A new chapter in Fermilab’s electron lens legacy

Sending bunches of protons speeding around a circular particle collider to meet at one specific point is no easy feat. Many different collider components work keep proton beams on course — and to keep them from becoming unruly.

Scientists at Fermilab invented and developed one novel collider component 20 years ago: the electron lens. Electron lenses are beams of electrons formed into specific shapes that modify the motion of other particles — usually protons — that pass through them.

The now retired Tevatron, a circular collider at Fermilab, and the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory have both benefited from electron lenses, a concept originally developed at Fermilab.

“Electron lenses are like a Swiss Army knife for accelerators: They’re relatively simple and inexpensive, but they can be applied in a wide variety of ways,” said Alexander Valishev, a Fermilab scientist who co-authored a recent study for a new electron lens application, which could be crucial to forthcoming colliders.

The innovation is detailed in an article published on Sept. 27 in Physical Review Letters. (The article was also recently selected for presentation in the Physics Central’s Physics Buzz Blog.)

“This little breakthrough in the physics of beams and accelerators is kind of a beginning of a bigger invention — it’s a new thing,” said Fermilab’s Vladimir Shiltsev, an author of the published paper. Shiltsev also played a major role in the origination of electron lenses in 1997. “Fermilab is known for inventions and developments that are, first, exciting, and then, functional. That’s what national labs are built for, and that’s what we’ve achieved.”

A lens into the future

This new type of electron lens, called the Landau damping lens, will be a critical part of a huge, prospective project in particle physics research: the Future Circular Collider at CERN. The FCC would push the boundaries of traditional collider design to further study the particle physics beyond the Higgs boson, a fundamental particle discovered only five years ago.

The proposed FCC has to be a high-luminosity machine: Its particle beams will need to be compact and densely packed. Compared with CERN’s Large Hadron Collider, the beams will also have a dramatic increase in energy — 50 trillion electronvolts, compared with the LHC’s beam energy of 7 trillion electronvolts. That involves an equally dramatic increase in the size of the accelerator. With a planned circumference of 100 kilometers, the FCC would dwarf the 27-kilometer LHC.

These high-energy, high-luminosity supercolliders all experience a problem, regardless of size: An intense beam of protons packed into the width of human hair traveling over a long distance can become unstable, especially if all the protons travel in exactly the same way.

In a collider, particles arrive in packets called bunches — roughly foot-long streams packed with hundreds of billions of particles. A particle beam is formed of dozens, hundreds or thousands of these bunches.

Imagine a circular collider as a narrow racetrack, with protons in a bunch as a tight pack of racecars. A piece of debris suddenly appears in the middle of the track, disrupting the flow of traffic. If every car reacts in the same way, say, by veering sharply to the left, it could lead to a major pileup.

Inside the collider, it’s not a matter of avoiding just one bump on the track, but adjusting to numerous dynamic obstacles, causing the protons to change their course many times over. If an anomaly, such as a kink in the collider’s magnetic field, occurs unexpectedly, and if the protons in the beam all react to it in the same way at the same time, even a slight change of course could quickly go berserk.

One could avoid the problem by thinning the particle beam from the get-go. By using lower-density proton beams, you provide less opportunity for protons to go off course. But that would mean removing protons and so missing out on potential for scientific discovery.

Another, better way to address the problem is to introduce differences into the beam so that not all the protons in the bunches behave the same way.

To return to the racetrack: If the drivers all react to the piece of debris different ways —some moving slightly to the right, others slightly to the left, one brave driver just skips over the top — the cars can all merge back together and continue the race, no accidents.

Creating differentiations within a proton bunch would do essentially the same thing. Each proton follows its own, ever-so-slightly different course around the collider. This way, any departure from the course is isolated, rather than compounded by protons all misbehaving in concert, minimizing harmful beam oscillations.

“Particles at the center of the bunch will move differently than particles around the outside,” Shiltsev said. “The protons will all be kind of messed up, but that’s what we want. If they all move together, they become unstable.”

These differences are usually created with a special type of magnet called octupoles. The Tevatron, before its decommissioning in 2011, had 35 octupole magnets, and the LHC now has 336.

But as colliders get larger and achieve greater energies, they need exponentially higher numbers of magnets: The FCC will require more than 10,000 octupole magnets, each a meter long, to achieve the same beam-stabilizing results as previous colliders.

