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Bevatron
Bevatron
Bevatron
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Bevatron
Donald Cooksey, Harold Fidler, Ernest Lawrence, William Brobeck, and Robert Thornton overlooking model of Bevatron, 1950
General properties
Accelerator typeSynchrotron
Beam typeproton
Target typefixed target
Beam properties
Maximum energy13 GeV
Physical properties
Circumference400 ft
LocationBerkeley, California
Coordinates37°52′39″N 122°15′03″W / 37.877392°N 122.250811°W / 37.877392; -122.250811
InstitutionLawrence Berkeley National Laboratory
Dates of operation1954 - 1993

The Bevatron (/ˈbɛvətrɒn/ BEV-ə-tron) was a particle accelerator – specifically, a weak-focusing proton synchrotron – located at Lawrence Berkeley National Laboratory, U.S., which began operations in 1954.[1] The antiproton was discovered there in 1955, resulting in the 1959 Nobel Prize in physics for Emilio Segrè and Owen Chamberlain.[2] It accelerated protons into a fixed target, and was named for its ability to impart energies of billions of eV ("billions of eV synchrotron").

Antiprotons

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When the Bevatron was designed, scientists strongly suspected—but had not yet confirmed—that every particle had a corresponding antiparticle with an opposite charge but otherwise identical properties, a concept known as charge symmetry.

The anti-electron, or positron, had been first observed in the early 1930s and theoretically understood as a consequence of the Dirac equation at about the same time. Following World War II, positive and negative muons and pions were observed in cosmic-ray interactions seen in cloud chambers and stacks of nuclear photographic emulsions. The Bevatron was built to be energetic enough to create antiprotons, and thus test the hypothesis that every particle has a corresponding anti-particle.[3] In 1955, the antiproton was discovered using the Bevatron.[4] The antineutron was discovered soon thereafter by the team of Bruce Cork, Glen Lambertson, Oreste Piccioni, and William Wenzel in 1956.[5] Confirmation of the charge symmetry conjecture in 1955 led to the Nobel Prize for physics being awarded to Emilio Segrè and Owen Chamberlain in 1959.[4]

Shortly after the Bevatron came into use, it was recognized that parity was not conserved in the weak interactions, which led to resolution of the tau-theta puzzle, the understanding of strangeness, and the establishment of CPT symmetry as a basic feature of relativistic quantum field theories.

Requirements and design

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BEV-938. Antiproton set-up with work group: Emilio Segre, Clyde Wiegand, Edward J. Lofgren, Owen Chamberlain, Thomas Ypsilantis, 1955

In order to create antiprotons (mass ~938 MeV/c2) in collisions with nucleons in a stationary target while conserving both energy and momentum, a proton beam energy of approximately 6.2 GeV is required. At the time it was built, there was no known way to confine a particle beam to a narrow aperture, so the beam space was about four square feet in cross section.[6] The combination of beam aperture and energy required a huge, 10,000 ton iron magnet, and a very large vacuum system.

A large motor–generator system was used to ramp up the magnetic field for each cycle of acceleration. At the end of each cycle, after the beam was used or extracted, the large magnetic field energy was returned to spin up the motor, which was then used as a generator to power the next cycle, conserving energy; the entire process required about five seconds. The characteristic rising and falling, wailing, sound of the motor–generator system could be heard in the entire complex when the machine was in operation.

In the years following the antiproton discovery, much pioneering work was done here using beams of protons extracted from the accelerator proper, to hit targets and generate secondary beams of elementary particles, not only protons but also neutrons, pions, "strange particles", and many others.

The liquid-hydrogen bubble chamber

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Two bright circles on dark background, both contain numerous thin black lines inside.
First tracks observed in liquid hydrogen bubble chamber at the Bevatron

The extracted particle beams, both the primary protons and secondaries, could in turn be passed for further study through various targets and specialized detectors, notably the liquid hydrogen bubble chamber. Many thousands of particle interactions, or "events", were photographed, measured, and studied in detail with an automated system of large measuring machines (known as "Franckensteins", for their inventor Jack Franck).[7]

This process allowed human operators to manually mark points along particle tracks and enter their coordinates onto IBM punch cards using a foot pedal. These card decks were then processed by early-generation computers, which reconstructed the three-dimensional trajectories through magnetic fields and calculated the particles’ momenta and energies. At the time, highly sophisticated computer programs were used to fit the track data for each event, enabling estimates of the particles’ energies, masses, and identities.

This period, when hundreds of new particles and excited states were suddenly revealed, marked the beginning of a new era in elementary particle physics. Luis Alvarez inspired and directed much of this work, for which he received the Nobel Prize in physics in 1968.

Bevalac

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The Bevatron received a new lease on life in 1971,[8] when it was joined to the SuperHILAC linear accelerator as an injector for heavy ions.[9] The combination was conceived by Albert Ghiorso, who named it the Bevalac.[10] It could accelerate a wide range of stable nuclei to relativistic energies.[11] It was finally decommissioned in 1993.

End of life

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The next generation of accelerators adopted "strong focusing," which allowed for much smaller beam apertures and, consequently, significantly cheaper magnets. The CERN PS (Proton Synchrotron, 1959) and the Brookhaven National Laboratory AGS (Alternating Gradient Synchrotron, 1960) were the first next-generation machines, with an aperture roughly an order of magnitude less in both transverse directions, and reaching 30 GeV proton energy, yet with a less massive magnet ring. For comparison, the circulating beams in the Large Hadron Collider (LHC) reach energies nearly 11,000 times greater than those in the Bevatron, with vastly higher intensities. Despite this, they are confined to a cross-sectional area of about 1 mm and are focused to just 16 micrometres at collision points, while the bending magnet fields are only about five times stronger.

