Target Fabrication at LLEMay, 2011
Transferring the target-production activities to a contractor has enabled LLE to concentrate on developing aspects of target-production capabilities that are unique to LLE requirements, such as direct-drive cryogenic capsules. For example, in the mid-1990s, a collaboration between GA, LLE, and Los Alamos National Laboratory (LANL) began designing a new Cryogenic Target Handling System to support hydrodynamically equivalent cryogenic target experiments on OMEGA. This system was completed and commissioned with deuterium in 2000, and commissioned with tritium in 2006. It remains the mainstay for producing cryogenic targets for all current OMEGA experiments.
In 2008, LLE developed direct-drive cryogenic targets with designs similar to those that will be used to demonstrate direct-drive ignition on the NIF. These targets achieved a compressed fuel density of over 500x that of liquid deuterium (approximately 4x the density achieved in the first LLE cryogenic experiments in 1989). This was an important step toward demonstrating the validity of direct-drive ignition on the NIF. The contributions of LLE’s Target Fabrication Group helped drive this milestone. By 2010, the areal density of cryogenic-DT implosions had been pushed up to 300 mg/cm2. These implosions benefited from improvements in target design, target-fabrication techniques, and specialized plasma diagnostics.
The Target Fabrication Laboratory, which houses the equipment needed to prepare and deliver targets, and to support development projects, helps to make these significant advances possible. Manipulators and stereo microscopes are used to assemble the submillimeter-scale components on precision-machined assembly fixtures at four target-assembly stations. Once the targets have been assembled, they are characterized with metrology equipment that determines the target dimensions and the angle between target structures. Targets are stored as fully assembled components in either a pressurized vessel (to maintain the gas fill, if applicable) or a sealed, individual container. Target assembly takes place in a class-1000 clean room. Targets used in cryogenic implosions are also tested on a vibration table to determine the dynamic stiffness of the target assembly and to quantify the response of the entire assembly at frequencies up to 800 Hz.
Mass production of low-density, plastic-foam capsules for inertial-fusion energy (IFE) is currently being explored in the Target Fabrication Laboratory in collaboration with Prof T. Jones of the Computer and Electrical Engineering Department of the University of Rochester. The current production process is performed at General Atomics Inc., and requires a labor-intensive effort to manufacture and select acceptable targets from a production run that produces thousands of capsules. LLE’s “lab-on-a-chip” concept endeavors to miniaturize and automate this process, incorporating precise electronic control into critical phases of the process. Such research is critical for demonstrating a low-cost, high-output source of fusion targets for future fusion-reactor operations.