That many magnets take up a lot of space: as much as 10 of the FCC’s 100 kilometers.

“That seems ridiculous,” Shiltsev said. “We’re looking for a way to avoid that.”

The scientific community recognizes the Landau damping nonlinear lens as a likely solution to this problem: A single one-meter-long electron lens could replace all 10,000 octupole magnets and possibly do a better job keeping beams stable as they speed toward collision, without introducing any new problems.

“At CERN they’ve embraced the idea of this new electron lens type, and people there will be studying them in further detail for the FCC,” Valishev said. “Given what we know so far about the issues that the future colliders will face, this would be a device of extremely high criticality. This is why we’re excited.”

Electron Legos

The Landau damping lens will join two other electron lens types in the repertoire of tools physicists have to modify or control beams inside a collider.

“After many years of use, people are very happy with electron lenses: It’s one of the instruments used for modern accelerators, like magnets or superconducting cavities,” Shiltsev said. “Electron lenses are just one of the building blocks or Lego pieces.”

Electron lenses are a lot like Legos: Lego pieces are made of the same material and can be the same color, but a different shape determines how they can be used. Electron lenses are all made of clouds of electrons, shaped by magnetic fields. The shape of the lens dictates how the lens influences a beam of protons.

Scientists developed the first electron lens at Fermilab in 1997 for use to compensate for so-called beam-beam effects in the Tevatron, and a similar type of electron lens is still in use at the Brookhaven’s RHIC.

In circular colliders, particle beams pass by each other, going in opposing directions inside the collider until they are steered into a collision at specific points. As the beams buzz by one another, they exert a small force on each other, which causes the proton bunches to expand slightly, decreasing their luminosity.

That first electron lens, called the beam-beam compensation lens, was created to combat the interaction between the beams by squeezing them back to their original, compact state.

After the success of this electron lens type in the Tevatron, scientists realized that electron beams could be shaped a second way to create another type of electron lens.

Scientists designed the second lens to be shaped like a straw, allowing the proton beam to pass through the inside unaffected. The occasional proton might try to leave its group and stray from the center of the beam. In the LHC, losing even one-thousandth of the total number of protons in an uncontrolled way could be dangerous. The electron lens acts as a scraper, removing these rogue particles before they could damage the collider.

“It’s extremely important to have the ability to scrape these particles because their energy is enormous,” Shiltsev said. “Uncontrolled, they can drill holes, break magnets or produce radiation.”

Both types of electron lens have made their mark in collider design as part of the success of the Tevatron, RHIC and the LHC. The new Landau damping lens may help usher in the next generation of colliders.

“The electron lens is an example of something that was invented here at Fermilab 20 years ago,” Shiltsev said. “This is a one of the rare technologies that wasn’t just brought to perfection at Fermilab: It was invented, developed and perfected and still continues to shine.”

 

As you walk down the stairs from the main floor of Wilson Hall (cafeteria area) to the auditorium lobby, look up to the near edge of the wood block ceiling. Slightly west of the center line is a “hole” where a wooden block supposedly should be. I have often observed this hole since the ceiling was finished about 1973 and can attest that a block has been missing ever since. (Over time a few other distant pieces have gotten lost but should not be confused with this one.)

For me this has raised two issues:

1. Was this just a mistake in assembling the structure and never corrected or
2. Was this done on purpose to destroy any symmetry that might exist in this ceiling?

Obviously, the first issue is trivial except that it gives a plausible alternative to the second issue which is certainly more intriguing.

Fermilab founding director Bob Wilson appreciated the concept of “Broken Symmetry.” He designed a sculpture with this name, and it stands at the Pine Street entrance to the laboratory. He also gave a conference dinner talk, “Symmetry in Art and Science.” In it he discussed an artist dilemma of making something too perfect: “Only the gods are perfect.” Therefore ancient Asian artists would leave a small flaw in their work, he said. Did Wilson do the same here? I guess we will never know but the possibility is interesting.

Or, is it an omen of missing pieces in our physics knowledge?

Note: The wood for this ceiling and supposedly throughout the auditorium is walnut. It was gotten from several walnut trees that were cut down by vandals during the very early days of NAL. They were soon after captured by the FBI and the wood recovered. See the Fermilab history website.

Charles Schmidt is a Fermilab scientist emeritus.

