background
Nowadays, the progress of frontier physics is inseparable from powerful particle accelerators. Through the collision of high-energy particles, physicists are constantly exploring the nature of the universe. Simply put, a particle accelerator is a machine that can accelerate elementary particles to very high energy. It realizes high energy by making charged particles controlled by magnetic field force and accelerating electric field force in high vacuum field.
Recently, scientists from the German Electron Synchrotron Research Institute (DESY) have set a new world record in the field of experimental particle accelerators. For the first time in history, this terahertz-driven accelerator has more than doubled the energy of injected electrons.
At the same time, as reported by Dr. Zhang Dongfang of DESY Free Electron Laser Science Center (CFEL) and his colleagues in Optics magazine, compared with the early experiments using this technology, the device has significantly improved the quality of the electron beam. Dr. Zhang said: "We have achieved the best beam parameters of terahertz accelerator so far."
Franz K, head of DESY ultra-high-speed optics and x-ray research group? Rtner stressed: "This achievement represents a key step to realize terahertz driving accelerator."
technology
Terahertz radiation lies between infrared and microwave frequencies in the electromagnetic spectrum, which is expected to bring a new generation of compact particle accelerators.
k？ Rtner explained: "The wavelength of terahertz radiation is about 1% of the radio wave currently used to accelerate particles. This means that the size of the accelerator assembly can also be made about one percent of the original size. " Terahertz scheme is expected to bring new applications to laboratory-scale accelerators, such as small X-ray sources for materials science and even medical imaging. This technology is currently under development.
Because the terahertz wave oscillates very fast, every component and every step must be synchronized accurately. Dr. zhang explained: "For example, in order to obtain the best energy gain, electrons must accurately hit the terahertz field within its acceleration half period." In accelerators, particles usually do not fly in the form of continuous particle beams, but are packed into beams. Because the field changes rapidly, these particle beams must be very short in terahertz accelerator, so as to ensure the equal acceleration state along the particle beams.
Dr. Zhang said: "In previous experiments, the electron beam was too long. Because the oscillation speed of terahertz field is very fast, some electrons in the beam are accelerated, while others are even reduced. Therefore, generally speaking, this will only produce a moderate energy gain, and more importantly, the energy will be widely dispersed, which will lead to the deterioration of particle beam quality. " To make matters worse, this effect greatly increases the emittance, which can measure the lateral constraint of the particle beam. The closer the particles are combined, the better (the lower the emittance).
In order to improve the beam quality, dr. zhang and his colleagues built a two-stage accelerator through their previously developed multi-purpose equipment: segmented terahertz electron accelerator and manipulator (STEAM), which can compress, focus, accelerate and analyze the electron beam with terahertz radiation.
The researchers arranged two steam devices. They first compressed the length of the incident electron beam from about 0.3 mm to 0. 1 mm, and then accelerated the compressed electron beam through the second steam device.
Dr. Zhang said: "This plan needs to be controlled at the level of one trillionth of a second, and we have done it. This will reduce the energy divergence to a quarter and the emittance to a sixth, thus obtaining the best terahertz accelerator particle beam parameters so far. "
The net energy gain of electrons injected with energy of 55keV is 70keV. Dr. zhang emphasized: "This is the first time to achieve an energy increase of more than 100% in a terahertz drive accelerator." The peak intensity generated by this coupling device is 200 million volts/meter, which is close to the most advanced and powerful traditional accelerator. But for practical application, there is still a lot of room for improvement.
Dr. zhang concluded: "Our research shows that it is possible to compress an electron beam even if it exceeds three times. Coupled with higher terahertz energy, an acceleration gradient of one billion volts per meter seems feasible. Therefore, the terahertz concept is increasingly promising to become a realistic choice for designing small electron accelerators. "
reference data
1 Zhang Dongfang, Arya Fallahi, Michael Hemmer, Moein Fakhari, Yi Hua, Huseyin Cankaya, Anne- Laurie Calendron, Luis E. Zapata, Nicholas H. Matlis, Franz X.K.? rtner。 Femtosecond phase control in ultra-fast electron source driven by high field terahertz. Optica，20 19； DOI: 10. 1364
2 http://www . desy . de/news/news _ search/index _ eng . html？ openDirectAnchor = 1654 & amp； two_columns= 1
3 http://www . desy . de/news/news _ search/index _ eng . html？ openDirectAnchor = 137 1 & amp； two_columns= 1