The crew successfully cooled the accelerator to -456 degrees Fahrenheit /2 Kelvin-at this temperature, the accelerator became superconducting, which could lift electrons to high energy, and the energy loss in the process was almost zero. This is the last milestone before LCLS-2 produces X-ray pulses. The average brightness of these X-ray pulses is 65,438+00,000 times that of LCLS, and it can reach 654,380+000 million times per second-this is the world record of the most powerful X-ray source today.
"In just a few hours, LCLS-II will generate more X-ray pulses than the current laser in its entire life cycle," said mike dunn, director of LCLS. "Data that may take months to collect can be generated in a few minutes. It will raise X-ray science to a new level, pave the way for a series of brand-new research, and promote our ability to develop revolutionary technologies, thus solving some of the most profound challenges facing our society. "
With the help of these advanced new functions, scientists can examine the details of complex materials with unprecedented resolution, promote new forms of calculation and communication, reveal rare and short-lived chemical events, teach people how to create more sustainable industrial and clean energy technologies, study how biomolecules perform life functions to develop new drugs, and spy on the strange world of quantum mechanics by directly measuring the movement of single atoms.
A frightening feat.
As the world's first hard X-ray free electron laser (XFEL), LCLS produced the first beam of light in April 2009, and the brightness of the X-ray pulse it produced was 654.38+billion times that of anything before. Because it accelerates electrons through a copper tube at room temperature, its speed is limited to 120 x-ray pulses per second.
In 20 13, SLAC started the LCLS-II upgrade project, which increased the pulse rate to1100,000 times and increased the power of X-ray laser by thousands of times. In order to achieve this goal, the staff dismantled a part of the old copper accelerator and installed a series of 37 cryogenic accelerator modules, including a string of niobium metal cavities like pearls. These modules are surrounded by three layers of nested cooling equipment, and each layer will reduce the temperature until it reaches almost absolute zero-under this condition, the niobium cavity will become superconducting.
"Unlike the copper accelerator that powers the LCLS, the operating temperature of the LCLS-II superconducting accelerator is 2 Kelvin, which is only about 4 degrees Fahrenheit higher than absolute zero, which is the lowest possible temperature," said Eric Foway, director of the cryogenic department of SLAC. "In order to reach this temperature, the linear accelerator is equipped with two world-class helium refrigerators, which makes SLAC one of the important low-temperature landmarks in the United States and the world. Throughout the epidemic, the SLAC cryogenic team worked on the spot, installed and debugged the cryogenic system, and cooled the accelerator in record time. "
A cryocooler specially built for LCLS-II cools helium from room temperature to liquid state above absolute zero, and provides coolant for the accelerator.
On April 15, the new accelerator reached the final temperature of 2K for the first time. Today (May 10), the accelerator is ready for initial operation.
"Cooling is a key process and must be carried out very carefully to avoid damaging the cryogenic module," said Andrew Burrill, director of SLAC Accelerator Bureau. "We are very excited. We have reached this milestone and can now focus on turning on the X-ray laser. "
Give it life
In addition to the new accelerator and cryostat, the project also needs other cutting-edge components, including a new electron source and two new fluctuating magnet strings, which can generate "hard" and "soft" X-rays. Among them, hard X-rays are more powerful, which enables researchers to image materials and biological systems at the atomic level. Soft X-rays can capture the energy flow between atoms and molecules, track chemical reactions, and provide insights for new energy technologies. In order to realize this project, SLAC cooperated with four other national laboratories-Argonne Laboratory, Berkeley Laboratory, Fermi Laboratory and Jefferson Laboratory-and Cornell University.
Jefferson Lab, Fermilab and SLAC pool their expertise to research and develop cryogenic modules. After the freezers were built, Fermilab and Jefferson Laboratories conducted extensive tests on each freezers, and then these containers were packed by trucks and transported to SLAC. The Jefferson Lab team also designed and helped purchase the components of the cryocooler.
"LCLS-II project needs the efforts of technicians, engineers and scientists from five different laboratories of the US Department of Energy and many colleagues from all over the world for many years," said Norbert Holtkamp, deputy director of SLAC and director of LCLS-II project. "Without these continuous partnerships and the expertise and commitment of our partners, we could not have achieved what we are now."
Toward the first x-ray
Now that the cavity has cooled, the next step is to pump it with microwave power exceeding 1 MW, thus accelerating the electron beam from the new source. Electrons passing through the cavity will get energy from the microwave, so when they pass through all 37 cryogenic modules, their speed will be close to the speed of light. Then, they will be guided through the undulator, which will force the electron beam to follow the herringbone path. If everything is arranged properly-within a fraction of the width of human hair-then electrons will emit the most powerful X-ray burst in the world.
This is the same process that LCLS uses to generate X-rays. However, because LCLS-II uses a superconducting cavity instead of a 60-year-old warm copper cavity, it can provide up to one million pulses per second, which is 1 10,000 times the number of X-ray pulses with the same power.
Once LCLS-II produces the first batch of X-rays, which is expected to happen later this year, two X-ray lasers will work in parallel, which will enable researchers to conduct experiments in a wider energy range, capture detailed snapshots of ultrafast processes, detect fragile samples, collect more data in a shorter time, and increase the number of experiments that can be carried out. It will greatly expand the scientific scope of the facility and enable scientists from all over the United States and around the world to pursue the most compelling research ideas.