Twin screw extrusion is anticipated to meet the pellet fueling demands of tokamak fusion devices. The twin-screw design principle has been proven by a functional prototype extruder at Oak Ridge National Laboratory (ORNL); however numerical models necessary for design optimization have yet to be validated due to system complexity. Characteristic measurements of solid flow during extrusion are difficult for any extruder and are exacerbated by the cryogenic environment necessary to solidify solid hydrogen. In this paper, we first discuss current modeling efforts to establish needs for experimental measurements and then present the design and construction status of a diagnostic twin-screw extruder to address these needs. Development is underway of a mass transfer analysis that predicts volumetric efficiency and augments an existing 1st order model of extrudate temperature. These predictive models are necessary for design and operation of hydrogenic twin screw extruders for fueling tokamaks, including ITER.