New facility makes accelerator cavities easy as pie

February 4, 2010 | 12:03 pm

Imagine a professional pie baker who stocks his kitchen with all the ingredients for great pies, makes his own crusts, stuffs them with delicious insides and sets them on baking sheets. But imagine that the baker has to travel a few hundred miles to get to an oven to bake the pies. Problems would arise quickly if the baker needed a pie immediately, or if something went wrong with a batch. “That’s no way to run a kitchen,” says Brookhaven National Laboratory accelerator physicist Ilan Ben-Zvi.

Ben-Zvi uses the pie baker metaphor to illustrate how frustrating it can be for accelerator scientists developing superconducting cavities, to have to send the cavities away for rigorous preparatory treatments before they can be used (although he notes that the treatments are actually much more complicated and costly than baking a pie). This is one primary reason why Brookhaven has invested in a new, private facility to treat the superconducting cavities within a few miles of the site. The new facility is top of the line, located almost next door, and shows the power of joining government and private industry.

“Basically we will have at our disposal a very modern and state of the art facility,” says Ben-Zvi, who is the associate chair for the Accelerator R&D in the Collider-Accelerator Department at Brookhaven. “When you build a cavity you really want to process it quickly and see if it works. If you have to send it to another laboratory, obviously the order from that lab will come first. Sometimes you have to go to the facility, sometimes more than once. And that can be very time consuming if you have to go far, and you have to spend the money to send people.”

The new facility is located at and run by the private company Advanced Energy Systems, Inc. (AES) of Medford, New York.  Brookhaven contributed $2 million dollars to purchasing equipment for the facility, and AES received a $200,000 grant from the Empire State Development Corporation to do upgrade its own infrastructure.

From a press release from Brookhaven:

“This facility is the result of a unique public/private partnership meant to spur technology advances on Long Island,” said Brookhaven Lab Director Sam Aronson. “The collaboration — the first of its kind that Brookhaven Science Associates has undertaken — will help us reach our scientific goals while contributing to the growth of a local company.”

While Brookhaven’s accelerator R&D is quite extensive, Ben-Zvi says it would not yet justify paying full time technicians to operate its own cavity treatment facility. These accelerator cavities may undergo a variety of different chemical treatments and cleaning procedures, all of which require extensive upkeep. The AES facility allows Brookhaven scientists to have local, immediate service, but also allows AES to keep other clients to maintain costs.

Besides its regular R&D program, Brookhaven will soon be gearing up for a major upgrade to its Relativistic Heavy Ion Collider, RHIC. The upgrade will require generating a large number of superconducting accelerator cavities. Ben-Zvi says Brookhaven invested in the facility both to meet its current needs and in anticipation of the increased work load during the RHIC upgrade.

Calla Cofield

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Confirmed: Hubble 3D will be awesome

February 3, 2010 | 6:55 pm

Photo: NASA

The word “awesome” has been over-used. It is now jokingly assigned as a term employed by people who can’t come up with more specific adjectives (or who surf). But it seems that looking down on Earth, from 350 miles above it, should reclaim the right to the word that means “inspiring awe.” An IMAX movie is the closest that many of us will get to seeing this wonderful sight, so it’s good to know that the new Hubble 3D movie, which documents the journey of space shuttle STS-125 to repair and upgrade the Hubble Space Telescope in May 2009, is looking truly awesome.

The film, set to be released on March 19, was made by the same crew that produced Space Station 3D in 2002, and the eye-feast Deep Sea 3D.

The movie documents the space shuttle crew’s preparation, the rocket launch, and Hubble itself. The crew brought an IMAX camera and eight minutes of film into space, plus took additional non-IMAX footage through helmet cameras and via satellite. Those images are not as detailed as IMAX, but are still mesmerizing.

STS-125 Mission Specialist Michael Massimino came back to his home state of New York this week to appear at a pre-screening of about 15 minutes of footage from the film.

Every time I’ve had the pleasure of hearing a former astronaut talk, they say that looking down at the Earth from above is one of the single greatest things they’ve ever experienced, and Massimino was no exception. He said he remembers thinking, “this is what heaven must look like.” The only sadness he felt at that moment came from realizing that he couldn’t share it with everyone. The film might not be quite as good as taking a space walk, but I could stare at the shots of Earth all day.

