Argonne Upgrades Enable Next-Generation Experiments

Building 203 looks unassuming, but behind—and beneath—its brick exterior, researchers are performing advanced experiments and developing support systems to answer some of physics’ biggest questions. In January, Cold Facts toured the physics building at Argonne National Laboratory (CSA CSM) in Lemont IL to learn more about the ongoing upgrades from the people helping to make them happen.

The elevator at the end of 203’s central hallway opens up into the basement facility that is the Argonne Tandem Linac Accelerator System (ATLAS), the world’s first superconducting accelerator for projectiles heavier than electrons. A Department of Energy (DOE) Office of Science User Facility, ATLAS comprises three ion sources, three target areas and three distinct linac sections: the PII linac, the booster linac and the ATLAS linac.

Hundreds of users come to conduct research at ATLAS annually and it has been the site of many important discoveries including the measurement of extremely neutron-rich nuclei and the analysis of highly unstable nuclei. ATLAS’ process of accelerating ions is often compared to surfing a wave. Ions are accelerated to match the speed of electromagnetic waves produced by one of the seven resonator designs at which point they “catch” at around 1% of the speed of light. The independently controlled resonators then accelerate the wave and thus, the particle, to roughly 15% the speed of light. Made mostly of niobium, ATLAS’ in-line resonators are ideal for studying the properties of atomic nuclei at energy levels near the Coulomb barrier. Its energy levels of 7-17 MeV per nucleon are lower than that of comparable accelerators like at Michigan State University’s Facility for Rare Isotope Beams (CSA CSM), while still being able to produce stable beams.

However, these relatively low energies are not to be underestimated: the accelerating structure inside the liquid helium cooled resonators oscillates an electric charge between drift tubes 97 million times a second and generates a potential difference of 800,000 volts. These parameters mean ATLAS can accelerate any ion, regardless of its mass.

Since the first successful ion beam acceleration in 1978’s prototype, ATLAS’ beam hours have been steadily growing; the accelerator operates 24/7 with most of that time being beam hours. In 2019 ATLAS was able to achieve 6,773 beam hours, with many different users and beam species; but January is different.

“You’re here at a great time,” says Mark Hetherington, cryogenics engineer for ATLAS. “It’s our maintenance month and just yesterday we opened the split-ring cryostat—it’s even a first for me,” he says as he enters a narrow staging area housing the deconstructed machine being serviced in a plastic-walled “room.” Joining him are Jason Anderson and Scott Borkowski, the two other cryogenic specialists who make up the group responsible for ATLAS’ cryogenics.

In that room, scientists and engineers tinker with the metal behemoth now positioned in two pieces; the exterior cover sits empty as the inner workings have been slid out into the workroom for the replacing of the pin diodes.

“The ‘B’ cryostat is the second in the booster series and operates at 4.5 K using liquid helium—‘A’ and ‘G’ are new tech,” says Hetherington, leading the group around the older split ring cryostat. “Inside are six splitring resonators used to modify the beam that are constantly changing intensity.” Directing us around a thick concrete shielding wall, he gestures towards a towering machine. “This is one of the three CTI 2800 refrigerators we have running on ATLAS. There are only eight in the world, and we have three here using recently rebuilt wet engines hooked up to these 1,000 liter dewars,” he states, as he turns to face a massive tank. “Everything should be back online by the end of January.”

While the cryogenics ends at the bunchers just after the ATLAS linac, Hetherington and Anderson snake through the increasingly narrow passageways and explain the target areas and ion source while the shutdown allows such close examination. Two of the ion sources are electron cyclotron resonance (ECR) sources that are coupled to the first, or PII, linac. The target areas include the atomtrap, the Canadian Penning trap mass spectrometer, the Enge split pole spectrograph, the fragment mass analyzer, large scattering chamber, the helical orbit spectrometer (HELIOS) and the Gammasphere—a device that looks more like a giant sci-fi prop than a sensitive scientific detector.

“Right now, we’re in the process of becoming a multibeam facility,” Hetherington says. “Alongside those upgrades, we’re also developing systems for the full recovery and purification of helium. We use so much liquid nitrogen for shielding and experience significant some helium losses, so we want to protect that non-renewable resource.”

