The DESY team of scientists has created a miniature accelerator with two particles, which can process part of the laser energy supplied to the system in order to increase the energy of accelerated electrons a second time. The device uses narrow-band terahertz radiation, which lies between the infrared and radio frequency ranges of the electromagnetic spectrum, and one accelerator tube has a length of only 1.5 centimeters and a diameter of 0.79 millimeters. Dongfang Zhang and his colleagues at the Center for Free Electron Laser Research (CFEL) at DESY present their experimental accelerator in the journal Physical Review X,
The miniature size of the device is possible due to the short wavelength terahertz radiation. “Terahertz-based accelerators have become promising candidates for next-generation compact electronic sources,” explains Franz Kertner, DESY's lead researcher and head of the CFEL team that created the device. Scientists have previously successfully experimented with terahertz accelerators, which could provide an application where large particle accelerators are simply not feasible or not needed. “However, this method is still at an early stage, and the performance of experimental terahertz accelerators was limited by a relatively short portion of the interaction between terahertz pulse and electrons, "says Kertner.
For the new device, the team used a longer pulse involving many cycles of terahertz waves. This multi-cycle impulse significantly expands the site of interaction with particles. “We feed a multi-cycle terahertz pulse into a waveguide coated with a dielectric material,” says Zhang. In the waveguide, the pulse velocity decreases. A beam of electrons enters the central part of the waveguide just in time to pass along with the pulse. “This circuit increases the interaction between the terahertz pulse and the electron bunch to the centimeter range – compared to a few millimeters in earlier experiments,” Zhang reports.
The device did not produce much acceleration in the laboratory. However, the team can prove this concept by showing that electrons receive energy in a waveguide. “This is a confirmation of the concept. Electron energy has increased from 55 to 56.5 kiloelectron-volts, ”says Zhang. "Stronger acceleration can be achieved by using a more powerful laser to generate terahertz pulses."
The setup is mainly intended for the nonrelativistic regime, that is, electrons have velocities that are not so close to the speed of light. Interestingly, this mode allows you to reuse the terahertz pulse for the second stage of acceleration. “As soon as the terahertz pulse leaves the waveguide and enters the vacuum, its speed is reset to the speed of light,” Zhang explains. “This means that momentum overtakes a slower bunch of electrons by a couple of centimeters. We placed the second waveguide at the correct distance at which electrons enter it, together with a terahertz pulse, which is again slowed down by the waveguide. Thus, we create the second interaction section, further increasing the energy of electrons. "
In a laboratory experiment, only a small portion of the terahertz pulse could be processed this way. But the experiment shows that recycling is possible in principle, and Zhang is confident that the processed fraction can be significantly increased. Nicholas Mattlis, Senior Researcher and Project Team Leader for the CFEL Group, stresses: “Our cascade design will significantly reduce the need for the necessary laser system to accelerate electrons in non-relativistic mode, opening up new possibilities for the design of terahertz accelerators.”
Dongfang Zhang et al., Cascading multi-cycle terahertz ultrafast electronic accelerations and manipulations, Physical Review X (2020). DOI: 10.1103 / PhysRevX.10.011067
German Electron Synchrotron
A tiny double accelerator recycles energy (2020, March 20)
retrieved March 20, 2020
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