Current research into utility-scale renewable energy includes studies in the feasibility of large-scale solar power collectors. This work investigated the conditions under which one achieves sub-100kW/m2 flux on a tower receiver with 1000kW/m2 aperture flux and other realistic receiver and heliostat field parameters. Specifically, this thesis focused on the Solar Flux behavior on narrow channels for a Near Black Body (NBB) particle receiver. Three different geometric cavity variations were developed and studied. MATLAB code was developed for post-processing output-data from proprietary, ray-tracing programs from the National Renewable Energy Laboratory (NREL) i.e. SOLTRACE and SOLARPILOT. Results were analyzed and used for the optimization of solar flux spread, thereby minimizing thermal gradients. We conclude that cavity-based CSP tower-receivers will likely require a range of material reflectivity other properties and heat transfer mechanisms in order to achieve realistic flux-uniformity and avoid critical thermal fatigue failures. Additionally, results demonstrate that cavity receivers with realistic heliostat-field to cavity aperture and depth ratios will benefit and enable the use of particle based heat transfer mediums. Our initial findings lead us to conclude that combinations of heat pipe, heat sink and other heat transfer technologies can be incorporated with large volumetric particle flows across a cavity receivers increased surface areas.