Neutron Generation: From tubes to chips

by Sue Major Holmes

It was a figurative whack on the head that started Sandia distinguished technical staff member Juan Elizondo-Decanini (2625) thinking outside the box — which in his case was a cylinder.

He developed a new configuration for commercial neutron generators by turning from conventional cylindrical tubes to the flat geometry of computer chips. For size comparison, he says small neutron generators, which are like mini accelerators, are 1 to 2 inches in diameter.

“The idea of a computer chip-shaped neutron source — compact, simple, and inexpensive to mass-produce — opens the door for a host of applications,” Juan says.

The most practical, and the most likely to be near-term, would be a tiny medical neutron source, implanted close to a tumor, that would allow cancer patients to receive a low neutron dose over a long period at home instead of having to be treated at a hospital, he says.

The technology is ready to be licensed for some commercial applications, but other more complex commercial applications could take five to 10 years, Juan says.

“It’s really revolutionary technology,” said Stewart Griffiths, who retired in December as a senior scientist/engineer in Center 2100.  “Juan’s knowledge, insights and creativity into this enabled this really big jump from today to how we might do neutron generators in the future.”

Stewart said the impact won’t be known for years, however. “The maturation of the technology is still needed, but if that process is successful, it will have a huge impact,” he said.

‘Deep in the proverbial box’

An independent committee of Sandia managers selected the technology as one of the Laboratories’ eight submissions to compete for the R&D 100 awards in 2012.

A three-year Laboratory Directed Research & Development (LDRD) project Juan led demonstrated the basic technology necessary for a tiny, mass-produced neutron generator that he said can be adapted to medical and industrial applications. He says his team is seeking funding to make sure it works reliably and can be scaled to meet needs.

Juan says it all started when now-retired Dept. 9610 senior manager Mike Sjulin told researchers he needed neutrons and he didn’t care how they were produced. Before that whack on the head, Juan says, “we were deep in the proverbial box, concentrating on making the cylinder more cylindrical.”

Traditionally, accelerator-based neutron generators with deuterium ion and tritium targets have operated on cylinders, which makes it easy to control the electric field and ion beam shape, he says. But that geometry also limits size, beam current, and neutron output. 

Could they produce one neutron per transistor?

 So members of Juan’s team turned to computer chip geometry. Noting chips have two transistors per bit, they wondered if they could produce one neutron per transistor — what one of Juan’s peers dubbed a “neutristor.”

“Once you see it, it’s kind of obvious … but before that nobody ever thought of it,” Juan says.

The fun began with the technology challenges that presented, he says.

The team’s first step was to discover whether it was possible to make a generator shaped like a flat computer chip with all surface-deposited components — everything from the ion source to the target, Juan says.

“We did not even know the proper scaling to go from cylindrical to flat, or from high operating voltages to lower operating voltages,” he recalls.

However, he says, a cross-section diagram of the simplest diode-based neutron tube translated into the ideal surface-mounted topology, and team members knew they had the tools to design it.

The LDRD project pulled together people from all over Sandia, including design, microelectronics, materials, ceramics, precision fabrication, ion gas loading, engineering, and detection calibration, Juan says. He also credits manager Mike Eatough (2735), saying, “It couldn’t have happened without his ability to open up space for me to be wild and crazy and talk nonsense.”

After seven months of working on an ion beam lens design and an additional six months doing the necessary modeling, the team scaled things down.

“The challenges switched to make the device micron size, and then nano size, until we could scale it down no more,” Juan says. To date, the project has demonstrated scaling to the millimeter and micron size, with neutron production demonstrated in the millimeter size and ion sources demonstrated in the micron size, Juan says.

The team moved from a millimeter package that looks a like a printed circuit board to a micron package to the concept of mounting the package on a computer chip. The chip configuration allows varying numbers of layers in a stack. That led to the idea of rotating those layers for radial discharge to ramp up output — a return, in a way, to the cylinder.

