DUNE collaboration completes Interim Design Report for gigantic particle detectors

On Aug. 21, a beam of electrons successfully circulated for the first time through a new particle accelerator at the Department of Energy’s Fermilab.

The milestone marks the beginning of a research program that positions the particle storage ring, called the Integrable Optics Test Accelerator, as a standout among the world’s accelerators — an innovative test bed dedicated to the science of particle acceleration. A high-precision machine with a flexible configuration, it will allow researchers to test theories, make discoveries and create inventions that push past the limits of existing machines.

“We’ve built a modern, next-generation accelerator for beam physics research that will have impacts in multiple areas of science,” said Vladimir Shiltsev, head of the Fermilab Accelerator Physics Center. “It opens opportunities for a new era of accelerators.”

The centerpiece of the Fermilab Accelerator Science and Technology facility, IOTA will send electrons and protons around its 40-meter circumference, giving scientists the latitude to explore new ways of manipulating particle beams that will pay dividends in other fields.

When Fermilab scientists began planning IOTA, about 10 years ago, they set out to design a machine for the deep exploration of techniques that could advance the numerous scientific fields that depend on accelerators. They came up with an elegant, compact ring for testing the concepts that they judged to be the most important.

“IOTA is one of a kind — a particle storage ring designed and built specifically to host novel experiments with both electrons and protons and develop innovative concepts in accelerator science,” said Fermilab physicist Alexander Valishev, head of the team that developed and constructed IOTA.

Fermilab has formed partnerships with others interested in advancing accelerator science and technology at FAST. The facility has already attracted 29 institutional partners, including European institutions, U.S. universities, national laboratories and members of industry.

“We’re seeking engagement from a wider community of scientists,” Valishev said.

The achievement of first beam is the pinnacle of many years of that intense, collaborative work.

“An eager and highly motivated group of particle beam physicists from universities and laboratories around the world have been awaiting the completion of IOTA for fundamental research,” said Northern Illinois University President’s Research Professor and Director of Accelerator Research Swapan Chattopadhyay, Fermilab distinguished scientist. “We congratulate the IOTA team for having reached this significant milestone.”

The beam’s the thing

Usually, the accelerators that make headlines — such as CERN’s Large Hadron Collider in Europe — operate in service to studies of the basic properties of subatomic particles. By accelerating particle beams to close to light speeds and smashing them apart, these machines expose nature’s fundamental constituents in the ensuing debris, allowing scientists to study them.

IOTA is different. The 40-meter-circumference ring will accelerate beams to investigate — not particles emerging from collisions — but rather the beams themselves. It’s one of only a handful of accelerators in the world for beam physics studies.

But even among this small group, IOTA is different. It’s also the only research accelerator that will be able to switch between beams of electrons and protons. (IOTA’s first proton beams are expected in 2019.)

And whereas many other research accelerators are linear, meaning that the beam travels down a straight path, IOTA is a circular accelerator dedicated to beam studies. This means it can send beam around its 40-meter path thousands to millions of times. With each pass, various beam effects are amplified, enabling scientists to better understand how they arise in the first place. It’s a way to mimic the processes limiting the operation of much larger and higher-energy machines, from Fermilab proton accelerators to the LHC and future supercolliders.

“This facility offers a flexibility that can be useful to a wider community — above and beyond the needs of high-energy physics,” Valishev said.

It’s an opportunity that’s unavailable at particle accelerators that provide beam dedicated to particle physics experiments, with operators who can’t afford to dedicate time to often disruptive beam experimentation.

“Running beam physics studies in an operational particle physics machine is a tremendous challenge. You can’t really mess with the background environment, the beam losses,” said Shiltsev, referring to undesirable beam effects. “But accelerator physicists want to mess with the beam losses, to study them in detail and explore ways to suppress them. We want to push those effects to their maximum.”

And they can take the knowledge they gain from that boundary-pushing to the drawing board to improve the design of future particle physics machines — and accelerators for everyday life.

Over 30,000 particle accelerators are in operation in the world. Most are used in industry and for broad applications, such as for the environment or medicine (accelerators for cancer research use X-rays generated with a small electron accelerator in a hospital or produce medical isotopes for imaging).

What’s in a beam?

IOTA’s rich research program spans the gamut from shaping beams packed with hundreds of millions or billions of electrons or protons to examining beams made of only a single particle. Scientists will use IOTA to explore multiple beam acceleration technologies, including several that have been proposed but never realized.

“With IOTA, scientists from around the world will be able to use the next-generation accelerator to collaborate and test innovative ideas, finding ways to reach the next level of accelerator beam power,” said Fermilab Head for Accelerator Science Programs Sergei Nagaitsev, one of the researchers who proposed the IOTA concept.

One area that could dramatically change the world of accelerators is the capability for generating ultrahigh-intensity beams.

Roughly translated, “intensity” is the number of particles that form a beam. The more particles a beam can carry, the more that can be smashed together at a time, and the more you can speed up the timeline for discovery. High intensity is a high priority for the field of particle physics.

