A miniature double particle accelerator to recycle some of the laser energy

Tiny double accelerator recycles energy.


Using a longer pulse comprising many cycles of terahertz waves, DESY scientists have devised a tiny double particle accelerator that can recycle some of the laser energy fed into the system to boost the energy of the accelerated electrons. The device significantly extends the interaction section with the particles.

The device uses narrowband terahertz radiation, which lies among infrared and radio frequencies in the electromagnetic spectrum, and a single accelerating tube that is simply 1.5 centimeters long and 0.79 millimeters in breadth.

Franz Kärtner, the Lead Scientist at DESY and head of the CFEL group that built the device, said, “The miniature size of the device is possible due to the short wavelength of terahertz radiation. Terahertz-based accelerators have emerged as promising candidates for next-generation compact electron sources. However, the technique is still in an early stage, and the performance of experimental terahertz accelerators has been limited by the relatively short section of interaction between the terahertz pulse and the electrons.”

Dongfang Zhang from the Center for Free-Electron Laser Science (CFEL) at DESY presents their experimental accelerator said, “We feed the multicycle terahertz pulse into a waveguide that is lined with a dielectric material. Within the waveguide, the pulse’s speed is reduced. A bunch of electrons shot into the central part of 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 centimeter range – compared to a few millimeters in earlier experiments.”

Scientists proved their concept by showing that the electrons gain energy in the waveguide. The electrons’ energy increased from 55 to about 56.5-kilo electron volts.

Zhang explained, “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 the recycling of the terahertz pulse for the second stage of acceleration. Once the terahertz pulse leaves the waveguide and enters the vacuum, its speed is reset to the speed of light. It means the pulse overtakes the slower electron bunch in a couple of centimeters. We placed a second waveguide at just the right distance that the electrons enter it together with the terahertz pulse, which is again slowed down by the waveguide. In this way, we generate a second interaction section, boosting the electrons’ energies further.”

Nicholas Mattlis, senior scientist and the team leader of the project in the CFEL group, emphasizes: “Our cascading scheme will greatly lower the demand on the required laser system for electron acceleration in the non-relativistic regime, opening new possibilities for the design of terahertz-based accelerators.”

The work is funded by the EU Synergy Grant AXSIS (frontiers in Attosecond X-ray Science: Imaging and Spectroscopy) at CFEL. CFEL is a joint venture of DESY, the University of Hamburg and the Max Planck Society.

Journal Reference
  1. Cascaded Multi-cycle terahertz driven ultrafast electron acceleration and manipulation. DOI: 10.1103/PhysRevX.10.011067


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