Experiments verify key aspect of Sandia nuclear fusion concept
by Neal Singer
Magnetically imploded tubes called liners, intended to help produce nuclear fusion conditions at scientific “break-even” energies or better within the next few years, have functioned successfully in preliminary tests at Sandia, according to a paper slated for publication on Sept. 14 in Physical Review Letters (PRL).
Exceeding scientific break-even is the holy grail of fusion research, where the energy released by a fusion reaction is greater than the energy put into it — an achievement that would have extraordinary energy and defense implications.
That the liners survived their electromagnetic drubbing is a key step in stimulating further testing of a Sandia nuclear fusion concept called MagLIF (Magnetized Liner Inertial Fusion), which will use magnetic fields and laser preheating in the quest for energetic fusion.
In the dry-run experiments, cylindrical beryllium liners remained reasonably intact as they were imploded by the huge magnetic field of Sandia’s Z machine, the world’s most powerful pulsed-power accelerator. Had they overly distorted, they would have proved themselves incapable of shoveling together nuclear fuel — deuterium and possibly tritium — to the point of fusing them. Sandia researchers expect to add deuterium fuel in experiments scheduled for 2013.
Consistent with earlier simulations
“The experimental results — the degree to which the imploding liner maintained its cylindrical integrity throughout its implosion — were consistent with results from earlier Sandia computer simulations,” says lead researcher Ryan McBride (1648). “These predicted that MagLIF will exceed scientific break-even.”
A simulation published in a 2010 Physics of Plasmas article by Sandia researcher Steve Slutz (1644) showed that a tube enclosing preheated deuterium and tritium, crushed by the large magnetic fields of the 25 million-ampere Z machine, would yield slightly more energy than is inserted into it.
A later simulation, published last January in PRL by Slutz and Roger Vesey (1644), showed that a more powerful accelerator generating 60 million amperes or more could reach “high-gain” fusion conditions, in which the fusion energy released greatly exceeds, by more than 1,000 times, the energy supplied to the fuel. (see https://share.sandia.gov/news/resources/news_releases/z-fusion-energy-output/ ).
These goals — both the near-term goal of scientific break-even on today’s Z machine and the long-term goal of high-gain fusion on a future, more powerful machine — require the metallic liners to maintain sufficient cylindrical integrity while they implode.
The liner is intended to contain fusion fuel, like a can holds peanut butter, and push it together in nanoseconds like two semicylindrical shovels compacting snow together.
‘The race is on’
An element of drama is present because the metallic liner doing the compressing also is being eaten away as it conducts the Z machine’s enormous electrical current along its outer surface. This electrical current generates the corresponding magnetic field that crushes the liner, but under the stress of passing that current, the outer surface of the liner begins to vaporize and turn into plasma, in much the same way as a car fuse vaporizes when a short circuit sends too much current through it. As this happens, the surface begins to lose integrity and becomes unstable. This instability works its way inward, toward the liner’s inner surface, throughout the course of the implosion.
“You might say: The race is on,” says Ryan. “The question is, can we start off with a thick enough tube such that we can complete the implosion and burn the fusion fuel before the instability eats its way completely through the liner wall?
“A thicker tube would be more robust in standing up to this instability, but the implosion would be less efficient because Z would have to accelerate more liner mass. On the flip side, a thinner tube could be accelerated to a much higher implosion velocity, but then the instability would rip the liner to shreds and render it useless,” he continues. “Our experiments were designed to test a sweet spot predicted by the simulations where a sufficiently robust liner could implode with a sufficiently high velocity.”
By following the tiny dimensions proposed by the earlier simulations the physical test proved successful, and the liner walls maintained their integrity throughout the implosion.
Radiographs taken at nanosecond intervals depicted the implosion of the initially solid beryllium liner through to stagnation — the point at which an implosion stops because the liner material has reached the cylinder’s central axis. The images show the outer surface of the imploding liner distorting until it resembles threads on a bolt. However, the more crucial inner surface remains reasonably intact all the way through to stagnation.
Says Ryan’s manager Dan Sinars (1648), “When Magnetized Liner Inertial Fusion was first proposed, our biggest concern was whether the instabilities would disrupt the target before fusion reactions could occur. We had complex computer simulations that suggested things would be OK, but we were not confident in those predictions. Then Ryan did his experiments, using liners with the same dimensions as our simulations, and the outcomes matched. This achievement is an important milestone because we are now confident enough to take the next steps on the Z facility of integrating in the new magnetic field and laser preheat capabilities that will be required to test the full concept. Consequently, we have signed up to take those first integration steps in 2013. I'm very proud of Ryan and his team.”
