[NEWS] "Swiss Army Knife" for Electron Beam Control
Traditional accelerators around the world are not only important tools for scientific research, but also huge national engineering projects. They consume a lot of manpower and financial resources, which greatly limits their wide application in many fields. In addition, traditional electron acceleration and shaping methods are achieved through methods such as radio frequency fields and magnetic coils, which are limited by the synchronization of light and electrons (~100 femtoseconds, 1 femtosecond = 10-15 seconds) and the damage threshold of the electric field (~100 MV/m). Research on higher time and space scales faces great challenges.
With the continuous development of THz technology in recent years, scientists have discovered that control of electron beams can also be achieved through precise control of the THz electric field or magnetic field.
"STEAM" is the world's first ultra-fast electronic micro-control device based on strong field THz. One of its core features is the perfect synchronization of light and electronics. This article will briefly introduce the working principle of "STEAM". The related work was published on the cover of the June issue of Nature Photonics (Figure 1).
Figure 1. "STEAM" related work published
Scientists first generate electron beams and drive THz electron accelerator and controller ("STEAM") by using multiple beams of light divided into the same mid-infrared laser pulse. This method can achieve perfect synchronization of light and electrons.
One of the laser beams generates ultraviolet light by doubling the frequency twice, injects it into the photocathode to generate hot electrons, and then accelerates it to 55 keV through a high-voltage DC power supply. The other two laser beams are used for optical rectification and difference frequency to generate THz, and are laterally incident into the "STEAM" to interact with electrons. The electric field at THz is parallel to the direction of electron propagation, and the magnetic field is perpendicular to the direction of electron propagation.
By adjusting the arrival time and relative phase of the two oppositely propagating THz beams, the interaction between the electron beam and THz after entering the device can be precisely controlled. At the same time, the influence of electric field and magnetic field components can be eliminated as needed to realize the function conversion of STEAM.
Specifically, adjusting the THz electric field can accelerate and compress electrons; using magnetic fields to deflect, diagnose, and focus electron beams. Thanks to the STEAM method's precise control of the THz field, its acceleration and focusing field gradient have reached world-leading levels.
Two lasers were used during the experimental verification of this work. A 550 fs, 4 mJ, 1 KHz, 1030 nm Yb:KYW laser is used to verify its stability under high frequency operation. At the same time, a 1.1 ps, 40 mJ, 10 Hz, 1020 nm Yb:YLF laser was used for verification at high energy, and this laser was used to generate 2×30 μJ near single-cycle THz with a center frequency of 0.3 THz. The scientists successfully coupled 2×6 µJ THz into the STEAM device and used it to verify the ultra-strong acceleration field (70 MV/m), focusing magnetic field (2 kT/m), nearly ten times compression of the electron pulse length, and ultra-short pulse time diagnostic capabilities on the femtosecond level (Figure 2).
Figure 2. Schematic diagram of "STEAM"
The biggest feature of "STEAM" is that it is very compact. On the one hand, because the wavelength of terahertz radiation is a hundred times shorter than the radiation wavelength used in today's radio frequency accelerators, all structures in the device can be reduced accordingly; on the other hand, this research integrates multiple functional applications in the same equipment unit, making compact design possible. The maximum area of a STEAM device is only two centimeters. In other words, it is a miniature device that can fit into a matchbox (Figure 3). Although this technology is still in the experimental stage, some of its functions can already be applied to accelerators and ultrafast electron microscopes, opening new doors for basic research in ultrafast physics, chemistry, biology, etc. CFEL physicists believe that STEAM will be the pioneer of the next generation of terahertz-driven particle accelerators.
Figure 3. Coin-sized “STEAM”
Original document:
[1] Dongfang Zhang, Arya Fallahi, Michael Hemmer, Xiaojun Wu, Moein Fakhari, Yi Hua, Huseyin Cankaya, Anne-Laure Calendron, Luis E. Zapata, Nicholas H. Matlis, Franz X. Kärtner,Segmented terahertz electron accelerator and manipulator (STEAM).Nature Photonics 12, 336–342 (2018); doi:10.1038/s41566-018-0138-z
Reference to the original English text link:
http://www.desy.de/news/news_search/index_eng.html?openDirectAnchor=1371&two_columns=1