Progress in 3D Space-charge Calculations in the GPT Code

The mesh-based 3D space-charge routine in the GPT (General Particle Tracer, Pulsar Physics) code scales linearly with the number of particles in terms of CPU time and allows a million particles to be tracked on a normal PC. The crucial ingredient of the routine is a non-equidistant multi-grid Poisson solver to calculate the electrostatic potential in the rest frame of the bunch. The solver has been optimized for very high and very low aspect ratio bunches present in state-of-the-art high-brightness electron accelerators. In this paper, we explore the efficiency and accuracy of the calculations as function of meshing strategy and boundary conditions

Novel electron bunch creation towards ultrafast electron diffraction

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RF Compression of sub-relativistic space-charge-dominated electron bunches for single-shot femtosecond electron diffraction

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3D Space-charge model for GPT simulations of high-brightness electron bunches

For the simulation of high-brightness electron bunches, a new 3D space-charge model is being implemented in the General Particle Tracer (GPT) code. It is based on a non-equidistant multigrid solver, allowing smooth transitions from a high to a low-aspect ratio bunch during a single run. The algorithm scales linearly in CPU time with the number of particles and the insensitivity to aspect ratio ensures that it can be used for a variety of applications. Tracking examples and field comparisons with an analytical model will be shown

Physics and Applications of Ultracold Plasmas and Rydberg Gases

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A bright ultracold atoms-based electron source

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Ultracold electron source

We propose a technique for producing electron bunches that has the potential for advancing the state-ofthe-art in brightness of pulsed electron sources by orders of magnitude. In addition, this method leads to femtosecond bunch lengths without the use of ultrafast lasers or magnetic compression. The electron source we propose is an ultracold plasma with electron temperatures down to 10 K, which can be fashioned from a cloud of laser-cooled atoms by photoionization just above threshold. Here we present results of simulations in a realistic setting, showing that an ultracold plasma has an enormous potential as a bright electron source

Granularity effects in high-brightness electron beams

Electron sources based on laser-cooling and trapping techniques are a relatively new reality in the field of charge particle accelerators. The dynamics of these sources are governed by stochastic effects, and not by the usually dominant space-charge forces. As the high-brightness field moves towards increasingly higher brightness, these stochastic effects will play an increasingly important role. In this presentation I will discuss the physics of these granularity effects and show their effect using molecular dynamics simulations with the GPT code where we track each and every particle in realistic fields and including all pair-wise interactions

Longitudinal phase-space manipulation of ellipsoidal electron bunches in realistic fields

Since the recent publication of a practical recipe to create ¿pancake¿ electron bunches which evolve into uniformly filled ellipsoids, a number of papers have addressed both an alternative method to create such ellipsoids as well as their behavior in realistic fields. So far, the focus has been on the possibilities to preserve the initial ¿thermal¿ transverse emittance. This paper addresses the linear longitudinal phase space of ellipsoidal bunches. It is shown that ellipsoidal bunches allow ballistic compression at subrelativistic energies, without the detrimental effects of nonlinear space-charge forces. This in turn eliminates the need for the large correlated energy spread normally required for longitudinal compression of relativistic particle beams, while simultaneously avoiding all problems related to magnetic compression. Furthermore, the linear space-charge forces of ellipsoidal bunches can be used to reduce the remaining energy spread even further, by carefully choosing the beam transverse size, in a process that is essentially the time-reversed process of the creation of an ellipsoid at the cathode. The feasibility of compression of ellipsoidal bunches is illustrated with a relatively simple setup, consisting of a half-cell S-band photogun and a two-cell booster compressor. Detailed GPT simulations in realistic fields predict that 100 pC ellipsoidal bunches can be ballistically compressed to 100 fs, at a transverse emittance of 0.7   ¿ with a final energy of 3.7 MeV and an energy spread of only 50 keV