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Posts Tagged ‘magnets’

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

This prototype represents one of 27 modules that will make up a critical section of the Mu2e experiment, the transport solenoid. Photo: Reidar Hahn

This prototype represents one of 27 modules that will make up a critical section of the Mu2e experiment, the transport solenoid. Photo: Reidar Hahn

If you’ve ever looked at a graphic of Fermilab’s future Mu2e experiment, you’ve likely noticed its distinctive, center s-shaped section. Tall and wide enough for a person to fit inside it, this large, curving series of magnets, called the transport solenoid, is perhaps the experiment’s most technologically demanding piece to build.

Last month a group in the Fermilab Technical Division aced three tests — for alignment, current and temperature — of a prototype transport solenoid module built by magnet experts at Fermilab’s Technical Division and INFN-Genoa in Italy.

The triple milestone means that Fermilab can now order the full set for production — 27 modules.

“The results were excellent,” said Magnet Systems Department scientist Mau Lopes, who is leading the effort.

There’s not much wiggle room when it comes to the transport solenoid, a crucial component for the ultrasensitive Mu2e experiment. Mu2e will look for a predicted but never observed phenomenon, the conversion of a muon into its much lighter, more familiar cousin, the electron, without the usual accompanying neutrinos. To do this, it will send muons into a detector where scientists will look for particular signatures of the rare process.

The transport solenoid generates a magnetic field that deftly separates muons based on their momentum and charge and directs slow muons to the center of the Mu2e detector. The maneuver requires some fairly precisely designed details, not the least of which is a good fit.

When put together, the 27 wedge-shaped modules will form a tube with the snake-like profile. Muons will travel down this vacuum tube. To guide them along the right path to the detector, the solenoid units must align with each other to within 0.2 degrees. The Magnet Systems team exceeded expectation: The prototype was aligned with 100 times greater precision.

The team achieved not just the right shape, but the right current. The electrical current running through the solenoid coil creates the magnetic field. The Mu2e team exceeded the nominal current of 1,730 amps, reaching 2,200 amps. As a bonus, while that amount of current has the potential to create a slight deformation in the module’s shape, the Mu2e team measured no change in the structure.

Nor was there much change in the model’s temperature, which must be very low. The team delivered 2.5 watts of power to the coil — well above what the coils will see when running. The module proved robust: The temperature changed by a mere whisker — 150 millikelvin, or 0.27 degrees Fahrenheit. The coils will be at 5 Kelvin when operating. The prototype sustained the nominal current at up to 8 Kelvin.

Fermilab has selected a vendor to produce the modules. Lopes expects that it will be two and a half years until all modules are complete.

“We thank all the smart people at INFN Genoa, the Fermilab Test and Instrumentation Department, the Magnet Systems Department and the Accelerator Division Cryogenics Department for this achievement,” Lopes said. “These seven months of hard work have paid off tremendously. Our project continues at full steam ahead.”

Leah Hesla

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This article appeared in Fermilab Today on July 24, 2015.

Argonne National Laboratory was attracted to the expertise of this Fermilab magnet team. The team recently developed a pre-prototype magnet for Argonne's APS Upgrade Project. Photo: Doug Howard, Fermilab

Argonne National Laboratory was attracted to the expertise of this Fermilab magnet team. The team recently developed a pre-prototype magnet for Argonne’s APS Upgrade Project. Photo: Doug Howard, Fermilab

A magnet two meters long sits in the Experiment Assembly Area of the Advanced Photon Source at Argonne National Laboratory. The magnet, built by Fermilab’s Technical Division, is fire engine red and has on its back a copper coil that doesn’t quite reach from one end to the other. An opening on one end of the magnet’s steel casing gives it the appearance of a rectangular alligator with its mouth slightly ajar.

“It’s a very pretty magnet,” said Argonne’s Glenn Decker, associate project manager for the accelerator. “It’s simple and it’s easy to understand conceptually. It’s been a very big first step in the APS Upgrade.”

The APS is a synchrotron light source that accelerates electrons nearly to the speed of light and then uses magnets to steer them around a circular storage ring the size of a major-league baseball stadium. As the electrons bend, they release energy in the form of synchrotron radiation — light that spans the energy range from visible to x-rays. This radiation can be used for a number of applications, such as microscopy and spectroscopy.

In 2013, the federal Basic Energy Sciences Advisory Committee, which advises the Director of the Department of Energy’s Office of Science, recommended a more ambitious approach to upgrades of U.S. light sources. The APS Upgrade will create a world-leading facility by using new state-of-the-art magnets to tighten the focus of the APS electron beam and dramatically increase the brightness of its X-rays, expanding its experimental capabilities by orders of magnitude.

