The Laser Megajoule CryoTarget Thermal Regulation

Publisher Summary The Laser Megajoule facility is the French equipment intended for studies of inertial fusion. Thermonuclear fusion is obtained by focusing 240 laser beams with an energy of 1.8 MJ on a cryotarget. The microballoon implosion, following laser beams impact, generates in its center the ignition conditions of temperature and pressure. The success of implosion strongly depends on the geometrical characteristics of the Deuterium Tritium ice layer: margin 1% for thickness, 1 μm for roughness. The Laser Megajoule requires a high resolution temperature regulation to obtain the cryotarget temperature conditions: a temperature slope of 1 mK/min with ±1 mK to reach the triple point 19.79 K and a regulation at constant temperature with ±1 mK. This regulation required a thermal model elaboration for the target and the process, a regulation module development with a ±50 μK resolution, and a specific algorithm of regulation. It runs on the prototype “Echelle 1,” the Cryotarget Positioner mock-up built at the Service des Basses Temperatures—CEA Grenoble. The temperature stability obtained on the cryostat “Echelle 1” is presented in the chapter.