Note that the film is not a collection of images produced by the Hubble, although the trailer suggests there will be a little bit of that sprinkled in. But rest assured that the images of the actual telescope are also jaw dropping. The massive instrument responsible for all of that incredible beauty and knowledge is laid bare on the screen. In the grandeur of IMAX and 3D, Hubble looks like a sleeping beast; both colossal and vulnerable as the crew operates on its insides.

Talkative and excited, Massimino opened up with the audience after the film, saying that it made him teary to look at the footage and remember his time in orbit. He answered a question about the infamous bolt incident, where a single bolt holding a door in place refused to come unscrewed, and with time running out, the engineering crew on the ground told Massimino to rip the door off. He succeeded without further incident, and everything worked out all right. Massimino says his helmet camera was running during the incident, but he’s not sure if the footage will show up in the film.

The impromptu stunt wasn’t the only time Massimino worried about whether or not he and the crew could get everything done, and done right. But despite the ominous music and gritty voice-over in the trailer, Massimino reminded the crowd that “this is a success story.”

No kidding. Images from the updated Hubble have already been released, along with data analyses that might identify the most distant galaxies ever seen.

Massimino also returned to New York to deliver the American flag that he and the crew brought with them into space. They are donating it to the 9/11 memorial museum.

Calla Cofield

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New MINOS results “strongly disfavor” sterile neutrino, neutrino decay

February 2, 2010 | 10:24 am

Finding the truth, whether that means solving a crime or describing the nature of fundamental particles, is just as much about eliminating the wrong answers as it is about finding the right ones. The same way that ruling out an alibi for a suspect is an important step toward finding the bad guy, disproving a theoretical prediction is necessary in order to find the correct theory that explains the whole story.

In the search for a better understanding of neutrinos, the Main Injector Neutrino Oscillation Search, MINOS, recently put forth results that help rule out a theorized fourth neutrino and strengthen the case against the hypothesis of neutrino decay. MINOS co-spokesperson Rob Plunkett says the results “really start to close the loop” on some major theories that neutrino experiments set out to investigate.

The MINOS experiment begins at Fermilab, in Batavia, Illinois, where a neutrino beam is generated, and its composition measured by the MINOS near detector. The beam then travels 735 kilometers to the Soudan mine in northern Minnesota, where the MINOS far detector catches it.

MINOS examines the neutrinos primarily through a process called charged current interaction. This method reveals the flavor of a neutrino–muon, tau, or electron–observed in a detector. But, from detection of charged current interactions, MINOS only has the capability to identify the muon and electron neutrinos in the beam. However, the experiment also detects what’s called neutral current interactions, which count all neutrinos, but do not reveal their flavors.

The first theory examined in this paper is the prediction of the existence of a fourth neutrino–known as the sterile neutrino. The standard model comprises only three neutrinos, which interact with ordinary matter via the weak nuclear force. But scientists know that the standard model isn’t perfect. It predicts that neutrinos have no mass, yet experiments like MINOS tell us that they do. Hence there could also be a fourth type of neutrino that has eluded experimental detection so far, especially one like the sterile neutrino, which is immune to the effect of the weak force.

The sterile neutrino didn’t have a strong case going into the MINOS analysis. Results from the indirect observation of neutrinos at experiments at the European laboratory CERN pinned the number of light neutrinos at three, and so far only three neutrino flavors have been observed. Then, in 2001, an experiment at Los Alamos known as the Liquid Scintillator Neutrino Detector, LSND, published some puzzling results that seemed to indicate the presence of a sterile neutrino. Since then, no one has been able to reproduce the LSND findings. A few years ago, data from the MiniBooNE experiment (Booster Neutrino Experiment) at Fermilab seemed to refute most of the LSND results.

Still, the ghost of a sterile neutrino continues to wander among scientists, and MINOS is looking for either its fingerprint or evidence that it does not exist.

“[Our result] strongly disfavors the existence of a sterile neutrino,” Plunkett said about the analysis presented in the recent MINOS paper.

