed in new ways to the field of slow ion induced electron emission. First, measurements of the total electron yield γ for impact of slow singly and multiply charged ions on atomically clean polycrystalline gold and graphite have been made. The respective yields were determined by current measurements and measurements of the electron number statistics. A new mechanism for kinetic emission (KE) below the so called 'classical threshold' was found and discussed. For a given ion species and impact velocity a slight decrease of the yields was found for ion charge state q = 1 toward 3, but no significant differences in KE yields for higher q values. Comparison of the results from gold and graphite showed overall similar behavior, but for C+ a relatively strong difference was observed and ascribed to more effective electron promotion in the C-C- than in the C-Au system. Secondly, for the very specific system H0 on LiF we investigated single electron excitation processes under grazing incidence conditions. In this way long-range interactions of hydrogen atoms with the ionic crystal surface could be probed. Position- and velocity-dependent electron production rates were found which indicate that an electron promotion mechanism is responsible for the observed electron emission. Thirdly, in order to investigate the importance of plasmon excitation and -decay in slow ion induced electron emission, measurements of electron energy distributions from impact of singly and doubly charged ions on poly- and monocrystalline aluminum surfaces were performed. From the results we conclude that direct plasmon excitation by slow ions occurs due to the potential energy of the projectile in a quasi-resonant fashion. The highest relative plasmon intensities were found for impact of 5 keV Ne+ on Al(111) with 5 % of the total yield. For impact of H + and H2+ characteristical differences were observed for Al(111) and polycrystalline aluminum. We show that structures in the spectrum for monocrystalline aluminum arise from diffraction of ejected electrons instead of plasmon excitation as previously assumed. (author)
[en] According to analytical calculations of the ion collision operator, the ion-electron collision terms could be larger than the ion-ion collision terms. In the previous work [J.-Y. Ji and E. D. Held, Phys. Plasmas 20, 042114 (2013)], the ion-electron collision effects are diminished by the ion temperature change terms introduced from unlikely assumptions. In this work, the high-collisionality closures for ions are calculated without the temperature change terms. The ion-electron collision terms significantly modify existing closure coefficients
[en] General theoretical methods for the calculation of indirect processes in the electron impact ionization of atomic ions are reviewed. Theory is compared with the results of recent crossed-beams experiments for several atomic ions. 35 refs.; 10 figs
[en] We point out that Bely's approximation for exchange in excitation cross sections by electronic collisions is equivalent to considering a contact interaction between free and bound electrons. This allows us to obtain the corresponding formula for relativistic wavefunctions and for many electron atoms, and to discuss the quality of the approximation
[en] The problem of the diffusion of an electron on an ion is examined in the framework of Louis de Broglie's double-solution theory. The solution we got is shown to disagree with experiment because of the persistency of the incoming wave. We suggest to start this study again with a wave-packet of finite length
[fr]Le probleme de la diffusion d'un electron par un ion est examine dans le cadre de la theorie du guidage. La solution obtenue n'est pas conforme a l'experience par suite de la persistance de l'onde incidente. Il conviendrait de reprendre l'etude a partir d'un paquet d'ondes initiales de largeur finie
[en] Complete text of publication follows. An intense laser pulse interacting with a thin foil produces separate bunches of high energy electrons and ions. At ultra-high intensities the energies of the accelerated particles are way above the threshold for the electron-positron pair production in the electron-ion collisions. The problem of laser induced pair production in the interaction with a foil received recently some attention, as there are hopes this might become a practical and prolific source of positrons. In this note we consider the problem of laser-induced positron production in a setting with a thin foil of low-Z material, as is often the case in the targets prepared primarily for the study of particle acceleration process. Our motivation is that the positron signal is an important complement of the electron and ion signals in the laser-foil interaction and therefore should be thoroughly studied. Additionally, the phase space distribution of the produced positrons could carry important information on the details of laser-plasma interaction within the target, shedding additional light on the fine details of the particle acceleration process. As a first step we consider the case of circularly polarized pulse, incident on a thin (1-50 μm) target of low Z fully ionized plasma. To estimate the positron production we solve numerically the equations of motion for collisionless plasma in one spatial dimension. We assume for simplicity that initially the plasma is quiescent and take the advantage of the fact that translational energies of electrons and ions accelerated by the laser pulse are typically much larger than any thermal energies. We provide estimates which in principle could be verified in the laser acceleration experiments.
[en] This report shows our progress in crab crossing consideration for future electron-ion collider envisioned at JLab. In this design phase, we are evaluating two crabbing schemes viz., the deflecting and dispersive. The mathematical formulations and lattice design for these schemes are discussed in this paper. Numerical simulations involving particle tracking through a realistic deflecting RF cavity and optics illustrate the desired crab tilt of 25 mrad for 1.35 MV. Evolution of beam propagation are shown which provides the physical insight of the crabbing phenomenon.
[en] Electron impact collisions with ground-state ions in a low-density plasma may cause ionization either by direct ejection of an electron from the ion, or by excitation of an inner-subshell electron to an autoionizing level. We investigate the importance of the indirect process in sodium-like Fe XVI by means of detailed calculations of excitation cross sections and of branching ratios for autoionization versus radiative decay; the estimated accuracy is about 20%. We find that radiative decay reduces the autoionization rate (at kT=300--500 eV) to only about 52% of the excitation rate; even so, the indirect ionization rate is about 1.4--1.6 times the direct ionization rate in this temperature range. The relative importance of indirect to direct ionization is approximately as great for Na-like Mo XXXII as for Fe XVI, but should be much smaller for most nonalkali-like ions except Cu-like, Zn-like, and perhaps Ga-like ions