Tevatron accelerator

The invention: 



A particle accelerator that generated collisions between

beams of protons and antiprotons at the highest energies

ever recorded.



The people behind the invention:



Robert Rathbun Wilson (1914- ), an American physicist and

director of Fermilab from 1967 to 1978

John Peoples (1933- ), an American physicist and deputy

director of Fermilab from 1987








Putting Supermagnets to Use



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 is a circular, tubelike track 6.4 kilometers in circumference

that employs a series of superconducting magnets to accelerate

beams of protons, which carry a positive charge in the atom, and

antiprotons, the proton’s negatively charged equivalent, at energies

up to 1 trillion electron volts (equal to 1 teraelectronvolt, or 1 TeV;

hence the name Tevatron). An electronvolt is the unit of energy that

an electron gains through an electrical potential of 1 volt.

The Tevatron is located at the Fermi National Accelerator Laboratory,

which is also known as Fermilab. The laboratory was one of

several built in the United States during the 1960’s.

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 electron volts, or 0.5 teraelectronvolt.

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, the director of Fermilab 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 using superconducting materials, however,

which have virtually no resistance to electrical current, would

make it possible for the Tevatron to achieve double the main ring’s

magnetic field strength, doubling energy output without significantly

increasing energy costs.





Tevatron to the Rescue



The Tevatron was conceived in three phases. 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

electron volts. More important still are the proton-anti proton colliding

beam experiments of Tevatron I. In this phase, beams of protons

and antiprotons rotating in opposite directions are caused to collide

in the Tevatron, producing a combined, or center-of-mass, energy

approaching 2 trillion electron volts, nearly three times the energy

achievable at the largest accelerator at Centre Européen de Recherche

Nucléaire (the European Center for Nuclear Research, or CERN).

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 in

which 120 billion electron volt 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. 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. On October 13, 1985,

Fermilab scientists reported a proton-antiproton collision with a

center-of-mass energy measured at 1.6 trillion electron volts, the

highest energy ever recorded.





Consequences



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 at energy levels that no other accelerator

could achieve.

Physics recognized four forces in nature: the electromagnetic

force, the gravitational force, the strong nuclear force, and the weak

nuclear force. A major goal of the physics community is to formulate

a theory that will explain all these forces: the so-called grand

unification theory. In 1967, one of the first of the so-called gauge theories

was developed that unified the weak nuclear force and the

electromagnetic force. One consequence of this theory was that the

weak force was carried by massive particles known as “bosons.”

The search for three of these particles—the intermediate vector bosons

W+, W-, and Z0—led to the rush to conduct colliding beam experiments

to the early 1970’s. Because the Tevatron was in the planning

phase at this time, these particles were discovered by a team of

international scientists based in Europe. In 1989, Tevatron physicists

reported the most accurate measure to date of the Z0 mass.

The Tevatron is thought to be the only particle accelerator in the

world with sufficient power to conduct further searches for the elusive

Higgs boson, a particle attributed to weak interactions by University

of Edinburgh physicist Peter Higgs in order to account for

the large masses of the intermediate vector bosons. In addition, the

Tevatron has the ability to search for the so-called top quark. Quarks

are believed to be the constituent particles of protons and neutrons.

Evidence has been gathered of five of the six quarks believed to exist.

Physicists have yet to detect evidence of the most massive quark,

the top quark.



See also:



Atomic bomb; Cyclotron; Electron microscope; Field ion

microscope; Geiger counter; Hydrogen bomb; Mass spectrograph;

Neutrino detector; Scanning tunneling microscope; Synchrocyclotron.