The 20k cryogenic grip for the laser megajoule cryo-targets

The cryogenic targets of the Laser Megajoule facility (LMJ) are hollow sphe res. Their internal walls are covered with a solid layer of frozen deuteriu m-tritium (D-T). One issue of inertial confinement fusion experiments is to guarantee the quality of the geometry of fuel layer. Cryogenic targets mus t be cooled at a temperature near the triple point (19K) with a very good s tability (0.2mK) for many hours. This period is used to position the target with an accuracy of +/-5 mu m at the center of the experimental vacuum ves sel where the 240 laser beams are focalized. A complex cryogenic infrastruc ture has been conceived to insure the continuity of the cryogenic chain fro m the filling station located at CEA/Valduc in Burgundy to the LMJ experime ntal chamber installed in the vicinity of Bordeaux. The design of the targe t and a detailed description of the infrastructure are presented. A first p rototype of cryogenic grip has been fabricated and characterized. Some expe rimental results are given.