For the first time, researchers have successfully used a nanodevice to accelerate electrons. Particle accelerators are important tools in many fields including industry, research and medicine. The space required for these machines ranges from a few square meters to large research centers. Using lasers to accelerate electrons in photonic nanostructures is a microscopic alternative that has the potential to significantly reduce costs and enable devices to be significantly smaller.
So far, there is no evidence that this approach can significantly increase energy. In other words, it has not been proven that the speed of electrons has actually increased significantly. Now, a team of laser physicists from the Friedrich-Alexander-University Erlangen-Nuremberg (FAU), together with colleagues from Stanford University, has successfully demonstrated the first nanophotonic electron accelerator.
Particle accelerators and their nanophoton evolution
When people hear "particle accelerator," most people probably think of the Large Hadron Collider at CERN in Geneva. This 27-kilometer-long circular tunnel is used by researchers from all over the world to study unknown elementary particles. However, this giant particle accelerator is an exception. We are more likely to encounter them elsewhere in our daily lives, such as during medical imaging procedures or radiation treatment of tumors. However, even so, these devices are still several meters in size, quite bulky, and leave much to be desired in terms of performance.
In an effort to improve and reduce the size of existing devices, physicists around the world are working on dielectric laser accelerators, also known as nanophoton accelerators. The structure they used is only 0.5 millimeters long, and the channel through which electrons are accelerated is only about 225 nanometers wide, making these accelerators as small as computer chips.
The particles are accelerated by ultrashort laser pulses that illuminate the nanostructures. "Our dream application would be to mount a particle accelerator on an endoscope to be able to deliver radiation therapy directly to affected parts of the body," explains Dr. Tomáš Chlouba, one of the four lead authors of the recently published paper.
This dream may still be out of reach for the FAU team from the Department of Laser Physics, led by Professor Peter Hommelhoff and composed of Drs. Tomáš Chlouba, Dr. Roy Shiloh, Stefanie Kraus, Leon Brückner and Julian Litzel, but they have now managed to take a decisive step in the right direction by demonstrating a nanophotonic electron accelerator. Dr. Roy Shiloh said excitedly: "For the first time, we can actually implement a particle accelerator on a chip."
Guided electrons + acceleration = particle accelerator
Just over two years ago, the research team achieved its first major breakthrough: they successfully used the alternating phase focusing (APF) method from early acceleration theory to control the long-distance flow of electrons in a vacuum channel. This is an important step on the road to building particle accelerators. Now, all you need to get a lot of power is acceleration.
"Using this technique, we have now succeeded not only in guiding electrons, but also in accelerating them in these nanofabricated structures, which are up to half a millimeter in length," explains Stephanie Kraus. "While this may not sound like much of an achievement to many, it is a huge success in the field of accelerator physics, and we achieve energies of 12 kiloelectronvolts," explains Leon Brückner.
To accelerate particles to such large distances (from the nanometer scale), physicists at FAU combined the APF method with a specially developed cylindrical geometry.
However, this demonstration is just the beginning. The goal now is to increase the energy and electron current gain so that on-chip particle accelerators are sufficient for medical applications. To do this, the energy gain must be increased by about a factor of 100. Tomáš Chlouba explains what’s next for FAU laser physicists.
The results of the Erlangen laser physicists' research were presented almost simultaneously by their colleagues at Stanford University in the United States: their results are currently under review but can be viewed in the database. In a project funded by the Gordon and Betty Moore Foundation, the two teams are collaborating to implement an "accelerator on a chip."
"In 2015, the FAU and Stanford-led ACHIP team had a vision for a revolutionary approach to particle accelerator design," said Dr. Gary Greenberg of the Gordon and Betty Moore Foundation. "We are pleased that our support has helped turn this vision into a reality."