New, highly automated system transforms NIF shots
For experiments performed at the National Ignition Facility (NIF), the goal is not just to measure the interaction between the target and the laser beams. Researchers also need to understand, on a fundamental level, what is happening to the material in the target and how it’s changing over time. This capability to see inside the target as it interacts with the laser beams is especially useful in high-energy-density experiments and those exploring material strength.
To this end, in 2013 the NIF team developed a unique long-delay backlighter (LDBL) technique, which allowed selected laser beams to arrive up to a microsecond after those that are directed at the target. The delayed laser beams irradiate an x-ray backlighter behind the target, using the radiation produced to see what’s happening to the target during the experiment, which can then be recorded by diagnostic equipment. This provides extraordinarily high-speed imaging of material interactions. To make the delay a reality, the optical fibers along which the chosen laser beams run must be lengthened. The extra length of fiber makes the laser travel farther and therefore arrive later than the others.
However, this seemingly simple change necessitates writing specialized software to redefine timing values for the lengthened fibers, as well as having subject matter experts available to review the changes. “It essentially required tricking the shot automation system so that it continued functioning without thinking that something’s gone wrong,” says Dave Mathisen, the shot timing systems engineer and shot automation architect. “The problem with this system was that it was incredibly time- and labor-intensive while only supporting a limited set of beams. The whole process took hours, with the manual inspection of hundreds of lines of data and the preparation of the fibers.”
The process required highly trained specialists to install and verify the correct lengths of fiber before every shot that needed a long delay. “Sometimes they’d be required to come in the middle of the night to make sure it would get done on time for the shot the next day,” notes Mathisen. “We really felt the need to improve upon that process. We knew that it could be better, and it presented a very unique systems engineering problem. Our goal was to improve the efficiency of conducting these shots by providing a seamless process for proposing, reviewing, scheduling, and conducting them.”
The introduction of fiber delay backlighter (FDBL) automation, a project lead by Mathisen, addresses all of these issues. The newly automated system organizes and controls the full lifecycle of a FDBL shot from the initial planning stage to the experiment itself, requiring input or action from a person only at a few key junctures. When a shot is requested by the responsible individual (RI), he or she inputs a packet of information that allows the system to automatically determine the corresponding fiber needs. With the approval of the RI, the system orders the fibers, places them in inventory, guides their installation, and automates the related timing changes during shot. Once that shot is complete, the system guides the actions required to return NIF equipment and software to a nondelayed configuration. This system of improved procedures and toolsets places the expertise for executing FDBL shots in the system, providing an alternative to requiring timing experts to be on hand.
“The automation that the system now provides has reduced the execution time for these types of shots by four to six hours per shot, representing a significant increase in efficiency,” says Mathisen. In addition, the new process and tools allow optimization of shot scheduling—a shot’s RI can see all the other shots requested in a certain time frame and organize them to minimize the time spent changing fibers between shots, further reducing the (usually higher) cost of a long-delay experiment. “Essentially, we’ve turned a very complex process into a far simpler one for all involved—not only is it simpler, it’s more usable, versatile, reliable, and efficient,” says Mathisen.
The FDBL automation project is one of the first wide-scale, interdepartmental systems engineering projects aimed at optimizing NIF efficiency, and has enjoyed great success and positive feedback since its deployment a few months ago. The success of the FDBL project required multidisciplinary collaboration, including shot experimentalists, laser engineering, facility operations, and more than 30 individual contributors from eight different software development teams.