Scientists pause each afternoon at Kirtland Air Force Base at Sandia National Laboratories in Albuquerque, New Mexico, awaiting the daily lightning flash and unmistakable floor jolt that accompanies a Z shot.
West Virginia University physics professor Mark Koepke and his students are often among them, taking advantage of approximately 20 of the more than 200 Z shots per year to examine the physical principles that govern extreme astrophysical environments through the study of high energy density physics. Through these experiments, which take months of preparation, they seek to improve the interpretation of signals from orbiting telescopes.
The Z facility drives 26 mega-amperes of current through a parallel array of 360 thin tungsten wires during 100 nanoseconds. This powerful pulse requires 85 kilovolts and 1.6 mega-joules of energy.
“The wires heat and vaporize into tungsten gas, and the sudden compression of the surrounding magnetic field energy pressurizes the gas into a tungsten plasma that emits a three-nanosecond blast of X-rays. The current is driven along one axis that we call the z axis, and the compression pinches the plasma-laden magnetic-field lines toward that axis to near-fusion temperature and density, so we refer to this device as a z-pinch,” said Koepke, WVU’s Robert C. Byrd Professor of Physics. “For three nanoseconds, we expose our target sample to the world’s brightest X-ray light bulb to study how intense radiation affects matter.”
The Z shots have been part of an ongoing Z Astrophysical Plasma Properties collaboration that was recently promoted to the Center for Astrophysical Plasma Properties (CAPP), a collaboration by the University of Texas, University of Nevada, WVU, University of Arizona, Sandia Labs, Lawrence Livermore Lab and NASA. The Z shot schedule is booked for over a year.
“We are striving to utilize the U.S. Department of Energy labs to push the cutting-edge of high energy density science and solve grand challenges in fundamental knowledge. Until this collaboration, the opportunities were fragmented, as some partners received intermittent funding and others were excluded from the resources,” Koepke said. “Now, the astronomers are supported and stable funding enables the participation of PhD students and postdoctoral research associates.”
Established in 2009 as the Z Astrophysical Plasma Properties (ZAPP), the collaboration conducts up to five physics experiments per Z shot, considered a high standard in sharing runtime economically at expensive national laboratories built for programmatic research into national security issues. Each experiment is designed by university investigators in collaboration with the scientists at Sandia Labs. The collaboration was promoted to a Center of Excellence, starting in 2018, with a $7 million five-year grant from the U.S. Department of Energy.
The Center of Excellence benefits ongoing research in WVU’s Department of Physics and Astronomy through partial support for graduate students, participation in Center activities and access to the Center’s intellectual resources, such as the computational physics simulation codes that are key to interpreting target-emission and target-absorption spectral data.
“For WVU plasma physics, which began in 1987, being a member of a center of excellence and engaged with the country’s best scientists helps recruit and engage ambitious graduate students who aspire to be nationally recognized scientists one day,” Koepke said. “Being put into the spotlight and having access to the best facilities and resources in the country lets them imagine that their dreams can come true.”
Cuyler Beatty, a first-year PhD student from southern California, looks forward to directly benefiting from ZAPP and CAPP.
“I applied to well over a dozen graduate programs in my senior year. I looked at every graduate program offering plasma research, but what really got me to WVU, out of all of the acceptances, was (Koepke),” said Beatty, who envisions participating in the CAPP research at Sandia National Laboratories. “He is willing to let me explore ideas for my research instead of just giving me a project. I love the possibilities for where this research can go.”