Scientists are a step closer to building an intense electron beam source without a laser. Using Fermilab’s High-Brightness Electron Source Lab (HBESL), a team led by RadiaBeam Technologies is testing a carbon nanotube cathode—about the size of a nickel—that completely eliminates the need for a room-sized laser system. Tests with the nanotube cathode have produced beam currents a thousand to a million times greater than the one generated with a large, pricey laser system. 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. A U.S. Department of Energy Small Business Innovation Research grant funds the collaboration between California-based RadiaBeam, Fermilab, and Northern Illinois University.
The new cathode appears at first glance like a smooth black button, but at the nanoscale it it is made of millions of nanotubes that function like tiny lightning rods. When a strong electric field is applied, it pulls streams of electrons off the surface of the cathode, creating the electron beam. The exceptional strength of carbon nanotubes prevents the cathode from being destroyed. Traditionally, accelerator scientists use lasers to strike cathodes in order to eject electrons through photoemission. The electric and magnetic fields of the particle accelerator then organize the electrons into a beam. The tested nanotube cathode requires no laser: it only needs the electric field already generated by an accelerator to siphon the electrons off, a process dubbed field emission.
This new technology has extensive applications in medical equipment and national security, since an electron beam is a critical component in generating X-rays. While carbon nanotube cathodes have been studied extensively in academia, Fermilab is the first facility to test the technology within a full-scale setting. 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, about one hundred times more expensive than RadiaBeam's cathode.
The team 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. The work represents the kind of research that will be further enabled at the Illinois Accelerator Research Center — a facility that brings together Fermilab expertise with that of industry and academia, for the benefit of the U.S. economy.