Development of hollow electron beams for proton and ion collimation

Magnetically confined hollow electron beams for controlled halo removal in high-energy colliders such as the Tevatron or the LHC may extend traditional collimation systems beyond the intensity limits imposed by tolerable material damage. They may also improve collimation performance by suppressing loss spikes due to beam jitter and by increasing capture efficiency. A hollow electron gun was designed and built. Its performance and stability were measured at the Fermilab test stand. The gun will be installed in one of the existing Tevatron electron lenses for preliminary tests of the hollow-beam collimator concept, addressing critical issues such as alignment and instabilities of the overlapping proton and electron beams.Comment: 3 pp. 1st International Particle Accelerator Conference: IPAC'10, 23-28 May 2010: Kyoto, Japa

Hollow Electron Beam Collimator: R&D Status Report

Magnetically confined hollow electron beams for controlled halo removal in high-energy colliders such as the Tevatron or the LHC may extend traditional collimation systems beyond the intensity limits imposed by tolerable material damage. They may also improve collimation performance by suppressing loss spikes due to beam jitter and by increasing capture efficiency. A hollow electron gun was designed and built. Its performance and stability were measured at the Fermilab test stand. The gun will be installed in one of the existing Tevatron electron lenses for preliminary tests of the hollow-beam collimator concept, addressing critical issues such as alignment and instabilities of the overlapping proton and electron beams.Comment: 5 pp. 14th Advanced Accelerator Concepts Workshop 13-19 Jun 2010: Annapolis, Marylan

Slow relaxation in the two dimensional electron plasma under the strong magnetic field

We study slow relaxation processes in the point vortex model for the two-dimensional pure electron plasma under the strong magnetic field. By numerical simulations, it is shown that, from an initial state, the system undergoes the fast relaxation to a quasi-stationary state, and then goes through the slow relaxation to reach a final state. From analysis of simulation data, we find (i) the time scale of the slow relaxation increases linearly to the number of electrons if it is measured by the unit of the bulk rotation time, (ii) during the slow relaxation process, each electron undergoes an superdiffusive motion, and (iii) the superdiffusive motion can be regarded as the Levy flight, whose step size distribution is of the power law. The time scale that each electron diffuses over the system size turns out to be much shorter than that of the slow relaxation, which suggests that the correlation among the superdiffusive trajectories is important in the slow relaxation process.Comment: 11pages, 19 figures. Submitted to J. Phys. Soc. Jp

Diagnosing the Velocity-Space Separatrix of Trapped Particle Modes

Trapped particle modes in pure electron plasmas are similar to modes in neutral plasmas and exhibit damping due to velocity diffusion across the separatrix between trapped and untrapped particles, as commonly occurs in neutral plasmas. Applied rf voltages cause resonant perturbation of particle velocities near the separatrix, giving a greatly enhanced mode damping. This diagnostic technique can determine the velocity-space separatrices for either electrostatic or magnetic trapping, or determine the particle distribution function along the separatrix

Equilibrium of charged plasmas with weak axisymmetric magnetic perturbations

The effect of weak axisymmetric magnetic and/or electrostatic perturbations on the equilibrium of a non-neutral plasma in a Malmberg-Penning trap is analyzed. A semi-analytic solution for the potential variations inside the trap is found in a paraxial limit of the perturbations for the case of global thermal equilibrium. The fraction of magnetically and electrostatically trapped particles is calculated for a bi-Maxwellian distribution function

Fast measurement of picoamp plasma flows using trapped electron clouds

We demonstrate that magnetized electron clouds can diagnose picoamp ion currents (or equivalent neutralized plasma flows) on a kHz time scale. This could be used to measure the dynamics of neutral plasma losses to the walls, e.g., along divertor field lines. In essence, a current passing through an electron cloud in a Penning trap transfers angular momentum to the cloud, driving an easily measured orbital "diocotron" instability (from ion currents) or orbital damping (from electron currents). With neutralized plasma flows, the predominant effect is from the lower velocity (i.e., higher density) charge species. Experiments with electron, ion, and neutralized currents have fully characterized this collective (collisionless) electrostatic interaction, and demonstrate the picoamp and kHz resolutions. (C) 2004 American Institute of Physics

Equilibrium of non-neutral plasmas with weak axisymmetric magnetic perturbations

The effect of weak external axisymmetric magnetic and electrostatic perturbations on the equilibrium of a non-neutral plasma confined in a Malmberg-Penning trap is analyzed. A semi-analytic solution for the potential variations inside the trap is found in a paraxial limit of the perturbations for the case of global thermal equilibrium. The populations of magnetically and electrostatically trapped particles created by the external perturbations are characterized, and their fractions are calculated explicitly for a bi-Maxwellian distribution function. 2D numerical simulations of the thermal equilibrium of a pure electron plasma in the presence of axial magnetic field perturbations are performed to check the limits of validity of the analytical 1D approximation