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In synchrotrons operated with intermediate charge state heavy ion beams, intensity dependent beam losses have been observed. The origin of these losses is the change of charge state of the beam ions at collisions with residual gas atoms. The resulting m/q deviation from the reference beam ion leads to modified trajectories in dispersive elements, which finally results in beam loss. At the impact on the beam pipe, gas molecules are released by ion stimulated desorption which increase the vacuum pressure locally. In turn, this pressure rise will enhance the charge change- and particle loss process and finally cause significant beam loss within a very short time. In order to suppress and control the gas desorption process, a dedicated ion catcher system incorporating NEG coated surfaces and low-desorption rate materials has been developed and two prototypes were installed in SIS18. The design of the scraper and measured effect on the dynamic residual gas pressure are presented.
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