LA³NET results in NIMA – selection of abstracts II

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‘Electron beam final focus system for Thomson scattering at ELBE’, J.M. Krämer, M. Budde, F. Bødker, A. Irman, A. Jochmann, J.P. Kristensen, U. Lehnert, P. Michel, U. Schramm, Nucl. Instr. Meth. A (2015), doi:10.1016/j.nima.2015.10.067


The design of an electron beam final focus system (FFS) aiming for high-flux laser-Thomson backscattering X-ray sources at ELBE is presented. A telescope system consisting of four permanent magnet based quadrupoles was found to have significantly less chromatic aberrations than a quadrupole doublet or triplet as commonly used. Focusing properties like the position of the focal plane and the spot size are retained for electron beam energies between 20 and 30 MeV by adjusting the position of the quadrupoles individually on a motorized stage. The desired ultra-short electron bunches require an increased relative energy spread up to a few percent and, thus, second order chromatic effects must be taken into account. We also present the design and test results of the permanent magnet quadrupoles. Adjustable shunts allow for correction of the field strength and compensation of deviations in the permanent magnet material. For a beam emittance of 13 mm mrad, we predict focal spot sizes of about 40 μm (rms) and divergences of about 10 mrad using the FFS.

‘Coulomb field strength measurement by electro-optic spectral decoding system at the CALIFES beam line’, R. Pan, S.P. Jamison, T. Lefevre, W.A. Gillespie, Nucl. Instr. Meth. A (2016), doi:10.1016/j.nima.2016.03.043


Electro-optic (EO) techniques are increasingly used for longitudinal bunch profile measurements. A bunch profile monitor, based on electro-optic spectral decoding (EOSD), has been developed and demonstrated on the CALIFES beam line at CERN. The EO response is analysed using a frequency domain description, and two methods for extraction of absolute Coulomb field strengths from the electron bunch are demonstrated. Measurements at field strengths up to 1.3 MV/m agree with the expectation based on independent charge measurements.