Particle Accelerators Drive Decades of Discoveries at Berkeley Lab and Beyond

by Glenn Roberts Jr., News Center author,

Accelerators have been at the heart of the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) since its inception in 1931, and are still a driving force in the Laboratory’s mission and its R&D program.

Ernest O. Lawrence’s invention of the cyclotron, the first circular particle accelerator—and the development of progressively larger versions—led him to develop the hillside overlooking the UC Berkeley campus that is now Berkeley Lab’s home. A variety of large cyclotrons are in use today around the world, and new accelerator technologies continue to drive progress.

“Our work in accelerators and related technologies has shaped the growth and diversification of Berkeley Lab over its long history, and remains a vital core competency today,” said James Symons, associate laboratory director for Berkeley Lab’s Physical Sciences Area.

Cyclotrons and Their Successors
Cyclotrons are “atom smashers” that accelerate charged particles along spiral paths with strong electric fields. Powerful magnetic fields guide them as they move outward from the device’s center.

They can be used to create different elements by bombarding a target material with a beam of protons, for example, or to explore the structures of atomic nuclei. Cyclotrons played a key role in the production and discovery of several elements, and Berkeley Lab scientists participated in the discovery of 16 elements and in the rearrangement of the periodic table.

Cyclotrons can also be used to create special isotopes—atoms of an element with the same number of protons but different numbers of neutrons packed into their nuclei—that can be used for medical treatments, imaging and other research purposes. As an example, technetium-99, which was created by Berkeley’s 37-inch cyclotron and discovered by Carlo Perrier and Emilio Segrè, is used for millions of medical imaging scans a year worldwide.

The first facility built on the Berkeley Lab site was a massive 184-inch cyclotron. The iconic dome over the cyclotron now houses another accelerator: the Advanced Light Source. Berkeley Lab scientists led the design and development of other new concepts in accelerators. After initial tests on an old cyclotron, the 184-Inch Cyclotron was rebuilt into a “synchro-cyclotron.”

Edwin McMillan then led the construction of a powerful ring-shaped electron accelerator, which he dubbed the “synchrotron,” that was based on a principle he co-discovered called phase stability. Within just a few years of its inception, construction began on an ambitious synchrotron, called the Bevatron for its 6 billion electron volts of energy, which reigned for several years as the most powerful in the world.

The Bevatron enabled the Nobel Prize-winning discovery of the antiproton, and two other Nobel Prizes were awarded based on research conducted at the Bevatron. Almost every accelerator built today operates using this same principle.

Accelerator R&D and experiments at the Lab—and Lab scientists’ participation in experiments at other sites—have enabled discoveries of many subatomic particles and their properties, including the Higgs boson.

Berkeley Lab scientists have also driven many innovations in linear accelerators, which accelerate particles along a straight path and offer some different capabilities than ring-shaped accelerators.

Using a linear accelerator called the HILAC—and its SuperHILAC upgrade—to accelerate heavy charged particles (ions), scientists added several new elements to the periodic table. The eventual use of the SuperHILAC to produce beams of charged particles for Bevatron experiments—the coupling led to the Bevatron’s rebranding as the Bevalac—gave rise to the study of nuclear matter at extreme temperatures and pressures.

Lab accelerators also launched pioneering programs in biomedical research, including the use of accelerator beam-based cancer therapies and the production of medical isotopes. Lawrence’s brother John, a medical doctor, was a pioneer in this early nuclear medicine research, which spawned new pathways in medical treatments that have since developed into well-established fields.

Berkeley Lab’s 88-Inch Cyclotron still supports cutting-edge nuclear science, including heavy-element research and tests that show how electronic components stand up to the effects of simulated space radiation. Staff at the 88-Inch Cyclotron have also played a central role in the development of ion sources that achieve high charge states. A new group—the Ion Source Group—at the Lab works on the machines that create beams driving this field of research.

Accelerators that Produce Light
Synchrotron light sources accelerate and bend particle beams using a magnetic field, causing them to give off light with special qualities. Berkeley Lab’s Advanced Light Source (ALS), launched in 1993, generates intense, focused beams of X-rays to support a wide range of experiments. Earlier light sources had been converted from accelerators built for high energy physics experiments.

The ALS is considered to be the first “third-generation” light source, a synchrotron designed specifically to support many simultaneous experiments and that features advanced magnetic devices such as wigglers and undulators to greatly increase the brightness of the X-ray beams. The late Berkeley Lab scientist Klaus Halbach pioneered the use of permanent magnets to create powerful, compact devices for use in accelerators.

Berkeley Lab is now preparing for a major upgrade of the ALS, known as the ALS Upgrade or ALS-U, that will increase the brightness of its low energy X-ray beams a hundredfold and focus them down to a few billionths of a meter. ALS-U will enable explorations of more complex materials and phenomena.

Light that Produces Acceleration
Light can also be used as a driver to accelerate particles. The Berkeley Lab Laser Accelerator (BELLA) Center features four high power laser systems that support an intense R&D effort in laser plasma acceleration. This technique uses lasers to drive the acceleration of electrons over a much shorter distance than is possible with conventional technology.

The BELLA petawatt laser is driving research toward the high energies required for a next-generation particle collider while reducing the size and cost of such a machine compared to those of conventional large-scale accelerators. Other laser systems are aiming for new light sources driven by powerful beams from portable and centimeter-sized accelerators.

Innovating Locally, Participating Globally
The revolutionary accelerators first developed at Berkeley Lab were large, complex machines that required innovations and expertise in science and engineering, and close coordination among specialists from many different disciplines.

Lawrence and his lab championed a “team science” approach as the means to realize the vision for large accelerators pushing the boundaries of discovery. The global scientific community still embraces this approach, and the world’s most powerful accelerators and colliders require large teams of scientists, engineers, technicians and others that can number into the thousands.

In addition to Berkeley Lab’s own accelerators, its scientists and engineers have been instrumental in bringing their expertise to bear in the design and construction of accelerators and their components for accelerator projects across the US and globally.

Berkeley Lab researchers are building powerful superconducting magnets for an upgrade of CERN’s Large Hadron Collider in Europe, which is the world’s largest particle collider, as just one example. They are also contributing an ion beam source magnet for the Facility for Rare Isotope Beams (FRIB) (CSA CSM) under construction at Michigan State University, and in designing and overseeing the construction and delivery of major components for an upgrade of the Linac Coherent Light Source X-ray laser at SLAC National Accelerator Laboratory in Menlo Park CA.

The lab also has rich experience in developing control systems and instrumentation to precisely tune beam performance. Modeling and simulation of particle beams enable researchers to use “virtual accelerators” to better understand, efficiently optimize, and predict beam properties in the design of advanced particle accelerators.

“We are thrilled to contribute to this continuing wave of innovation and progress that is ‘accelerating the future,’” said Thomas Schenkel, interim director of the Accelerator Technology and Applied Physics Division at Berkeley Lab. “The rich history of excellence in accelerator technologies here is the foundation upon which we are building the next generation of these powerful tools for scientific discoveries and industrial applications.”

The Advanced Light Source and Linac Coherent Light Source are DOE Office of Science User Facilities, and the Facility for Rare Isotope Beams, now under construction, will also be a DOE Office of Science User Facility.