The first cyclotrons and detectors
The Lawrence-Livingstone cyclotrons
In January 1931 Ernest Orlando Lawrence (1901-1958) and his graduate student Milton Stanley Livingstone brought into being a device about 4.5 inches in diameter and using a potential of 1,800 volts to accelerate hydrogen ions up to energies of 80,000 electron volts. In summer 1931 his eleven-inch cyclotron achieved a million volts. It accelerated particles around a carousel at higher and higher energies. Lawrence thought to use a magnetic field to bend the charged particles into circular trajectories and thus pass them through the same accelerating region over and over again. He called it a “proton merry go round”[1].
Lawrence did not remain satisfied with the million-volt protons provided by his eleven-inch cyclotron, but hoped to increase the energy by a factor of ten or more. Higher energies required bigger magnets and faster oscillators. It also demanded more money. In August 1931 he fathered a new 27-inch cyclotron, with an 80-ton magnet originally built to power a transatlantic radio link in World War I. By September 1932 the cyclotron was accelerating protons up to 3.6 million electron-volts. In 1937 he had a 37-inch cyclotron operating, followed two years later by a 60-inch device. His cyclotrons continued to grow in size, one eventually requiring a 200 tonne magnet[2].
The Gargamelle bubble chamber
Gargamelle was a bubble chamber at CERN designed to detect neutrinos. It operated from 1970 to 1976 with a muon-neutrino beam produced by the CERN Proton Synchroton before moving to the Super Proton Synchroton (SPS) until 1979. Standing 2 metres tall and 4.8 meters in diameter, it weighed 1000 tonnes and held nearly 12 cubic metres of heavy-liquid freon (CF3Br). It captured images of particle tracks through the 1970s. It was named after a giantess in the books of François Rabellais.
Gargamelle revealed previously unseen types of particle collisions. As neutrinos have no charge, they do not leave tracks in detectors. The freon in the Gargamelle detector revealed any charged particles set in motion by the neutrinos and so revealed the interactions indirectly. Using freon instead of the more typical liquid hydrogen increased the probability of seeing neutrino interactions.
Early results from Gargamelle during 1972-4 provided crucial evidence for the existence of quarks, the fundamental constituents of particles such as protons and neutrons. Combining the neutrino results with those from experiments using an electron beam at the Stanford Linear Accelerator Centre (SLAC) in the US showed that the quarks must have charges that are 1/3 or 2/3 the charge of the proton, just as predicted. In 1979 the chamber ceased operation after cracks had appeared that proved impossible to repair[3].
The US-CERN race culminated in the 6 km round Tevatron near Chicago. Containing hundreds of superconducting magnets, a technology exploited by the LHC, it was completed in 1983 at a cost of 120 million. The Tevatron discovered the top quark, the heaviest known fundamental particle, in 1984 and made an important contribution to the discovery of the Higgs boson. It was the first accelerator to produce antiprotons[4]. However, by 2011, it could no longer compete with the larger and more powerful LHC and was closed.
The proposed Superconducting Super Collider
In 1988, the US also began the construction of the ambitious Superconducting Super Collider (SSC). Housed in a 83 km tunnel beneath the Texas plains, it would have collided particles at nearly 3 times the energy of the LHC. The project lost support in Congress and it was cancelled by President Clinton in 1993.
In 1988, the US also began the construction of the ambitious Superconducting Super Collider (SSC). Housed in a 83 km tunnel beneath the Texas plains, it would have collided particles at nearly 3 times the energy of the LHC. The project lost support in Congress and it was cancelled by President Clinton in 1993.
Completed in 1989, the Large Electron-Positron (LEP) Collider at CERN collided particles at phenomenal speeds. It was dismantled in 2000, leaving its 27 km tunnel ready for the installation of the even more powerful LHC.
Left: LEP Collider accelerating cavity, c 1989. Source: Science Museum London's travelling exhibition on display at the Sydney Powerhouse Museum, August - October 2016.
[1] Science Museum London's travelling exhibition at the Powerhouse Museum, Sydney, August - October 2016.
[2] On Lawrence, see https://www.aip.org/history/exhibits/lawrence/first.htm and successive pages.
[3] On Gargamelle, see https://home.cern/about/experiments/gargamelle
[4] Tony Hey and Patrick Walters, The New Quantum Universe, Cambridge, 2003, 232.