Scientists using the Dark Energy Camera have captured images of the aftermath of a neutron star collision, the source of LIGO/Virgo’s most recent gravitational wave detection

A team of scientists using the Dark Energy Camera (DECam), the primary observing tool of the Dark Energy Survey, was among the first to observe the fiery aftermath of a recently detected burst of gravitational waves, recording images of the first confirmed explosion from two colliding neutron stars ever seen by astronomers.

Scientists on the Dark Energy Survey joined forces with a team of astronomers based at the Harvard-Smithsonian Center for Astrophysics (CfA) for this effort, working with observatories around the world to bolster the original data from DECam. Images taken with DECam captured the flaring-up and fading over time of a kilonova — an explosion similar to a supernova, but on a smaller scale — that occurs when collapsed stars (called neutron stars) crash into each other, creating heavy radioactive elements.

This particular violent merger, which occurred 130 million years ago in a galaxy near our own (NGC 4993), is the source of the gravitational waves detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo collaborations on Aug. 17. This is the fifth source of gravitational waves to be detected — the first one was discovered in September 2015, for which three founding members of the LIGO collaboration were awarded the Nobel Prize in physics two weeks ago.

This latest event is the first detection of gravitational waves caused by two neutron stars colliding and thus the first one to have a visible source. The previous gravitational wave detections were traced to binary black holes, which cannot be seen through telescopes. This neutron star collision occurred relatively close to home, so within a few hours of receiving the notice from LIGO/Virgo, scientists were able to point telescopes in the direction of the event and get a clear picture of the light.

“This is beyond my wildest dreams,” said Marcelle Soares-Santos, formerly of the U.S. Department of Energy’s Fermi National Accelerator Laboratory and currently of Brandeis University, who led the effort from the Dark Energy Survey side. “With DECam we get a good signal, and we can show how it is evolving over time. The team following these signals is a well-oiled machine, and though we did not expect this to happen so soon, we were ready for it.”

The Dark Energy Camera is one of the most powerful digital imaging devices in existence. It was built and tested at Fermilab, the lead laboratory on the Dark Energy Survey, and is mounted on the National Science Foundation’s 4-meter Blanco telescope, part of the Cerro Tololo Inter-American Observatory in Chile, a division of the National Optical Astronomy Observatory. The DES images are processed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.

Texas A&M University astronomer Jennifer Marshall was observing for DES at the Blanco telescope during the event, while Fermilab astronomers Douglas Tucker and Sahar Allam were coordinating the observations from Fermilab’s Remote Operations Center.

“It was truly amazing,” Marshall said. “I felt so fortunate to be in the right place at the right time to help make perhaps one of the most significant observations of my career.”

The kilonova was first identified in DECam images by Ohio University astronomer Ryan Chornock, who instantly alerted his colleagues by email. “I was flipping through the raw data, and I came across this bright galaxy and saw a new source that was not in the reference image [taken previously],” he said. “It was very exciting.”

Once the crystal clear images from DECam were taken, a team led by Professor Edo Berger, from CfA, went to work analyzing the phenomenon using several different resources. Within hours of receiving the location information, the team had booked time with several observatories, including NASA’s Hubble Space Telescope and Chandra X-ray Observatory.

LIGO/Virgo works with dozens of astronomy collaborations around the world, providing sky maps of the area where any detected gravitational waves originated. The team from DES and CfA had been preparing for an event like this for more than two years, forging connections with other astronomy collaborations and putting procedures in place to mobilize as soon as word came down that a new source had been detected. The result is a rich data set that covers “radio waves to X-rays to everything in between,” Berger said.

“This is the first event, the one everyone will remember,” Berger said. “I’m extremely proud of our entire group, who responded in an amazing way. I kept telling them to savor the moment. How many people can say they were there at the birth of a whole new field of astronomy?”

Adding to the excitement of this observation, this latest gravitational wave detection correlates to a burst of gamma rays spotted by NASA’s Fermi Gamma-ray Space Telescope. Combining these detections is like hearing thunder and seeing lightning for the very first time, and it opens up a world of new scientific discovery.

“Each of these — the gravitational waves from merging neutron stars, the gamma ray burst and the optical counterpart — could have been separate groundbreaking discoveries, and each could have taken many years,” said Daniel Holz of the University of Chicago, who works on both the DES and LIGO collaborations. “In less than a day, we did it all. This has required many different communities working together to make it all happen. It’s so gratifying to have it be so successful.”