‘One more step on a long path’
Slated for December are the first tests of the final two components of the MagLIF concept: laser preheating to put more energy into the fuel before magnetic compression begins, and the testing of two secondary electrical coils placed at the top and bottom of the can. Their magnetic fields are expected to keep charged particles from escaping the hot fuel horizontally. This is crucial because if too many particles escape, the fuel could cool to the point where fusion reactions cease.
Sandia researchers intend to test the fully integrated MagLIF concept by the close of 2013.
“This work is one more step on a long path to possible energy applications,” says senior manager Mark Herrmann (1640).
The liner implosion experiments also served to verify that simulation tools like the popular LASNEX code are accurate within certain parameters, but may diverge when used beyond those limits — information of importance to other labs that use the same codes.
Ryan will give an invited talk on his work this fall at the American Physical Society’s annual Division of Plasma Physics meeting in Providence, R.I. He is also preparing an invited paper for the journal Physics of Plasmas to explain the PRL results in greater depth.
The work was funded by Sandia’s Laboratory Directed Research and Development program and the National Nuclear Security Administration.-- Neal Singer
Lifelike, cost-effective Sandia Hand can disable IEDs
Sandia has developed a cost-effective robotic hand that can be used in disarming improvised explosive devices, or IEDs.
The Sandia Hand addresses challenges that have prevented widespread adoption of other robotic hands, such as cost, durability, dexterity, and modularity.
“Current iterations of robotic hands can cost more than $250,000. We need the flexibility and capability of a robotic hand to save human lives, and it needs to be priced for wide distribution to troops,” says Sandia senior manager Philip Heermann (6530).
The Sandia Hand project is funded by the Defense Advanced Research Projects Agency.
Principal investigator Curt Salisbury (6533) says the goal was to build a capable but affordable robotic system.
“Hands are considered the most difficult part of the robotic system, and are also the least available due to the need for high dexterity at a low cost,” Curt says.
The Sandia Hand is modular, so different types of fingers can be attached with magnets and quickly plugged into the hand frame. The operator has the flexibility to quickly and easily attach additional fingers or other tools, such as flashlights, screwdrivers, or cameras. Modularity also gives the Sandia Hand a unique durability. The fingers are designed to fall off should the operator accidentally run the hand into a wall or another object.
“Rather than breaking the hand, this configuration allows the user to recover very quickly, and fingers can easily be put back in their sockets,” Curt says. “In addition, if a finger pops off, the robot can actually pick it up with the remaining fingers, move into position and resocket the finger by itself.”
Even easy for first-time users
The operator controls the robot with a glove, and the lifelike design allows even first-time users to manipulate the robot easily. The robot’s tough outer skin covers a gel-like layer to mimic human tissue, giving the Sandia Hand the additional advantage of securely grabbing and manipulating objects, like a human hand.
Using Sandia’s robotic hand to disable IEDs also might lead investigators to the bomb makers themselves. Often, bombs are disarmed simply by blowing them up. While effective, that destroys evidence and presents a challenge to investigators trying to catch the bomb maker. A robotic hand that can handle the delicate disarming operation while preserving the evidence could lead to more arrests and fewer bombs.
Sandia partnered with researchers at Stanford University to develop the hardware and worked with consulting firm LUNAR to drive costs down drastically. In current commercially available robotic hands, each independently actuated degree of freedom costs roughly $10,000.
“The Sandia Hand has 12 degrees of freedom, and is estimated to retail for about $800 per degree of freedom — $10,000 total — in low-volume production. This 90 percent cost reduction is really a breakthrough,” says Curt. Additionally, because much of the technology resides in the individual finger modules, hands with custom numbers and arrangements of fingers will be quite affordable.
“At this price point, the Sandia Hand has the potential to be a disruptive technology,” Philip says. “Computers, calculators, and cell phones became part of daily life and drastically changed how we do things when the price became affordable. This hand has the same potential, especially given that high-volume production can further reduce the cost.”
DARPA is funding a separate software effort in a parallel track to the hardware work.-- Stephanie Hobby
Explosive Destruction System keeps pace with changing mission
by Patti Koning
The Explosive Destruction System (EDS), developed by Sandia for the US Army, is a modern technology that is being used to deal with remnants of our military history. Those remnants — in the form of recovered chemical munitions — continue to emerge in unusual places. Even though the battles of World War I and World War II were fought on foreign soil, munitions from those two wars continue to surface all over the country at current and formerly used defense sites and at burial sites.
EDS was developed in response to the need for a mobile system to safely destroy World War I-era chemical mortars and shells found in the Spring Valley neighborhood of Washington, D.C. The Spring Valley munitions were World War I artifacts, left behind when American University conducted chemical weapons research for the US Army.
EDS was first used in 2001 at Rocky Mountain Arsenal in Colorado and then at other locations including Spring Valley. Sandia next created a larger version of EDS, capable of destroying more munitions at once and handling munitions with a higher explosive charge.
