Newswise — Thirty years ago, a newly assembled team of scientists, engineers and technicians set out to build the world’s first automated test and qualification facility for superconducting radiofrequency, or SRF, accelerator components. Today, the Vertical Test Area at the Department of Energy’s Thomas Jefferson National Accelerator Facility (Jefferson Lab’) is still going strong, more than 5,000 SRF accelerator component tests later.
Charles Reece, a senior staff scientist in Jefferson Lab’s SRF Institute, led the team that built the VTA.
“It’s the best place in the world for testing SRF cavities - still is. Our throughput is higher than anybody else in the world,” he said.
The VTA was originally built out of necessity. In 1985, the fledgling Continuous Electron Beam Accelerator Facility was slated as the site of the world’s first large-scale SRF particle accelerator. The CEBAF accelerator was built for basic nuclear physics research. It was designed to accelerate electrons by increasing the energy of each electron in a beam to 4 billion electron-volts to probe the structure of matter.
This first-of-its-kind accelerator would be powered by superconducting radio-frequency (SRF) cavities, which are metal structures that harness microwave energy and direct it into the electron beam, thus accelerating the electrons for use in studies of the internal structure of the atom’s nucleus.
The original CEBAF accelerator required more than 330 SRF cavities to power it, and each cavity needed to be quality tested. To test a superconducting cavity, it is cooled down to 2 Kelvin, and then its performance is rated on how efficiently it can harness the energy needed to accelerate electrons or other particles for which it is designed.
“We want to ensure that a cavity meets certain requirements in terms of its accelerating capability, while producing a minimum amount of heat,” Reece explained. “We measure that by measuring the Q of the cavity: We want a very high quality factor.”
Building the first automated accelerator cavity testing facility
Reece arrived on-site just as work began ramping up to build CEBAF. The proposed home to the VTA was the former NASA Space Radiation Effects Laboratory, which had been built in the mid-1960s to research what would happen to living tissue if it were exposed to the radiation found in space. NASA had long-since vacated the property, leaving behind the structure that would later be re-named the Test Lab.
“When I got here in 1985, there was no power in the building. There was a fence around it, and the building needed renovating to bring it up to current building standards,” he recalled.
At the time, he and his team were tasked with envisioning a facility that could not only meet the immediate needs of quality checking the cavities being built for CEBAF, but also one that could meet the future needs of the new laboratory and beyond.
“There had never been an automated Vertical Test Facility for SRF before,” he said. “Part of setting up the Test Lab for construction of CEBAF was creating a facility like none that had ever existed before in the world and still doesn’t.”
In 1987, Reece’s team began designing the facility. Every aspect of the VTA was designed in-house, from the physical testing area itself, to the cryogenic distribution piping, to the radiation barriers, to the computerized control system. Joe Susta, a Jefferson Lab staff member, engineered the cryogenic system, and another staff member, Tom Powers, engineered the cryogenic and radiofrequency controls.
According to Peter Kushnick, a Jefferson Lab staff member who helped build the facility and who has been responsible for its operations for more than 25 years, the VTA first came online in April 1991. The first component tested was a CEBAF SRF accelerator cavity.
“And we’ve been performing tests almost continually over that time period. We keep a logbook of all of our tests. And we have several additions to that logbook now, because we’ve been doing it so long,” Kushnick said. “It’s the largest facility of its type in the world, and it’s also one of the busiest.”
Enabling research facilities for the nation
Throughout its nearly 30-year history, the VTA has contributed to the success of large-scale superconducting radiofrequency accelerators across the United States and around the world. In addition to CEBAF, the facility design-tested and performance-tested the SRF cavities used in the Spallation Neutron Source at Oak Ridge National Lab, as well as the cavities that powered the record-setting Jefferson Lab Free-Electron Laser, which was located in the lab’s Low Energy Research Facility.
Most recently, the facility began performance testing cavities for the Linac Coherent Light Source facility, located at SLAC National Accelerator Lab in Menlo Park, Ca. LCLS is the brightest X-ray laser in the world, and the additional capability that is being added to the facility as part of the LCLS-II project will make it even brighter. Jefferson Lab is in the process of building, testing and delivering 21 finished sections of particle accelerator for LCLS-II.
Over the course of the LCLS-II project, more than 150 SRF cavities will go through testing in the VTA, as Jefferson Lab builds roughly half of the SRF accelerator that will power the upgraded machine.
According to Kushnick, the 5,000th accelerator cavity test conducted in the VTA was for an LCLS-II cavity, as noted in the logbook on October 18, 2018.
“No one else has hit 5,000 tests. No one else on the planet can say that,” Kushnick said.
Advancing research through accelerator science for the world
The innovations in accelerator component design, fabrication and testing methods developed by Jefferson Lab accelerator scientists and technicians through using the VTA continues to have far-reaching impacts on the practice of accelerator science and future directions in accelerator research.
“When we designed this facility, we also made sure that it would be built to accommodate R&D for the future,” Reece said. “Support from the Department of Energy for these research and development programs have enabled Jefferson Lab R&D to continue to innovate in the field of SRF accelerator components."
The facility has been used to research and develop new materials and processing techniques for SRF cavities, hosting ~20 Ph.D. research programs, as well as research carried out by Jefferson Lab scientific staff.
The information revealed by this advanced accelerator R&D has been folded into exciting and unique new accelerator application designs. Recent prototype cavities that have been tested in the VTA include a cavity designed for a proposed Electron-Ion Collider, several designs for the proposed International Linear Collider, and yet more for a potential addition to the Large Hadron Collider at CERN.
Through the years, the facility has been used to not only test cavities, but also other accelerator components.
“We have six cryostats that can test cavities and two more for materials. It’s a great resource,” Reece added.
These components can range from SRF windows to cryogenic components to new materials for SRF accelerator applications. Component tests aren’t counted in the total tally of SRF accelerator cavity tests.
Reece said a program to upgrade the facility as new technologies, safety codes and testing requirements are developed ensures that it remains current and available to support R&D efforts from facilities in the U.S. and around the world. The facility’s latest upgrade took place in 2015.
The Jefferson Lab team has also lent its considerable and unique expertise to colleagues around the world to help establish accelerator cavity testing facilities elsewhere, including at DESY in Germany in 1996, at DOE’s Fermi National Accelerator Laboratory in 2006, and at Daresbury Lab in England in 2016.
He said with the demand that they’ve seen for quality testing of SRF cavities, he has little doubt that Jefferson Lab’s Vertical Test Area will one day celebrate its 10,000th successful test as it continues to enable researchers to expand the frontiers of accelerator science and serve the needs of cutting-edge particle accelerator research facilities worldwide.
Jefferson Science Associates, LLC, a joint venture of the Southeastern Universities Research Association, Inc. and PAE, manages and operates the Thomas Jefferson National Accelerator Facility, or Jefferson Lab, for the U.S. Department of Energy's Office of Science.
Jefferson Lab is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.