Modern modulators for Fermilab accelerators

Take a walk along the hall that houses Fermilab’s linear accelerator, and you’ll see tall sets of brightly lit shelves that resemble fancy vending machines. But instead of snacks and beverages, they hold boxy structures that resemble gleaming car batteries. Arranged in neat columns and rows, these cells — known as Marx cells and installed during the last 36 months — have rejuvenated the aging Fermilab linear accelerator, or Fermilab Linac, and help guarantee its exceptional performance for the decade to come.

The installation of five new Marx modulators — each comprising 54 Marx cells — marks the conclusion of a five-year-long project to modernize critical components of the Linac. They replace equipment that had helped power accelerator components since the late 1960s.

“We needed a long-term replacement,” said Fermilab engineer Howie Pfeffer, who began designing the lab’s Marx modulator system in 2013. “We did a lot of modeling and experiments to see if the Marx structure would work. It wasn’t obvious that it would. And we determined that, yeah, we can do it. Along the way we built a number of circuits with smaller numbers of cells before committing to the full 54-cell modulators. Each circuit led us to important changes in the next.”

Most of the power that is fed to an accelerator is used to propel particles. The job of the modulator is to regulate those pulses of power — to shape them in a way that helps kick the particle beam forward at just the right time and right energies.

At Fermilab, the Marx modulators shape the pulses from a 5-million-watt amplifier, and the amplifier’s modulated power is used to accelerate protons in the Fermilab Linac. The specially formed waves propel the proton beam at a pulse rate of 15 times per second.

“The beam energy has to be exact, and most of the task of power regulation is to make sure that, as the particle beams accelerate through the Linac, they settle quickly to within one 10th of one percent of the accuracy level we want,” said Bill Pellico, leader of the Fermilab Proton Improvement Project, under which the Marx modulators were design and installed.

Capitalizing on the beam-tuning flexibility of the Marx modulators, Pfeffer and his engineering team perfectly filled the pulse prescription — a superfast, 350-microsecond pulse with a special shape specifically for injecting beam into the Linac. They also designed the modulators to make real-time corrections during the pulse, ensuring its shape would meet the accelerator’s stringent requirements. These machine learning capabilities enable the modulators to use past beam performance in improving pulse generation.

“This may be the first high-power Marx modulator with real-time pulse shaping feedback,” Pellico said.

The new modulators have improved regulation of the beam energy and also resulted in a nearly 50 percent savings in power over the older power-hungry modulators.

Marx modulators replace technology once common in analog radios and televisions — vacuum tube systems — with solid-state technology. Industry began using Marx modulators in the 1990s. Scientists, engineers and technicians have since developed a number of Marx modulators for particle accelerators, taking advantage of their efficient power use and better beam regulation.

“A lot of the old tubes in our accelerator had become obsolete. We couldn’t buy some of that stuff anymore,” Pellico said. “But now, we have not only a modern system, but also one where you can turn various cells on or off to modulate the power as desired. The design will have lots of applications in powering future particle accelerators — not just at Fermilab, but at other labs and facilities, too.”

The new, easy-to-maintain system enables the lab to generate easy-to-control particle beams, just one part of Fermilab’s effort to modernize its accelerator complex.

“Fermilab’s science program entirely depends on this working,” Pfeffer said. “It was a big responsibility. If we hadn’t gotten this work done, there’s no beam anywhere. So it feels great to see the Marx modulators completely installed and running. And thanks to our people who put it together, it’s the most beautiful circuit I’ve ever seen.”

The Proton Improvement Project is supported by the U.S. Department of Energy Office of Science.

Editor’s note: This is a version of an article that appeared in University of Chicago News.

The U.S. Department of Energy has awarded more than $22 million to scientists at the University of Chicago, Argonne National Laboratory and Fermi National Accelerator Laboratory for quantum science research, spanning the search for dark matter to more powerful computing.

The funding for more than a dozen projects will help scientists explore quantum engineering, which is rapidly becoming reality after decades consigned to theory.

“These are exciting new research programs aimed at creating the foundations of a new technology grounded in the laws of quantum mechanics,” said David Awschalom, the Liew Family Professor at the Institute for Molecular Engineering at the University of Chicago and a scientist at Argonne. “The projects offer a unique opportunity to not only deepen our knowledge of quantum science and what it has to offer across many fields, but also to continue building a framework of collaboration for quantum science between academic institutions and the national laboratories.”

Awschalom heads the Chicago Quantum Exchange — a partnership between all three institutions to foster an emerging Chicago-area ecosystem of quantum research and commercialization.

Among the projects funded:

• At the University of Chicago, Professor Cheng Chin will build a system called a “quantum matter synthesizer,” designed to achieve a dream long held by quantum physicists: to fully control individual atoms in a quantum system. This system will help scientists understand and harness the physics of quantum materials, as well as offer promising ways to process information using quantum technology.
• Argonne scientists will explore how to connect light particles via quantum entanglement, test long-distance entanglement, search for bosonic dark matter — a possible explanation for the mysterious phenomenon known as dark matter—and partner with the National Institute of Standards and Technology to tap quantum to improve scientists’ ability to measure very tiny effects, a field called quantum metrology.
• At Fermilab, scientists will explore applications and theory behind quantum computing, particularly for use in particle physics and accelerators, and use superconducting qubits to search for two other hypothetical particles proposed as explanations for dark matter: axions, extremely tiny particles with no spin, and dark photons, the dark “twins” of regular light particles.

