The heat is on: Testing heats up at Sandia’s Solar Tower with high-temperature falling particle receiver

Technologists John Kelton and Daniel Ray inspect the Falling Particle Receiver during a cloud delay atop the National Solar Thermal Test Facility at Sandia National Laboratories.  (Photo by Randy Montoya)

by Rebecca Brock

Sandia researchers are working to lower the cost of solar energy systems and improve efficiencies in a big way, thanks to a system of small particles.

In June, engineers lifted Sandia’s continuously recirculating falling particle receiver to the top of the tower at the National Solar Thermal Test Facility, marking the start of first-of-its-kind testing that will continue through 2015. The Sandia-developed falling particle receiver works by dropping sand-like ceramic particles through a beam of concentrated sunlight, capturing and storing the heated particles in an insulated tank. The technology can capture and store heat at high temperatures without breaking down, unlike conventional molten salt systems.

Conventional central receiver technologies are limited to temperatures close to 600 degrees Celsius (1,112 degrees Fahrenheit), while operating temperatures for the falling particle receiver could exceed 1,000 degrees Celsius. Higher temperatures mean more available energy and cheaper storage costs because less material is needed to transfer heat.

Sandia engineer Cliff Ho (6123), the project’s principal investigator, says the goal of the testing is to develop a prototype, cost-competitive falling particle receiver that demonstrates the potential for thermal efficiency greater than 90 percent, while achieving particle temperatures of at least 700 degrees Celsius.

“This technology will enable higher temperatures and higher-efficiency power cycles that will bring down the cost of electricity produced from concentrating solar power,” Cliff says. “In addition, the ability to cheaply and efficiently store thermal energy directly in the heated particles will enable power production at night and on cloudy days.”

Falling particle receiver technology is expected to further advance the state-of-the art in concentrating solar power tower systems capable of generating up to 100 megawatts of electricity.

Sandia’s partners in the DOE project are the Georgia Institute of Technology, Bucknell University, King Saud University in Saudi Arabia, and the German Aerospace Center. The project is funded by DOE’s SunShot Initiative, which aims to reduce solar energy costs and expand the use of solar energy technologies throughout the United States.

Sandia design engineer Josh Christian (6123) says the on-sun testing at the solar tower will occur in two phases. First, researchers will test an insert designed by Georgia Tech that slows falling particles inside the receiver like a Pachinko board to increase the temperatures of the particles as they fall through.

Later this summer, Sandia engineers will remove the Georgia Tech insert from the receiver and evaluate free-falling curtain configurations.

Weather and other factors will affect the pace of the testing.

“New Mexico is great for this project because our state has pretty consistent solar insolation throughout the year,” Josh explained. “However the biggest thing we need to know is how much power is going into the falling particle receiver. So a cloudy or hazy day is a big challenge for us. An ideal day for testing is a clear day with no clouds and no wind.”

The tower at Sandia’s National Solar Thermal Test Facility stands 200 feet tall and is the only testing facility of its kind in the United States. 

-- Rebecca Brock

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How does Saturn hide its age?

Results from Sandia’s Z machine provide hard data for an 80-year-old theory that could correct mistaken estimates of the planet Saturn’s age. In this false-color image made from data taken in 2008 by Cassini's visual and infrared mapping spectrometer, heat emitted from the interior of Saturn shows up as red. (Image credit: NASA/JPL/ASI/University of Arizona)

by Neal Singer

The unexplained heat has caused a 2-billion-year discrepancy for computer models estimating Saturn’s age. “Models that correctly predict Jupiter to be 4.5 billion years old find Saturn to be only 2.5 billion years old,” says Thomas Mattsson, high-energy-density physics theory group manager (1641).

Experiments at Sandia’s Z machine may have helped solve that problem when they verified an formerly untested 80-year-old proposition that molecular hydrogen, normally an insulator, becomes metallic if squeezed by enough pressure.  Physicists Eugene Wigner and Hilliard Huntington predicted in 1935 that a pressured lattice of hydrogen molecules would break up into individual hydrogen atoms, releasing free-floating electrons that could carry a current.

“That long-ago prediction would explain Saturn’s temperature because when hydrogen metallizes and mixes with helium in a dense liquid, it can release helium rain,” says Mike Desjarlais (1600). Helium rain is an energy source that can alter the evolution of a planet.

“Essentially, helium rain would keep Saturn warmer than calculations of planetary age alone would predict,” says Marcus Knudson (1646). Marcus and Mike are the lead authors of a June 26 Science article, “Direct observation of an abrupt insulator-to-metal transition in dense liquid deuterium.”

This proposed density-driven hydrogen transition had never been observed experimentally until Sandia’s recent experiments.

