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Posts Tagged ‘SLAC’

This article appeared in Fermilab Today on Feb. 11, 2015.

Fermilab is developing superconducting accelerating cavities similar to this one for SLAC's Linac Coherent Light Source II. Photo: Reidar Hahn

Fermilab is developing superconducting accelerating cavities similar to this one for SLAC’s Linac Coherent Light Source II. Photo: Reidar Hahn

Now one year into its five-year construction plan, the Linac Coherent Light Source II, an electron accelerator project at SLAC, will produce a high-power free-electron laser for cutting-edge scientific explorations ranging from refined observations of molecules and cellular interactions to innovative materials engineering. Cornell University as well as Argonne National Laboratory, Lawrence Berkeley National Laboratory, Fermilab and Thomas Jefferson National Accelerator Facility are partners in the SLAC-directed project.

“We at the laboratories are all developing close ties,” said Richard Stanek, Fermilab LCLS-II team leader. “The DOE science lab complex will be stronger for this collaboration.”

In 2015, Fermilab will intensify its LCLS-II contribution in the overlapping areas of superconducting radio-frequency (SRF) accelerator technology and cryogenics, critical components that distinguish LCLS-II from SLAC’s current LCLS facility, whose laser production has enabled noted scientific investigations in cancer treatment and other important areas.

SLAC physicist Marc Ross, LCLS-II cryogenics systems manager, said LCLS cannot keep up with scientists’ requests for use. The existing LCLS facility and LCLS-II combined will offer researchers laser X-rays with a wide range of properties.

“This new approach will transform the repetition rate of LCLS — from 120 pulses per second to up to 1 million per second,” Ross said. “This will allow a completely new class of experiments and, eventually, a much larger number of experimental stations operated in parallel.”

Fermilab Technical Division physicists Hasan Padamsee, division head, and Anna Grassellino and their team are working on SRF technology for LCLS-II, in particular on implementing Fermilab’s two recent findings to reduce the needed cryogenic power. In one innovation, known as nitrogen doping, Grassellino found that infusing a small amount of nitrogen gas when preparing the superconducting cavities — the structures through which beam is accelerated — reduces two main causes of the usually expected resistance to radio-frequency currents.

“It is exciting to see our discovery becoming an enabling technology for LCLS-II,” Grassellino said.

Grassellino’s high-Q team has also found that the cavities’ cooling dynamics significantly helps expel magnetic flux, another major source of cavity power dissipation. The Fermilab high-Q team, together with Cornell University and Jefferson Lab, are currently working on calibrating the cooling thermogradient for LCLS-II.

Stanek said Fermilab is advancing its SRF work with its LCLS-II participation.

“I see this project taking us from an R&D phase of SRF technology, which is where we have been the past six to eight years, and moving our expertise into production,” Stanek said. “This is a big step forward.”

Fermilab and Jefferson Lab are working closely together on the cooling systems that enable the cavities’ superconductivity. Fermilab scientist Camille Ginsburg leads LCLS-II cryomodule production at Fermilab, and Fermilab engineer Arkadiy Klebaner manages the LCLS-II cryomodules distribution system.

“To build a high-energy beam using SRF technology, LCLS-II needed expertise in cryogenics,” Klebaner said. “So Jefferson Lab and Fermilab, who both have special expertise in this, were ready to help out.”

A cryogenic plant generating the refrigeration, a cryogenic distribution system for transporting the refrigeration into cryomodules and the cryomodules themselves make up the LCLS-II cryogenics. Jefferson Lab will provide the cryogenic plant, and Fermilab is in charge of developing the cryogenic distribution system. Jefferson Lab and Fermilab are jointly developing LCLS-II’s 35 cryomodules, each one about 10 meters long.

Fermilab’s contribution draws on the Tevatron’s cryogenics and on SRF research begun for the proposed International Linear Collider. The lab’s LCLS-II experience will also help with developing its planned PIP-II accelerator.

“So when we build the next accelerator for Fermilab, PIP-II, then we will have already gotten a lap around the production race course,” Padamsee said.

All labs have something special to contribute to LCLS-II, Ross said.

“The Fermilab team have figured out a way to make this kind of accelerator much better operating in the cold temperature that superconducting technology requires,” Ross said. “It is worthy of special recognition.”

Rich Blaustein

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J/ψ

Wednesday, August 6th, 2014

The particle with two names: The J/ψ Vector Meson. Again, under 500 words.

jpsi_NOVA

Trident decay of J/Psi Credit: SLAC/NOVA

Hi All,

The J/ψ (or J/psi) is a very special particle. Its discovery was announced in 1974 independently by two groups: one lead by Samuel Ting at Brookhaven National Laboratory (BNL) in New York and the second lead by Burton Richter at Standford Linear Accelerator Center (SLAC) in California. J/ψ is special because it established the quark model as a credible description of nature. Having been invented by Gell-Man and Zweig as a bookkeeping tool, it was not until Glashow, Iliopoulos and Maiani (GIM) that the concept of quarks as real particles was taken seriously. GIM predicted that if quarks were real, then they should come in pairs, like the  up and down quarks. Candidates for the up, down, and strange were identified, but there was no partner for the strange quark. J/ψ was the key.

ting-group-335px_BNL

Samuel Ting and his BNL team. Credit: BNL

Like the proton or an atom, the J/ψ is a composite particle. This means that J/ψ is made of smaller, more elementary particles. Specifically, it is a bound state of  one charm quark and one anticharm quark. Since it is made of quarks, it is a “hadron“. But since it is made of exactly one quark and one antiquark, it is specifically a “meson.” Experimentally, we have learned that the  J/ψ has an intrinsic angular momentum (spin) of 1ħ (same as the photon), and call it a “vector meson.” We infer that the charm and anticharm, which are both spin ½ħ, are aligned in the same direction (½ħ + ½ħ = 1ħ). The J/ψ must also be electrically neutral because charm and anticharm quarks have equal but opposite electric charges.

richter_SLAC

Burton Richter following the announcement of co-winning the 1976 Nobel Prize. Credit: SLAC

At 3.1 GeV/c², the J/ψ is a about three times heavier than the proton and about three-quarters the mass of the bottom quark. However, because so few hadrons are lighter than it, the J/ψ possesses a remarkable feature: it decays 10% of the time to charged leptons, like an electron-positron pair. By conservation of energy, it is forbidden to decay to heavier hadrons. Because there are so few  J/ψ decay modes, it is appears as a very narrow peak in experiments. In fact, the particle’s mass and width are so well-known that experiments like ATLAS and CMS use them as calibration markers.

Credit: CMS

Drell-Yan spectrum data at 7 TeV LHC Credit: CMS

The J/ψ meson is one of the coolest things in the particle zoo. It is a hadronic bound state that decays into charged leptons. It shares the same quantum numbers as the photon and Z boson, so it appears as a Drell-Yan processes. It established the quark model, and is critical to new discoveries because of its use as a calibration tool. In my opinion, not too shabby.

Happy colliding.

Richard (@BraveLittleMuon)

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