But the same way that it is difficult to put the rumors about ghosts to rest, ruling out the existence of a sterile neutrino is nearly impossible.

The MINOS paper strengthens the constraints on the sterile neutrino’s existence. Past analyses have shown that if muon neutrinos are oscillating into sterile neutrinos, only 68% of the disappearing neutrinos can do so. The new analysis shrinks that percentage to 50%, and more data will most likely reduce it further.

The second hypothesis up for investigation is the process of muon neutrino decay. Scientists know that the three neutrino flavors can oscillate among themselves. So, for example, a muon neutrino can turn into a tau neutrino. The transformations take place when neutrinos travel long distances, such as the 735 kilometers from Fermilab to Soudan. When scientists use neutral current detection techniques to analyze the beam, they find that the total number of neutrinos detected in Soudan agrees with expectations, given the measured number of neutrinos leaving the Fermilab site. But the composition of the beam changes dramatically. While the beam traversing the near detector at Fermilab consists almost entirely of muon neutrinos, the fraction of the beam that arrives at Soudan as muon neutrinos, as determined by their charged current interactions, is way down. The accepted interpretation is that the total number of neutrinos remains the same and that the missing muon neutrinos oscillated into tau  (and possibly electron) neutrinos.

An alternative theory says that the missing muon neutrinos may have decayed. The MINOS scientists looked at two scenarios: first, the possibility that only decay and no oscillation takes place. Second, the situation when both decay and oscillation contribute to the observed effect.

In both analyses, the MINOS collaboration found its data  to be inconsistent with neutrino decay. Plunkett said the results provide strong evidence against the existence of neutrino decay.

“This paper is really a terrific summary of a lot of stuff that’s going on [in neutrino physics] right now,” said Plunkett. “The paper shows the consistency of the whole picture. At the same time, it explores ways that the picture might be wrong or puts limitations on how wrong it might be.”

The paper has been submitted to Physical Review D, and is available on the physics website arxiv.org. The analysis was lead by Alexandre Sousa of Harvard University, Brian Rebel of Fermilab, and Anthony Mann of Tufts University.

Calla Cofield

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CERN’s new LHC plan: Two years at 3.5 TeV

February 1, 2010 | 5:53 pm

CERN’s new plan for the next phase of the Large Hadron Collider: run the accelerator for up to two years at an energy of 3.5 TeV per beam. The run, expected to start at the end of this month, would end no later than December 2011 and be followed by a long shutdown to prepare the accelerator to run at its full energy of 7 TeV per beam.

The goal for the next two years is for the LHC experiments to collect a certain amount of data – one inverse femtobarn – at 3.5 TeV per beam. With that amount of data at that energy, the LHC experiments would be competitive with the experiments at Fermilab’s Tevatron in the hunt for the big physics discoveries on the horizon: the Higgs boson and supersymmetry. If this goal is reached before December 2011, the accelerator and experiments may shut down earlier to begin the long process of readying the machine to run at the energy it was originally designed for.

The new schedule differs from that announced in August 2009 in two main ways: the length of the lower-energy run and its maximum energy. In August, it was announced that the LHC would begin its first run at 3.5 TeV per beam, perhaps increasing as high as 5 TeV per beam by the end of 2010. The accelerator would then shut down in 2011 in preparation for running at the full energy of 7 TeV per beam. The lower maximum energy decided on last week, and the longer running time at that lower energy, are a consequence of the problematic connections between superconducting LHC magnets. One such connection melted in September 2008 and led to one year of repairs,  and during the long shutdown in 2012, virtually all such connections will be re-made.

This news was first reported Friday by John at Cosmic Variance, following the conclusion of the LHC Performance Workshop in Chamonix, France. The annual workshop provides the team operating CERN’s accelerators a chance to retreat from the hustle and bustle of everyday work at the laboratory and focus on the near- and far-term future of the accelerator complex.  All of the presentations from last week’s workshop are available online. A summary of the workshop will be presented at CERN on February 5.

Update, February 3: CERN has officially confirmed the new LHC schedule.

