Xavier Nuel Gavaldà awarded PhD degree

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Xavier defended successfully the PhD of the University of Paris-Saclay on September 6 2016.

The thesis was hosted in Synchrotron SOLEIL and it was dedicated to the optimization of the nonlinear beam dynamics of synchrotron radiation light sources using Multi-Objective Genetic Algorithms (MOGA-ELEGANT). In the first part the ELEGANT code was benchmarked against TRACY3; then MOGA was tuned and used to find the best settings of quadrupole and sextupole magnets in order to maximize the dynamic and momentum apertures, strongly related to the Touschek lifetime and the injection efficiency respectively. Solutions obtained after one month of computation in the high level computational cluster of SOLEIL using 200 CPUs were analyzed. The improvement of the Touschek lifetime obtained with MOGA was confirmed by the beam-based experiments. The beam lifetime of the SOLEIL storage ring was increased by 40–50 % while keeping the 95% injection efficiency.

The second part of the PhD work was devoted to study experimentally the beam lifetime of the SOLEIL storage ring to improve the understanding of the beam lifetime and its contributions: the Touschek and gas lifetimes. The beam lifetime was measured in function of important parameters as coupling, horizontal and vertical scrapers, and bunch current. The experimental results were compared with the simulated ones. The composition of the residual gas and the local pressure along the entire machine vary significantly between the arcs and the in-vacuum insertion devices: new effective atomic numbers were obtained. This type of measurement remains difficult to analyze without a large error margin; in-vacuum insertions have a dominant contribution. The shape of the experimental curves is closed to the expected ones and compatible with an effective atomic number of about 7.

Xavier would like to thank the support received of oPAC during his work at Synchrotron SOLEIL.

The thesis is available here: http://www.theses.fr/2016SACLS205



Optimized solutions of the SOLEIL2013 storage ring lattice obtained by MOGA-ELEGANT after 1 month of computation using 200 CPUs in terms of area of dynamic aperture and Touschek lifetime. The red point is the SOLEIL2013 lattice called starting point and the cyan points with ID numbers are points of the Pareto-optimal front. The solutions chosen for experiments are highlighted in green (#56), magenta (#37292) and orange (#43370). The black points are the solutions dominated by the Pareto-optimal front. 6D-tracking parameters: 2.665 MV of RF-voltage and 1,000 of turns including the synchrotron radiation and the radiation damping for the off-momentum acceptance calculation.