Optimization of a Solenoid for an Electron Lens in SIS18

An electron lens - a novel instrument in accelerator physics to manipulate hadron beams with a magnetically confined electron beam - is under development at GSI, Darmstadt. It will be used to compensate the ion beam's space charge by an overlapping electron beam and therefore may help to increase the intensity of primary beams in the synchrotron SIS18 for FAIR. The main element of the lens is a solenoid with the longitudinal magnetic field of Bz = 600 mT and the requirements to the field homogeneity of ΔB/B less than ±5 × 10
^-4
relative units. The magnetic field in the solenoid will be ramped with the rate of up to 20 T/s. Acceptable geometry of the solenoid has been found by optimization of the coil parameters and the iron shield geometry. For this purpose we have combined the 2D finite element technology for the magnetic field modeling and the Nelder-Mead optimization strategy. Thorough investigation of the solenoid 3D model confirmed a quality and feasibility of the developed magnetic system.