The geometric effects of plasma processing tools on the ion bombardment uniformity are studied through a plasma model that employs the first two and three moments of the Boltzmann equation for ions and electrons, respectively. The reactor considered is a parallel plate rf diode enclosed with insulators. The governing equations coupled with Poisson's equation are self-consistently solved using a simplified 4(th) order accurate ENO scheme which determines the choice of stencils depending only on the characteristic direction. Reactor geometries are varied so as to improve the ion bombardment uniformity on the wafer while operating conditions are fixed. Two dimensional simulation results indicate that uniformity of ion bombardment impinging on the wafer can be improved by using a thicker insulating sidewall due to its higher impedance to rf currents. A longer electrode and a larger reactor diameter also improve the uniformity because sudden changes of electrical properties at the interface between electrode and insulator or between the bulk and sheath regions, can be located away from the wafer edge. These results demonstrate that plasma reactors can be more carefully designed to obtain a better reactor performance through multidimensional simulations.