Continuous electron beam accelerator facility benchmark

This paper has been made over 40 years. A study published in Physical Review Accelerators and Beams re-evaluated benchmarks for the main particle accelerator at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility. The original and upgraded operating parameters of the accelerator are captured, and its major systems and subsystems, features and limitations are described in detail.

The research was led by Jeffrey Craft, a member of the Center for Advanced Accelerator Research at the Jefferson Institute, director of the Accelerator Education Program, and a Jefferson Institute professor at Old Dominion University’s Accelerator Science Center. The 63-page paper focuses on the Continuous Electron Beam Accelerator Facility at the Jefferson Research Institute, also known as CEBAF.

“An accelerator like CEBAF has never been built before, so it is not easy to explain how it is built and how it works,” he said.

A unique machine that explores atomic nuclei

Forty years ago, in August 1983, Congress authorized the first funding for research, development, and design of what would soon become the Continuous Electron Beam Accelerator Facility. The purpose of the particle accelerator was to deliver high-energy electron beams for nuclear physics experiments.

Each of these electrons is sent to a machine to be accelerated to higher speeds and packed with up to 4 billion electron volts (4 GeV) of additional energy. These electrons are sent to the target and interact with the target’s protons and neutrons, revealing details about the structure of these particles and their interactions within ordinary matter.

As the 1980s progressed and the facility began to take shape, it was clear that this would be a unique new particle accelerator.

For one, the design of the machine was radically changed in 1985. The original design called for a room-temperature copper-based linear accelerator (and pulse stretcher ring) with an operating energy of 4 GeV. But by 1985, the facility’s first director, Hermann Glander, decided to abandon that conservative design and try something new: an accelerator using superconducting radiofrequency technology. It was hoped that this material would allow machines to reach even higher energies, making accelerators upgradeable in the future.

SRF technology is built on a material called niobium, which becomes superconducting when cooled to near absolute zero. This allows the SRF accelerator to use the niobium SRF accelerator cavity to propel particle beams with significantly less thermal energy loss. Unlike existing copper-based particle accelerators at the time, the SRF accelerator can deliver these beams almost continuously, allowing researchers to perform the same experiment over and over again without the accelerator overheating.

The technology had shown promise in several university labs, but had never been built into large-scale machines. The facility proceeded with a new design and construction began on site by 1988.

CEBAF was beginning to take shape.

The machine was completed in December 1993, and the final section of the accelerator, called the cryomodule, was installed. The completed machine houses two and a quarter cryomodules within the machine’s injector, where the electron beam is formed.

A further 40 of these cryomodules were arranged end-to-end in two linear accelerators (20 in each linear accelerator) connected by two circular arcs. The racetrack design, 7/8 of a mile in circumference, would allow electrons to pass through the machine up to five times, gaining additional energy with each pass before being guided into an experimental hall for research. Masu.

By 1995, CEBAF was already capturing data for nuclear physics experiments, some of which had been conceived nearly 20 years earlier. Less than two years later, all three of CEBAF’s experimental halls (Halls A, B, and C) were operational.

By 2001, Kraft and accelerator scientist colleagues Christoph Riemann (who later became the second director of the Jefferson Institute) and David Douglas had gathered enough information to publish a benchmark paper on CEBAF. . “The Continuous Electron Beam Accelerator Facility: CEBAF at the Jefferson Laboratory” was published in the Annual Review of Nuclear and Particle Science and has since served as a source for all things CEBAF.

This technical magazine article provided nuclear physicists and accelerator physicists with everything they need to know about CEBAF, including its key technologies, operating specifications, and demonstrated capabilities.

And just a few years later, it became clear that big changes were on the horizon.

Benchmark updates

The original particle accelerator performed surprisingly well, exceeding its design goal of 4 GeV by 50% and eventually reaching 6 GeV. Additional features beyond the initial design were also demonstrated, including a highly polarized electron beam, simultaneous experiments in up to three experimental halls, the ability to deliver a beam with lower energy than designed (called a half-pass beam), and energy recovery. Ta.

Nuclear physicists who wanted to further leverage CEBAF’s capabilities advocated in a white paper published in 2001 to upgrade the machine to realize new nuclear physics research goals.

In 2004, DOE recognized that there was a “mission need” for upgrades to CEBAF. The $338 million 12 GeV CEBAF upgrade project will triple the operating energy of CEBAF’s original design (from 4 GeV to 12 GeV), commission a new experiment area (Experiment Hall D), and increase the energy reach. We also make other updates that allow for expansion. CEBAF was closed for much of the upgrade process in May 2012, and the upgrade project was completed five years later in fall 2017.

“Many different subsystems within the accelerator had to be improved and made better. A lot of equipment was refurbished,” Kraft said.

After the upgrade, Kraft and his colleagues felt it was time to benchmark the machine again. More than 20 years after the first landmark paper was published, it has now been replaced by “12 GeV Continuous Electron Beam Accelerator Facility,” recently published in Physical Review Accelerators and Beams.

This new informative article reviews the operational details of the original CEBAF, provides information on technical upgrades made to the machine, and benchmarks CEBAF’s accelerator performance at 12 GeV. This document currently serves as a convenient reference for the DOE Office of Science User Facility, a research hub for more than 1,650 nuclear physicists around the world.

“This is a summary of the technical achievements within the 12GeV CEBAF upgrade project and ultimately how the project actually performed,” said Kraft. “We hope that this book will become a standard reference for nuclear physicists making measurements at CEBAF, as it provides a thorough description of the new accelerator and its performance characteristics and will soon Because you can refer to it.”

The paper also touches on future possibilities, mentioning opportunities to improve CEBAF operations through machine learning, the development of new photon sources, and several major nuclear physics projects.

In the meantime, does anyone have questions about CEBAF and its features that are not covered in the paper?

“All they have to do is ask,” Kraft added. “The approach we took was that anyone who contributed in any way technically to the upgrade project would be a co-author on the paper. There are more than 100 people on the paper.”