Initial Commissioning Test Results of the Wendelstein 7-X Continuous Pellet Fueling System

A continuous pellet fueling system (CPFS) for use on the Wendelstein 7-X (W7-X) stellarator has been fabricated and assembled with commissioning tests completed at the Oak Ridge National Laboratory (ORNL). Continuous fueling is accomplished by cutting pellets from the cross section of a continuous solid extrusion produced by a twin-screw extruder and accelerated by a gas gun cutter mechanism. The pellets travel through a series of straight guide tubes before entering the stellarator through a curved guide tube. The CPFS has an array of diagnostics that include the extruder torque, rotation rate, and thrust. A shock and pressure sensor provide verification of proper pellet cutting and acceleration. Two ORNL-developed microwave cavity diagnostics within the injection line guide tubes provide pellet speed and relative mass measurements. For commissioning, a high-speed camera has been positioned at the base of the extruder to verify extrusion speed and quality as well as the pellet cutting process, and a third microwave cavity has been mounted after the curved guide tube to verify pellet quality and size. Maximum injection rate, pellet speed, barrel and guide tube induced erosion, and pellet survivability data have been recorded. This paper presents the laboratory experimental setup and results of these commissioning tests.