Katie Yurkewicz

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Next-generation accelerators, neutrino research get boost with new test beam

January 27, 2010 | 9:53 am

Accelerator operator Salah Chaurize performs a diagnostic test on the RFQ at Fermilab. Courtesy Fermilab.

Fermilab has taken a major step toward laying the technical groundwork for Project X by creating a new test beam for superconducting radiofrequency cavities and components.

Earlier this month, the High Intensity Neutrino Source (HINS) collaboration successfully accelerated a proton beam to 2.5 MeV in a radiofrequency quadrupole accelerator, or RFQ, for the first time at Fermilab.

“This will provide a beam platform to facilitate development of components critical for Project X,” says Bob Webber, APC/HINS department head.

The 10-foot-long RFQ serves as the driving force of a proton linac in the Meson Detector Building. It will enable collaborators to test the ground-breaking application of superconducting radiofrequency (SRF) cavities for the acceleration of a high-intensity proton beam from very low energies.

Gary Lauten, a radiation safety officer, observes while Bob Webber, APC/HINS Department head, and Bruce Hanna, engineering physicist, inspect the RFQ beamline at Fermilab. Courtesy Fermilab.

“On the first attempt the RFQ achieved the design acceleration,” says Giorgio Apollinari, head of Fermilab’s Technical Division. “This type of  technical achievement is the groundwork that will support Fermilab’s research in the second decade of this century.”

The RFQ uses strong electrical fields to accelerate ionized hydrogen into a low-energy proton beam. That beam will then accelerate through 18 copper, room-temperature cavities up to a minimum energy compatible with the superconducting cavities that make up the remainder of the linac. The SRF cavities use stored radiofrequency energy to accelerate particles as they pass.

In February 2009, the HINS collaboration successfully tested the first 325-MHz single-spoke resonator SRF cavity. Collaborators expect to become the first in the world to accelerate beam through this type of cavity using the RFQ as a power source.  This would lay the ground work for stringing many cavities together to create a unique linear accelerator for discovery at the intensity frontier.

This new use of SRF technology enables efficient production of the intense proton beam that will give Project X its versatility as a front end for a muon collider or a neutrino factory. SRF cavities can effectively increase the particle beam energy while minimizing the required electrical power by all but eliminating electrical resistance.

Collaborators from Fermilab and Argonne national laboratories designed the RFQ system to meet anticipated Project X physics needs in early 2006. AccSys Technology Inc., a private manufacturing firm, supplied the mechanical design and fabrication work.

Jim Steimel, engineer, inspects the RFQ beam absorber. Courtesy Fermilab.

“It’s not like there is only one small piece of the lab working on this,” Webber says. “It is the result a great deal of effort from the Technical Division, the Accelerator Division and the Accelerator Physics Center.”

 Along with testing SRF cavities, the RFQ will provide beam to test other components of Project X, including beam diagnostic equipment and the beam chopper that determines the time structure within the beam pulses.

The HINS R&D program comprises contributions from Fermilab, Argonne, Lawrence Berkeley National Laboratory, Brookhaven National Laboratory and the Oak Ridge Spallation Neutron Source.

For the test linac, Berkeley provided two of the non-superconducting cavities and Brookhaven devised prototype beam instrumentation.

Tona Kunz

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This month at the LHC

January 22, 2010 | 4:49 pm

Late last year the Large Hadron Collider collided its first protons at a record-breaking energies. On December 16, the collider shut down so  teams could prepare the machine to run at even higher energies in 2010. So what are the scientists, engineers and technicians at CERN doing during this approximately two-month-long “technical stop?”

The goal of the many activities taking place during the technical stop is to prepare the LHC to accelerate beams to an energy of 3.5 TeV. The three main tasks are replacement of about 4000 connectors in the quench detection system; testing components of the new quench protection system to bring it to full functionality; and maintenance for the CMS experiment.

The LHC’s superconducting magnets are kept at the very low temperature of 1.9 K in order to carry the high currents needed to bend fast-moving particles. At a beam energy of 3.5 TeV, 6000 amps of current will flow through the LHC’s main bending magnets, the dipoles. A quench occurs when part of the superconducting cable within a magnet heats up and can no longer conduct electricity without resistance.  The first line of defense against quenches is detection using a complex electronics system that monitors the magnets and surrounding technology.