The demolition of the Bevatron began in 2009 and was completed in early 2012.[12]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Bevatron

View on Grokipedia
from Grokipedia
The Bevatron was a weak-focusing located at (LBNL) in , designed to accelerate protons to energies of up to 6.2 GeV and operational from 1954 to 1993. Constructed in the early 1950s under the direction of Ernest O. Lawrence at a cost of $9.6 million, it represented a pinnacle of postwar "" funded by the U.S. Atomic Energy Commission, occupying 125,000 square feet and weighing 10,000 tons with its massive 184-inch magnet. The accelerator gained worldwide renown for enabling the 1955 discovery of the by physicists and , a breakthrough in confirming the existence of that earned them the 1959 . In the 1960s, Bevatron beams interacting with liquid-hydrogen bubble chambers developed by Luis Alvarez revealed numerous subatomic resonances and provided key evidence for SU(3) flavor symmetry, contributing to Alvarez's 1968 Nobel Prize in Physics for his work on particle classification. Overall, research at the Bevatron was linked to four Nobel Prizes in Physics during its early decades, underscoring its role in advancing hadron physics and the . In the 1970s, the Bevatron was upgraded by coupling it with the SuperHILAC linear accelerator to create the Bevalac, which accelerated heavy ions to relativistic speeds and pioneered studies in nuclear matter under extreme conditions as well as ion-beam cancer radiotherapy. Decommissioned in 1993 as higher-energy facilities like the Tevatron emerged, the Bevatron was demolished between 2009 and 2012 to make way for modern infrastructure, including the Integrative Genomics Building housing the DOE Joint Genome Institute, with additional major research facilities completed by 2025. In 2021, its site was designated a National Historic Physics Site by the American Physical Society, recognizing its enduring legacy in particle physics and beyond.

History and Development

Conception and Construction

In the aftermath of , Ernest O. Lawrence, director of the Radiation Laboratory, envisioned a new to probe fundamental questions in . Motivated by Paul Dirac's 1928 theoretical prediction of particles, including the as the negatively charged counterpart to the proton, Lawrence proposed in 1946 a capable of accelerating protons to energies up to 10 GeV—sufficient to produce antiproton-proton pairs through high-energy collisions. This ambition marked a shift from earlier cyclotrons toward synchrotrons, leveraging weak focusing principles to achieve unprecedented energies for testing Dirac's hypothesis. Securing funding proved challenging amid postwar budget constraints, but Lawrence's persistence paid off. In 1947, he sought approval from the Atomic Energy Commission (AEC) for an initial $9.6 million budget to construct a 10 GeV , designed primarily by the lab's chief engineer William Brobeck. The AEC granted approval in 1948, adjusting the to a more feasible 6 GeV machine while maintaining the core objective; the final cost aligned closely with the original estimate at approximately $9.6 million. Key contributors to the conception included Edwin McMillan, who advanced the synchrotron's phase stability concept essential for beam control, and Robert Thornton, who contributed to the overall framework. Construction commenced with groundbreaking in September 1949 at the Radiation Laboratory site on the "hill" above the UC Berkeley campus, selected for its existing infrastructure and proximity to facilities. Under Brobeck's engineering leadership and oversight from associate director Cooksey, who managed lab operations and resource allocation, the project progressed rapidly: the massive 9,700-ton yoke began installation in August 1950, encircling a 120-foot-diameter within a dedicated circular building. The featured a 220-foot-diameter, 40-foot-high magnet room with attached shop-and-office and mechanical wings (310 by 71.5 feet), designed for efficient integration of the accelerator's components, including injection systems and control areas. The first proton beam was circulated on February 15, 1954, with the machine reaching its full design energy of 6.2 GeV on April 1, 1954.

Initial Operation and Milestones

The Bevatron's commissioning began shortly after construction completion in late January 1954, with the first low-energy proton beam successfully circulated through the accelerator in February of that year. Initial operations focused on ramping up beam energies as tuning progressed, with the machine attaining its full design energy of 6.2 GeV in , marking a key milestone that positioned it as the world's highest-energy accelerator at the time and enabling prompt high-energy physics experiments. Early operation encountered several technical challenges, including vacuum system issues where initial pump-downs of the 100,000-cubic-foot required up to 72 hours to reach pressures of 10^{-5} mm Hg, later improved to 12-24 hours through enhanced drying procedures. Magnet tuning proved critical for beam stability, necessitating adjustments to the field index (n value) by about 0.1 to optimize focusing and prevent beam loss. Radiation shielding also demanded attention, with the accelerator enclosed in 5-foot-thick walls to mitigate and gamma from beam interactions, ensuring safe access for operators during non-pulse periods. The Bevatron operated in pulsed mode, with each cycle lasting approximately 5 seconds—comprising a 2-second magnet current ramp-up to 8,333 amperes and a 3-second flat-top—driven by two motor-generator sets delivering a combined peak power of 100 MW through . Repetition rates reached up to 10 pulses per minute, supporting sustained experimental runs. Initial beam intensities were very low, around 10^5 protons per pulse in early operation, growing rapidly to 10^{10} protons per pulse by October 1954, providing sufficient flux for early target bombardments. These operational benchmarks, achieved ahead of initial projections for full capability, facilitated immediate investigations into predicted particles like the , aligning with the accelerator's foundational motivations.

Design and Technical Features

Accelerator Principles and Specifications

The Bevatron functioned as a weak-focusing , relying on the principle of weak focusing to achieve radial and vertical beam stability. In this method, the varies with radius such that the field index n=−rBdBdr≈0.6n = -\frac{r}{B} \frac{dB}{dr} \approx 0.6, ensuring oscillatory motion of particles around the equilibrium orbit without strong focusing elements. This value of nn balances stability conditions, with radial tune νr=1−n\nu_r = \sqrt{1 - n}
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