The US Defense Threat Reduction Agency, the US Department of Energy, and the US Air Force Office of Scientific Research have funded a research titled “Multi-MeV electron acceleration by sub-terawatt laser pulses” and carried out by researchers from the University of Maryland.
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The research was carried out by Andrew Goers, George Hine, Linus Feder, Bo Miao, Fatholah Salehi, Jared Wahlstrand and Howard Milchberg, and published in the November 6, 2015 issue of the journal Physical Review Letters. The research is developing a new method to constructing particle accelerators that could be used for materials imaging and safe medical imaging.
Scientists are aware that normal particle accelerators are large machines that occupy lots of spaces due to their large hardware, radiation shielding, and power supplies. But the latest innovation developed by the UMD scientists provide new ways to make the particle accelerators without spending so much or taking up too much space.
The team used accelerated electron beams to almost the speed of light under very low laser energies, and this cuts out the mechanical problem of developing portable particle accelerators.
“We have accelerated high-charge electron beams to more than 10 million electron volts using only millijoules of laser pulse energy. This is the energy consumed by a typical household lightbulb in one-thousandth of a second.” said Howard Milchberg, professor of Physics and Electrical and Computer Engineering at UMD and senior author of the study.
“Because the laser energy requirement is so low, our result opens the way for laser-driven particle accelerators that can be moved around on a cart,” Milchberg added. “As an unexpected bonus, the accelerator generates an intense flash of optical light so short that we believe it represents only one-half of a wavelength cycle.”
The aim of the scientists is to deploy the ultrashort flashes of light to develop optical light strobes that can be used to collect electron motions as it passes through atomic orbits – something that is crucial to developing material science and nanotechnology.
Creating a technique called laser-driven plasma wakefield acceleration, the researchers were able to shoot a pulse of laser into plasma – an hydrogen gas which has been ionized to delete all seen electrons from the gas atoms.
“Unless your laser pulse can induce the plasma wake in the first place—and it takes a very intense pulse to do that—you’re out of luck,” Milchberg noted.
Ultimately, the UMD team was able to create a relativistic self-focusing effect which was sued to raise the density of plasma to nearly 20 times the amount used in normal tests, developing a situation whereby they reduced the amount of laser pulse energy needed to create a strong plasma wake.
“If you increase the plasma density enough, even a pipsqueak of a laser pulse can generate strong relativistic effects,” Milchberg said.
“From a practical standpoint, the key difference here is the footprint of the accelerator. What once required a room full of equipment and a very powerful laser could eventually be done with a small machine on a movable cart, with a standard wall-socket plug,” said Andrew Goers, a graduate student in Physics at UMD and the study’s lead author.
“We started with a very powerful laser and found that we were able to keep dialing the energy back. Eventually we got down to about 1 percent of the laser’s peak energy, but we were still seeing an effect. We were blown away by this,” Goers added.