The Tevatron particle accelerator generated collisions between beams of protons and antiprotons at the highest energies ever recorded up to that time.
The Tevatron is a particle accelerator, a large electromagnetic device used by high-energy physicists to generate subatomic particles at sufficiently high energies to explore the basic structure of matter. The Tevatron consists of a circular, tubelike track 6.4 kilometers (almost 4 miles) in circumference that employs a series of superconducting magnets to accelerate beams of protons, which carry the positive charge in the atom, and antiprotons, the proton’s negatively charged equivalent, at energies up to 1 trillion electronvolts equal to 1 tera-electronvolt (TeV), hence the name Tevatron. An electronvolt is the unit of energy that a unit charge, such as an electron, gains through an electrical potential of 1 volt.
The Tevatron is located at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois. The laboratory was one of several accelerator labs built in the United States during the 1960’s. Most of the accelerator studies prior to World War II were conducted at the University of California’s Radiation Laboratory, now the Lawrence Berkeley Radiation Laboratory, named in honor of Ernest Orlando Lawrence’s contributions to the study of nuclear physics, which include his design of the cyclotron particle accelerator.
After the war, the European Council for Nuclear Research (later renamed the European Organization for Nuclear Research), known as CERN
The heart of the original Fermilab was the 6.4-kilometer main accelerator ring. This main ring was capable of accelerating protons to energies approaching 500 billion electronvolts, or 0.5 TeV. The idea to build the Tevatron grew out of a concern for the millions of dollars spent annually on electricity to power the main ring, the need for higher energies to explore the inner depths of the atom and the consequences of new theories of both matter and energy, and the growth of superconductor technology. Planning for a second accelerator ring, the Tevatron, to be installed beneath the main ring began in 1972.
Robert Rathbun Wilson, Fermilab director at that time, realized that the only way the laboratory could achieve the higher energies needed for future experiments without incurring intolerable electricity costs was to design a second accelerator ring that employed magnets made of superconducting material. Extremely powerful magnets are the heart of any particle accelerator; charged particles such as protons are given a “push” as they pass through an electromagnetic field. Each successive push along the path of the circular accelerator track gives the particle more and more energy. The enormous magnetic fields required to accelerate massive particles such as protons to energies approaching 1 trillion electronvolts would require electricity expenditures far beyond Fermilab’s operating budget. Wilson estimated that with the use of superconducting materials, which have nearly no resistance to electrical current, the Tevatron could achieve double the main ring’s magnetic field strength, doubling energy output without a significant increase in energy costs.
The superconducting magnets are constructed of twenty-three thin strands of copper wire within which twenty-one hundred filaments made of a niobium-titanium alloy are embedded. Such alloys are known to exhibit superconducting properties. During construction, Fermilab was the world’s largest single consumer of this material. To construct the magnets for the Tevatron, Fermilab obtained almost fifty tons of this material more than 30 million meters of superconductor, nearly enough to circle the earth. More than 1,000 magnets were constructed of this material, 774 to guide the protons along the track and 240 to focus the beams. The magnets are cooled with liquid helium, which is produced by the largest liquid helium plant in the world.
An aerial photograph of the Fermilab accelerators shows the Main Injector (completed in 1999) in the foreground and the 6.4-kilometer-long Tevatron in the background.
The Tevatron was conceived in three phases: the Energy Saver, Tevatron I, and Tevatron II. In the energy-saving mode, protons are generated in the main ring at an energy of 150 billion electronvolts and subsequently transferred to the Tevatron, where they are accelerated to 500 billion electronvolts. Recall that this is the maximum energy at which the older main ring could accelerate protons. In this new mode, the protons can be accelerated to the same energy in the Tevatron at a greatly reduced cost. From the Tevatron, these proton beams are directed to experimental areas, where they are aimed at a series of targets and detectors. The collision of these beams and the targets generates other, more interesting particles, such as neutrinos, which are investigated by the sophisticated electronics embedded in the detectors.
Most important, however, were Tevatron I and Tevatron II, where the highest energies were to be generated and where it was hoped new experimental findings would emerge. Tevatron II experiments were designed to be very similar to other proton beam experiments, except that in this case, the protons would be accelerated to an energy of 1 trillion electronvolts. At this energy, Fermilab physicists believed that the neutrinos produced by the interaction of the proton beam and suitable targets or more slowly moving proton beams would be far more energetic than naturally occurring neutrinos or those from other, less powerful accelerators. More important still are the proton-antiproton colliding beam experiments of Tevatron I. In this phase, counterrotating beams of protons and antiprotons are induced to collide in the Tevatron, producing a combined, or center-of-mass, energy approaching 2 trillion electronvolts, nearly three times the energy achievable at the largest accelerator at CERN.
