Ernest Courant served as Adjunct Professor at Stony Brook from
1966 until 1986.
Also known as alternating gradient focusing, this principle
was a breakthrough in accelerator design. At Brookhaven it resulted in
the construction of the successful Alternating Gradient Synchrotron (AGS),
which achieved its design energy on 29 July 1960.
"If you can't do two things together, you just do
one after the other - that's all there is to it!" Ernest Courant,
Brookhaven distinguished scientist emeritus, was describing how he came
to think of the strong-focusing principle that he, together with M Stanley
Livingston and Hartland Snyder, co-discovered in 1952.
This article originally appeared in the 4 August 2001
issue of the Brookhaven Bulletin.
Maurice Goldhaber and Ernest Courant
In previous circular accelerators, such as Brookhaven's
Cosmotron, particles had been guided round the ring by a magnetic field
made by outward-facing magnets. The magnets bent the particles' trajectories
and at the same time weakly focused them both horizontally and vertically.
The particles' energy could only be increased by enlarging the ring with
wider magnets, requiring far more steel - at great cost - to make the larger
number of magnets.
However, Courant and his colleagues calculated that
energy could be increased dramatically with much smaller magnets if the
particles were strongly focused first vertically then horizontally.
The particles' energy could only be increased by enlarging the ring. (It
turned out that this idea had been proposed earlier by Nick Christofilos
in Greece, but his innovation had gone unrecognized and was then forgotten.
Later he was invited to Brookhaven.)
The practicality of the principle was demonstrated
in 1954 by Cornell University's 1.3 GeV electron accelerator, and in 1959,
well before the AGS was finished, by CERN's 24 GeV Proton Synchrotron.
On 17 May 1960 a 50 MeV beam completed one turn round the AGS ring. In
July that year the 30 GeV design energy was reached and even surpassed.
"But," Courant recalled, "although we were all very excited by how quickly
things were going, we were a little disappointed that we'd been scooped
One reason why Brookhaven had fallen behind was
because it had built an electron analogue before starting construction
of the AGS, Courant says. The analogue was designed to explore what is
called the "transition energy" - a potentially serious problem with the
synchronization behaviour. The analogue could also give information on
nonlinear resonances that might affect the orbit stability of the particles
as they circled the AGS ring. "These resonances were not a big problem,
but it was good to know what was happening," said Courant . "Using the
analogue, we found that the transition problem could be overcome. We also
found out a lot about higher-order resonances that we hadn't expected,
and we confirmed that we could go forward with the design as planned. So
the delay was worth it."
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Last Updated: January 22, 2001