One main task for the technical stop is the replacement of some connectors in the new quench detection system’s 250 km of high-voltage cable. The connectors, initially installed in 2009, are being replaced after it was discovered that they were easily damaged if cables were bent.

Once a quench is detected, the stored energy must be safely channeled away from the magnet. The new quench protection system, installed in November, includes about 10,000 new cables designed to de-energize specific sectors of the LHC in the event of quenching. The updated system also incorporates better programming and electronics to detect quenches. The software and equipment for this system are being tested during this technical stop to ensure that everything is functioning properly for this year’s maximum beam energies.

The last main task for the current stop is to replace 272 corroding portions within the CMS detector’s yoke endcaps that were causing the detector’s water cooling lines to fail.

The technical stop should be completed by mid-February, and beam is expected back in the LHC shortly afterward.

For more details, read the articles in the CERN Bulletin or CMS Times, or watch today’s episode of LHC News, which focuses on the quench protection system.

by Daisy Yuhas

Symmetry Intern

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Strongly interacting dark matter ruled out by observations

January 22, 2010 | 9:30 am

The possibility that dark matter could be made of heavy, strongly interacting particles has been ruled out by neutrino observations at the IceCube detector, according to physicists Ivone Albuquerque of Fermilab and Universidade de São Paulo and Carlos Pérez de los Heros of Uppsala University.

Although the majority of physicists favor models of dark matter that only rely on weakly interacting massive particles, or WIMPs, some theoretical models allow for strongly interacting massive particles, or SIMPs. Massive versions of each of these particles are whimsically referred to as wimpzillas or simpzillas.

Prior to this study, this plot represents the excluded types of simpzilla based on mass and interaction strength. The colored regions are all excluded by experiment with just the white triangles remaining as possible types of SIMPs.

Like the other plot, this shows the SIMP types ruled out but with new data added. It cuts out the white triangles, leaving only a patch in the lower right, which does not correspond to any favored theories as the dark matter would be too massive.

During recent years, a range of underground and space-borne experiments have ruled out various combinations of interaction strengths and masses for dark matter particles, but there had always been a few openings left for particles of just the right combinations of interaction strength and mass.

If simpzillas did exist, they would become captured by the gravity of massive objects such as the Sun. Then they would bump into each other, lose energy, and accumulate near the center of the Sun where they would annihilate, giving off neutrinos. Those extra neutrinos should be detectable by a neutrino telescope such as IceCube in Antarctica. Using data collected from 22 strings of IceCube’s optical modules, a fraction of the 80 strings that make up the entire detector, the physicists determined there was no excess of neutrinos coming from the Sun with enough confidence to rule out the existence of simpzillas.

The paper concludes, “…strongly interacting heavy relics from the early universe can only account for the dark matter if they have masses above 10¹⁵ GeV. As these ultra heavy masses are not currently favored by any model, the window for simpzillas as the only component of dark matter can be closed.”

David Harris

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Fermilab seeks new associate director, Steve Holmes focuses on Project X

January 22, 2010 | 6:26 am

The increasing momentum behind the proposed Project X accelerator facility has swept Steve Holmes into a new position at Fermilab and put in motion the search for a new associate director.

Holmes is beginning the transition out of the post of associate laboratory director for accelerators, which he has held for the past decade, so that he can focus solely on Project X. He has been acting project manager for Project X since August 2008, but could rarely dedicate more than 15 percent of his time to the development effort of the high-intensity proton facility.

Steve Holmes

“I’ve been here a long time and frankly, the lab could probably benefit from new blood in this office,” Holmes said. “I would like to dedicate myself full time to Project X. I think that is the most important thing I can do for the lab right now.”

To the Project X team he brings project management experience shepherding the Main Injector to completion. He has had a strong role in the evolution of Project X since its 2004 inception and has put together a strong team, including outside collaborators. During the past year, the team has generated two initial configuration options and cost estimates, as well as initial concepts of how Project X would further a future muon collider. He is hopeful the project will receive the first stage of DOE approval, Critical Decision-0, by the end of FY2010.