But unchecked, an increasingly intense beam becomes increasingly unstable and can produce unwanted effects, including beam loss phenomena, in which particles depart from the pack. That limits the beam’s performance, making it far less useful for discovery.

“We want to push the physics to do more, so we have to push the beam to lose less,” Shiltsev said. “Having this ring gives us the chance to really understand how to attack this problem.”

Accelerator scientists have proposed various methods to tame or compensate for beams’ unruly behavior. With IOTA, scientists have a high-tech platform to fully explore these techniques, including several that could not be tested previously. One of them uses low-energy electrons as a kind of focusing lens. Another uses instruments collectively known as integrable optics — the “IO” in IOTA.

“These are new techniques for beam control,” Shiltsev said. “Nobody’s done this before.”

But “IO” is only the beginning.

With IOTA, accelerator scientists will also capitalize on Fermilab’s existing strengths in beam acceleration. Beam cooling, for example, is a method for creating tighter, more orderly beams, making them easier to manipulate and accelerate. Fermilab has a strong history in its development. Between 2005 and 2011, it operated the highest-energy electron cooler in the world.

The focus of the current beam cooling effort has a fancy name: optical stochastic cooling. Building on the lab’s current expertise, IOTA scientists will take the technology to the next level.

“If the technology is successful, it could pave the way for electron-ion colliders in an energy range that isn’t currently accessible,” Valishev said.

IOTA invites research in other tantalizing topics. For example, scientists can use the test accelerator to dive deep into little understood quantum phenomena, such as the physics of beams made of a single electron. Scientists could learn whether their behavior is “textbook or has some additional strangeness,” Shiltsev said.

“We can get to the essence of the deep quantum physics of these objects. So there are other nice things we can do using IOTA — unique experiments in fundamental physics,” Shiltsev said.

“While IOTA promises to open up new vistas to reach higher-intensity charged particle beams in the future, more fundamentally it will allow, for the first time in history, classical feedback control of a single electron,” Chattopadhyay said. “We want to understand how its quantum nature blurs this point-like fundamental particle in space.”

IOTA outlook

With first beam comes both the satisfaction of accomplishment and the prospect of doing impactful science.

“Seeing first beam in a research accelerator is a rare experience in the life of a scientist, or an accelerator physicist, when you know you’ve accomplished something big — even though it’s just first beam,” Valishev said. “I’m proud for our team.”

Over the next year, the Fermilab team will install the device that will supply protons to IOTA, the proton injector. Once it is in place, it will complete the trio of particle accelerators that make up the FAST facility: the proton injector, the electron injector (completed in 2017) and the IOTA ring.

“IOTA is unique, and what’s ahead is years of exciting, very interesting research,” Shiltsev said. ” We look eagerly forward to it.”

Learn more about IOTA at the FAST website and in the Journal of Instrumentation. You can see presentations at two recent IOTA workshops in 2015 and 2018.

The IOTA program is supported by the DOE Office of Science.

Editor’s note: This article has been edited with updated information about the Global Physics Photowalk.

On July 28, nearly 50 professional and amateur photographers from the Midwest and beyond were invited behind the scenes at the U.S. Department of Energy’s Fermi National Accelerator Laboratory. Cameras in hand, they were granted access to locations on the Fermilab site not usually accessible by the public, and they emerged with photographs that capture the fascinating science happening at one of the world’s premier particle physics laboratories.

Now the winning photos from Fermilab’s Photowalk have been chosen and will be entered into the international Global Physics Photowalk sponsored by the Interactions collaboration. The winning images were selected by a three-member jury and whittled down from 196 submissions. The top images offer a different perspective of visually interesting locations on the Fermilab site.

The top photos are now available to view online.

The winning photo, an overhead shot of a sculpture known as the Mobius Strip, was taken from the 15th floor of Fermilab’s Wilson Hall by Ken Wickham of St. Charles, Illinois. The second-place photo offers a unique view of the inside of the atrium of Wilson Hall and was taken by Ted Trimble of Elgin, Illinois. Rounding off the top three is a shot of the pi-shaped poles that bring power to the Fermilab site, snapped by David Berg of Minneapolis, Minnesota.

July’s event was the fourth Fermilab Photowalk and the first since 2015. The Fermilab event is part of the Global Physics Photowalk, organized by the Interactions collaboration and hosted this summer at 17 labs around the world. This year’s event features labs and institutions in Australia, Europe and Asia, as well as four (Fermilab, Brookhaven National Laboratory in New York, Sanford Underground Research Facility in South Dakota and SLAC National Accelerator Laboratory in California) in the United States.

The global competition opened on Monday, Aug. 27, and includes a public vote as well as a juried selection. Each laboratory has entered its top three images into the global contest, and a public online vote will choose the top three, while a panel of expert photographers and scientists will also choose their three favorites. Read more about voting online, or go directly to www.interactions.org.

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.

