Bevatron
Encyclopedia
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
— specifically, a weak-focusing
Weak focusing
In particle accelerators Weak focusing occurs when particles are kept in reasonably strong, uniform magnetic fields that causes them to move in circles under the influence of the Lorentz force....
proton synchrotron
Synchrotron
A synchrotron is a particular type of cyclic particle accelerator in which the magnetic field and the electric field are carefully synchronised with the travelling particle beam. The proton synchrotron was originally conceived by Sir Marcus Oliphant...
— at Lawrence Berkeley National Laboratory
Lawrence Berkeley National Laboratory
The Lawrence Berkeley National Laboratory , is a U.S. Department of Energy national laboratory conducting unclassified scientific research. It is located on the grounds of the University of California, Berkeley, in the Berkeley Hills above the central campus...
, U.S.A., which began operating in 1954. The antiproton
Antiproton
The antiproton is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy....
was discovered there in 1955, resulting in the 1959 Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
in physics for Emilio Segrè and Owen Chamberlain
Owen Chamberlain
Owen Chamberlain was an American physicist, and Nobel laureate in physics for his discovery, with collaborator Emilio Segrè, of antiprotons, a sub-atomic antiparticle.-Biography:...
. It accelerated protons into a fixed target, and was named for its ability to impart energies of billions of eV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
. (Billions of eV Synchrotron.)
Antiprotons
At the time the Bevatron was designed, it was strongly suspected but not known, that each particle had a corresponding anti-particle of opposite charge, identical in all other respects, a property known as charge symmetryC-symmetry
In physics, C-symmetry means the symmetry of physical laws under a charge-conjugation transformation. Electromagnetism, gravity and the strong interaction all obey C-symmetry, but weak interactions violate C-symmetry.-Charge reversal in electromagnetism:...
.
The anti-electron, or positron
Positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
had been first observed in the early 1930s, and theoretically understood as a consequence of the Dirac equation
Dirac equation
The Dirac equation is a relativistic quantum mechanical wave equation formulated by British physicist Paul Dirac in 1928. It provided a description of elementary spin-½ particles, such as electrons, consistent with both the principles of quantum mechanics and the theory of special relativity, and...
at about the same time. Following World War II, positive and negative muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
s and pion
Pion
In particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
s were observed in cosmic-ray interactions seen in cloud chamber
Cloud chamber
The cloud chamber, also known as the Wilson chamber, is a particle detector used for detecting ionizing radiation. In its most basic form, a cloud chamber is a sealed environment containing a supersaturated vapor of water or alcohol. When a charged particle interacts with the mixture, it ionizes it...
s and stacks of nuclear photographic emulsions
Nuclear emulsion
In a Particle and Nuclear physics, a nuclear emulsion plate is a photographic plate with a particularly thick emulsion layer and with a very uniform grain size. Like bubble chambers, cloud chambers, and wire chambers nuclear emulsion plates record the tracks of charged particles passing through...
.
The Bevatron was built to be energetic enough to create antiprotons, and thus test the hypothesis that every particle has a corresponding anti-particle. The antineutron
Antineutron
The antineutron is the antiparticle of the neutron with symbol . It differs from the neutron only in that some of its properties have equal magnitude but opposite sign. It has the same mass as the neutron, and no net electric charge, but has opposite baryon number...
was discovered soon thereafter by Oreste Piccioni
Oreste Piccioni
Oreste Piccioni was an Italian-American physicist who made important contributions to elementary particle physics during the early years of its history....
and co-workers, also at the Bevatron. Confirmation of the charge symmetry conjecture in 1955 led to the Nobel Prize for physics being awarded to Emilio Segrè and Owen Chamberlain in 1960.
Shortly after the Bevatron came into use, it was recognized that parity
Parity
Parity may refer to:* Parity , a symmetry property of physical quantities or processes under spatial inversion* Parity , indicates whether a number is even or odd...
was not conserved in the weak interaction
Weak interaction
Weak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
s, which led to resolution of the tau-theta puzzle, the understanding of strangeness
Strangeness
In particle physics, strangeness S is a property of particles, expressed as a quantum number, for describing decay of particles in strong and electromagnetic reactions, which occur in a short period of time...
