26th Symposium on Plasma Physics and Technology

List of abstract

Electronic effects in radiation damage simulations in metals

Radiation damage has traditionally been modelled using classical molecular dynamics, in which the role of the electrons is con�fined to describing bonding via the interatomic potential. This is generally sufficient for low radiation energies. However high energy atoms lose a signi�ficant proportion of their energy to electronic excitations, therefore a simulation of the relaxation of a metallic lattice after a high energy event requires a description of the energetic interaction between atoms and electrons. The mechanisms of inelastic collisions between electrons and ions, coupling between electrons and phonons and the di�ffusion of energy through the electronic system to the rest of the lattice become signfi�cant. We have coupled large scale MD simulations of the lattice to a continuum model for the electronic temperature evolution. Energy lost by the atoms due to elastic and inelastic electronic collisions is gained by the electronic system and evolves according to a heat di�ffusion equation. The electronic energy is coupled to the lattice via a modifi�ed Langevin thermostat, representing electron-phonon coupling. Results of the simulation of both displacement cascades and ion tracks, representing the low and high extremes of incident ion energy respectively, are presented. The eff�ect of annealing of pre-existing damage by electronic excitation is studied and the behaviour under swift heavy ion irradiation in iron and tungsten is compared. In simulations of displacement cascades, the strength of coupling between the atoms and electrons emerges as the main parameter determining residual damage. Our new methodology gives rise to reduced damage compared to traditional methods in all cases. Ion track simulations demonstrated that the relaxation dynamics, and hence the residual damage, was dependent on the magnitude and temperature dependence of the electronic thermal parameters

Joint CARE-ELAN, CARE-HHH-APD, and EUROTEV-WP3 Workshop on Electron Cloud Clearing

This report contains the Proceedings of the joint CARE-HHH-APD, CARE-ELAN, and EUROTEV-WP3 Mini-Workshop on 'Electron Cloud Clearing - Electron Cloud and Technical Consequences', "ECL2", held at CERN in Geneva, Switzerland, 1-2 March 2007). The ECL2 workshop explored novel technological remedies against electron-cloud formation in an accelerator beam pipe. A primary motivation for the workshop was the expected harmful electron-cloud effects in the upgraded LHC injectors and in future linear colliders, as well as recent beam observations in operating facilities like ANKA, CESR, KEKB, RHIC, and SPS. The solutions discussed at ECL2 included enamel-based clearing electrodes, slotted vacuum chambers, NEG coating, and grooves. Several of the proposed cures were assessed in terms of their clearing efficiency and the associated beam impedance. The workshop also reviewed new simulation tools like the 3D electron-ion build-up 'Faktor', modeling assumptions, analytical calculations, beam experiments, and laboratory measurements. Several open questions could be identified. The workshop reinforced inter-laboratory collaboration on electron-cloud suppression, and it concluded with a discussion of the next steps to be taken

Fast Magnetic Reconnection in Relativistic Laser-Plasma Interactions.

Magnetic reconnection is a fundamental plasma process involving the transfer of magnetic potential energy to plasma kinetic energy through changes in the magnetic field topology. Results are presented of experimental measurements as well as numerical modeling of relativistic magnetic reconnection driven by short-pulse, high-intensity lasers that produce relativistic plasma along with extremely strong magnetic fields. Evidence of fast magnetic reconnection was identified by the plasma's x-ray emission patterns, changes to the electron energy spectrum, optical probing techniques, and by measuring the time over which reconnection occurs, while numerical modeling suggests the process occurs within the relativistic regime wherein the magnetic energy density exceeds the electron rest mass energy density. Accessing these conditions in the laboratory may allow for further investigation to provide insight into previously inaccessible regimes relevant to space and astrophysical plasmas.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135743/1/aeraym_1.pd