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Posts Tagged ‘applications’

This article appeared in Fermilab Today on Sept. 22, 2014.

Harsha Panunganti of Northern Illinois University works on the laser system (turned off here) normally used to create electron beams from a photocathode. Photo: Reidar Hahn

Harsha Panunganti of Northern Illinois University works on the laser system (turned off here) normally used to create electron beams from a photocathode. Photo: Reidar Hahn

Lasers are cool, except when they’re clunky, expensive and delicate.

So a collaboration led by RadiaBeam Technologies, a California-based technology firm actively involved in accelerator R&D, is designing an electron beam source that doesn’t need a laser. The team led by Luigi Faillace, a scientist at RadiaBeam, is testing a carbon nanotube cathode — about the size of a nickel — in Fermilab’s High-Brightness Electron Source Lab (HBESL) that completely eliminates the need for a room-sized laser system currently used to generate the electron beam.

Fermilab was sought out to test the experimental cathode because of its capability and expertise for handling intense electron beams, one of relatively few labs that can support this project.

Tests have shown that the vastly smaller cathode does a better job than the laser. Philippe Piot, a staff scientist in the Fermilab Accelerator Division and a joint appointee at Northern Illinois University, says tests have produced beam currents a thousand to a million times greater than the one generated with a laser. This remarkable result means that electron beam equipment used in industry may become not only less expensive and more compact, but also more efficient. A laser like the one in HBESL runs close to half a million dollars, Piot said, about hundred times more than RadiaBeam’s cathode.

The technology has extensive applications in medical equipment and national security, as an electron beam is a critical component in generating X-rays. And while carbon nanotube cathodes have been studied extensively in academia, Fermilab is the first facility to test the technology within a full-scale setting.

“People have talked about it for years,” said Piot, “but what was missing was a partnership between people that have the know-how at a lab, a university and a company.”

The dark carbon-nanotube-coated area of this field emission cathode is made of millions of nanotubes that function like little lightning rods. At Fermilab's High-Brightness Electron Source Lab, scientists have tested this cathode in the front end of an accelerator, where a strong electric field siphons electrons off the nanotubes to create an intense electron beam. Photo: Reidar Hahn

The dark carbon-nanotube-coated area of this field emission cathode is made of millions of nanotubes that function like little lightning rods. At Fermilab’s High-Brightness Electron Source Lab, scientists have tested this cathode in the front end of an accelerator, where a strong electric field siphons electrons off the nanotubes to create an intense electron beam. Photo: Reidar Hahn

Piot and Fermilab scientist Charles Thangaraj are partnering with RadiaBeam Technologies staff Luigi Faillace and Josiah Hartzell and Northern Illinois University student Harsha Panuganti and researcher Daniel Mihalcea. A U.S. Department of Energy Small Business Innovation Research grant, a federal endowment designed to bridge the R&D gap between basic research and commercial products, funds the project. The work represents the kind of research that will be enabled in the future at the Illinois Accelerator Research Center — a facility that brings together Fermilab expertise and industry.

The new cathode appears at first glance like a smooth black button, but at the nanoscale it resembles, in Piot’s words, “millions of lightning rods.”

“When you apply an electric field, the field lines organize themselves around the rods’ extremities and enhance the field,” Piot said. The electric field at the peaks is so intense that it pulls streams of electrons off the cathode, creating the beam.

Traditionally, lasers strike cathodes in order to eject electrons through photoemission. Those electrons form a beam by piggybacking onto a radio-frequency wave, synchronized to the laser pulses and formed in a resonance cavity. Powerful magnets focus the beam. The tested nanotube cathode requires no laser as it needs only the electric field already generated by the accelerator to siphon the electrons off, a process dubbed field emission.

The intense electric field, though, has been a tremendous liability. Piot said critics thought the cathode “was just going to explode and ruin the electron source, and we would be crying because it would be dead.”

One of the first discoveries Piot’s team made when they began testing in May was that the cathode did not, in fact, explode and ruin everything. The exceptional strength of carbon nanotubes makes the project feasible.

Still, Piot continues to study ways to optimize the design of the cathode to prevent any smaller, adverse effects that may take place within the beam assembly. Future research also may focus on redesigning an accelerator that natively incorporates the carbon nanotube cathode to avoid any compatibility issues.