Following the ATLAS tour, we were escorted to the Accelerator Test and Development Facility (ATDF), also located in Building 203, for an explanation of the Advanced Photon Source upgrade (APS-U) and the status of the helium recovery and purification system from Steve MacDonald, cryogenic systems manager at the APS.

The APS-U is an $815 million project focusing on building the brightest storage-ring based X-ray source in the US. Functioning like a gigantic X-ray microscope, but a billion times brighter than a commercial X-ray source, the new APS-U will “see” through dense materials to allow researchers to study their compositions at the structural, chemical and atomic levels.

“The installation of the upgrade is currently targeted for mid-2022 and we expect it to take about a year,” says MacDonald. “We’ll shut it down, rip everything out and have everything installed within a year.”

“One of the most important aspects of the upgrade will be the addition of more magnets,” he goes on to explain. “Right now, if you were to slice the beam and look at a cross-section, there’d be a flat, skinny profile. We want to focus it down to a tiny point and make it much more powerful. One of the consequences of this tighter focusing is referred to as the Touschek effect—beam scattering in the individual electron bunches that leads to particle loss and low beam lifetime. It can be effectively combatted by increasing the electron bunch length. We’re building this cryomodule to do just that.”

He guides the group to the cryomodule in the middle of the large workshop. Roughly the size of a commercial freezer, the device sits near the middle of the room. Without its exterior housing, the MLI-wrapped piping and two large, drum-like components are exposed.

“This whole device is to reduce the losses from the Touschek effect but it’s fairly complex,” he says. “We bought a brand new turbine machine from Linde (CSA CSM), an LR140 liquefier and refrigerator, which should be delivered by the end of this year. It’s 400 W, which is 100 W more than the CTI 2800s at ATLAS.”

Although the LR140 will be delivered new to the APS, much of the ADTF is a collection of recycled machines. MacDonald begins to point out equipment around the workshop to explain their origins, emphasizing that a large portion of the project falls
under the “any means necessary” category.

“I took that CTI 1600 from ATLAS and installed it here. This used to be the Dynamitron accelerator,” he says as he gestures toward the enormous tank across the room. MacDonald now works at the APS but was a cryogenic engineer at ATLAS during the creation of the cryogenic systems in the ADTF. “That compressor is from the Intense Pulse Neutron Source. This water system is from the Dynamitron. This liquid nitrogen line comes from ATLAS. That wet expander is from Fermilab (CSA CSM). Almost everything here has been recycled.” This type of creative repurposing is typical of the ingenuity CSA has found at many laboratories.

MacDonald is also responsible for a developing aspect of the recycling mentality at Argonne. Around 2016, the lab began planning a helium recovery system.

“The lab wanted to build a centralized helium recovery system,” says MacDonald. “I proposed to Argonne that they use this plant—which only gets used about 10% of the year—as the center for reclamation. To buy all of this new would cost around $2 million, but we were able to piece it together for $300,000. Of course, we still needed components to process that recycled helium including high pressure compressors, a purifier and a way to collect it in bags.”

After proposing the “up-cycling” of the plant to the lab, MacDonald and his team were given funding to develop the rest of the helium recovery facility in the ATDF. Helium will be collected around the lab’s campus and transported to the ATDF in groups of individual containers referred to as “12-packs.” That helium is processed, purified and liquefied in the ATDF. Above the workshop sit two large bags that are used to collect the reclaimed helium before it will be distributed back around the lab.

“We’d like to have a more efficient way of collecting and distributing the helium around campus like we will with ATLAS,” says MacDonald. Because the two projects share a building and are in close proximity, ATLAS’ helium will be piped in from the source. There are plans to have other experiments deliver their helium directly to the recovery plant in the near future.

ATLAS, APS and helium recovery upgrades are just three projects that reinforce Argonne’s commitment to leading the country’s scientific community. With more than 5,500 researchers from around the world conducting experiments at Argonne annually, upgrades like these will continue to enable breakthroughs and discoveries that will benefit all.