The target cooling system for the Laser Megajoule Facility

The cryogenic targets of the Laser Megajoule Facility (LMJ) are hollow spheres. Their internal wall is covered by a solid cryogenic fuel layer. One issue of inertial confinement fusion experiments is to guarantee the quality of the geometry of fuel layer. Cryogenic targets must be cooled at a temperature near the triple point (19 K) with a very good stability (0.2 mK) for a long time (many hours). This period is used to position the target with accuracy at the centre of an experimental vacuum vessel of 10 m diameter where the laser beams are focused. A complex cryogenic infrastructure has been imagined to insure the continuity of the cryogenic chain from the filling station located in Valduc in Burgundy to the experimental chamber installed close to Bordeaux. The design of the target and a succinct description of the infrastructure are presented. A first prototype of cryogenic grip has been built and characterised. Some experimental results are given.