Instead of the APS’ present magnet configuration, which uses two bending magnets in each of 40 identical sectors, the upgraded ring will deploy seven bending magnets per sector to produce a brighter, highly focused beam.

Because the APS Upgrade requires hundreds of magnets — many of them quite unusual — Argonne called on experts at Fermilab and Brookhaven National Laboratory for assistance in magnet design and development.

Fermilab took on the task of designing, building and testing a pre-prototype for a groundbreaking M1 magnet — the first in the string of bending magnets that makes up the new APS arrangement.

“At Fermilab we have the whole cycle,” said Fermilab’s Vladimir Kashikhin, who is in charge of magnet designs and simulations. “Because of our experience in magnet technology and the people who can simulate and fabricate magnets and make magnetic measurements, we are capable of making any type of accelerator magnet.”

The M1’s magnetic field is strong at one end and tapers off at the other end, reducing the impact of processes that increase the beam size, producing a brighter beam. Because of this change in field, this magnet is different from anything Fermilab had ever built. But by May, Fermilab’s team had completed and tested the magnet and shipped it to Argonne, where it charged triumphantly through a series of tests.

“The magnetic field shape they were asking for was a little bit challenging,” said Dave Harding, the principal investigator leading the project at Fermilab. “Getting the shape of the steel to produce that distribution and magnetic field required some tinkering. But we did it.”

Although this pre-prototype magnet is unlikely to be installed in the complete storage ring, scientists working in this collaboration view the M1 development as an opportunity to learn about technical difficulties, validate their designs and strengthen their skills.

“Getting our hands on some real hardware injected a dose of reality into our process,” Decker said. “We’re going to take the lessons we learned from this M1 magnet and fold them into the next iteration of the magnet. We’re looking forward to a continuing collaboration with Fermilab’s Technical Division on magnetic measurements and refinement of our magnet designs, working toward the next world-leading hard X-ray synchrotron light source.”

Ali Sundermier

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This article appeared in Fermilab Today on June 22, 2015.

Steve Gould of the Fermilab Technical Division prepares a cold test of a short quadrupole coil. The coil is of the type that would go into the High-Luminosity LHC. Photo: Reidar Hahn

Steve Gould of the Fermilab Technical Division prepares a cold test of a short quadrupole coil. The coil is of the type that would go into the High-Luminosity LHC. Photo: Reidar Hahn

Last month, a group collaborating across four national laboratories completed the first successful tests of a superconducting coil in preparation for the future high-luminosity upgrade of the Large Hadron Collider, or HL-LHC. These tests indicate that the magnet design may be adequate for its intended use.

Physicists, engineers and technicians of the U.S. LHC Accelerator Research Program (LARP) are working to produce the powerful magnets that will become part of the HL-LHC, scheduled to start up around 2025. The plan for this upgrade is to increase the particle collision rate, or luminosity, by approximately a factor of 10, so expanding the collider’s physics reach by creating 10 times more data.

“The upgrade will help us get closer to new physics. If we see something with the current run, we’ll need more data to get a clear picture. If we don’t find anything, more data may help us to see something new,” said Technical Division’s Giorgio Ambrosio, leader of the LARP magnet effort.

LARP is developing more advanced quadrupole magnets, which are used to focus particle beams. These magnets will have larger beam apertures and the ability to produce higher magnetic fields than those at the current LHC.

The Department of Energy established LARP in 2003 to contribute to LHC commissioning and prepare for upgrades. LARP includes Brookhaven National Laboratory, Fermilab, Lawrence Berkeley National Laboratory and SLAC. Its members began developing the technology for advanced large-aperture quadrupole magnets around 2004.

The superconducting magnets currently in use at the LHC are made from niobium titanium, which has proven to be a very effective material to date. However, they will not be able to support the higher magnetic fields and larger apertures the collider needs to achieve higher luminosities. To push these limits, LARP scientists and engineers turned to a different material, niobium tin.

Niobium tin was discovered before niobium titanium. However, it has not yet been used in accelerators because, unlike niobium titanium, niobium tin is very brittle, making it susceptible to mechanical damage. To be used in high-energy accelerators, these magnets need to withstand large amounts of force, making them difficult to engineer.

LARP worked on this challenge for almost 10 years and went through a number of model magnets before it successfully started the fabrication of coils for 150-millimeter-aperture quadrupoles. Four coils are required for each quadrupole.

