Researchers shrink terahertz accelerator for electron beams

March 23, 2020 //By Julien Happich
A team of researchers at the Deutsches Elektronen-Synchrotron (DESY) has developed a novel type of terahertz-based accelerator that can recycle some of the laser energy fed into it to boost the energy of the accelerated electrons a second time.

Only 0.79 millimetres in diameter, the 1.5 centimetres long device uses a longer pulse of narrowband terahertz radiations at many different wavelengths. The multicycle pulse is reported to significantly extend the interaction section with the particle

Dongfang Zhang and his colleagues from the Center for Free-Electron laser Science (CFEL) at DESY presented their experimental accelerator in the journal Physical Review X.

"We feed the multicycle terahertz pulse into a waveguide that is lined with a dielectric material", says Zhang. Within the waveguide, the pulse's speed is reduced. A bunch of electrons is shot into the central part of the waveguide just in time to travel along with the pulse. "This scheme increases the interaction region between the terahertz pulse and the electron bunch to the centimetre range—compared to a few millimetres in earlier experiments," reports Zhang.

The device did not produce a large acceleration in the lab. However, the team could prove the concept by showing that the electrons gain energy in the waveguide. "It is a proof of concept. The electrons' energy increased from 55 to about 56.5 kilo electron volts," says Zhang. "A stronger acceleration can be achieved by using a stronger laser to generate the terahertz pulses."

The set-up is mainly designed for the non-relativistic regime, meaning the electrons have speeds that are not so close to the speed of light. Interestingly, this regime enables a recycling of the terahertz pulse for a second stage of acceleration.

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