Colliding beams

On 27 January, colliding beams were achieved at the Intersecting Storage Rings for the first time.

On 25 January, Ring 2 was brought into action. [Ring 1 had been successfully tested in October (CERN Courier November 2013 p12)]. At 19.47h, the first beam of protons from the PS was injected, went round and stayed going round, 3.5 mA circulating. At 20.20h, 15 mA were injected and the r.f. accelerating cavities were brought on. At 21.20h, stacking was tried and the circulating current built up to 370 mA. At 22.32h, the peak current of 720 mA was stacked.

On 27 January, it was decided to go for colliding beams. The run began at 10.00h. Shortly after midday, a very clean stack built the current in Ring 1 to 930 mA. After a few minutes, this dropped abruptly to 586.6 mA but didn’t change for more than an hour. At 14.30h, well over two hours later, the monitors were reading 586.5 mA, proving that they hadn’t got stuck. So good were conditions in the ring that hardly a measurable proton was lost. The decay rate was 5 × 10–8 per second, corresponding to a half-life of many months. One wisecrack was that the ISR had made itself independent of PS shutdowns.

Meanwhile an even more significant event occurred. At 13.26h, a single shot from the PS was fired into Ring 2 and 14.7 mA were left circulating. The one remaining worry was that the big beam in Ring 1 would cause serious loss on the small beam in Ring 2. No such noticeable beam–beam interaction was observed. The last remaining fear of the ISR team, that they would not be able to deliver a usable machine for physics, was swept aside.

Close on top of this came the news from the physicists at the intersections. At first tentatively, then with confidence, they fed to the control room the information that they were recording particles coming from collisions in the intersecting beams. At about 13.40h, Kjell Johnsen moved to the microphone [see the February cover thumbnail] to announce the first ever observation of proton–proton interactions in colliding beams.

• Compiled from texts on pp31–33.

Booster beams

Another "milestone" en route to completion of the 200–500 GeV accelerator at the National Accelerator Laboratory was passed at the beginning of February when beams were accelerated for the first time in the Booster.

The Booster is designed to take the 200 MeV beam from the Linac and to accelerate it to 8 GeV for injection into the Main Ring. The last of the magnets moved into the Booster ring on 14 December and installation was virtually complete a week later.

On 23, 24 January the beam was injected and taken full circle. A pulsed kicker was installed to push the beam from its injection orbit and on 29 January the first multiple turn tests were carried out. On 6 February, half the r.f. cavities were brought on and protons were accelerated to an energy of 1  GeV. It looks as if the Booster will be in excellent shape to feed beams to the Main Ring in a few months’ time.

Construction of the Booster has been brought to completion by Roy Billinge with Helen Edwards as associate section leader. The section are feeling very pleased with themselves.

• Compiled from texts on p47.

Compiler’s Note

The ISR was shut down in 1984, as CERN shifted its sights to the Large Electron Positron collider, but its legacy lives on (CERN Courier January/February 2011 p27).

The machine was to be the proving ground for some pivotal concepts in accelerator physics, most notably stochastic cooling, which made it possible to accumulate antiparticle beams of sufficient intensity for useful physics. This paved the way for proton–antiproton collisions, first in 1981 at the ISR itself and at the Super Proton Synchrotron operating as a collider, and from 1987 in the Tevatron at Fermilab. Since 2006, stochastic cooling has been used at Brookhaven’s Relativistic Heavy-Ion Collider.

The first role of the Batavia (later Fermilab) Booster was to accelerate protons from the linac into the 400 GeV Main Ring for fixed-target experiments – and the discovery in 1977 of the bottom quark. In 1983, the Main Ring became injector to the superconducting Tevatron ring, which was soon to be transformed into a proton–antiproton collider. The Booster supplied protons from the linac and antiprotons from a high-intensity source that used stochastic cooling. After acceleration in the Main Ring, these beams were further accelerated in the Tevatron, before colliding at 1.8 TeV in the centre of mass – allowing the discovery of the top quark in 1995. The Tevatron retired in September 2011, as CERN’s LHC came into operation (CERN Courier November 2011 p28).