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electromagnetic-fields

 
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TUP94 Parallel Particle in Cell Computation of an Electron Gun with GdfidL gun, acceleration, scattering, electron 498
 
  • W. Bruns
    TU Berlin TET, Berlin
  The paper describes an efficient algorithm to integrate the equations of a fast moving charge cloud of small size in a large electron gun. Particle in cell computations of a realistic electron gun is challenging due to the large discrepancy between the size of the cavity and the size of the cloud. A fine grid must be used to resolve the small volume of the charge, with a grid spacing in the order of 0.1 mm. The cavity has extensions of about 100 mm. Therefore one has to deal with about 1000 million gridcells. Such a large grid is handled best with parallel systems. Each node of the parallel system computes the electromagnetic field in its subvolume. As the extension of the charge keeps being small during the flight, at each timestep the charged particles will be located in only a few subvolumes of the nodes of the parallel system. This would lead to a strong load imbalance, if the particle related computations for each particle would be performed by the node where the particle is in. GdfidL instead spreads the data of all particle over all processors, which perform the particle related computations, and send back the results to the processors where the particles are in.  
 
THP43 Reduction of RF Power Loss Caused by Skin Effect vacuum, simulation 700
 
  • Y. Iwashita
    Kyoto ICR, Kyoto
  RF current flows only on a metal surface with very thin skin depth, which decreases with RF frequency. Thus the surface resistance increases with the frequency. Because the skin depth also decreases when the metal conductivity increases, the improvement of the conductivity does not contribute much; it is only an inverse proportion to the square root of the conductivity. Recently, it is shown that such a power loss can be reduced on a dielectric cavity with thin conductor layers on the surface, where the layers are thinner than the skin depth. Some possibilities to implement the idea and to extend the application to general cavities and transmission lines will be discussed.  
 
THP55 Electromagnetic Design of New RF Power Couplers for the S-DALINAC electron, emittance, simulation, linac 736
 
  • M. Kunze, M. Brunken, H.-D. Gräf, W.F.O. Müller, A. Richter, T. Weiland
    TU Darmstadt, Darmstadt
  New rf power couplers for the Superconducting Darmstadt Linear Accelerator (S-DALINAC) injector have to be designed to transfer rf power of up to 2 kW to the electron beam. This allows injector operation at beam currents from 0.15 mA to 0.2 mA and electron energies up to 14 MeV. The new couplers should possibly provide a external Q of 5·106. The transverse kick should be as small as possible. The asymmetric field distribution of the couplers causes emittance growth of the electron beam and therefore the transverse kick has to be minimized. Electromagnetic simulations are applied to investigate different coupler designs and to localize possible problems at an early stage. Cavity external Q and transverse kick can be calculated from 3D electromagnetic eigenmode solutions. The present coaxial-coaxial input couplers at the S-DALINAC are limited to power operation below 500 W under full reflection. In order to reach power operation up to 2 kW a realizations of a low-kick waveguide coupler for the S-DALINAC injector is presented, namely a twin-waveguide coupler.  
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