A brush includes a substrate, a number of brush bristles, a storage bag, and a pushing element. The protective structure has at least one irregular side surface. The illuminating system andor the projection optics system comprise particle-optical lenses having lens elements common to more than one particle beam. The end wall is positioned radially inward a distance from the inner surface. The method and system includes a circuit that reduces the clock frequency for the processor system in response to thermal characteristics satisfying a pre-determined threshold that allows maximal thermal temperature limit utilization without substantially degrading processor performance.