In early 2023, the SLAC National Accelerator Laboratory in California will utilize high-speed electrons to generate the strongest X-rays ever observed on Earth.
These unprecedentedly strong X-rays will be produced in a tunnel using a new version of the Coherent Light Source X-ray laser (LCLS), enabling researchers to explore atoms and molecules in ways never before possible. LCLS-II is the fastest and most powerful X-ray laser in the world, as reported by Science Times on January 2.
X-ray laser gun powering the LCLS-II machine. (Photo: Marilyn Chung/Lawrence Berkeley)
LCLS-II is a hard X-ray free electron laser (XFEL) that can create ultra-fast, high-resolution images of microscopic objects. Its predecessor, LCLS, has been used for a variety of purposes, including imaging viruses, simulating conditions at the center of stars, evaporating water into a plasma state hotter than the Earth’s core, generating extreme noise, and creating “diamond rain,” similar to phenomena observed on many planets like Neptune.
The second phase of LCLS-II has recently been completed and is expected to be much more capable than its predecessor. The new system can produce X-ray pulses that are, on average, 10,000 times brighter than those from LCLS and generates one million pulses per second, far exceeding the original’s 120 pulses per second.
In just a few hours, LCLS-II will generate more X-ray pulses than current lasers produce throughout their entire lifespan, according to Mike Dunne, director of LCLS. This increase in capability will allow researchers to collect data in minutes rather than months, significantly advancing the field of X-ray science and enabling the development of new technologies to address major societal challenges.
LCLS-II operates on principles similar to LCLS. Electrons are generated and accelerated in a tube, causing them to oscillate and emit X-rays. However, the new system also improves every step of the process. The most significant change is the upgraded accelerator. While the original machine used room-temperature copper tubes to shoot electrons, LCLS-II utilizes a set of 37 superconducting radiofrequency cavities cooled to nearly absolute zero (-271 degrees Celsius), using liquid helium from two large refrigeration plants. This cooling allows the equipment to operate at higher energy levels, resulting in brighter and stronger X-ray pulses.
At these extremely low temperatures, the niobium metal cavities inside the superconducting radiofrequency cavities become superconductive, allowing electrons to pass through without resistance. Microwave fields create oscillating electric fields that resonate within the cavities, synchronized with the electron beam’s timing and transferring energy to them. This additional energy accelerates the electrons to speeds close to the speed of light as they pass through all 37 superconducting cavities.
After passing through the accelerator, the high-energy electrons enter a wave detector, a device that uses a strong magnetic field to cause the electrons to oscillate and emit X-rays. The new wave detectors can produce both hard and soft X-rays. Hard X-rays can capture detailed images of individual atoms, while soft X-rays can reveal energy flows between atoms and molecules.
The superconducting cavities achieved low temperatures in April of last year. Currently, the research team is preparing to test the equipment using the first electrons. Once X-ray production begins, LCLS-II is expected to provide new insights into fields such as chemistry, biology, computing, and quantum mechanics.