Two of the larger systems were used from 2006 to 2010 to destroy more than 1,200 munitions, including 450 German Traktor rockets at the Army’s Pine Bluff Arsenal in Arkansas (see the July 30, 2010 issue of Sandia Lab News). This enabled the Army to complete its mission to destroy all non-stockpile materiel declared when the United States entered into the 1993 Chemical Weapons Convention, an international treaty mandating the destruction of chemical warfare materiel.
Almost as soon as that mission was complete, Brent Haroldsen, John Didlake (both 8123), and other Sandia engineers went to work modifying the existing EDS design to increase speed. Called the Phase 2 Pilot, or P2P, this model incorporates several design changes that halved the processing time, from two days to one.
“When we first designed EDS, speed was not a priority,” explains Brent. For the original application of safely destroying munitions in populated areas, the design emphasized transportability, flexibility, redundancy, certainty of destruction, and simplicity of manual operation.
Significantly reduced processing time
But the EDS process is not inherently slow. By changing the heating and cooling system and design of the door clamps, the researchers were able to significantly reduce processing time without sacrificing any of the attributes and strengths that have made EDS successful.
Now EDS may be used to clean up burial sites in places like Alaska’s Fort Glenn, a World War II-era secret airfield that played a critical role in the Aleutian Islands Campaign. Records indicate that during the war munitions may have been buried there, but it isn’t known if those munitions were ever recovered.
“A burial site remediation could take several years and in a remote place like Fort Glenn, the costs really add up,” says Brent. “So if we can cut the processing time in half, that’s a huge savings.” Fort Glenn is just one of many suspected burial sites all over the country.
The core of EDS is a leak-tight vessel, in which munitions are placed. An explosive shaped charge opens the metal shell, exposing the chemical agent and burster, a small explosive that disperses the agent. The burster explodes or deflagrates safely inside the vessel. A reagent is then pumped into the chamber to neutralize the chemical agent. The chamber is heated and turned to mix the chemicals and facilitate the reaction.
Heating and cooling the vessel is the most time consuming part of the whole process. One of the biggest changes was a switch from heating the entire vessel from the outside in to pumping in steam to heat the vessel from the inside out. That reduced the heating time down from about 90 minutes to about 20 minutes, a total savings of more than two hours, since the vessel is heated in two stages.
“This was a significant change,” says Brent. “Commercial steam fittings usually allow a little leakage, which is not acceptable for our process. And the whole vessel rotates as the steam is injected, adding another layer of complexity. It’s more difficult to maintain the integrity of the seals with the big shifts in temperature that occur when the steam is turned on and off. So it took some time and work to develop fittings and valves that met our safety requirements.”
“Not all of the safety issues were intuitively obvious,” adds John. “The EDS is housed inside a vapor containment structure with a carbon filtration system that provides an extra layer of defense against an agent release. The filtration system does not like water, so we had to think about accident scenarios that might release steam into the building.”
Cooling the vessel rapidly posed another problem. The vessel can’t be opened until it has cooled to 60 degrees C, which used to take overnight. The researchers built an intermediate holding container, so the hot effluent can be drained as soon as the operation finishes. Cold water is then pumped into the vessel to accelerate cooling. Injecting steam actually made it easier to cool the vessel because the vessel walls don’t get as hot.
Testing at Aberdeen Proving Grounds
The researchers also changed the clamps on the door of the vessel. In the Phase 1 and Phase 2 EDS, the clamp on the door was attached to the trailer when the vessel door was opened. “As you closed the door, you had to disconnect the clamp from the trailer to allow the vessel to rotate during operation,” explains Brent. “The nuts on those clamps had to be tightened by hand.”
The Phase 2 vessel is about 3 feet in diameter and the clamps weigh about 1,500 pounds each. Tightening the clamps required nearly an hour’s worth of brute, physical work. The new design uses a clamp designed for undersea operations in the oil industry. Using a pneumatic wrench, the new door design can be closed in about five minutes.
Since February, the Army has been testing the P2P with live mustard agent at the Aberdeen Proving Ground in Maryland. The Sandia researchers are also working on additional modifications that will further reduce processing time and simplify the operation.
Before the vessel can be drained, liquid and gas samples must be collected and analyzed in a lab to confirm destruction of the agent. “We’re working on gas and liquid monitoring systems based on MicroChemLab technology that will take regular samples throughout the process to give continuous feedback,” says Brent. “Automating these two processes could save another two to three hours.”
The P2P performed well in the Aberdeen Proving Grounds tests earlier this year. The Army is now considering if it is better to retrofit the existing EDS units or create a Phase 3 system. Brent expects work on either option to start sometime next year.-- Patti Koning