Beam dynamics in magnetic quadrupole triplets

The Frankfurt Neutron source at the Stern-Gerlach-Zentrum (FRANZ) will produce high intensity neutron pulses in the energy range of 1 to 500 keV at a very short repetition rate. The neutrons are gained from 7Li(p,n)7Be reactions induced by 2 MeV protons and will be used to examine the nucleosynthesis during the s-process as it occurs in stars, cross sections of neutron capture reactions as well as the behaviour of non-neutral plasmas. In the linear accelerator section, consisting of a 4-rod-radio-frequency-quadrupole and a H-type drift tube linac, the proton pulses are accelerated to 2.03 MeV. Inside the drift tube cavity a magnetic quadrupole triplet will be integrated, in order to compensate transversally defocussing effects and therefore avoid losses. Behind the linear accelerator section the proton beam ist rebunched in a 5-cell CH-rebuncher which is framed by two more quadrupole triplets. To investigate the beam dynamics inside the magnetic quadrupole triplets, various magnetostatic and particle tracking codes like CST Studio and LORASR were used to simulate the beam transport properties of the magnets and compare the individual magnetic field distributions with the ones measured at the magnet laboratory at GSI. In doing so, important aspects to be considered are the longitudinal and transversal fringe fields and the saturation effects which all possibly cause emittance growth and geometrical aberrations.