Way cool: UVA professor developing ‘freeze ray’ technology for the Air Force
IMAGE: DOCTORAL CANDIDATES SARA MAKAREM HOSEINI AND DANIEL HIRT OBSERVE THE PLASMA RAY SETUP. THOUGH HIRT WEARS A KNIT CAP AND PUFFY JACKET FOR EFFECT, THE COOLING IS LOCALIZED AND DOESN’T HAVE MUCH INFLUENCE ON THE SURROUNDING ROOM TEMPERATURE. view more
CREDIT: TOM COGILL
You know that freeze-ray gun that “Batman” villain Mr. Freeze uses to “ice” his enemies? A University of Virginia professor thinks he may have figured out how to make one in real life.
The discovery – which, unexpectedly, relies on heat-generating plasma – is not meant for weaponry, however. Mechanical and aerospace engineering professor Patrick Hopkins wants to create on-demand surface cooling for electronics inside spacecraft and high-altitude jets.
“That’s the primary problem right now,” Hopkins said. “A lot of electronics on board heat up, but they have no way to cool down.”
The U.S. Air Force likes the prospect of a freeze ray enough that it has granted the professor’s ExSiTE Lab (Experiments and Simulations in Thermal Engineering) $750,000 over three years to study how to maximize the technology.
From there, the lab will partner with Hopkins’ UVA spinout company, Laser Thermal, for the fabrication of a prototype device.
The professor explained that, on Earth – or in the air closer to it – the electronics in military craft can often be cooled by nature. The Navy, for example, uses ocean water as part of its liquid cooling systems. And closer to the ground, the air is dense enough to help keep aircraft components chilled.
However, “With the Air Force and Space Force, you’re in space, which is a vacuum, or you’re in the upper atmosphere, where there’s very little air that can cool,” he said. “So what happens is your electronics keep getting hotter and hotter and hotter. And you can’t bring a payload of coolant onboard because that’s going to increase the weight, and you lose efficiency.”
Hopkins believes he’s on track toward a lightweight solution. He and collaborators recently published a review article about this and other prospects for the technology in the journal ACS Nano.
The Fourth State of Matter
The matter we encounter every day exists in three states: solid, liquid and gas. But there’s a fourth state: plasma. While it may seem relatively rare to us on Earth, plasma is the most common form of matter in the universe. In fact, it’s the stuff that stars are made of.
Plasmas can occur when gas is energized, Hopkins said. That powers their unique properties, which vary based on the type of gas and other conditions. But what unites all plasma is an initial chemical reaction that untethers electrons from their nuclear orbits and releases a flow of photons, ions and electrons, among other energetic species.
The eye-popping results can be witnessed in the sudden flash of a lightning strike, for example, or the warm glow of a neon sign.
Though plasma screen televisions were once a thing, then phased out, don’t let that fool you. Plasma is increasingly being used in technology. It’s already utilized in the engines of many of the Air Force’s speediest jets. The plasma assists combustion, improving speed and efficiency.
But Hopkins pictures plasma also being used in the interior of the craft.
The typical solution for air and space electronics has been a “cold plate,” which conducts heat away from the electronics toward radiators, which release it. For advanced electronics, however, that may not always be sufficient.
Hopkins thinks the revised setup may be something like a robotic arm that roves in response to temperature changes, with a short, close-up electrode that zaps hot spots.
“This plasma jet is like a laser beam; it’s like a lightning bolt,” Hopkins said. “It can be extremely localized.”
The Plasma Enigma
Cool fact: Plasma can reach temperatures as hot as the surface of the sun. But it also seems to have this weird characteristic – one that would appear to violate the second law of thermodynamics. When it strikes a surface, it actually chills before heating.
Hopkins and his collaborator, Scott Walton of the U.S. Navy Research Laboratory, made the unexpected discovery several years ago, just before the pandemic hit.
“What I specialize in is doing really, really fast and really, really small measurements of temperature,” Hopkins said of his custom-made microscopic instruments, which can record specialized heat registries.
