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Refurbished Booster cavities in place, PIP begins 15-hertz operations

With the installation of the 17th Booster cavity, the PIP team has begun 15-hertz operations critical for the laboratory's neutrino program. Photo: Reidar Hahn

For nearly four years, the Proton Improvement Plan team in the Accelerator Division have been refurbishing radio-frequency cavities for the Booster accelerator.

Last week the final cavity in need of refurbishment was removed from the tunnel and replaced with a refurbished one. With 17 refurbished cavities in place, the Booster is now capable of operating at the nominal beam intensity at a rate of 15 hertz, meaning that it can accelerate and deliver 15 proton batches every second, double what it was able to handle before the improvement work began. The increased rate will allow the Fermilab accelerator complex to deliver the higher proton flux required for the laboratory's neutrino experiments.

This is a critical step for PIP, though additional cavity work and tasks remain in the plan. The next step of 15-Hz beam operations testing is already under way; the team demonstrated low-intensity 15-Hz beam operations for the first time on Monday.

The Booster is the third component in Fermilab's accelerator chain, preceded by the RFQ and the Linac. The roughly quarter-mile-circumference ring sends proton beam into the 2-mile-around Recycler, which offloads beam into the Main Injector, Fermilab's flagship accelerator. Beam then exits the Main Injector to myriad experiments.

Congratulations to the Proton Improvement Plan team on this important milestone.

Photo of the Day

Green heron, green sea

If you know where to look, you can see green herons around the Fermilab site. This one was spotted at Bulrush Pond. Photo: Bridget Scerini, TD
From symmetry

Bringing neutrino research back to India

The India-based Neutrino Observatory will provide a home base for Indian particle physicists. Image courtesy of India-based Neutrino Observatory

Pottipuram, a village in southern India, is mostly known for its farming. Goats graze on the mountains and fields yield modest harvests of millets and pulses.

Earlier this year, Pottipuram became known for something else: The government announced that, nearby, scientists will construct a new research facility that will advance particle physics in India.

Read more

Troy Rummler

Physics in a Nutshell

The wonderful thing about triggers

Somehow, you have to get those marvelous tracks to film.

Imagine you're a particle physicist in 1932. You have a cloud chamber that can show you the tracks of particles, and you have a camera to capture those tracks for later analysis. How do you set up an apparatus to take pictures whenever tracks appear?

At first, you might just try to be quick with your finger, but since the tracks disappear in a quarter of a second, you'd end up with a lot of near misses. You might give up and snap pictures randomly, since you'll be lucky some fraction of the time. Naturally, this wasteful process doesn't work if the type of event you're looking for is rare. You could also leave the shutter open and expose the film to anything that appears over a long interval. All events would overlap in the same picture, making it harder to interpret.

Now suppose you have another piece of equipment: a Geiger counter. This device emits an electric signal every time a charged particle passes through it. Two physicists, Blackett and Occhialini, surrounded their cloud chamber with Geiger counters and used the electric signals to trigger the cloud chamber and take pictures. This kind of apparatus is crucial to detectors today.

Experiments such as CMS only record one in a million LHC collisions — the rest are lost to further analysis. Collisions that break up protons but do not create new particles are 10 billion times more common than collisions that produce Higgs bosons, so modern triggers must be extremely selective.

Blackett and Occhialini's original trigger system relied on two Geiger counters: one above and one below the cloud chamber. Each Geiger counter was noisy and therefore prone to taking bad pictures, but both counters were unlikely to accidentally trigger at the same time. The two electronic signals were passed through a circuit that registered only if both counters triggered.

Today, triggers combine millions of data channels in complex ways, but the main idea is the same. Events should be selected only if signals in adjacent detectors line up. The desired geometric patterns are encoded into microchips for fast, coarse decisions and then are computed in detail using a farm of computers that make slower decisions downstream.

The modern trigger filter resembles a pipeline: Microchips make tens of millions of decisions per second and then pass on hundreds of thousands of candidates per second to the computing farm. By comparison, Google's computing farm handles 40,000 search queries per second.

Jim Pivarski

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In the News

Dwarf galaxies loom large in quest for dark matter

From The Kavli Foundation, June 23, 2015

Editor's note: For this roundtable discussion, The Kavli Foundation sat down with Dark Energy Survey Director Josh Frieman of Fermilab and the University of Chicago, Alex Drlica-Wagner of Fermilab, and Andrea Albert of SLAC and Stanford University.

In its inaugural year of observations, the Dark Energy Survey has already turned up at least eight objects that look to be new satellite dwarf galaxies of the Milky Way. These miniature galaxies — the first discovered in a decade — shine with a mere billionth of our galaxy's brightness and each contain a million times less mass. Astronomers believe the vast majority of material in dwarf galaxies is dark matter, a mysterious substance composing 80 percent of all matter in the universe. Dwarf galaxies have therefore emerged as prime targets for gathering potential clues about dark matter's composition.

Read the discussion transcript