Lifetime reduction due to insertion devices at BESSY II

After closing insertion devices at BESSY II to smallest gaps beside appearance of a vertical tune-shift due to the natural focusing of the IDs, it is observed that beam lifetime is considerably reduced, up to 30 %. The reduction neither depends on machine tune nor on the settings of the four BESSY II harmonic sextupole circuits. Here measurements and analytical results to explain and cure this effect are presented.