A Fast and Universal Vlasov Solver for Beam Dynamics Simulations in 3D
The Vlasov equation can describe the evolution of a particle density under the effects of electromagnetic fields and thus it is possible to describe the evolution of a charged particle beam within an accelerator beam line. The Vlasov equation forms a partial differential equation in a 6D phase space witch renders it very expensive if it is solved via classical methods. A more efficient approach consists in representing the particle distribution function by a discrete set of characteristic moments. For each moment a time evolution equation can be stated. These ordinary differential equations can then be integrated efficiently by means of numerical methods if all acting forces together with a proper initial condition are given. The beam dynamics simulation tool V-Code has been implemented at TEMF on the basis of the moment approach. In this paper the numerical model, main features and designated use cases of the V-Code will be presented.
Beam tomography research at Daresbury Laboratory
Beam tomography research at Daresbury Laboratory has focussed on the development of normalised phase space techniques—starting with the idea of sampling tomographic projections at equal phase advances. This idea has influenced the design and operation of the tomography sections at the Photo Injector Test Facility at Zeuthen (PITZ) and at the Accelerator and Lasers in Combined Experiments (ALICE) at Daresbury. We have studied the feasibility of using normalised phase space to measure the effect of space charge. Quadrupole scan measurements are carried out at two different parts of a beamline. Reconstructions at the same location give results that are clearly rotated with respect to each other in normalised phase space. We are able to show that a significant part of this rotation can be attributed to the effect of space charge. We show how the normalised phase space technique can be used to increase the reliability of the Maximum Entropy Technique (MENT). While MENT is known for its ability to work with just a few projections, the accuracy of its reconstructions has seldom been questioned. We show that for typical phase space distributions, MENT could produce results that look quite different from the original. We demonstrate that a normalised phase space technique could give results that are closer to the actual distribution. We also present simpler ways of deriving the phase space tomography formalism and the Maximum Entropy Technique.
Resonant Auger decay study of C1s -> pi* core-excited OCS
The present work aims at characterizing short-lived C1s((-1)) pi*((1)) core-excited states of the OCS molecule based on the analysis of the vibrational fine structure and lineshape profiles of the high-resolution resonant Auger decay spectra recorded at the excitation energies along the C1s -> pi* resonance in the binding energy region 15-19eV. Very different behavior in terms of lineshape and resonant enhancement is observed for the (A) over tilde, (B) over tilde and (C) over tilde final states. This is explained by (1) the variation in the C-O bond lengths for the states involved in the electronic relaxation and (2) different contributions in terms of Mulliken population to the molecular orbitals determining the electronic character of the corresponding states. Since the final-state geometries are known from a number of previous experiments and ab initio calculations, the geometry of the C1s((-1)) pi*((1)) intermediate states can be predicted in analogy with e.g. the N-2, CO2 and N2O molecules. (C) 2009 Elsevier B.V. All rights reserved. (Less)