To illustrate that, Juan pins down one end of a sample rectangular millimeter design and rotates the free end in a circle, much like rotating a protractor.

Will present at TVC’s Deal Stream Summit

“All of a sudden you have a cylindrical cavity like a pill box,” he says. “It’s still flat but now it looks like a pill box, and I have increased the number of neutrons by one or two orders of magnitude.”

He says that if a neutron can be produced from each bit, "that's a neutron source that you can use almost anywhere, in medical applications, in sensors for contraband, for nonproliferation."

Juan presented a paper, "Surface Mounted Neutron Generators," at the NNSA 2011 LDRD Symposium in Washington, D.C., in July as one of three featured technical speakers chosen by each of the NNSA labs to showcase their top LDRD research activity.

A patent has been filed for the millimeter-size hybrid — hybrid because everything is solid state except a vacuum gap — that would be used for neutron capture cancer therapy. In addition, the project sparked half a dozen technical advances, the team is testing micron-size neutron source arrays built using Sandia’s MicroElectricoMechanical Systems facilities, and it's initiated commercial technology transfer work.

Technology Ventures Corporation (TVC) accepted Juan's application to present his work at the April 3 Technology Ventures Deal Stream Summit's Parade of Posters, which gives researchers an opportunity to talk with possible investors. The nonprofit TVC was founded and funded by Lockheed Martin to help commercialize technology from the national laboratories.

Juan's vision for the neutron generator of the future is one that uses no tritium and no vacuum, is made in a solid state package and is fabricated at Sandia's Microsystems and Engineering Sciences Applications (MESA) complex.

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Experiments may force revision of astrophysical models of universe

by Neal Singer

That water expands when boiled, rattling pot tops on stoves, is no secret. But that it can be compressed is foreign to our daily experience.

Nevertheless, an accurate estimate of water's shrinking volume under the huge gravitational pressures of large planets is essential to astrophysicists trying to model the evolution of the universe. They need to assume how much space is taken up by water trapped under high density and pressure, deep inside a planet, to calculate how much is needed of other elements to flesh out the planet’s astronomical image.

Overstating water's compressibility

In a challenge to current astrophysical models, researchers at Sandia and the University of Rostock in Germany have found that current calibrations of planetary interiors overstate water’s compressibility by as much as 30 percent. The work was reported in the paper "Probing the Interior of the Ice Giants" in the Feb. 27 Physical Review Letters.

"Our results question science's understanding of the internal structure of these planets," says lead researcher Marcus Knudson (01646), "and should require revisiting essentially all the modeling of ice giants within and outside our solar system."

To come up with the composition of the so-called ice-giants Neptune and Uranus, as well as any of the ice-giant exoplanets being discovered in distant star systems,  astrophysicists begin with the orbit, age, radius, and mass of each planet. Then, using equations that describe the behavior of elements as the forming planet cooled, they calculate what light and heavy elements might have contributed in its evolution to end up with the current celestial object.

 But if estimates of the volume of water are off-target, then so is everything else.

 The measurements — 10 times more accurate than any previously reported — at Sandia’s Z accelerator agree with results from a modern simulation effort that uses the quantum mechanics of Schrödinger’s wave equation — the fundamental equation of wave mechanics — to predict the behavior of water under extreme pressure and density.

The model, developed through a University of Rostock and Sandia collaboration, is called "First Principles Modeling" because it contains no tuning parameters.

"You're solving Schrödinger's equation from a quantum mechanical perspective with hydrogen and oxygen as input; there aren't any knobs for finagling the result you want or expect," says Marcus.

The model's results are quite different from earlier chemical pictures of water's behavior under pressure, but agree quite well with the Z machine's test results, says Marcus.

These results were achieved by using Z’s magnetic fields to shoot tiny plates 40 times faster than a rifle bullet into a water sample target a few millimeters away.  The impact of each plate into the target created a huge shock wave that compressed the water to roughly one-fourth its original volume, momentarily creating conditions similar to those in the interior of the ice giants.

