Physics

What Is It Like To Work at a Particle Accelerator?

LCLS-II Superconducting Accelerator,

LCLS-II will add a superconducting accelerator, occupying one-third of SLAC’s original 2-mile-long linear accelerator tunnel, which will generate an almost continuous X-ray laser beam. In addition to the new accelerator, LCLS-II requires a number of other cutting-edge components, including a new electron source, a powerful cooling plant that produces refrigerant for the accelerator, and two new undulators to generate X-rays. Credit: SLAC National Accelerator Laboratory

A day in the life of two accelerator experts

Kathleen Ratcliffe and Tien Fak Tan have cooperated over the last several years to help create the superconducting accelerator that will power new scientific breakthroughs at SLAC’s X-ray laser. According to Kathleen Ratcliffe and Tien Fak Tan, managers of the Department of Energy’s SLAC National Accelerator Laboratory, upgrading an accelerator is similar to modernizing a home. It only takes a little more teamwork and a deep grasp of the physics and technology that makes accelerators work.

They’re both in charge of teams at SLAC’s Accelerator Directorate, which has been working on a major upgrade to the LCLS X-ray laser. The LCLS-II project includes the addition of a superconducting accelerator that will create a second X-ray laser beam that is 10,000 times brighter and fires 8,000 times faster than its predecessor, up to a million pulses per second.

The LCLS-II X-ray laser (blue, at left) is shown alongside the previous LCLS (red, at right). LCLS uses the last third of SLAC’s 2-mile-long linear accelerator – a hollow copper structure that operates at room temperature and allows the generation of 120 X-ray pulses per second. For LCLS-II, the first third of the copper accelerator will be replaced with a superconducting one, capable of creating up to 1 million X-ray flashes per second. Credit: SLAC National Accelerator Laboratory

Ratcliffe’s job includes coordinating the manufacturing, distribution, and installation of the accelerator’s components. Tan is in charge of the engineers that design the parts. When problems develop during the installation, Tan collaborates with other engineers to come up with a solution. Ratcliffe takes their designs and turns them into physical components and systems. The parts are then assembled into an accelerator by Ratcliffe, Tan, and their teams of engineers and technicians.

Essentially, Tan is like an architect making and tweaking the designs, and Ratcliffe is like the contractor working to make their implementation possible. The two are constantly feeding information and ideas to each other to ensure the final product works as intended. Their work also requires cooperation and coordination with hundreds of different people across multiple departments at SLAC.

LCLS-II beamlines. Credit: SLAC National Accelerator Laboratory

And now, after years of that work, Ratcliffe and Tan are eager for the accelerator’s time to shine: LCLS-II is set to turn on in 2022. The upgrade will allow SLAC to host new types of cutting-edge experiments, leading to advancements in materials, physical, chemical, and biological sciences.


Responding to a call to build a revolutionary new X-ray laser, SLAC is developing an upgrade of its Linac Coherent Light Source (LCLS) that will be at the forefront of X-ray science.

‘A mountain of parts’

As installation manager for the LCLS-II upgrade, Ratcliffe ensures that the entire accelerator comes together safely and according to the physics requirements that will enable the machine to focus, steer and accelerate the electron beam. Building nearly 4 kilometers of accelerator also requires a lot of materials, and since she’s also the department head of technical planning in the directorate, Ratcliffe organizes all of them.

SLAC’s Kathleen Ratcliffe coordinates the manufacturing, distribution and installation of the parts that make up the new superconducting accelerator for LCLS-II, a major upgrade to the lab’s Linac Coherent Light Source X-ray free-electron laser. Credit: Jacqueline Ramseyer Orrell/SLAC National Accelerator Laboratory

“It’s really intense work, but she just keeps continuing with the same intensity,” says Dian Yeremian, a physicist at SLAC who has worked with Ratcliffe at SLAC for over three decades.

The work’s intensity only increased during the coronavirus pandemic. While California residents sheltered in place, parts for the new accelerator continued to come in from outside suppliers. The inventory and installation teams adopted COVID-19 safety protocols that allowed them to quickly resume manufacturing and construction. But they still had catching up to do.

“There was just this mountain of parts,” Ratcliffe says. “If you were standing in front of the pile, you couldn’t see the back of the building.” It was immensely satisfying to watch that mountain transform into an accelerator, she says.