The tests ran on Sandia’s Z machine, the world’s most powerful pulsed-power machine, which sends a huge but precisely tuned sub-microsecond pulse of electricity at a target. The correspondingly strong magnetic field surrounding the pulse was used to shocklessly squeeze deuterium — a heavier variant of hydrogen — at relatively low temperatures. Previous experiments elsewhere used gas guns to shock the gas. This increased its pressure but at the same time raised its temperature beyond the range of interest for the density-driven phase transition.

A transition at 3 megabars of pressure

“We started at 20 degrees Kelvin, where hydrogen is a liquid, and sent a few-hundred kilobar shock — a tiny flyer plate pushed by Z’s magnetic field into the hydrogen — to warm the liquid,” says Marcus. “Then we used Z’s magnetic field to further compress the hydrogen shocklessly, which kept it right above the liquid-solid line at about 1,000 degrees K.”

Says Mike, “When the liquid was compressed to over 12 times its starting density, we saw the signs that it became atomic rather than molecular. The transition, at 3 megabars of pressure, gives theorists a solid figure to use in their calculations and helps identify the best theoretical framework for modeling these extreme conditions.”

The results need to be plugged into astrophysical models to see whether the now-confirmed transition to atomic hydrogen significantly decreases the age gap between the two huge planets.

“The Sandia work shows that dense hydrogen can be metallic, which in turn changes the coexistence of hydrogen and helium in the planet,” says Thomas. “The mechanism of helium rain that has been proposed is therefore very plausible, given our results, but the scientific discussion will continue over the next few years in establishing a new consensus.”

Interestingly, the determination that a metallic phase was reached was made optically. “There’s too much electrical noise in Z to make an electrical test, though we plan to directly measure current down the road,” Marcus says.

Optical tests rely on the transition from zero reflectivity (insulators) to the reflectivity achieved by metals.

“The only way you get reflectivity is when a material is metallic,” Marcus says. Reflectivity was tested across the visible spectrum because the experiment itself produced light. “We collected it, put it through a spectrometer to disperse it, and passed it into a camera to observe it.”

When the hydrogen insulator reached enough pressure to become metallized, the researchers observed 45 percent reflectivity, an excellent agreement with theoretical calculations, says Mike.

“This is a very nice merging of theory and experiment,” he says. “We threw all our computational tools — which are significant — at providing verification and interpretation of the complex experimental observations at Z.”

The work was done in collaboration with professor Ronald Redmer’s research group at University of Rostock in Germany and is a part of the Z Fundamental Science Program at Sandia. The multidisciplinary team included researchers with expertise in innovative experimental design, diagnostics, and pulse-shaping capabilities, matched with theoretical analysis using methods based on quantum mechanics.

Other authors besides Marcus, Mike, and Thomas include Redmer and Andreas Becker at University of Rostock, Ray Lemke and Kyle Cochrane (both 1641), Mark Savage (1651), and Dave Bliss (1675).

The Z machine is a National High Energy Density Science Facility supported by the NNSA.


-- Neal Singer

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Tracing the evolution of a drug-resistant pathogen

IDENTIFYING MECHANISMS BACTERIA USE — Sandia researchers Kelly Williams, left, and Corey Hudson (both 8633) view a segment of the Klebsiella pneumoniae genome around two genomic islands. The two researchers and their colleagues have identified several mechanisms that bacteria use to share genes and expand their antibiotic resistance.    (Photo by Dino Vournas)

by Sue Major Holmes

To fight a pathogen that’s highly resistant to antibiotics, first understand how it gets that way.

Klebsiella pneumoniae strains that carry a particular enzyme are known for “their ability to survive any antibiotics you throw at them,” says Corey Hudson (8633) of Sandia/California.

Using Sandia’s genome sequencing capabilities, Corey and colleagues Robert Meagher (8621) and Kelly Williams (8633), along with former postdoctoral employee Zach Bent, identified several mechanisms that bacteria use to share genes and expand their antibiotic resistance. They found that in some cases, bacteria can receive a new set of genes all at once and in the process become pathogenic.

To better understand how the process works, they focused on the large mobile DNAs, such as plasmids, which exist as free DNA circles apart from the bacterial chromosome, and genomic islands, which can splice themselves into the chromosome. These mobile DNAs are major mechanisms for evolution in organisms that lack a true nucleus. Genomic islands and plasmids carry genes that contribute to everything from metabolism to pathogenicity, and move whole clusters of genes all at once between species.

Identifying how genomic islands move and their effect on bacterial physiology could lead to new approaches to bypass bacterial defenses, Corey says.

Eventually, the effort might lead to a way to predict new pathogens before they emerge as public health threats.

“We’re just starting on this path,” Kelly says. “It’s a harder problem to predict emerging pathogens, rather than just observe them. Determining what is pathogenic in the first place and how it might become more pathogenic is a research challenge.”