LARP and CERN collaborated closely on the design of the coils. After the first coil was built in the United States earlier this year, the LARP team successfully tested it in a magnetic mirror structure. The mirror structure makes possible tests of individual coils under magnetic field conditions similar to those of a quadrupole magnet. At 1.9 Kelvin, the coil exceeded 19 kiloamps, 15 percent above the operating current.

The team also demonstrated that the coil was protected from the stresses and heat generated during a quench, the rapid transition from superconducting to normal state.

“The fact that the very first test of the magnet was successful was based on the experience of many years,” said TD’s Guram Chlachidze, test coordinator for the magnets. “This knowledge and experience is well recognized by the magnet world.”

Over the next few months, LARP members plan to test the completed quadrupole magnet.

“This was a success for both the people building the magnets and the people testing the magnets,” said Fermilab scientist Giorgio Apollinari, head of LARP. “We still have a mountain to climb, but now we know we have all the right equipment at our disposal and that the first step was in the right direction.”

Diana Kwon

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This article appeared in Fermilab Today on May 1, 2015.

Fermilab Director Nigel Lockyer shakes hands with Jefferson Lab Director Hugh Montgomery by a superconducting coil and its development and fabrication team at Fermilab. Six coils have been made and shipped to Jefferson Lab for use in the CLAS12 experiment. Photo: Reidar Hahn

Fermilab Director Nigel Lockyer shakes hands with Jefferson Lab Director Hugh Montgomery by a superconducting coil and its development and fabrication team at Fermilab. Six coils have been made and shipped to Jefferson Lab for use in the CLAS12 experiment. Photo: Reidar Hahn

A group of Fermilab physicists and engineers was faced with a unique challenge when Jefferson Lab asked them to make the superconducting coils for an upgrade to their CEBAF Large Acceptance Spectrometer experiments. These are some of the largest coils Fermilab has ever built.

Despite obstacles, the sixth coil was completed, packed on a truck and sent to Jefferson Lab to become the last piece of the torus magnet in the lab’s CLAS detector. It arrived on Thursday.

The CLAS detector’s upgrade (CLAS12) will allow it to accept electron beams of up to 11 GeV, matching the beam energy of the Virginia laboratory’s CEBAF electron accelerator after five passes. These improvements will allow Jefferson Lab to more accurately study the properties of atomic nuclei.

A major component of the enhanced detector is the torus magnet, which will be made from the six superconducting coils created at Fermilab. Aside from cleaning, insulating and winding the coils, one of the most important parts of the process is vacuum epoxy impregnation. During this step, air and water vapor are removed from the coils and replaced with an epoxy.

This process is particularly difficult when you’re working on magnets as big as the CLAS12 coils, which are 14 feet long and seven feet wide. Fermilab’s Magnet Systems Department fabrication team, the group responsible for making these massive coils, encountered a major obstacle at the end of March 2014 after finishing the first practice coil.

What they found were dry areas within the coil where the epoxy couldn’t penetrate. These were places where the coils weren’t fixed into place, meaning they could move and generate heat and resistance. This can lead to magnet quench, the transition from superconducting to a normal state — a highly undesirable consequence.

The Fermilab group and Jefferson Lab staff collaborated to come up with a solution. By trying new materials, new temperature profiles and adjusting the time that the epoxy was left to sit and be adsorbed, the team was able to prevent the dry areas from forming.

Fred Nobrega, the lead engineer at Fermilab for the CLAS12 coil project, joined the effort last August.

“It was rewarding for me to join the project near its low point, be able to help get through the hurdle and see this completed,” he said.

Production has been steady since December, with Fermilab sending roughly one coil a month to Jefferson Lab. Although the sixth coil will become the last piece of the torus magnet, the project isn’t complete just yet — the ultimate goal is to make eight identical coils, the six for the magnet and two spares.

“We’re succeeding because we have great people and a productive collaboration with Jefferson Lab, who helped us at difficult moments,” said George Velev, head of the Magnet Systems Department. “We worked together on a tough problem and now we see the results.”

Diana Kwon

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Researchers at the ALPHA experiment at CERN made major news today with the announcement that they’ve trapped antimatter atoms for 1,000 seconds. That’s more than 16 minutes and 5,000 times longer than their last published record of two tenths of a second.

The ALPHA magnet being wound at Brookhaven

The new feat will allow scientists to study the properties of antimatter in detail, which could help them understand why the universe is made only of matter even though the Big Bang should have created equal amounts of matter and antimatter.

These studies have been made possible, in part, by a bottle-like, anti matter-catching device called a minimum magnetic field trap. At the heart of the trap is an octupole (eight-magnetic-pole) magnet that was fabricated at Brookhaven Lab in 2006.

