73 research outputs found
Microwave TM010 cavities as versatile 4D electron optical elements
No full textThe realization of high quality ultrashort pulsed beams requires ultrafast time-dependent electron optics. We present derivations of closed expressions both for the longitudinal and transverse focusing powers of resonant microwave TM010 cavities. The derived expressions are validated by particle tracking simulations using realistic cavity fields. For small field amplitudes, in which case the weak lens approximation holds, the focusing powers obtained from simulations are in good agreement with the derived expressions. Furthermore, the required phase and temperature stability for synchronization of electron bunches generated by femtosecond photoemission are discussed
Revision of (sub)nanosecond pulser for IRI Van de Graaff electron accelerator aided by field propagation calculations
No full textThe shorted air line stub used for subnanosecond pulsing of the grounded-grid cathode gun structure of the IRI 3 MV Van de Graaff electron accelerator is revised. Three-dimensional high-frequency field propagation calculations provide better insight into the performance of different geometrical shapes. Effects on rise- and decay time, and ringing on the output pulses are considered. Practical possibilities for improvement are discussed. Comparison with sampling measurements on several device modifications confirms the reliability of the calculations. The calculation method is subsequently used as design aid for the construction of a 1 ns device using a quartz loaded shorted stub to fit into the geometry of the existing variable pulse length unit. Capabilities for short pulsing of the accelerator are improved and extended by application of the results obtained
Electrodynamic simulations of a photoconductively switched high voltage spark gap
No full text\u3cp\u3eWe present a full three-dimensional electrodynamic model to simulate a photoconductively switched high voltage spark gap. This model describes the electromagnetic field-propagation in a coaxial spark gap set-up, which determines the rise time of the switched pulse and reveals the influence of discontinuities, such as view ports, on the pulse shape and the rise time. Existing inductive lumped element and transmission line models, used to model laser-triggered spark gaps, are compared with our electrodynamic model. The rise time of the switched pulses in the different models does not differ significantly. In the electrodynamic simulation, a curvature of the electric field wave front is visible, resulting from the presence of non-TEM modes near the gap. Furthermore, oscillations on the output signal are revealed. These oscillations are caused by internal reflections on the inner and outer conductors. Our electrodynamic model is able to visualize the rise time evolution by monitoring the electric field-propagation in the gap region. The presence of view ports in the set-up increases the rise time at the output significantly and induces, owing to internal reflections, extra oscillations in the signal.\u3c/p\u3
RF Compression of sub-relativistic space-charge-dominated electron bunches for single-shot femtosecond electron diffraction
No full textAbstract only
Progress in 3D Space-charge Calculations in the GPT Code
No full textThe 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
Multigrid Algorithms for the Fast Calculation of Space-Charge Effects in Accelerator Design
No full textNumerical prediction of charged particle dynamics in accelerators is essential for the design and understanding of these machines. Methods to calculate the self-fields of the bunch, the so-called space-charge forces, become increasingly important as the demand for high-quality bunches increases. We report on our development of a new three-dimensional (3-D) space-charge routine in the general particle tracer (GPT) code. It scales linearly with the number of particles in terms of CPU time, allowing over a million particles to be tracked on a normal PC. The model is based on a nonequidistant multigrid Poisson solver that has been constructed to solve the electrostatic fields in the rest frame of the bunch on meshes with large aspect ratio. Theoretical and numerical investigations of the behavior of SOR relaxation and PCG method on nonequidistant grids emphasize the advantages of the multigrid algorithm with adaptive coarsening. Numerical investigations have been performed with a wide range of cylindrically shaped bunches (from very long to very short) occuring in recent applications. The application to the simulation of the TU/e DC/RF gun demonstrates the power of the new 3-D routine
An ultracold electron source as an injector for a compact SASE-FEL
No full textUltracold electron sources based on near-threshold photoionization of laser-cooled atomic gases can produce ultrashort electron pulses with a brightness potentially exceeding conventional pulsed electron sources. They are presently being developed for single shot ultrafast electron diffraction, where a bunch charge of 100 fC is sufficient. For application as an injector for x-ray free electron lasers (FEL) a larger bunch charge is generally required. Here we present preliminary calculations of an ultracold electron source operating at bunch charges up to 1 pC. We discuss the relevant bunch degradation processes that occur when the charge is increased. Using general particle tracer tracking simulations we show that bunches can be produced of sufficient quality for driving a 1 Å self amplified spontaneous emission free electron laser (SASE-FEL) at 1.3 GeV electron energy. In addition we speculate on the possibility of using the ultracold source for driving a 15 MeV SASE-FEL in Compton backscatter configuration into the quantum FEL regime
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