Bacteria share genetic material with other bacteria

Bacteria share genetic material through free virus particles or through a cell-to-cell process called conjugation, where one bacterium sends out a tube from its surface into another’s and injects genes into the other cell, Kelly says.

A hypothetical example of sharing: A local water supply is contaminated with a pathogenic E. coli strain that is not antibiotic-resistant. Klebsiella pneumoniae enters the water, comes into contact with the E. coli, and donates genes. Now a pathogenic E. coli has acquired resistance, making it harder to eradicate.

“The great challenge is that bacteria can easily share their defenses,” Kelly says.

Over the two decades that various bacterial genomes have been sequenced, researchers have found rampant gene sharing. “They are not so much generating new genes all the time — that does happen slowly — but what they mainly do is shuffle genes around,” Kelly says. “The new gene combinations can quickly give bacteria a new pathogenic niche. They may then invade more tissues or survive in even more conditions.”

For the first time last year, Sandia microbiologists studying infectious diseases sequenced the entire genome of a Klebsiella pneumoniae strain that encodes New Delhi metallo-beta-lactamase (NDM-1). This enzyme makes the strain resistant to carbapenems, antibiotics of last resort. Klebsiella pneumoniae is the most common species of carbapenem-resistant Enterobacteriaceae (CRE) in the US, often having resistance to nearly all antibiotics in use. CREs also are dangerous because they can spread antibiotic resistance to other bacteria.

These opportunistic bacteria can grow on hospital surfaces or in lungs and tissues. The Centers for Disease Control and Prevention says about one in 25 hospital patients has an antibiotic-resistant infection, and it’s lethal in up to one in nine cases.

Since publishing the genomic analysis in June 2014, Sandia researchers have developed an experimental technique that detects genomic islands on the move. The team applies a computational or bioinformatics technique to identify islands in genomes and does particular studies of gene expression to see which antibiotic-resistance and other genes get turned on during an infection.

Research shows ‘the bug is always armed’

The research showed the beta-lactamase genes in Klebsiella pneumoniae were on all the time, whether or not the bacteria were infecting human cell cultures. In essence, Kelly says, “the bug is always armed” against antibiotics.

The team built a database of genomic islands they found in a survey of all sequenced bacteria. So far, the database contains nearly 4,000 genomic islands — only a partial list of what bacteria share, Corey says. The database reveals both global features of genomic islands and unique features in select groups of bacteria.

Rather than relying solely on such bioinformatics, the team invented a new experimental approach to detect islands as they pop out of the genome. The team stimulates this beginning stage of island mobilization by stressing the cells in certain ways. During this stage, the mobilized islands take circular form, independent of the chromosome. The islands are now free to move into other bacterial cells, bringing with them new sets of genes.

Experiments and bioinformatics work together, each yielding information the other did not and confirming each other. “We do what we can with the computer, but we like to test the resulting hypotheses in the lab,” Kelly says.


-- Sue Major Holmes

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Animal planet

A GLOBAL MISSION – Melissa Finley has made 21 trips to Afghanistan as part of Sandia’s International Biological and Chemical Threat Reduction organization, working closely with the country’s veterinary services on biosafety and biosecurity. In this photo, Melissa, an accomplished veterinarian, treats a local herd of cattle. (Photo courtesy of Melissa Finley)

by Nancy Salem

A veterinarian at a national lab might sound odd, but Sandia’s Melissa Finley helps make the world safer through livestock health and biosecurity

Melissa Finley’s credibility was on the line as she worked, surrounded by skeptics, to save the life of a dehydrated calf in rural Afghanistan. As a woman and foreigner she had to earn the trust of the villagers she was trying to help.

“They had never given fluids before, so I sent them to the market to get dextrose solution, a baby bottle, catheter, and antibiotics. I had to reassure them I wasn’t going to kill the calf, that they could trust me,” she says. “When the calf started to come around I had instantaneous respect.”

Melissa has been working in Afghanistan since 2009 as a member of Sandia’s International Biological and Chemical Threat Reduction organization (IBCTR). A seasoned veterinarian, she travels throughout the country teaching safe laboratory practices, providing continuing veterinary education to reduce the spread of infectious disease, and collaborating with the government’s animal health agencies.

Sandia’s hiring of a vet was outside the box. “It was off-the-charts nontraditional from what I was told,” Melissa says. But there is a tie between infectious diseases of animals, public health, and bioterrorism. Veterinarians play an important role by encouraging and helping governments implement animal-health policies.

Veterinary medicine is linked to biological threat reduction because about 75 percent of the agents that can be used as biological weapons are animal in origin. Melissa and her Sandia colleagues establish biorisk management practices at laboratories worldwide and improve the ability of veterinary and public health workers to reduce the potential for criminal acquisition of biological agents such as Bacillus anthracis, Brucella sp., and foot and mouth disease virus.

