It was a time of fierce (but friendly) international competition, when physicists still built things with their own two hands. Dotted with barracks and trenches, Brookhaven was yet to fully transform its face from army camp to research institution.

In the early 1950s, the physics community was at the horizon of the boom of discoveries that define our understanding of the universe.

Before quarks, neutrinos, and CP violation could be found, scientists needed a tool much more powerful than Brookhaven’s Cosmotron — the leading particle accelerator of the time. The problem: building an accelerator 10 times more powerful than the Cosmotron would require 100 times more steel for larger magnets with larger apertures. The resulting 200,000-ton behemoth was much too costly to take on.

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Brookhaven’s Cosmotron, the first accelerator in the world to send particles to energies in the billion electron volt, or GeV, region

In preparation for a visit from their European colleagues at CERN, a trio of Brookhaven scientists came up with a simple but groundbreaking solution that changed the particle accelerator world forever.

By reversing the direction of some of the Cosmotron’s “C”-shaped magnets (originally arranged facing outward around the machine’s circular track), a young Brookhaven physicist named Ernest Courant calculated that the resulting proton beam would focus much more tightly. The strong-focusing principle was born.

Courant’s discovery*, developed with fellow Brookhaven physicists M. Stanley Livingston and Hartland Snyder, meant that more powerful machines could be built with smaller magnets (and, of course, much less cash).

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Gathered around a quarter-scale model of a Cosmotron magnet are the co-discoverers of strong focusing: (from left) Ernest Courant, M. Stanley Livingston, and Hartland Snyder. At right is Brookhaven physicist John Blewett, who, shortly after the discovery, extended the principle to linear accelerators. Livingston holds a cardboard cutout of a quarter-scale strong focusing magnet to show the great reduction in size possible with strong focusing.

The “children” of this principle are scattered around the world today, in the form of light sources like Brookhaven’s National Synchrotron Light Source and Argonne National Laboratory’s Advanced Photon Source, and colliders like CERN’s Large Hadron Collider and Brookhaven’s Relativistic Heavy Ion Collider (RHIC).

Courant recently reflected on this discovery at a Brookhaven celebration honoring his 90th birthday, the 50th anniversary of the lab’s Alternating Gradient Synchrotron, and the 10th year of RHIC operations.

You can watch his talk on Brookhaven’s “90-50-10″ webpage, which features video remarks from almost 20 pioneering physicists — including Nobel-prize-winning researchers Sam Ting and James Cronin.

*Updated 6/29/10: Strong focusing was first conceived, although unrecognized, in 1949 by Nicolas Christofilos, who later worked at Brookhaven for a short period of time. Unaware of Christofilos’ unpublished manuscript (as referred to in PRL), the Brookhaven team independently developed strong focusing three years later.