The Laser MegaJoule (LMJ) program plans to obtain Deuterium-Tritium (DT) mixture ignition leading to a fusion gain of ten. Cryogenic targets are hollow spheres whose interior is covered with a solid cryogenic fuel layer. The success of DT ignition depends on quality of the fuel layer uniformity. These targets must be cooled and kept at temperatures near the triple point (19.8 K) with a very good stability (+/-1 mK) for many hours, in the center of the 5 m radius experimental vacuum chamber with a position accuracy of a few microns. In order to validate our current device concepts, we have manufactured scale one prototypes to confirm all thermal and mechanical challenges, such as sharp thermal regulation, cooling autonomy and cryogenic target transfer.