“The most likely repository for biological material is a laboratory. What happens when you secure all of the laboratories? You are forced to think more broadly about biorisk management and reducing the biological threat,” Melissa says.

Another possible reservoir of biological material exists in naturally occurring infectious disease outbreaks. “If you target animal populations and help countries prevent and control infectious diseases then there is less available in the environment for acquisition and fewer positive samples to be sent to laboratories for analysis,” she says. “I like to think we help developing nations bridge the gap between biosecurity and veterinary medicine.”

An early love of horses

Melissa is an Albuquerque native who grew up around animals. “We had dogs and my grandfather had a small farm with chickens, pigs, and a cow or two,” she says. “When I turned nine I pleaded with my parents to get me a horse.”

They did, and in high school Melissa decided she wanted to be a vet. She did a three-year pre-veterinary program at New Mexico State University then went to Colorado State University where in four years she earned a Doctor of Veterinary Medicine, or DVM.

Melissa wanted to focus on horses and landed a yearlong internship in private practice at the exclusive Alamo Pintado Equine Medical Center in Los Olivos, California. She worked on horses belonging to the renowned thoroughbred trainer D. Wayne Lukas, singers Jackson Browne and Wayne Newton, and rapper MC Hammer. She played with Michael Jackson’s monkeys and went to Ronald Reagan’s ranch. “It was very cool,” she says.

Her next stop was Cornell University in Ithaca, New York, where she did a two-year residency in large-animal internal medicine. “I was told the caseload was primarily horses, but when I got there it was dairy cattle,” she says. “I came to really appreciate bovine medicine. It was a whole new area of interest for me.”

After a brief stint in private practice that ended when she found herself wrestling a pig in mud while his buddies piled on, Melissa joined the University of California, Davis as a post-graduate researcher studying the impact of Neospora caninum, a protozoa, on bovine abortions. “It was an important project because N. caninum is one of the leading causes of abortion in cattle. It was my introduction into using animals for laboratory purposes,” she says. “But it was tough because I got attached to all of the cattle, even the one that kicked me more than once.”

Melissa moved on to Kansas State University as an assistant professor in clinical sciences in the College of Veterinary Medicine. Two years later she became a graduate student and teaching assistant in the college’s Department of Anatomy and Physiology. She taught sophomore, junior, and senior veterinary students internal medicine and pharmacology, and pursued her PhD investigating the molecular basis of repolarization of the equine cardiac action potential.

“I enjoyed working with animals but also found the research component interesting,” she says. “My research career started there.”

Melissa’s postdoctoral fellowship was at the Salk Institute for Biological Studies in La Jolla, California, where she continued to study repolarizing potassium channels, this time the structure and function of those that maintain resting membrane potential of heart and brain cells. “I was shaping my career to balance clinical relevance and research,” she says. “I wanted to bridge fundamental science and clinical practice.”

Mother was right

On a visit home to Albuquerque, Melissa’s mom suggested she look into jobs at Sandia. “I told her there weren’t any positions at Sandia for a veterinarian with a graduate degree in cellular physiology. It is an engineering laboratory,” she says. “I decided to look anyway and show her.”

But there was one. Sandia was looking for someone with a biosciences background to work in global security and biological weapons nonproliferation. Melissa was hired in 2005. “Biological threat reduction was the main goal, but the focus was on fundamental biosafety and biosecurity,” she says.

Melissa has traveled to about two dozen countries but spent most of her time in Afghanistan and Iraq. She focused on Afghanistan because she could work closely with its veterinary services and support IBCTR’s mission there. She has made 21 trips to the country.

Melissa developed a comprehensive training course to enhance veterinarians’ ability to detect and control infectious diseases. The country has challenges including rampant rabies, brucellosis, and anthrax.

Sandia’s strategy in Afghanistan is to piece small projects into a large, comprehensive program. “We started with fundamental work in laboratory biorisk management. We then looked at naturally occurring outbreaks as repositories for biological materials,” says Melissa, whose field experience contributed to the development of Sandia’s portable laboratory platforms Syndromic SpinDx and BaDx.

Sandia has hired two other veterinarians: Van Brass and Carrie McNeil who work in Mali and Southeast Asia, among other places.

Some scary moments

Melissa, who had to conquer a serious fear of flying to do her job, has had a few scary moments in the field. “You have to be a little scared or you’re not aware,” she says.

She recalls rickety helicopter rides over Afghan mountains and military escorts into danger zones. “I got used to it, how body armor fits, how to wear a helmet,” she says. “I know the do’s and don’ts.”

But she says she wouldn’t trade her Sandia work for anything else the veterinary world has to offer. “I never dreamed I would have a job like this,” she says. “It’s been exciting for me as a veterinarian and as a person who works in global security. I’ve watched areas like Afghanistan and Iraq transition from war to sovereignty. It’s part of history.”

-- Nancy Salem

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