In their experiment, they fired a purple jet of plasma generated from helium through a hollow needle encased in ceramic. The target was a gold-plated surface. The researchers chose gold because it’s inert, and as much as possible, they wanted to avoid surface etching by the focused beam, which could skew the results.
“So when we turned on the plasma,” Hopkins said, “we could measure temperature immediately where the plasma hit, then we could see how the surface changed. We saw the surface cool first, then it would heat up.
“We were just puzzled at some level about why this was happening, because it kept happening over and over. And there was no information for us to pull from because no prior literature has been able to measure the temperature change with the precision that we have. No one’s been able to do it so quickly.”
What They Realized
What they finally determined, in association with then-UVA doctoral researcher John Tomko and continued testing with the Navy lab, was that the surface cooling must have been the result of blasting an ultrathin, hard-to-see surface layer, composed of carbon and water molecules.
A similar process happens when cool water evaporates off of our skin after a swim.
“Evaporation of water molecules on the body requires energy; it takes energy from body, and that’s why you feel cold,” the professor said. “In this case, the plasma rips off the absorbed species, energy is released, and that’s what cools.”
Hopkins’ microscopes work by a process called “time-resolved optical thermometry” and measure something called “thermoreflectance.”
Basically, when the surface material is hotter, it reflects light differently than when it’s colder. The specialized scope is needed because the plasma would otherwise obliterate any directly touching temperature gauges.
So how cold is cold? They determined they were able to reduce the temperature by several degrees, and for a few microseconds. While that may not seem dramatic, it’s enough to make a difference in some electronic devices.
After the pandemic delay, Hopkins and collaborators published their initial findings in Nature Communications last year.
Then the question became: Could they get a reaction to be colder and last longer?
Refining the Freeze Ray
Previously working with the Navy’s borrowed equipment – so lightweight and safe it was often used for school demonstrations – the UVA lab now has its own setup, thanks to the Air Force grant.
The team is looking at how variations on their original design might improve the apparatus. Doctoral candidates Sara Makarem Hoseini and Daniel Hirt are considering gases, metals and surface coatings that the plasma can target.
Hirt provided a lab update.
“We haven’t really explored the use of different gasses yet, as we’re still working with helium,” he said. “We have experimented so far with different metals, such as gold and copper, and semiconductors, and each material offers its own playground for investigating how plasma interacts with their different properties.
“Since the plasma is composed of a variety of different particles, changing the type of gas used will allow us to see how each one of these particles impact material properties.”
Hirt said working with Hopkins on a project with such significant implications has rejuvenated his interest in research, in large part due to the supportive lab environment the professor fosters.
“I feel like it’s night and day comparing not only where I was as a scientist, but also my enjoyment of science, to where I am today,” he said.
New Directional Plasma Cooling Ray
The plasma jet in this example is made from helium, which creates a purple glow. The lab will experiment with other gases, too, to identify which is ideal for cooling.
CREDIT
Tom Cogill
JOURNAL
ACS Nano
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Ultrafast and Nanoscale Energy Transduction Mechanisms and Coupled Thermal Transport across Interfaces
Frosty hydrogen as target
New method improves proton acceleration with high power laser
IMAGE: SHADOWGRAPHS (BLUE) AT THE TIME OF IMPACT OF THE HIGH-INTENSITY LASER PULSE ON THE JET OF HYDROGEN. A WEAKER LIGHT PULSE SENT IN ADVANCE DELIBERATELY CHANGED THE HYDROGEN JET INTO THREE DIFFERENT INITIAL STATES. view more
CREDIT: HZDR
Bringing protons up to speed with strong laser pulses – this still young concept promises many advantages over conventional accelerators. For instance, it seems possible to build much more compact facilities. Prototypes to date, however, in which laser pulses are fired at ultra-thin metal foils, show weaknesses – especially in the frequency with which they can accelerate protons. At the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), an international working group has tested a new technique: In this approach, frozen hydrogen acts as a "target" for the laser pulses. In the future, the method could serve as a basis for advanced tumor therapy concepts, as the team describes in the journal Nature Communications (DOI: 10.1038/s41467-023-39739-0).
