Exciting beginning, interesting future: Z machine turns 20
It was a “mere” 20 years ago on Dec. 11, 1985, that a 108-ft.-diameter Sandia machine then called PBFA-II first made the ground shake, lit up the surface of the water surrounding its tiny target area with electrical arcs and sparks, and generated talk of controlled nuclear fusion from jubilant researchers.
Tension had built for weeks in Area 4 as to whether the huge machine, which sent massive electrical currents surging through 36 transmission lines to activate a lithium ion beam, would work as planned. Some thought it might not. Some thought it might explode.
The tension, reported the Lab News at that time, was similar to that before the last game of a tight World Series.
Theme music of the TV series “Star Trek” played over loudspeakers with voice-overs reminding the listeners that Sandia “boldly goes where no man has ever gone before.”
“Most exciting moment of my life”
This exhilarating message was soon replaced by a dour disclaimer, humorously borrowed from the television show “Mission Impossible”: “As always, if you fail, Sandia and DOE will disavow any knowledge of your mission.”
“The most exciting moment of my life,” said former Sandia VP Pace VanDevender, then director of pulsed power sciences, when the first shot proved successful.
VP Gerry Yonas (7000), one of the machine’s founding fathers, listened on a telephone line from Washington, where he was serving as the Strategic Defense Initiative’s chief scientist. He afterwards declared himself speechless, then said, “I could feel the machine’s vibrations up my spine all the way across the country.”
More measurably, according to Mary Ann Sweeney (1670), who was present at the time, scientists and engineers who could not fit into the building’s crowded control room felt the ground shake in Bldg. 960 hundreds of feet away.
Believe it or not
Since then, many things have happened.
The machine was featured in Ripley’s “Believe It Or Not” list of oddities with this somewhat obscure citation: “At Sandia National Laboratories in Albuquerque, N.M., a futuristic research center can make more power than all US utilities produce at any one time dance on the head of a pin.”
Ktech technicians Dan Jobe (1670) and Scott Drennan (1654), who took the first photos of PBFA-II firing, found that their photographic techniques lived on. Open-shutter methods they employed were used subsequently by Walt Dickenman (dec.), and nearly a decade later by Sandia staff photographer Randy Montoya (3651) who created the most widely reproduced picture Sandia ever released: the “arcs and sparks” light show of the accelerator firing.
“Dan and Scott knew the pond,” says Randy, “and they showed the rest of us where to stand to get the best fish.”
The two technicians had experimented with open-shutter photography to aid them in looking for breakdowns in the accelerator when it fired. Among media that published images based on the pair’s early expertise was National Geographic magazine. Among the many places a Sandia-taken “arcs and sparks” photo appeared was the cover of the book Physics in the 20th Century, published by the American Physical Society to celebrate its 100th anniversary. The author, former Washington Post writer Curt Suplee, learned of Z at a meeting with Sandia media staff.
Probably one of the most significant moments in the machine’s later history occurred ten years ago when researchers replaced the lithium ion beam diode with a simple Z-pinch containing many wires.
Soon afterwards, the Particle Beam Fusion Accelerator exchanged its wordy moniker for a single letter — Z — but controlled nuclear fusion remains a goal for Sandia’s Z machine.
Sandia refines Z-pinch concept
A Z-pinch wire array is essentially the size of a spool of thread, with tungsten wires about a tenth the thickness of a human hair hung vertically over the spool, rather than wrapped around it horizontally as is the practice with cotton thread.
While wire-array Z pinches had been used for decades, Sandia’s innovation was to dramatically increase the number of wires — something that had never been satisfactorily done.
Electrical current surging through the tiny wires obliterates them in what is effectively a massive short circuit. The magnetic field of the current compresses the resultant cloud of tungsten ions like a fist closing on a sponge. When the ions have nowhere further to go — at about the thickness of a pencil lead in the vertical, or Z, direction — their sudden braking from speed that is a significant fraction of the speed of light releases more energy and power in X-rays than ever before achieved in a laboratory.
The immediate surge in X-ray power output at that time led many to wish their stock market holdings produced graphs with such vertical rises in prices.
As the X-ray power output doubled, tripled, and then quadrupled, Sandia researchers were able to produce fusion neutrons — a feat reported at the March Meeting of the American Physical Society two years ago.
The story continues into the present with the addition of one of the world’s most powerful lasers, dubbed Z-Beamlet, to image Z’s compression of target capsules.
The X-ray intensities needed to drive capsules to the still-distant goal of break-even fusion, researchers say, must be generated by a much larger machine.
Meanwhile, the Z machine will soon take a rest while its 20-year-old capacitors and switches are replaced by more modern technology. And then the flashes and groundshakings and onward march toward fusion will continue, with attendant work in testing materials under huge compression, launching swift flyer plates with magnetic propulsion, characterizing the composition of the cores of planets and the sun, simulating environments around neutron stars and black holes, and observing defense-related tests not suitable for discussion here.
As the wry joke goes, break-even with controlled nuclear fusion is probably still only 20 years away. But given recent progress, along with anticipation of new results made possible by the coming upgrade, the role of Z as a possible avenue to the high-energy future cannot be understated.
Says current director Keith Matzen (1600), “Our intensity and enthusiasm remain high to create a significant fusion burn.”