A microbeam slit system for high beam currents

A new microbeam slit system for high beam currents of 10 mu A was built up to improve the brightness transport of a proton beam with a kinetic energy of up to 25MeV into the microprobe SNAKE. The new slit system features a position accuracy of less than 1 mu m under normal operating conditions and less than 2 mu m if the beam is switched on and off. The thermal management with a powerful watercooling and potential-free thermocouple feedback controlled heating cables is optimized for constant slit aperture at thermal power input of up to 250W. The transparent zone is optimized to 0.7 mu m due to the use of tungsten formed to a cylindrical surface with a radius 100mm and mechanically lapped surface to minimize small angle scattering effects and to minimize the number of ions passing the slits with low energy loss. Electrical isolation of the slit tip enables slit current monitoring, e.g. for tandem accelerator feedback control. With the ability to transport up to 10 mu A of protons with the new microslit system, the brightness transported into the microprobe was increased by a factor of 2 compared to low current injection using the old slit system.