For lunch, do you enjoy having your tomato whole, in slices or finely chopped? It probably depends on the dish: The tomato could serve as a standalone fruit snack, as part of a sandwich or as a salad topping. Similarly, different Fermilab experiments may want particles beams coming to them in different chunks. Now they have a chopping “knife” to prepare the beam to their taste: the new beam chopper for the future Fermilab linear accelerator.

Scientists can create custom particle beams by removing select particle bunches — or packets of particles each containing about 200 million particles — from a longer, continuous queue. For example, experts can adjust settings to eject every third bunch, with the remaining bunches forming a particular pattern that’s optimized for an experiment. The beam chopper is the device that carries out this high-precision bunch removal.

Beam choppers are ubiquitous in ion accelerators. But when, several years ago, a team of Fermilab accelerator experts set out to design the chopper that would become part of the lab’s upgraded accelerator complex, nothing even close to what was needed existed.

The program of upgrades called Proton Improvement Plan-II (PIP-II) will meet the demands of Fermilab’s future experiments for more and more intense particle beams. While the new PIP-II linear accelerator uses superconducting resonators to increase the particles energy to 800 million electronvolts, the chopper is placed upstream in the section called the medium-energy beam transport, MEBT. It will pass for acceleration only those bunches that are requested by the experiments and remove all others.

A beam chopper has two main parts: kicker and absorber. The kicker removes unneeded bunches. The absorber receives them.

The kicker is essentially two parallel plates between which voltage can change quickly, and it is situated at an optimal point in the beam path for bunch removal. So when a bunch to be removed flies between the kicker plates, a voltage is applied — a nanosecond-long, roughly 1,000-volt burst of electric potential. That pulse kicks the bunch out of the main queue and into the beam absorber downstream.

PIP-II asks a great deal of the chopper. The MEBT chopper must act rapidly, able to remove bunches at a high frequency. It must be able to generate a pulse strong enough to completely eject entire bunches. It has to be precise enough to pick off single bunches without perturbing its neighbors — removing the unneeded bunches and only the unneeded bunches. The propagation of the voltage through the kicker plates has to sync perfectly with the path of the hydrogen ion bunches. And with record-power ion beams barreling through the accelerator, the chopper must be hardy enough to handle the increased power and radiation.

It was a collection of demands beyond the current state of the art.

The Fermilab accelerator team experimented with various designs, timings, electromagnetic variables and beam parameters. They developed two different kicker prototypes — a 50-ohm and a 200-ohm kicker, each requiring a specific way to create the electric signal. For example, the 200-ohm version would use a switch: open the switch and close it quickly back, and a short voltage pulse runs into the kicker. (It is almost like making a flash of the light by pushing a button of your flashlight, except the voltage is more than 100 times higher and “pushing” needs to be done in a billionth of second, tens of millions times per second.)

Ding Sun began development, prototyping, and eventually testing of the 50-ohm kicker version. Greg Saewert led the development of both the 200-ohm kicker and its switch driver, later joined by Daniil Frolov. Alex Chen led the mechanical design of both kicker versions.

Even with kickers redefining the state-of-the-art and combining deflection of two of them, the orientation and size of the beam are such that there was not much room to negotiate the placement of the absorber, which would have to deal with a high power density from the beam. The absorber is a piece of metal that intercepts the removed portion of the beam. Curtis Baffes sketched contours of the future absorber and then made a quarter-size prototype. Of course, the rapid expansion of the absorber material under fast heating from the tightly focused beam was the biggest issue. Eventually, the team came up with a workable design, and another quarter-size prototype was successfully tested to maximum power density envisioned for the future accelerator, ready to be exposed to ions.

Their final PIP-II chopper design comprised two kickers of the same type and one absorber. Each kicker fires as the unneeded bunch flies through the first and then the next, deflecting the bunch from the main beam. The absorber, like an outfielder on a baseball team, readily receives these high-frequency, high-power bunches.

When tests of the chopper components were conducted, to everybody’s excitement, several instruments showed how the beam envelope was splitting into two distinctive trajectories! Then, remove one of them, and a monitor downstream showed a sequence of bunches selected according to a predetermined pattern.

The excitement was followed by multiple shifts answering multiple questions. Does each kicker deflect the beam as expected? Does the velocity of electric pulse propagation through the kicker match the ion speed? Can the deflections by two kickers be efficiently summed? Do kickers survive if the beam is passed through them for a day? Does the absorber prototype behave with the ion beam as it was predicted from experiments with electrons? Each “yes” was adding confidence that the chopper will work, and heart of future PIP-II can beat as it has been envisioned eight years ago.

In 2018, the team plans to demonstrate operation of PIP2IT with a high-power beam, manufacture and install a full-size absorber, and order two final-design kickers, which will be slightly modified version of the present 200 Ohm kicker. In a year or so, the team hopes to have a chopper capable of fulfilling the first tasks foreseen for PIP-II, injection into the Booster and supplying the beam for the upgraded version of the Mu2e experiment.

Learn more in proceedings from the recent HB2018 conference or from a recent IEEE conference.