From the January and February 1975 issue

TRIUMF triumph

On 15 December the 500 MeV cyclotron at Vancouver produced its first full energy beams. After a month of gradually spiralling the beam further and further out in the machine, success came precipitately.

On 14 December an energy of 360 MeV had been reached at 690 cm machine radius and beam transmission out to this energy was looking good. By 12 noon the following day, protons were again at 360 MeV. In the next hour, appropriately with the TRIUMF Director J R Richardson at the helm, the beam was taken to the design energy of 500 MeV by tuning the trim coils.

An hour later, extracted beam of 10 nA was detected and soon manoeuvred over 15 m to a beam dump. Using quadrupoles, it could be focused on a 1 cm2 spot.

By 16.00 hours the champagne corks had been popped.

We congratulate Professor Richardson and his team on their success in bringing such an adventurous machine into action. They join Los Alamos and Villigen as the world’s three major ‘meson factories’.

•  Compiled from texts on pp11–12.

Superconducting muon channel begins operation

Operation of the 590 MeV cyclotron at the Swiss Institute for Nuclear Research, SIN, is going very well following improvements carried out during a shutdown last year. The most satisfying success was the smooth start of operation of the new superconducting muon channel.

Muon beamlines at intermediate energies have almost always used quadrupoles to focus the pions produced when the ejected proton beam hits a target, and to retain some of the muons produced as the pions decay. The idea of a solenoid is to produce a beam of pions on large spirals with small radii, close to the axis, so that the decay muons are much less likely to escape. Close on 100% efficiency can be expected.

Long, large aperture solenoids are needed – the SIN solenoid is 8 m long with a 12 cm aperture and a field of 5 T. To provide these conditions with a conventional magnet would involve a power consumption of 10 MW.

The solenoid uses copper stabilized niobium-titanium superconductor wound in sixteen sections on reinforced epoxy resin. The outer surface is in contact with a layer of copper pipes carrying the helium cooling, all enclosed in a thick walled steel tube, which is a magnetic return path. Gas cooled current leads connect the solenoid to a 1 kA supply. Cooling is by supercritical helium under a pressure of 6 to 10 atmospheres.

In the first test of the full solenoid in December, the current climbed to 690 A before a quench. After repair, on 15 January the magnet immediately reached 5 T and stayed there for days. Since then it has operated continuously with no problems in following the shutdown and re-starts of the accelerator schedule.

Pions are focused on the entrance to the solenoid and it can take a wide range of momenta. Muons emerge from the solenoid within a 20 cm2 area and can be transported to two experimental regions by conventional magnets.

When the solenoid worked so well on 15 January, pions of 200 MeV/c were fed to the channel. The muon extraction was slowly brought down to lower momenta and at 180 MeV/c a pure muon beam was achieved. Maximum muon flux was reached at 115 MeV/c. The design intensity was 2.4 × 107 muons per second. After only a preliminary tuning 2 × 107 was achieved. Already the SIN cyclotron has the world’s highest muon fluxes.

•  Compiled from texts on pp36–37.

Compiler’s Note

The photo of TRIUMF triumphant shows the prevailing gender demographics. Data aides and scanners apart, females were rare in physics, the Nobel category in which they are the least represented. Of the 206 physics Nobel prize winners since 1901, only two have been women: Marie Curie in 1903 with a 1/4 share, and Maria Goeppert-Mayer in 1963 also with a 1/4 share, Curie however becoming the sole recipient of the 1911 chemistry Nobel.

The lack of role models for women has long been overwhelming. The Royal Greenwich Observatory, founded in 1675, took almost 300 years before entrusting executive responsibility to a woman, Margaret Burbidge in 1972, though denying her the associated illustrious post of Astronomer Royal. In 1945 she had been turned down for a Carnegie Fellowship because only men were allowed to observe at Mount Wilson. But things look brighter for the daughters of today and tomorrow. In 2016, barely a year beyond its 60th anniversary, CERN appointed its first female Director-General, Fabiola Gianotti.

About the author

Compiled by Peggie Rimmer