This event also provides a completely new and unique way to measure the present expansion rate of the universe, the Hubble constant, something theorized by Holz and others. Just as astrophysicists use supernovae as “standard candles” (objects of the same intrinsic brightness) to measure cosmic expansion, kilonovae can be used as “standard sirens” (objects of known gravitational wave strength).

LIGO/Virgo can use this to tell the distance to these events, while optical follow-up from DES and others determines the red shift or recession speed; their combination enables scientists to determine the present expansion rate. This new kind of measurement will assist the Dark Energy Survey in its mission to uncover more about dark energy, the mysterious force accelerating the expansion of the universe.

“The Dark Energy Survey team has been working with LIGO for more than two years, refining their process of following up gravitational wave signals,” said Fermilab Director Nigel Lockyer. “It is immensely gratifying to be on the front lines of a discovery this significant, one that required the combined skills of many supremely talented people in many fields.”

The Dark Energy Survey recently began the fifth and final year of its quest to map an area of the southern sky in unprecedented detail. Scientists on DES will use this data to learn more about the effect of dark energy over eight billion years of the universe’s history, in the process measuring 300 million galaxies, 100,000 galaxy clusters and 3,000 supernovae.

Six papers relating to the DECam discovery of the optical counterpart are planned for publication in The Astrophysical Journal. Preprints of all papers are available here: https://www.darkenergysurvey.org/des-gravitational-waves-papers.

“It is tremendously exciting to experience a rare event that transforms our understanding of the workings of the universe,” said France A. Córdova, director of the National Science Foundation (NSF), which funds LIGO and supports the observatory where DECam is housed. “This discovery realizes a long-standing goal many of us have had — that is, to simultaneously observe rare cosmic events using both traditional as well as gravitational-wave observatories. Only through NSF’s four-decade investment in gravitational-wave observatories, coupled with telescopes that observe from radio to gamma-ray wavelengths, are we able to expand our opportunities to detect new cosmic phenomena and piece together a fresh narrative of the physics of stars in their death throes.”

 

 

The Dark Energy Survey is a collaboration of more than 400 scientists from 26 institutions in seven countries. Funding for the DES Projects has been provided by the U.S. Department of Energy Office of Science, U.S. National Science Foundation, Ministry of Science and Education of Spain, Science and Technology Facilities Council of the United Kingdom, Higher Education Funding Council for England, ETH Zurich for Switzerland, National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, Kavli Institute of Cosmological Physics at the University of Chicago, Center for Cosmology and AstroParticle Physics at Ohio State University, Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and Ministério da Ciência e Tecnologia, Deutsche Forschungsgemeinschaft, and the collaborating institutions in the Dark Energy Survey, the list of which can be found at www.darkenergysurvey.org/collaboration. 

Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation.

Fermilab is America’s premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC, a joint partnership between the University of Chicago and the Universities Research Association, Inc. Visit Fermilab’s website at www.fnal.gov and follow us on Twitter at @Fermilab.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

 

Professor Steven Lund of Michigan State University has been named the new director of the U.S. Particle Accelerator School (USPAS). His four-year renewable term begins on Dec. 1. He will succeed Professor William Barletta of the Massachusetts Institute of Technology, who has been director since 2006.

The USPAS is recognized as the nation’s premier training program in accelerator science and engineering. USPAS started in 1981 and convenes twice a year to offer a broad range of graduate-level accelerator science and engineering courses in an intensive-school format. Training and documentation produced by the sessions has been recognized for excellence and has had a profound positive impact on the field. All business and activities of the school are coordinated by the director and the USPAS office at the U.S. Department of Energy’s Fermi National Accelerator Laboratory.

“I am delighted about this appointment and eager to continue the outstanding work of the USPAS in educating current and future accelerator scientists and engineers,” Lund said. “It is a great honor to be selected, and I look forward to guiding the school to continued success.”

Lund has been a professor at MSU since 2014 and currently serves on both the Director’s Advisory Council and the Curriculum Committee for the USPAS, working with Director Barletta to coordinate school programs in the community interest. Lund’s position at MSU is at the Facility for Rare Isotope Beams (FRIB), and his focus is theoretical accelerator physics, emphasizing analytic theory and numerical modeling. He also teaches graduate courses in accelerator physics and advises students.

