** How to Realize
Uniform Three-Dimensional Ellipsoidal Electron Bunches**

Phys. Rev. Lett. 93, 094802 (2004)

DOI: 10.1103/PhysRevLett.93.094802

O. J. Luiten, S. B. van der Geer, M. J. de Loos, F. B. Kiewiet, and M. J. van der Wiel, TU-Eindhoven

Uniform three-dimensional ellipsoidal distributions of charge are the ultimate goal in charged particle accelerator physics because of their linear internal force fields. Such bunches remain ellipsoidal with perfectly linear position-momentum phase space correlations in any linear transport system. We present a method, based on photoemission by radially shaped femtosecond laser pulses, to actually produce such bunches.

** Design
considerations for table-top, laser-based VUV and X-ray free electron
lasers**

Appl. Phys. B. 86, 431-435 (2007)

DOI: 10.1007/s00340-006-2565-7

F. Grüner, S. Becker, U. Schramm, T. Eichner, M. Fuchs, R. Weingartner, D. Habs, J. Meyer-ter-vehn, M. Geissler, M. Ferrario, L. serafini, B. van der geer, H. backe, W. Lauth, S. Reiche,

A recent breakthrough in laser-plasma accelerators, based upon ultrashort high-intensity lasers, demonstrated the generation of quasi-monoenergetic GeV electrons. With future Petawatt lasers ultra-high beam currents of ~ 100 kA in ~ 10 fs can be expected, allowing for drastic reduction in the undulator length of free-electron-lasers (FELs). We present a discussion of the key aspects of a table-top FEL design, including energy loss and chirps induced by space-charge and wakefields. These effects become important for an optimized table-top FEL operation. A first proof-of-principle VUV case is considered as well as a table-top X-ray-FEL which may also open a brilliant light source for new methods in clinical diagnostics.

** Ultracold
Electron Source**

Phys. Rev. Lett. 95, 164801 (2005)

DOI: 10.1103/PhysRevLett.95.164801

B. J. Claessens, S. B. van der Geer, G. Taban, E. J. D. Vredenbregt, and O. J. Luiten, TU-Eindhoven

We propose a technique for producing electron bunches that has the potential for advancing the state-of-the-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.

** Radiation sources based on laser–plasma
interactions**

Philosophical Transactions of the Royal Society A: Volume 364, Number
1840, (2006), p. 689 - 710

DOI: 10.1098/rsta.2005.1732

D.A. Jaroszynski, R. Bingham, E. Brunetti, B. Ersfeld, J. Gallacher, B. van der Geer, R. Issac, S.P. Jamison, D. Jones, M. de Loos, A. Lyachev, V. Pavlov, A. Reitsma, Y. Saveliev, G. Vieux, S.M. Wiggins, University of Strathclyde

Plasma waves excited by intense laser beams can be harnessed to produce femtosecond duration bunches of electrons with relativistic energies. The very large electrostatic forces of plasma density wakes trailing behind an intense laser pulse provide field potentials capable of accelerating charged particles to high energies over very short distances, as high as 1GeV in a few millimetres. The short length scale of plasma waves provides a means of developing very compact high-energy accelerators, which could form the basis of compact next-generation light sources with unique properties. Tuneable X-ray radiation and particle pulses with durations of the order of or less than 5fs should be possible and would be useful for probing matter on unprecedented time and spatial scales. If developed to fruition this revolutionary technology could reduce the size and cost of light sources by three orders of magnitude and, therefore, provide powerful new tools to a large scientific community. We will discuss how a laser-driven plasma wakefield accelerator can be used to produce radiation with unique characteristics over a very large spectral range.

** Electron source concept for
single-shot sub-100 fs electron diffraction in the 100 keV range**

Journal of Applied Physics 102, 093501 (2007)

DOI: 10.1063/1.2801027

T. van Oudheusden, E. F. de Jong, S. B. van der Geer, W. P. E. M. Op ’t Root, and O. J. Luiten, and B. J. Siwick

We present a method for producing sub-100 fs electron bunches that are suitable for single-shot ultrafast electron diffraction experiments in the 100 keV energy range. A combination of analytical estimates and state-of-the-art particle tracking simulations show that it is possible to create 100 keV, 0.1 pC, 30 fs electron bunches with a spot size smaller than 500 µm and a transverse coherence length of 3 nm, using established technologies in a table-top setup. The system operates in the space-charge dominated regime to produce energy-correlated bunches that are recompressed by radio-frequency techniques. With this approach we overcome the Coulomb expansion of the bunch, providing a single-shot, ultrafast electron diffraction source concept.

** Multigrid algorithms
for the fast calculation of space-charge effects in accelerator design**

IEEE Transactions on magnetics, Vol 40, No. 2, (2004), p. 714.

DOI: 10.1109/TMAG.2004.825415

Gisela Pöplau, Ursula van Rienen, Bas van der Geer, and Marieke de Loos

Numerical 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.

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

Phys. Rev. ST Accel. Beams 9, 044203 (2006)

DOI: 10.1103/PhysRevSTAB.9.044203

S. B. van der Geer, M. J. de Loos, T. van Oudheusden, W. P. E. M. op ’t Root, M. J. van der Wiel, and O. J. Luiten, Eindhoven University of Technology

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 μm, with a final energy of 3.7 MeV and an energy spread of only 50 keV.