A direct test of First Principles model

Sub-nanosecond observations captured the behavior of water under pressures and densities that occur somewhere between the surface and core of ice giants.

“We took advantage of recent, more precise methods to measure the speed of the shock wave moving through the water sample by measuring the Doppler shift of laser light reflected from the moving shock front, to 0.1 percent accuracy,” says Marcus.

The re-shocked state of water was also determined by observing its behavior as the shock wave reflected back into the water from a quartz rear window (its characteristics also determined) in the target. These results provided a direct test of the First Principles model along a thermodynamic path that mimics the path one would follow if one could bore deep into a planet’s interior.

Multiple experiments were performed, providing a series of results at increasing pressures to create an accurate equation of state. Such equations link changes in pressure with changes in temperatures and volumes.

Z can create more pressure— up to 20 megabars— even than at Earth's core (about 3.5 megabars) and millions of times Earth’s atmospheric pressure. The Z projectiles, called flyer plates, achieve velocities from 12 to 27 kilometers a second, or up to 60,000 mph. The pressure at the center of Neptune is roughly 8 megabars.

Reducing uncertainty

Water at Z's ice-giant pressures also was found to have reflectivity indicative of a weak metal, raising the possibility that water's charged molecular fragments might be capable of generating a magnetic field. This attribute could help explain certain puzzling aspects of the magnetic fields around Neptune and Uranus.

"Reducing uncertainty on the composition of planetary systems by precisely measuring the equation of state of water at extreme conditions can only help us understand how these systems formed," says Marcus.

These techniques also are used to study materials of critical importance to the nuclear weapons program.

In addition to producing the largest amount of laboratory X-rays on Earth when firing, the huge pressures generated by Z make it useful to astrophysicists seeking data similar to that produced by black holes and neutron stars .

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SPIDERS microgrid project secures military installations

by Stephanie Hobby

When the lights go out, most of us find flashlights, dig out board games, and wait for the power to come back. But that’s not an option for hospitals and military installations, where lives are on the line. Power outages can have disastrous consequences for such critical organizations, and it’s especially unsettling that they rely on the nation’s aging, fragile, and fossil fuel-dependent grid.

A three-phase, $30 million, multi-agency project known as SPIDERS, or the Smart Power Infrastructure Demonstration for Energy Reliability and Security, is focused on lessening those risks by building smarter, more secure and robust microgrids that incorporate renewable energy sources.

Sandia was selected as the lead designer for SPIDERS, the first major project under a memorandum of understanding (MOU) signed by DOE and DoD to accelerate joint innovations in clean energy and national energy security. The effort builds on Sandia’s decade of experience with microgrids — localized, closed-circuit grids that both generate and consume power — that can be run connected to or independent of the larger utility grid.

The goal for SPIDERS microgrid technology is to provide secure control of on-base generation.

"If there is a disruption to the commercial utility power grid, a secure microgrid can isolate from the grid and provide backup power to ensure continuity of mission-critical loads. The microgrid can allow time for the commercial utility to restore service and coordinate reconnection when service is stabilized," says Col. Nancy Grandy, oversight executive of the SPIDERS Joint Capability Technology Demonstration (JCTD). "This capability provides much-needed energy security for our vital military missions."

SPIDERS is addressing the challenge of tying intermittent clean energy sources such as solar and wind to a grid.

"People run single diesel generators all the time to support buildings, but they don’t run interconnected diesels with solar, hydrogen fuel cells, and so on, as a significant energy source. It’s not completely unheard of, but it’s a real integration challenge,” says Jason Stamp (6111), Sandia’s lead project engineer for SPIDERS.

Currently, when power is disrupted at a military base, individual buildings switch to backup diesel generators, but that approach has several limitations. Generators might fail to start, and if a building's backup power system doesn't start, there is no way to use power from another building's generator. Most generators are oversized for the load and run at less-than-optimal capacity, and excess fuel is consumed. Furthermore, safety requirements state that all renewable energy sources on base must disconnect when off-site power is lost.

