A repetitive two-stage gas gun with porous cell cryostat pellet generator for continuous high-speed fuelling

In order to respond to the next generation Tokamak need, PELIN Laboratory at Saint Petersburg, CEA-DRFC at Cadarache and CEA-SBT at Grenoble started in 2000 a tripartite collaboration to promote new pellet injector technologies. The aim was to merge the laboratories knowledge to provide pellet injectors able to deliver pellets, either at low velocities (0.2–1 km/s) and high frequencies (up to 20 Hz) or at high velocities (>3 km/s) and low frequency (0.1 Hz) in steady state mode. Researches and developments are, respectively, carried out at Saint Petersburg and at Grenoble. This paper reports the first results obtained at Grenoble on a repetitive two-stage gas gun (TSGG) coupled to a porous cell pellet generator. Such a TSGG was developed in 1992 by SBT for the single shot mode. Several modifications have been made to reach the repetitive mode. The TSGG breech peak pressure ranges from 20 to 160 MPa. Therefore, porous cell design was modified to stand these pressure levels. Pellet speeds from 1600 to 3000 m/s were performed with a cycle period from 15 to 34 s. The first campaign has produced promising results, firstly on the porous cell pellet generator technology that can provide repetitive deuterium ice formation, and secondly on the TSGG used also in a repetitive mode. For further experiments, improvements on cryostat design and on remote control system should be undertaken. New cryostat design will give access to lower cell temperature, necessary to improve the ice resistance and thus to allow higher pellet speeds. A fully automatic remote control system will improve the overall reliability of the injector and ease the sequence setting for shorter period operation.