Getting up to speed

Tan is the lead mechanical engineer and also an installation manager for LCLS-II, so he and his team work to integrate those parts and systems into the accelerator. He also heads the Mechanical Engineering Department in the directorate and has worked at SLAC for nearly four years.

SLAC’s Tien Fak Tan oversees the engineers who design the parts for LCLS-II, a major upgrade to the lab’s Linac Coherent Light Source X-ray free-electron laser. His team also addresses any challenges that arise during installation. Credit: Jacqueline Ramseyer Orrell/SLAC National Accelerator Laboratory

“What’s impressive about Tien is that he doesn’t come from the accelerator world,” Yeremian says. “In a very short time, he has gained enough understanding of the physics so he can work out engineering solutions that mesh with what the accelerator needs to operate.”

During the LCLS-II project, Ratcliffe and Tan worked closely together. “We both need each other in a lot of ways for the project to be successful,” Ratcliffe says.

But they’ve also worked with massive teams beyond their home departments. “We’re just two of the people who work on the accelerator,” Tan says. “And this thing takes everyone here. It really takes a lot of folks.”

Piecing together a puzzle

Each section of the accelerator comes with different needs and challenges, and Ratcliffe and Tan work with section leads to tailor their expertise to all of them. Yeremian has been particularly impressed with Tan and Ratcliffe’s work on the LCLS-II section she oversees, the injector. After particles emerge from the electron source, this 90-meter section of the machine increases their energy 100-fold, getting their speed ever closer to the speed of light. The injector is particularly crowded — many parts and assemblies need to fit together in a cramped space.

Tan and Ratcliffe were faced with a tall order: They needed to make sure all these parts fit correctly without disturbing the very precise physics required for the injector to work.

“Every day, you’re basically trying to make sense of a very interesting puzzle,” Tan says.

Even as the installation was underway, Tan had to constantly integrate new information about how the plans for the accelerator were coming together in real life. When parts needed tweaking, he and Ratcliffe worked together and with their teams to manufacture and install them with precision and efficiency.

“What they learn in the downstream systems, I take advantage of at the injector,” Dian says. “They transferred what they learned in my section to the other team leads, and the other leads were able to improve their sections because of that.”

Building a legacy

All of this creative puzzle-solving takes place in a special environment: the 60-year-old accelerator tunnel.

“If you go into the accelerator after it’s been raining, it’s warm and humid,” Ratcliffe says. “It has a distinct smell about it. Not a bad smell, but I don’t think you would find it anywhere else.”

While much of the tunnel has received updates over the years, some of the areas involved in the LCLS-II upgrade remained eerily untouched before Tan and his team entered them.

In some stretches of the accelerator, old parts were removed to make room for the upgraded components. But in many sections, equipment for the new accelerator needed to be integrated with existing machinery which is still crucial for research at SLAC.

“It’s like remodeling a historical house, which is more challenging and exciting than building a house from scratch,” Ratcliffe says. “There’s a lot of really cool stuff that you want to keep, but you might want to modernize it. So you have the old and the new all combined together.”

This remodeling makes Ratcliffe and Tan part of a 60-year-old legacy of accelerator builders at SLAC. “It was pretty cool to go in there to see all the history of all the things that someone else had worked on,” Tan says. “You’re trying to figure out how some engineer 40 or 50 years ago was thinking and why they built things the way they did.”

Ratcliffe and Tan are both aware that the machine they’ve worked so hard on for the past few years will be used to answer fundamental questions about physics. “It’s cool that we get to help out in small ways each day, and somehow it fits into this big picture,” Tan says.

Now that the new accelerator is nearly complete. The next step is to begin cooling it to the cryogenic temperatures needed for the superconducting technology to kick into gear before it produces its first light this year. “You see the light at the end of the tunnel,” Ratcliffe says.

LCLS is a DOE Office of Science user facility.

SLAC is a vibrant multiprogram laboratory that explores how the universe works at the biggest, smallest and fastest scales and invents powerful tools used by scientists around the globe. With research spanning particle physics, astrophysics and cosmology, materials, chemistry, bio- and energy sciences and scientific computing, we help solve real-world problems and advance the interests of the nation. SLAC is operated by Stanford University for the U.S. Department of Energy’s Office of Science.

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