October 6, 2015

Physicists shrink particle accelerator

Terahertz accelerator modules easily fit into two fingers.
Credit: DESY/Heiner Müller-Elsner

(October 6, 2015)  Prototype demonstrates feasibility of building terahertz accelerators

An interdisciplinary team of researchers has built the first prototype of a miniature particle accelerator that uses terahertz radiation instead of radio frequency structures. A single accelerator module is no more than 1.5 centimetres long and one millimetre thick. The terahertz technology holds the promise of miniaturising the entire set-up by at least a factor of 100, as the scientists surrounding DESY’s Franz Kärtner from the Center for Free-Electron Laser Science (CFEL) point out. They are presenting their prototype, that was set up in Kärtner's lab at the Massachusetts Institute of Technology (MIT) in the U.S., in the journal Nature Communications. The authors see numerous applications for terahertz accelerators, in materials science, medicine and particle physics, as well as in building X-ray lasers. CFEL is a cooperation between DESY, the University of Hamburg and the Max Planck Society.

In the electromagnetic spectrum, terahertz radiation lies between infrared radiation and microwaves. Particle accelerators usually rely on electromagnetic radiation from the radio frequency range; DESY’s particle accelerator PETRA III, for example, uses a frequency of around 500 megahertz. The wavelength of the terahertz radiation used in this experiment is around one thousand times shorter. “The advantage is that everything else can be a thousand times smaller too,” explains Kärtner, who is also a professor at the University of Hamburg and at MIT, as well as being a member of the Hamburg Centre for Ultrafast Imaging (CUI), one of Germany’s Clusters of Excellence.

For their prototype the scientists used a special microstructured accelerator module, specifically tailored to be used with terahertz radiation. The physicists fired fast electrons into the miniature accelerator module using a type of electron gun provided by the group of CFEL Professor Dwayne Miller, Director at the Max Planck Institute for the Structure and Dynamics of Matter and also a member of CUI. The electrons were then further accelerated by the terahertz radiation fed into the module. This first prototype of a terahertz accelerator was able to increase the energy of the particles by seven kiloelectronvolts (keV).

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