Troy Rummler

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This article appeared in Fermilab Today on July 21, 2014.

Members of the prototype proton CT scanner collaboration move the detector into the CDH Proton Center in Warrenville. Photo: Reidar Hahn

Members of the prototype proton CT scanner collaboration move the detector into the CDH Proton Center in Warrenville. Photo: Reidar Hahn

A prototype proton CT scanner developed by Fermilab and Northern Illinois University could someday reduce the amount of radiation delivered to healthy tissue in a patient undergoing cancer treatment.

The proton CT scanner would better target radiation doses to the cancerous tumors during proton therapy treatment. Physicists recently started testing with beam at the CDH Proton Center in Warrenville.

To create a custom treatment plan for each proton therapy patient, radiation oncologists currently use X-ray CT scanners to develop 3-D images of patient anatomy, including the tumor, to determine the size, shape and density of all organs and tissues in the body. To make sure all the tumor cells are irradiated to the prescribed dose, doctors often set the targeting volume to include a minimal amount of healthy tissue just outside the tumor.

Collaborators believe that the prototype proton CT, which is essentially a particle detector, will provide a more precise 3-D map of the patient anatomy. This allows doctors to more precisely target beam delivery, reducing the amount of radiation to healthy tissue during the CT process and treatment.

“The dose to the patient with this method would be lower than using X-ray CTs while getting better precision on the imaging,” said Fermilab’s Peter Wilson, PPD associate head for engineering and support.

Fermilab became involved in the project in 2011 at the request of NIU’s high-energy physics team because of the laboratory’s detector building expertise.

The project’s goal was a tall order, Wilson explained. The group wanted to build a prototype device, imaging software and computing system that could collect data from 1 billion protons in less than 10 minutes and then produce a 3-D reconstructed image of a human head, also in less than 10 minutes. To do that, they needed to create a device that could read data very quickly, since every second data from 2 million protons would be sent from the device — which detects only one proton at a time — to a computer.

NIU physicist Victor Rykalin recommended building a scintillating fiber tracker detector with silicon photomultipliers. A similar detector was used in the DZero experiment.

“The new prototype CT is a good example of the technical expertise of our staff in detector technology. Their expertise goes back 35 to 45 years and is really what makes it possible for us to do this,” Wilson said.

In the prototype CT, protons pass through two tracking stations, which track the particles’ trajectories in three dimensions. (See figure.) The protons then pass through the patient and finally through two more tracking stations before stopping in the energy detector, which is used to calculate the total energy loss through the patient. Devices called silicon photomultipliers pick up signals from the light resulting from these interactions and subsequently transmit electronic signals to a data acquisition system.

In the prototype proton CT scanner, protons enter from the left, passing through planes of fibers and the patient's head. Data from the protons' trajectories, including the energy deposited in the patient, is collected in a data acquisition system (right), which is then used to map the patient's tissue. Image courtesy of George Coutrakon, NIU

In the prototype proton CT scanner, protons enter from the left, passing through planes of fibers and the patient’s head. Data from the protons’ trajectories, including the energy deposited in the patient, is collected in a data acquisition system (right), which is then used to map the patient’s tissue. Image courtesy of George Coutrakon, NIU

Scientists use specialized software and a high-performance computer at NIU to accurately map the proton stopping powers in each cubic millimeter of the patient. From this map, visually displayed as conventional CT slices, the physician can outline the margins, dimensions and location of the tumor.

Elements of the prototype were developed at both NIU and Fermilab and then put together at Fermilab. NIU developed the software and computing systems. The teams at Fermilab worked on the design and construction of the tracker and the electronics to read the tracker and energy measurement. The scintillator plates, fibers and trackers were also prepared at Fermilab. A group of about eight NIU students, led by NIU’s Vishnu Zutshi, helped build the detector at Fermilab.

“A project like this requires collaboration across multiple areas of expertise,” said George Coutrakon, medical physicist and co-investigator for the project at NIU. “We’ve built on others’ previous work, and in that sense, the collaboration extends beyond NIU and Fermilab.”

Rhianna Wisniewski

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A second chance at sight

Monday, February 17th, 2014

This article appeared in symmetry on February 4, 2014.

Silicon microstrip detectors, a staple in particle physics experiments, provide information that may be critical to restoring vision to some who lost it.