“I don’t think the US can have a world-leading, sustainable, competitive particle physics program based solely on overseas accelerators,” Holmes said. “When we build Project X, it will form the basis of a world-leading program for 30 years.”

Holmes will handle the day-to-day work of Project X, including guiding it through the DOE requirements for approval and construction.

“Project X would be an extraordinary machine at the intensity frontier for neutrino, kaon, muon and nuclear physics,” said Fermilab Director Pier Oddone. “It would develop the technologies to support a future global facility at the energy frontier. We are fortunate that Steve will lead Project X on the path forward. He has experience in leading large accelerator projects successfully, and he has repeatedly proven his ability to build collaborations and large-scale projects.”

Holmes will work closely with his replacement, who will hold management and oversight responsibilities for all Fermilab accelerator operations, accelerator science and technology R&D, and construction support for new accelerator facilities. In addition his replacement will serve as line manager for the Accelerator Division, Technical Division and Accelerator Physics Center.

Located 45 miles west of Chicago, Fermilab’s particle accelerator complex provides beam to particle physics experiments, test facilities and a cancer treatment center. The proposed Project X would replace the 40-year-old linear accelerator and booster ring.

The associate director for accelerators plays a central role in developing and implementing the strategy for future development of the accelerator complex at Fermilab and aligning this strategy within an international context.  

“My replacement will be responsible for assuring there is a coherent vision for the accelerator complex into the future and that the R&D to support that vision is effectively organized and executed,” Holmes said. “The job is to figure out how to build on the base we expect to establish over the next decade: the Long Baseline Neutrino Experiment, Mu2e and Project X.” Long range opportunities are expected to include a muon collider, the ILC (organized in collaboration with the ILC program director), US contributions to upgrades of the LHC, and other options that might open up via the advanced accelerator R&D program.

“Fermilab has a vibrant and flexible plan to keep the laboratory and US particle physics on the pathway to discovery,” Oddone said. “The next associate director of accelerators at Fermilab will lead the accelerator development that is critical to research at the energy and intensity frontiers.”

The search committee includes: Maury Tigner of Cornell  University (chair); Young-Kee Kim, Fermilab’s deputy director (deputy chair);  Roland Garoby, of CERN;  Helen Edwards, Roger Dixon, David Harding and Sergei Nagaitsev, all of Fermilab.

The committee welcomes applications from and nominations of qualified candidates from around the world. The detailed job description of the ALDA position has been posted on the Fermilab employment pages.

Tona Kunz

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PHENIX rises: A detector gets a new life

January 21, 2010 | 6:14 am

Fermilab's Bert Gonzalez handles silicon detector components at the lab's silicon detector facility. Photo: Fermilab

For the first time, Fermilab technicians have completed design work for a 4000-ton particle detector over the phone.

“The benefit of our past experience allowed us to design through conference calls,” said Bert Gonzales, Fermilab technical supervisor on the design project. “This is a new endeavor. We’ve never assembled a project in this fashion. Usually we’ve had everything in-house.”

Scientists in the PHENIX collaboration at Brookhaven National Laboratory have enlisted the expertise of a group of technicians at Fermilab’s SiDet facility in upgrading their particle detector, originally constructed in 2000.

Technicians at SiDet, which is short for silicon detector, have in the past built components that track particles in the hearts of the CDF and DZero detectors at Fermilab’s Tevatron. The technicians also contributed a large number of components for the CMS silicon detector at CERN’s Large Hadron Collider.

Originally Brookhaven planned to build new parts at academic institutions, said Columbia University physicist Dave Winter, who coordinates between Brookhaven and Fermilab in a portion of the design and production effort. But they were impressed by the extensive related experience technicians had at SiDet.

“Once we saw what was already at Fermilab, it was a no-brainer,” Winter said. “We’d be crazy to do it ourselves.”

The Pioneering High Energy Nuclear Interaction Experiment, or PHENIX, detector combs through the subatomic chaos produced by collisions at the Relativistic Heavy Ion Collider, or RHIC. Scientists at RHIC crash protons, gold nuclei, and the nuclei of a hydrogen isotope called deuterium together in an effort to recreate the conditions of the early universe.