Several special features of the coil design and a unique machine used to wind it contributed to the suc­cess of this magnet. For exam­ple, the magnet generates a very pure octupole field, which keeps the antimatter away from the walls of the trap, preventing them from annihilating.

Antiprotons and positrons are brought into the ALPHA trap from opposite ends and held there by electric and magnetic fields. Brought together, they form antiatoms neutral in charge but with a magnetic moment. If their energy is low enough they can be held by the octupole and mirror fields of the Minimum Magnetic Field Trap.

To figure out how many antiprotons were in the trap, the scientists “quench,”  or abruptly switch off the superconducting magnet, releasing the antimatter. The anti-atom’s subsequent annihilation into particles called pions is recorded by a three-layer silicon vertex detector similar to those used in high-energy experiments like Fermilab’s Tevatron and the Large Hadron Collider.

But the pions must travel through the magnets of the trap before reaching the silicon. To prevent the particles from scattering multiple times during their journey to the detector, Brookhaven physicists and engineers had to figure out how limit the amount of material used in the magnet. A specially developed 3D winding machine allowed the researchers to build the magnet directly onto the outside of the ALPHA vacuum chamber. The result is a magnet that looks far different from the bulky, steel-surrounded instrumentation in most particle colliders. In fact, only the superconducting cables are metal.

–Kendra Snyder, BNL Media & Communications

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Magnets magnets everywhere…

Tuesday, May 17th, 2011

In my previous posts, I’ve mentioned that LHCb contains a dipole magnet to help measure particle momenta. Particles normally travel in straight lines, but in a magnetic field the paths of charged particles curve, with positive and negative particles moving in opposite directions.
By examining the curvature of the path, it is possible to calculate the momentum of a particle. Particles with greater momentum bend less than those lesser momentum. This is because a particle with greater momentum will spend less time in the magnetic field and thus be affected less.Note that both the above images are from The Particle Adventure which is a fantastic website to learn the basics of particle physics.

Here is an image of the LHCb dipole magnet with some people for size comparison. The magnet is essentially a very large horseshoe magnet with the upper coil being one polarity (N for example) and the lower coil the opposite (S) where the magnetic field is the strongest between them.

Of the major LHC experiments (ALICE, ATLAS, CMS and LHCb), the only other that uses a dipole magnet to bend charged tracks is ALICE. Actually, ALICE has quite an interesting magnet configuration, which you can see from the following schematic. There is a large solenoid magnet (coloured red which was used in the L3 experiment at LEP) in the central region, and a dipole magnet on the single arm forward muon detector.

What’s a solenoid magnet? Here is a schematic of one from physics animations. This type of coil configuration generates a nearly uniform field inside the windings and a comparably weak and divergent field outside. It is the preferred type of magnet within cylindrically symmetric detectors. In fact both ATLAS and CMS use solenoid magnets.

Actually, solenoid is part of the CMS acronym, Compact Muon Solenoid. At 12.9 meters long with an inner radius of 2.95 metres, an outer radius of 3.8 metres, and weighting 12,000 tonnes, the experiment contains the world’s largest superconducting solenoid magnet.

ATLAS on the other hand is named after its other magnet system, A Toroidal LHC ApparatuS. One of the key design features of the ATLAS detector is the unique hybrid superconducting magnet system. It is an arrangement of a central solenoid surrounded by a system of three large air-core toroids, measuring 26 m in length and 20 m in diameter.

What’s a toroidal magnet field? Again, thanks to physics animations, here is a schematic. As you can see, coils are oriented so that the magnetic field goes around in a doughnut type shape. (Toroidal is just a fancy mathematical description for a doughnut shaped object.)

Of course, the LHC experiments aren’t the only uses of magnets at the LHC. The accelerator system is full of them. Dipole magnets are used to steer the protons around the ring, quadrupole magnets are used to focus the beam, sextupole magnets are used to correct chromaticity, octupole magnets are used to correct field errors. What are all these magnets? Here is a nice diagram from some lecture slides I found. As you can see, they are named after the number of magnetic poles they contain (2, 4, 6 and 8, the n in the diagram counts the number of pole pairs). The arrows on the diagram shows the direction of the magnetic fields that each of the magnets produces.

In terms of beam acceleration, dipoles and quadruples are the most important. In fact, if you look carefully at the Fermilab logo below, you might notice the superposition of a quadrupole and a dipole magnet…

I could continue, but this post is getting very long. I hope this very brief introduction illustrates how important magnets are in experimental particle physics. Personally, I wish I had known this when I was taking electromagnetism and electrodynamics in my undergraduate studies, which were actually my worse physics subjects in terms of marks. I really should have paid more attention!

