Fabrication and Characterization of Planar Cryogenic Targets for GEKKO-XII Mitsuo Nakai, Tianxuan Huang, Keisuke Shigemori, Hiroyuki Shiraga, Tatsuhiro Sakaiya, Takeshi Watari, Kazuto Ohtani, Takeshi Shiota, Kazuo Takeda, Hiroshi Azechi, Mizuho Nagata, Takayoshi Norimatsu, Keiji Nagai, Toshiyuki Mito, and Akifumi Iwamoto INTRODUCTION In the inertial confinement fusion, cryogenic targets help to maximize compression of fuel (DT or D 2 ) and hence high gain. Due to its simplicity and convenience for diagnostics, a planar cryogenic target is employed to simulate the multi-layered structure in the fuel capsule, with which one can investigate RT growth, ablative acceleration, shock compression and so on. [1, 2] A cryogenic target system has been developed to be applicable to the HIPER laser and PW laser at ILE, which can be used to perform above experimental studies. The target cell is mounted on the tip of cryostat, with which one can make a sandwich-like planar cryogenic target. A typical target is formed with liquid deuterium sealed with polyimide films. An interferometric method was also used to characterize the cryogenic target before laser shot. The in situ target thickness and shape could be obtained with acceptable accuracy. TARGET SYSTEM As shown in Fig. 1, the entire target system comprised three parts: low temperature bath, target supporter, and gas supply. We employ a liquid helium compressor as a low temperature bath. The cryogenic cooling head (cryo head) is combined together with the target positioner, which has capability of three dimensional translation and rotation around the vertical axis. The cryo head is provided with a 10-K two staged cryogenic cooler. A copper shielding shell connected to the first stage of the cooler with the temperature of 50K serves as a heat insulator against the room temperature. A copper “cryo rod” connected to the 10 K stage of the cooler serves as the cryo-finger, which supports the target cell on its lower tip. With help of extra heaters, the temperature of the target cell can vary from 14 K to 25 K, without stopping the compressor. An electronic pressure gauge serves as an indicator to the gas supply, which can evacuate or let deuterium gas of given pressure into the target cell. The copper target cell has four windows. Two of them are large ones normal to the laser illumination direction. Another two small ones are to observe the target from the orthogonal direction. All of them are sealed with polyimide films. As shown in Fig. 2, the target cell forms a small room between two parallel polyimide films sealed with double-flanges. After the system is cooled down to low temperature, deuterium gas was let in through a metal tube, and condensed into liquid in the cell. In the center of the target cell, a deuterium target sandwiched with polyimide films was provided. A set of double-flanges comprises two flanges (i.e. a sealing flange and an extra flange). As the sealing flange helped to fix the polyimide film and seal the cell, the extra one was employed to stretch the film from outside to enhance its tension. And more important, the distance between two films could be adjusted to change the target thickness with proper spacers. TARGET CHARACTERIZATION Though the distance between the front and rear side surface is fixed with the inner spacers, the thickness of liquid deuterium is still uncertain, due to the bulging resulted from the pressure difference. Fig. 2. Schematic drawing of the liquid target. Fig.1.Schematic drawing for the cryogenic target system. Cryo Head & Target Positioner