PHENIX collaboration members meeting at Brookhaven in May 2008. Photo: Brookhaven National Laboratory

Brookhaven scientists have collected evidence that the RHIC has created quark-gluon plasma, a state of matter in which quarks float unbound from one another. Scientists theorize that quarks behaved this way in the split second after the big bang.

They hope that by upgrading the PHENIX detector, they can better measure the number of beauty and charm quarks created in collisions. Fermilab scientists will design additional components that will extend the detector closer to the beam, zooming in on the collision point. Quark-gluon plasma tends to suppress the particles into which quarks decay. So in order to find out whether a particle collision created quarks, scientists must look for those particles as close to the collision point as possible.

Fermilab technicians will begin production of parts for the PHENIX detector this month. Engineers in Fermilab’s Particle Physics Department are also designing, producing, and testing the readout chips needed for the upgrade.

Fermilab’s involvement goes deeper than doing work-for-hire, said Fermilab scientist Hogan Nguyen. “We feel as though we are part of the project; we want it to be successful.”

Kathryn Grim

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US flexes its developing SRF muscles

January 19, 2010 | 4:54 am

Horizontal test stand at Fermilab. Courtesy of Fermilab.

US researchers recently proved their ability to process and test world-class superconducting radiofrequency, SRF, cavities.

In preparing two dressed, high-gradient nine-cell ILC-type cavities for use in the S1-global effort, a prototype at KEK of the International Linear Collider main linac, researchers had to climb multiple technical hurdles.

SRF cavities enable accelerators to increase particle beam energy levels while minimizing the use of electrical power by all but eliminating electrical resistance. Future experiments into the origins of the universe and nature of matter, including the proposed ILC and Project X, both of which Fermilab would like to host, will require advanced SRF technology.

The shipped cavities show the US is well on its way to meeting those technology needs.

The processing and assembly of the cavities depended heavily on the contribution of scientists and engineers across the globe, including at Argonne National Laboratory, Thomas Jefferson National Accelerator Facility, SLAC National Accelerator Laboratory, Cornell University, INFN and DESY.

AES004 cavity during tuner test. Courtesy of Fermilab.

Initial testing of the cavities involved dipping them in liquid helium andsupplying a low-power RF source. Cavities that reached the needed accelerating field got sealed into a helium vessel and outfitted, or dressed, with auxiliary components necessary for high-power operation in an accelerator. These components include input couplers to feed RF power into the cavity and tuners to adjust the cavity’s resonant frequency.

The first cavity, dubbed AES004, was fabricated by Advanced Energy Systems in New Jersey and is the first dressed cavity assembled and tested at Fermilab. The fact that the cavity’s power gradient did not degrade between the processing steps shows that the US can operate world-class SCRF cavity facilities. Jefferson National Laboratory oversaw the chemical processing of the cavity, including etching and baking; Fermilab welded the helium tank and connection components onto the cavity, and then Argonne National Laboratory conducted high-pressure rinses to eliminate microscopic dust particles inside the cavity.

ACC011 cavity during helium vessel welding. Courtesy of Fermilab.

The second cavity, dubbed ACCO11, was fabricated by a German manufacturer but is the first cavity fully prepared—dressed and chemically tested – in the US to operate above 30 megavolts per meter, or MV/M. The cavity will be able to accelerate particles to 33 MV/M, exceeding the ILC’s design gradient of 31.5 MV/M. The AES004 cavity successfully passed a horizontal test with a gradient of 28 MV/M, similar to the best vertical test of this cavity type.

Because of a time crunch to get the cavities to Japan, Fermilab essentially combined quality testing steps and for the first time put a dressed cavity through vertical testing. The successful test opens the door to quicker turnaround of cavities, though with some limitations.

This pair of successful tests of two dressed ILC-type cavities with Blade tuners demonstrates the viability of the US as a provider of finished cavities for international research projects, says Tug Arkan, Fermilab project engineer for the cryomodule assembly facilities group.

Tona Kunz

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