Silicon microstrip detectors, a staple in particle physics experiments, provide information that may be critical to restoring vision to some who lost it.

In 1995, physicist Alan Litke co-wrote a particularly prescient article for Scientific American about potential uses for an emerging technology called the silicon microstrip detector. With its unprecedented precision, this technology was already helping scientists search for the top quark and, Litke wrote, it could help discover the elusive Higgs boson. He further speculated that it could perhaps also begin to uncover some of the many mysteries of the brain.

As the article went to press, physicists at Fermilab announced the discovery of the top quark, using those very same silicon detectors. In 2012, the world celebrated the discovery of the Higgs boson, aided by silicon microstrip detectors at CERN. Now Litke’s third premonition is also coming true: His work with silicon microstrip detectors and slices of retinal tissue is leading to developments in neurobiology that are starting to help people with certain kinds of damage to their vision to see.

“The starting point and the motivation was fundamental physics,” says Litke, who splits his time between University of California, Santa Cruz, and CERN. “But once you have this wonderful technology, you can think about applying it to many other fields.”

Silicon microstrip detectors use a thin slab of silicon, implanted with an array of diode strips, to detect charged particles. As a particle passes through the silicon, a localized current is generated. This current can be detected on the nearby strips and measured with high spatial resolution and accuracy.

Litke and collaborators with expertise in, and inspiration from, the development of silicon microstrip detectors, fabricated two-dimensional arrays of microscopic electrodes to study the complex circuitry of the retina. In the experiments, a slice of retinal tissue is placed on top of one of the arrays. Then a movie—a variety of visual stimuli including flashing checkerboards and moving bars—is focused on the input neurons of the retina, and the electrical signals generated by hundreds of the retina’s output neurons are simultaneously recorded. This electrical activity is what would normally be sent as signals to the brain and translated into visual perceptions.

This process allowed Litke and his collaborators to help decipher the retina’s coded messages to the brain and to create a functional connectivity map of the retina, showing the strengths of connections between the input and output neurons. That in itself was important to neurobiology, but Litke wanted to take this research further, to not just record neural activity but also to stimulate it. Litke and his team designed a system in which they stimulate retinal and brain tissue with precise electrical signals and study the kinds of signals the tissue produces in response.

Such observations have led to an outpouring of new neurobiology and biomedical applications, including studies for the design of a retinal prosthesis, a device that can restore sight. In a disease like retinitis pigmentosa or age-related macular degeneration, the eye’s output system to the brain is fine, but the input system has degraded.

In one version of a retinal prosthesis, a patient could wear a small video camera—something similar to Google Glass. A small computer would process the collected images and generate a pattern of electrical signals that would, in turn, stimulate the retina’s output neurons. In this way, the pattern of electrical signals that a naturally functioning eye would create could be replicated. The studies with the stimulation/recording system are being carried out in collaboration with neurobiologist E. J. Chichilnisky (Salk Institute and Stanford University) and physicist Pawel Hottowy (AGH University of Science and Technology, Krakow). The interdisciplinary and international character of the research highlights its origins in high energy physics.

In another approach, the degraded input neurons—the neurons that convert light into electrical signals—are functionally replaced by a two-dimensional array of silicon photodiodes. Daniel Palanker, an associate professor at Stanford University, has been using Litke’s arrays, in collaboration with Alexander Sher, an assistant professor at UCSC, who completed his postdoctoral work with Litke, to study how a prosthesis of this type would interact with a retina. Palanker and Sher are also researching retinal plasticity and have discovered that, in patients whose eyes have been treated with lasers, which can cause scar tissue, healthy cells sometimes migrate into an area where cells have died.

“I’m not sure we would be able to get this kind of information without these arrays,” Palanker says. “We use them all the time. It’s absolutely brilliant technology.”

Litke’s physics-inspired technology is continuing to play a role in the development of neurobiology. In 2013, President Obama announced the BRAIN—Brain Research through Advancing Innovative Neurotechnologies—Initiative, with the aim of mapping the entire neural circuitry of the human brain. A Nature Methods paper laying out the initiative’s scientific priorities noted that “advances in the last decade have made it possible to measure neural activities in large ensembles of neurons,” citing Litke’s arrays.

“The technology has enabled initial studies that now have contributed to this BRAIN Initiative,” Litke says. “That comes from the Higgs boson. That’s an amazing chain.”

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