A charged particle apparatus, with multiple electrically conducting semispheric grid electrodes, the grid electrodes mounted in a dielectric mounting ring, with hidden areas or regions to maintain electrical isolation between the grid electrodes as sputter deposits form on the grid electrodes and mounting ring. The grid electrodes are mounted to the mounting ring with slots and fastening pins that allow sliding thermal expansion and contraction between the grid electrodes and mounting ring while substantially maintaining alignment of grid openings and spacing between the grid electrodes. Asymmetric fastening pins facilitate the sliding thermal expansion while restraining the grid electrodes. Electrical contactors supply and maintain electrical potentials of the grid electrodes with spring loaded sliding contacts, without substantially affecting the thermal characteristics of the grid electrodes.