Conventional proton accelerators such as the Large Hadron Collider at CERN in Geneva are based on the particle acceleration via strong radio frequency waves. In laser acceleration, on the other hand, ultra-bright light pulses give the particles a boost: Extremely short and powerful laser pulses are fired at wafer-thin metal foils. The light heats the material to such an extent that electrons are ejected in large numbers, while the heavy atomic nuclei remain in place. Since the electrons are negatively charged and the atomic nuclei are positively charged, a strong electric field forms between them.
This field can then launch a pulse of protons with enormous force over a distance of only a few micrometers, thus bringing them to energies for which much longer systems would be needed with conventional accelerator technology. Another advantage: "With laser acceleration, we can pack a huge number of particles into one proton bunch," explains HZDR physicist Dr. Karl Zeil. "This could be interesting for radiation therapy of tumors."
However, the previous method of firing laser pulses at metal foils has drawbacks. Firstly, it is difficult to generate several proton pulses per second – the foil is already destroyed by a single laser shot and therefore has to be replaced again and again. Secondly, the acceleration process is quite complex and relatively difficult to control. The reason: The protons to be accelerated come from hydrocarbons that have accumulated on the metal foils as a layer of contaminants – not exactly ideal for perfect control of the experiment.
Filament instead of foil
Therefore, the German-American research team around Karl Zeil came up with an alternative: "Instead of a metal foil, we use a fine, strongly cooled hydrogen jet," the researcher describes. "This jet serves as a target for our high-intensity laser pulses." Specifically, the experts cool hydrogen gas in a copper block to such an extent that it becomes liquid. The liquid hydrogen then flows through a nozzle into a vacuum chamber. It thus cools further and solidifies into a micrometer-thin filament: the target for the laser pulses. And since the hydrogen filament renews itself, the laser has a new, intact target in its sight for every shot.
Another benefit is that the setup allows for a more favorable acceleration mechanism: Instead of just heating the material, the laser pulses use radiation pressure to push the electrons out of the hydrogen and create the extreme electric fields needed to accelerate the protons. The team was able to optimize the process by sending a short, weaker light pulse in front of the main laser pulse. This preheated the frozen hydrogen filament, causing it to expand and its cross-section to grow from five micrometers to several times that size. This made it possible to increase the acceleration distance and optimize the process.
Prospects for tumor therapy
The result: "We were able to bring protons up to an energy of 80 MeV," reports Karl Zeil. "This is close to the previous record for laser proton acceleration. But unlike previous facilities, our technique has the potential to generate multiple proton bunches per second." Furthermore, the acceleration process is comparatively easy to simulate for hydrogen targets using high-performance computing – a task that also involved the Center for Advanced Systems Understanding (CASUS) at HZDR. "This allows us to better understand and optimize the interaction between laser and matter," Zeil said. Now the experts want to use AI algorithms to increase the "hit rate" between the laser pulses and the frozen hydrogen jet.
The technology could be interesting for a future type of radiation therapy. Already today, some tumors are successfully irradiated with protons. Laser acceleration could increase the dose and thus shorten the irradiation time. And – as an HZDR study suggests – this could better protect the healthy tissue surrounding the tumor.
Publication:
M. Rehwald, S. Assenbaum, C. Bernert, F. Brack, M. Bussmann, T. Cowan, C. Curry, F. Fiuza, M. Garten, L. Gaus, M. Gauthier, S. Göde, I. Göthel, S. Glenzer, L. Huang, A. Huebl, J. Kim, T. Kluge, S. Kraft, F. Kroll, J. Metzkes-Ng, T. Miethlinger, M. Loeser, L. Obst-Huebl, M. Reimold, H. Schlenvoigt, C. Schoenwaelder, U. Schramm, M. Siebold, F. Treffert, L. Yang, T. Ziegler & K. Zeil: Ultra-short pulse laser acceleration of protons to 80 MeV from cryogenic hydrogen jets tailored to near-critical density, in Nature Communications, 2023 (DOI: 10.1038/s41467-023-39739-0)
Further information:
Dr. Karl Zeil
Institute of Radiation Physics at HZDR
Phone: +49 351 260 2614 | Email: k.zeil@hzdr.de
Media contact:
Simon Schmitt | Head
Communication and Media Relations at HZDR
Phone: +49 351 260 3400 | Email: s.schmitt@hzdr.de
The Helmholtz-Zentrum Dresden-Rossendorf (HZDR) performs – as an independent German research center – research in the fields of energy, health, and matter. We focus on answering the following questions:
• How can energy and resources be utilized in an efficient, safe, and sustainable way?
