• S.B. van der Geer
  Pulsar Physics, Eindhoven
• G.J.H. Brussaard, O.J. Luiten, W.P.E.M. Op 't Root, M.J. de Loos, W. van Dijk, W.J. van Hemmen, S.B. van der Geer
  TUE, Eindhoven
• W. Knulst, M.J.W. Vermeulen
  Delft University of Technology, Opto-electronic Section, Delft

Three different S-band rf-photoguns have been constructed by Eindhoven University of Technology in the Netherlands: A 1.5-cell, a 100 Hz 1.6-cell, and a 2.6-cell. They share a design concept that differs from the ‘standard’ BNL-gun in many aspects: Individual cells are clamped and not brazed saving valuable manufacturing time and allowing damaged parts to be replaced individually. The inner geometry employs axial incoupling, inspired by DESY, to eliminate any non-cylindrically symmetric modes. Elliptical irises, identical to a 2.6-cell design of Strathclyde University, reduce the maximum field on the irises and thereby reduce electrical breakdown problems. The manufacturing process uses single-point diamond turning based on a micrometer-precise design. The overall precision is such that the clamped cavities are spot-on resonance and have near-perfect field balance without the need for any post-production tuning. Operational performance of the three Dutch rf-photoguns will be presented.

• S.B. van der Geer, B. Fleskens, O.J. Luiten, M.P. Reijnders, G. Taban, E.J.D. Vredenbregt
  TUE, Eindhoven
• S.B. van der Geer
  Pulsar Physics, Eindhoven

Ultrafast electron diffraction (UED) enables single-shot studies of structural dynamics at atomic length and time scales, i.e. 0.1 nm and 0.1 ps. At present UED experiments are based on femtosecond laser photoemission from solid state cathodes. We propose a new type of electron source, based on near-threshold photoionization of a laser-cooled and trapped atomic gas. The electron temperature of these sources can be as low as 10 K. This implies an increase in brightness by orders of magnitude and enables single-shot studies of, e.g., biomolecular samples. In this contribution we numerically investigate the performance of a laser-cooled electron source by GPT tracking simulations with realistic fields and all pairwise Coulomb interactions.

• M.J. de Loos, O.J. Luiten
  TUE, Eindhoven
• M.J. de Loos, S.B. van der Geer
  Pulsar Physics, Eindhoven

The General Particle Tracer (GPT) code is a well established package for the design of charged particle accelerators and beam lines. A crucial component of this code is the calculation of Coulomb interactions. In this contribution we present two different numerical algorithms for the calculation of these particle-particle effects: The standard Particle-In-Cell (PIC) method and a Barnes-Hut (B&H) treecode approach. The PIC method is fast and reliable, but it does not include binary interactions. The method is therefore inapplicable when disorder induced heating plays a role, for example in electron microscopes and focused ion beams. The Barnes-Hut method, borrowed from the astrophysics community, calculates all pair wise interactions in an efficient manner. This approach covers all Coulomb effects, but it is potentially much slower. A realistic test case is presented highlighting the strengths and weaknesses of both approaches.