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This 4-meter-long quadrupole coil recently achieved the ultimate magnetic-field strength expected for niobium tin coils of this design. Credit: Fermilab

This month, scientists are celebrating the centennial of the discovery of superconductivity, a fundamental phenomenon that has made possible the newest achievement in Fermilab’s Technical Division.

Shortly before the anniversary, researchers with the laboratory’s High Field Magnet (HFM) program successfully demonstrated optimal performance of a 4-meter-long niobium tin quadrupole coil in the temperature range from 1.9 to 4.6 Kelvin.

The achievement is an important milestone toward developing niobium tin magnets as a viable technology for accelerators.

“We’ve finally achieved the ultimate niobium tin coil performance,” said Alexander Zlobin, head of the HFM program.

Magnet coils in accelerators such as the Tevatron and the Large Hadron Collider are made of niobium titanium. Scientists would like to ramp up accelerators’ magnetic-field strength by instead using niobium tin, a brittle but more highly superconducting material.

Since 2005 Fermilab scientists have conducted niobium tin studies in support of the LHC Accelerator Research Program (LARP), a U.S. collaboration that contributes R&D for LHC upgrades. One of LARP’s goals is to demonstrate by 2014 that the technology is a good option for the LHC.

To that end, the HFM group has been experimenting with new processes for making quadrupole coils.

In recent months, the HFM group developed new coil insulation. They also redesigned the conductor previously used in LARP’s long quadrupole magnet by implementing twice as many smaller-diameter niobium tin filaments.

The Fermilab-developed and -assembled mirror structure used in tests of 4-meter-long niobium tin quadrupole coil. In a quadrupole mirror structure, three of the four poles are iron blocks rather than coils. The design produces conditions close to the real magnet but drastically reduces cost and processing time. Credit: Fermilab

After many tests using shorter coils and a so-called mirror structure, they tested the new niobium tin conductor and insulation in a 4-meter-long LARP quadrupole coil.

The group achieved a stable field of 12.3 Tesla at 4.5 Kelvin. At 1.9 Kelvin, they achieved a stable 13.3 Tesla.

“The small filaments worked great,” said Giorgio Ambrosio, leader of the LARP long-quadrupole program. “Once you make this technology available for accelerator magnets, it can be used for the LHC, a muon collider, or a neutrino factory. It can be used anywhere.”

–Leah Hesla

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Blooming Dipoles

Tuesday, March 25th, 2008

The Geneva area is really quite ideal in terms of climate. During the winter the many mountains in the area get tons of snow but there is rarely snow in the city or surrounding towns. As a result you have the best of both worlds: great skiing very nearby without the drudgery of constantly digging out your car. But occasionally we do get snow storms in the lower altitudes, such as this past weekend. For me this serves as a reminder of why I don’t live in places like Buffalo, NY, for example. Although, I do rather enjoy the occasional digging out of my car from a foot or so of soft, fluffy snow. It is quite therapeutic. It is not, however, therapeutic to dig out my car from 4 feet of very compact snow, dumped by the snowplow directly in front of the car. This being the situation I found myself in this morning. Honestly, snowplow person? Did you not see my car there?

Those frustrations aside, as a native Californian I was raised with the belief that the end of March is Spring (go ahead, laugh. But ask any Californian when Spring is and you will get a similar response. This is because Californians deep down believe that seasons are really just fictional, made up by Northerners and East-coasters to discourage us from vacationing there). So as April looms, I expect to wake up to my garden flowers blooming, not to my front-door stairs becoming a ramp of snow.

But apparently the LHC magnets are responding to the call of Spring. Over the past few weeks, magnets have been popping up everywhere. In the center of round-a-bouts, outside supermarkets, and several places around CERN, such as this superconducting dipole magnet which is just outside my office building.

dipole_magnet

All of these magnets are being displayed in anticipation of CERN’s ‘open days’, which take place during the first weekend of April. During the open days, all access points including the beam tunnel and all experiments are open to the public for tours. If you are in town, go! It is a great opportunity to see the guts of the LHC and the detectors.

This dipole magnet shown in the picture is what one of the main dipole magnets used in the accelerator ring looks like. Of which there are 1232 in total. Actually there are almost 9600 different magnets used in the LHC. This fact guide (linked at the bottom of the page) gives a description of the purpose of the many different magnet types.

And of course if you are entering a round-a-bout and happen to see one of these huge magnets in the center, don’t worry about your car being sucked into it, these are just shells. But anyone can see the real ones during the open day.

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