, and the establishment of CPT symmetry
CPT symmetry
CPT symmetry is a fundamental symmetry of physical laws under transformations that involve the inversions of charge, parity, and time simultaneously.-History:...
as a basic feature of relativistic
Theory of relativity
The theory of relativity, or simply relativity, encompasses two theories of Albert Einstein: special relativity and general relativity. However, the word relativity is sometimes used in reference to Galilean invariance....
quantum field theories
Quantum field theory
Quantum field theory provides a theoretical framework for constructing quantum mechanical models of systems classically parametrized by an infinite number of dynamical degrees of freedom, that is, fields and many-body systems. It is the natural and quantitative language of particle physics and...
.
Requirements and design
In order to create antiprotons (mass ~938 MeV/cSpeed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
2) 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.
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
Liquid hydrogen
Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...
bubble chamber
Bubble chamber
A bubble chamber is a vessel filled with a superheated transparent liquid used to detect electrically charged particles moving through it. It was invented in 1952 by Donald A. Glaser, for which he was awarded the 1960 Nobel Prize in Physics...
.
Many thousands of particle interactions, or "events", were photographed, measured, and studied in detail with an automated system of large measuring machines (known as "Frankensteins") allowing human operators (typically the wives of graduate students) to mark points along the particle tracks and punch their coordinates into IBM cards, using a foot pedal.
The cards decks were then analyzed by early-generation computers, which reconstructed the three-dimensional tracks through the magnetic fields, and computed the momenta and energy of the particles.
Computer programs, extremely complex for their time, then fitted the track data associated with a given event to estimate the energies, masses, and identities of the particles produced.
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
Luis Alvarez
Luis W. Alvarez was an American experimental physicist and inventor, who spent nearly all of his long professional career on the faculty of the University of California, Berkeley...
inspired and directed much of this work, for which he received the Nobel Prize in physics in 1968.
BEVALAC
The Bevatron received a new lease on life in 1971, when it was joined to the SuperHILAC linear accelerator as an injector for heavy ions. The combination was conceived by Albert GhiorsoAlbert Ghiorso
Albert Ghiorso was an American nuclear scientist and co-discoverer of a record 12 chemical elements on the periodic table. His research career spanned five decades, from the early 1940s to the late 1990s.-Early life:...
, who named it the Bevalac. It could accelerate any nuclei in the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
to relativistic energies. It was finally decommissioned in 1993.
End of life
The next generation of accelerators used "strong focusing", and required much smaller apertures, and thus much cheaper magnets. The AGS (Alternating Gradient SynchrotronAlternating Gradient Synchrotron
The Alternating Gradient Synchrotron is a particle accelerator located at the Brookhaven National Laboratory in Long Island, New York, USA....
) at Brookhaven was the first next-generation machine, 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
Large Hadron Collider
The Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....
, the latest and greatest descendant of the Bevatron (with ~11,000 times higher energy and enormously higher intensity), are confined to a space on the order of 1 mm in cross-section, and focused down to 16 micrometres at the intersection collision regions, while the field of the bending magnets is only about five times higher.
The demolition of the Bevatron began in 2009 by Clauss Construction of Lakeside CA and is scheduled for completion in 2011.
See also
- Particle acceleratorParticle acceleratorA particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
: Generalities on various types - Alternating Gradient SynchrotronAlternating Gradient SynchrotronThe Alternating Gradient Synchrotron is a particle accelerator located at the Brookhaven National Laboratory in Long Island, New York, USA....
: 33 GeV strong-focusingStrong focusingIn accelerator physics strong focusing or alternating-gradient focusing is the principle that the net effect on a particle beam of charged particles passing through alternating field gradients is to make the beam converge...
synchrotron, next step after Bevatron - TevatronTevatronThe Tevatron is a circular particle accelerator in the United States, at the Fermi National Accelerator Laboratory , just east of Batavia, Illinois, and is the second highest energy particle collider in the world after the Large Hadron Collider...
: Fermi Lab accelerator, 1 TeV proton-antiproton collider, largest current US machine - Large Hadron ColliderLarge Hadron ColliderThe Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....
: CERNCERNThe European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
machine, the world's most powerful when it became operational in December 2009.