A smart, cybersecure microgrid addresses these issues by allowing renewable energy sources to stay connected and run in coordination with diesel generators, which can all be brought online as needed. Such a system would dramatically help the military increase power reliability, lessen its need for diesel fuel, and reduce its "carbon bootprint."

"The military has indicated it wants to be protected against disruptions, to integrate renewable energy sources, and to reduce petroleum demand," Jason says. "SPIDERS is focused on accomplishing those tasks. The end result is having better energy delivery for critical mission support, and that is important for every American.”

SPIDERS uses existing, commercially available technologies for implementation, so the individual technologies are not novel. "What's novel is the system integration of the various technologies, and demonstrating them in an operational field environment," says Bill Waugaman (6512), SPIDERS operational lead. "Microgrid concepts are still fairly new, and that's where Sandia's microgrid design expertise is coming into play."

An unprecedented level of cybersecurity

It is common practice to connect diesel generators to buildings, but integrating significant amounts of energy from intermittent clean sources such as solar and wind to that system is unique, and it is a challenge that

Sandia and SPIDERS are working to address.

Such integration requires data to determine the most efficient and effective way to operate, but that can open system vulnerabilities, so cybersecurity is paramount. SPIDERS addresses that issue by incorporating an unprecedented level of cybersecurity into the system from the outset.

"Any perturbation of information flow by an adversary would possibly cause an interruption to electrical service, which can have significant consequences,” Jason says. “It’s important that if we build a microgrid system that depends explicitly on greater information flow, that it operate as intended: reliably and securely."

SPIDERS is funded and managed through the DoD's JCTD, which joins the efforts of other government organizations and companies to rapidly develop, assess, and transition needed capabilities to support DoD missions. With DOE's support, the SPIDERS transition plan includes civilian facilities.

Applications beyond military use

"The SPIDERS approach has many applications beyond military uses. Our interest in SPIDERS extends to organizations, like hospitals, that are critical to our nation's functionality, especially in times of emergency," says Merrill Smith, DOE program manager.

Sandia’s microgrid expertise spans the past decade, beginning when Sandia designed microgrids for DOE's Federal Energy Management Program and DOE's Office of Electricity Delivery and Energy Reliability. DOE initially asked Sandia to develop a conceptual design for a microgrid at Fort Carson in Colorado Springs, Colo., and another for Camp H.M. Smith in Hawaii.

After Sandia conducted a feasibility analysis and modeling and simulation work for the two bases, US Pacific Command (USPACOM) and US Northern Command (USNORTHCOM) asked Sandia to prove the concept through field work under a JCTD. The two commands pulled together a team of national labs and defense organizations, and selected Sandia to lead the development of the initial designs for three separate microgrids, each more complex than the previous.

The Army Construction Engineering Research Laboratory will use the Sandia designs as a basis for developing contracts with potential system integrators, who will construct the actual microgrids. Other partners in the SPIDERS JCTD include National Renewable Energy Laboratory for renewable energy and electrical vehicle expertise, Pacific Northwest National Laboratory for testing and transition, Oak Ridge National Laboratory to assist with control system development, and Idaho National Laboratory for cybersecurity.

The first SPIDERS microgrid will be implemented at Joint Base Pearl Harbor Hickam in Honolulu, and will take advantage of several existing generation assets, including a 146-kW photovoltaic solar power system, and up to 50 kW of wind power. The integrator for the project has been selected and the final design and construction process is under way.

The second installation, at Fort Carson, is much larger and more complex and will integrate an existing 2 MW of solar power, several large diesel generators, and electric vehicles. Large-scale electrical energy storage also will be implemented to ensure microgrid stability and to reduce the effects of PV variability on the system. Camp H.M. Smith, the most ambitious project, will rely on solar and diesel generators to power the entire base, which will be its own self-sufficient 5 MW microgrid when the national grid is unavailable.

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