“Over the past 35 years the USPAS has developed a program filling a critically important role in the training and education for the national laboratories that use accelerators as research tools,” said Rod Gerig of Argonne National Laboratory, chair of the USPAS Director’s Advisory Council. “Those of us who represent the national laboratory and university community want to thank the outgoing director, Dr. William Barletta, for his service to USPAS over the past 11 years. Also, we have enjoyed and benefited from working with Dr. Lund on the USPAS Director’s Advisory Council, and now look forward to working with him as the USPAS director as we move forward in carrying out this important mission.”

Accelerators are a key driver of discovery science and industry and are central to the discovery missions of the U.S. DOE Office of Science. The USPAS collaboration includes seven U.S. DOE Office of Science laboratories, one U.S. DOE National Nuclear Security Agency lab and two universities. (See full list below.)

“Over its 35-year history, the USPAS has welcomed students of all levels of expertise and in many cases introduced them to the science of particle accelerators,” said Jim Siegrist, associate director of the U.S. DOE Office of Science for the Office of High Energy Physics. “I look forward to Steven Lund continuing this great tradition.”

The USPAS offers a continually updated curriculum of courses ranging from fundamentals of accelerator science to advanced physics and engineering concepts. The school is intended not only to meet the needs of national laboratories, but also to educate people on the many uses of particle accelerators in other fields, including industrial and medical applications.

“Fermilab is proud of its work with USPAS and eager to continue that work with Steven Lund at the helm,” said Fermilab Director Nigel Lockyer. “With thousands of particle accelerators in use around the world for dozens of different applications, teaching students the basics of accelerator technology is more important now than ever.”

MSU is developing its own world-class particle accelerator. FRIB will be a new scientific user facility for the Office of Nuclear Physics in DOE’s Office of Science. Under construction on campus and operated by MSU, the heart of FRIB is a high-power superconducting linear accelerator that will accelerate heavy ions to half the speed of light. FRIB will enable scientists to make discoveries about the properties of rare isotopes, supporting a community of currently 1,400 scientists.

FRIB is presently under construction—slated for completion by 2022—with first portions currently undergoing commissioning. Lund’s research aims to identify, understand and control processes that can degrade the quality of the particle beam.

“Steve is an outstanding researcher and a passionate educator, both of which will serve him well in his new position,” said Thomas Glasmacher, FRIB Laboratory director. “I am pleased he was selected and know he will excel in this new role.”

Before arriving at MSU in 2014 to work on FRIB, Lund held a joint appointment at Lawrence Livermore National Laboratory and Lawrence Berkeley National Laboratory working on physics issues associated with the transport of beams with high charge intensity, design of accelerator and trap systems, large- and small-scale numerical simulations of accelerators, support of laboratory experiments, and design of electric and magnetic elements to focus and bend beams. Lund received his Ph.D. in physics from MIT in 1992.

“The U.S. Particle Accelerator School has educated next-generation accelerator physicists and engineers for decades and through that made sure that we can build ever better accelerators and develop new important technologies,” said Norbert Holtkamp of SLAC National Accelerator Laboratory, a member of the USPAS Institutional Board. “SLAC wants thank Bill Barletta for his strong leadership during his tenure and we look forward to seeing Steven Lund implement his compelling vision. We also thank MSU and FRIB for their strong continued support.“

The USPAS collaboration includes Argonne National Laboratory, Brookhaven National Laboratory, Fermi National Accelerator Laboratory, Lawrence Berkeley National Laboratory, Oak Ridge National Laboratory, SLAC National Accelerator Laboratory and Thomas Jefferson National Accelerator Facility, all U.S. DOE Office of Science labs; Los Alamos National Laboratory, a U.S. DOE National Nuclear Security Agency lab; Cornell University and Michigan State University.

Michigan State University has been advancing the common good with uncommon will for more than 160 years. One of the top research universities in the world, MSU pushes the boundaries of discovery and forges enduring partnerships to solve the most pressing global challenges while providing life-changing opportunities to a diverse and inclusive academic community through more than 200 programs of study in 17 degree-granting colleges.

Fermilab is America’s premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC, a joint partnership between the University of Chicago and the Universities Research Association, Inc. Visit Fermilab’s website at www.fnal.gov and follow us on Twitter at @Fermilab.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.