Fermilab physicist John Peoples was faced with the problem of generating a beam of antiprotons of sufficient intensity to collide efficiently with a beam of protons. Knowing that he had the use of a large proton accelerator the old main ring Peoples employed the two-ring mode whereby 120 billion electronvolt protons from the main ring are aimed at a fixed tungsten target, generating antiprotons, which scatter from the target. These particles were extracted and accumulated in a smaller storage ring. As in the Energy Saver mode, these particles could be accelerated to relatively low energies. After sufficient numbers of antiprotons were collected, they were injected into the Tevatron, along with a beam of protons for the colliding beam experiments.
One problem of accumulating the antiprotons is the fact that as they scatter from the tungsten target, they do so along highly divergent and irregular paths. This beam could not be injected into the smaller storage ring until the divergent beam was corrected. The physics of such storage, known as “beam cooling,” was developed by the Soviet physicist Gersh Budker. Low-energy electrons are directed parallel to the antiproton beam, where the higher-energy antiprotons transfer some energy to the slower electrons. This process, also known as emittance reduction, provides a more coherent beam of antiprotons. An alternative method employing electronic sensors and correcting signals, known as stochastic cooling, was developed by CERN physicist Simon van der Meer.
The Tevatron’s success at generating high-energy proton-antiproton collisions affected future plans for accelerator development in the United States and offered the potential for important discoveries in high-energy physics of which no other accelerator is capable.
Physics recognizes four forces in nature: the electromagnetic, gravitational, and strong and weak nuclear forces. A major goal of the physics community is to explain all these forces by one theory, the so-called grand unified theory.
It is widely believed that the Tevatron is the only particle accelerator in the world with the power to conduct further searches for the more elusive Higgs boson,
The success of the Tevatron from a technological perspective, with its superconducting magnets accelerating protons to energies only imagined in the early years of American high-energy physics, led the Department of Energy to abandon its funding for the half-completed proton beam collider “Isabelle” at the Brookhaven Laboratory. Isabelle would have made possible proton-proton collisions at 200 billion electronvolts. In 1983, the Department of Energy focused its attention on the design and construction of a gigantic collider that came to be known as the Superconducting Super Collider,
-
Kerr, Richard A., and Arthur L. Robinson. “Fermilab Tests Its Antiproton Factory.” Science 229 (September, 1985): 1374-1376. Brief article, written in a nontechnical manner, provides a general introduction to collider experiments. Discusses the antiproton production capabilities of the Tevatron as well as its proton-antiproton collision capacity. Stresses the technical problems of producing antiprotons and discusses the various techniques of beam cooling. -
Lee, S. Y. Accelerator Physics. 2d ed. Hackensack, N.J.: World Scientific Publishing, 2004. Text intended for college physics majors or graduate students begins with a chapter on the history of the development of particle accelerators. -
Robinson, Arthur L. “Proton-Antiproton Collisions at Fermilab.” Science 230 (November, 1985): 529. Offers a brief, nontechnical introduction to the first proton-antiproton collision at Fermilab. Describes some of the logistical problems of operating a particle accelerator that is partially under construction and renovation. -
Wilson, Edmund. An Introduction to Particle Accelerators. New York: Oxford University Press, 2001. Moderately technical text devotes its first chapter to the history of particle accelerators. Includes bibliographic references and index. -
Wilson, Robert. “The Next Generation of Particle Accelerators.” Scientific American 242 (January, 1980): 42-57. Relatively technical and copiously illustrated article discusses the rationale behind the new generation of particle accelerators, of which the Tevatron is one. Discusses both scientific and engineering details and the role of multinational and public sponsorship of accelerator construction. An especially informative section illustrates the physics of beam cooling. -
_______. “The Tevatron.” Physics Today, October, 1977, 23-27. One of the best works available for readers interested in learning more about the technical details of how the Tevatron works. Wilson, director of Fermilab during the Tevatron’s design and construction, discusses the technical and scientific details of the Tevatron with a special emphasis on the superconducting magnet technology. Includes extensive bibliography. -
_______. “U.S. Particle Accelerators at Age 50.” Physics Today 34 (November, 1981): 86-103. Places the development of the Tevatron in historical context by showing its place in the development of American accelerator technology. Discusses almost every aspect of accelerator technology, from funding to engineering.
Rubbia and van der Meer Isolate the Intermediate Vector Bosons
Bednorz and Müller Discover a High-Temperature Superconductor
Construction Begins on the Superconducting Super Collider