• How can malignant tumors be more precisely visualized, characterized, and more effectively treated?
• How do matter and materials behave under the influence of strong fields and in smallest dimensions?
To help answer these research questions, HZDR operates large-scale facilities, which are also used by visiting researchers: the Ion Beam Center, the Dresden High Magnetic Field Laboratory and the ELBE Center for High-Power Radiation Sources.
HZDR is a member of the Helmholtz Association and has six sites (Dresden, Freiberg, Görlitz, Grenoble, Leipzig, Schenefeld near Hamburg) with almost 1,500 members of staff, of whom about 670 are scientists, including 220 Ph.D. candidates.
JOURNAL
Nature Communications
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Ultra-short pulse laser acceleration of protons to 80 MeV from cryogenic hydrogen jets tailored to near-critical density
Scientists create novel approach to control energy waves in 4D
University of Missouri scientists engineered a synthetic metamaterial to direct mechanical waves along a specific path, which adds an innovative layer of control to 4D reality, otherwise known as the synthetic dimension.
Peer-Reviewed PublicationIMAGE: GUOLIANG HUANG view more
CREDIT: GUOLIANG HUANG/UNIVERSITY OF MISSOURI
Everyday life involves the three dimensions or 3D — along an X, Y and Z axis, or up and down, left and right, and forward and back. But, in recent years scientists like Guoliang Huang, the Huber and Helen Croft Chair in Engineering at the University of Missouri, have explored a “fourth dimension” (4D), or synthetic dimension, as an extension of our current physical reality.
Now, Huang and a team of scientists in the Structured Materials and Dynamics Lab at the MU College of Engineering have successfully created a new synthetic metamaterial with 4D capabilities, including the ability to control energy waves on the surface of a solid material. These waves, called mechanical surface waves, are fundamental to how vibrations travel along the surface of solid materials.
While the team’s discovery, at this stage, is simply a building block for other scientists to take and adapt as needed, the material also has the potential to be scaled up for larger applications related to civil engineering, micro-electromechanical systems (MEMS) and national defense uses.
“Conventional materials are limited to only three dimensions with an X, Y and Z axis,” Huang said. “But now we are building materials in the synthetic dimension, or 4D, which allows us to manipulate the energy wave path to go exactly where we want it to go as it travels from one corner of a material to another.”
This breakthrough discovery, called topological pumping, could one day lead to advancements in quantum mechanics and quantum computing by allowing for the development of higher dimension quantum-mechanical effects.
“Most of the energy — 90% — from an earthquake happens along the surface of the Earth,” Huang said. “Therefore, by covering a pillow-like structure in this material and placing it on the Earth’s surface underneath a building, and it could potentially help keep the structure from collapsing during an earthquake.”
The work builds on previous research by Huang and colleagues which demonstrates how a passive metamaterial could control the path of sound waves as they travel from one corner of a material to another.
The study, “Smart patterning for topological pumping of elastic surface waves,” was published in Science Advances, a journal of the American Association for the Advancement of Science (AAAS). It is supported by grants from the Air Force Office of Scientific Research and the Army Research Office.
JOURNAL
Science Advances
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Smart patterning for topological pumping of elastic surface waves
ARTICLE PUBLICATION DATE
28-Jul-2023
A rendering of the new synthetic metamaterial with 4D capabilities designed by scientists at the University of Missouri. It includes the ability to control energy waves on the surface of a solid material.
CREDIT
Guoliang Huang/University of Missouri