“Scientists have understood the practical potential of quantum physics for decades, but only recently has the technology advanced to the point that we could tap into it,” said Joe Lykken, Fermilab chief research officer and deputy director. “Quantum physics has been Fermilab’s bread and butter for a half-century. With that accumulation of expertise and the technological innovation that comes with it, there’s hardly a place better positioned to explore — as a focused, dedicated program — the ways we can take full advantage of nature’s quantum behavior.”

“This is an opportunity to respond to a major emerging scientific challenge, which the national laboratories are uniquely positioned to do,” said Supratik Guha, a professor in University of Chicago’s Institute for Molecular Engineering and director of the Center for Nanoscale Materials at Argonne. “By delving into the fundamental science and then building devices and systems that exploit quantum mechanics, we expect enormous advantages in many fields.”

More information and the full list of funded quantum projects is available from the Department of Energy.

Earlier this month, one of two prototype detectors for the international Deep Underground Neutrino Experiment, (DUNE), saw its first particle tracks. It was a major milestone for the ProtoDUNE detector, as it’s called, which is located at CERN. Capturing the tracks of particles that pass through the detector’s time projection chamber — the part of the detector that contains the liquid argon detection material — is a successful demonstration of the detector technology.

It’s also a testament to the world-class computing resources and expertise at Fermilab and CERN.

The ProtoDUNE experiments present a set of unique computing challenges for both laboratories. Even though the ProtoDUNE time projection chambers are small compared to the planned DUNE far detectors, the data volume that these detectors produce are similar in size to what is coming out of the largest LHC experiments.

With the appearance of the first tracks in the detector, this flood of data has begun. Over the next three months, scientists plan to run the detectors to take over 6 petabytes of data. Extrapolate those rates over the course of a year, and the numbers are breathtaking.

Over the past year, Fermilab and CERN have engaged in a joint venture to stand up a system that allows both labs to effectively host and process all of this information coming off the detector. The beginning of data taking is a triumph for the computing teams involved because they have worked together at every stage of the data’s life cycle, from acquisition, to storage, to processing and analysis.  They have produced a system that provides transparent access to the data for all the DUNE scientists, regardless of where they are in the world. This has allowed contributions to the computing to come from multiple international facilities, including the GridPP collaboration, based in Great Britain, the National Institute of Nuclear and Particle Physics (IN2P3), based in France, and many universities throughout the United States and Europe.

The role of the Fermilab Scientific Computing Division (SCD) has been to ensure that all of this computing worked flawlessly from day one so that, once the ProtoDUNE detector was turned on, scientists would be able to access, analyze and look at what was happening in the detector. This required real expertise, to research and find solutions to the problem and to coordinate between the various labs and organizations. Three members of SCD in particular — Igor Mandrichenko, Steve Timm and Ken Herner, each representing expertise in our abilities to record accelerator beam data, manage large-scale data sets and conduct large-scale processing and reconstruction — were at CERN as the detector was turned on, filled with liquid argon and ran its first tracks. These individuals were able to work on the ground with the CERN team and work out the final details as they arose, then and there.

Many other individuals and groups across SCD directly contributed to this effort and share in its success. These teams accomplished amazing things to ensure that the software, hardware and processes would work as expected for everything from the lowest levels of the data acquisition to the final stages of data processing.  Even the brand new mass storage tape libraries, which were brought online in August, have been tasked immediately with storing ProtoDUNE data.

These efforts are vital to the success of DUNE. There is a very limited window of time that beam will be available at CERN before the start of a two-year shutdown. This time-critical work and the data from the detectors are needed to inform us whether this technology would work at full scale for DUNE. Lessons learned and data on detector performance will directly shape the design of the detector and will be put directly in the experiment’s technical design report.

Congratulations to all in SCD for this success.

Panagiotis Spentzouris is the head of Fermilab’s Scientific Computing Division.

How long will you be at Fermilab?

I just started a postdoc appointment, so I will be here for three years, potentially longer. I did my Ph.D. at the University of Liverpool and was here for a year last year working on the Muon g-2 experiment for my thesis.

What is your role in Muon g-2?

Muon g-2 is an experiment to measure properties of muons. We are particularly measuring something called its magnetic moment. We measure it by injecting a beam of muons into a big magnet. I work on the team that helps store the muon beam inside the magnet. Half the time I’m working on hardware things, and half the time I’m doing data analysis.

What intrigues you about muons and Muon g-2?

The reason Muon g-2 is so exciting is that it is a really niche way to try to answer some key questions in particle physics. The muon in particular is really exciting because it can tell scientists if there are new, as yet unobserved, particles and forces that exist in nature.

To me, the experiment seems like a really different way of approaching this question. Instead of doing something speculative, where you are trying to find a hint of something new by measuring loads of different things, we are trying to measure just one number really accurately and test it against an equally accurate prediction.

What is the most exciting part about working on Muon g-2?

The measurement is exciting in itself. It is also nice working with a lot of other people who are already interested in the work. I think, in a lot of jobs, you might be really interested in what you are doing, but it’s hard to convince other people that what you are doing is exciting. As part of Muon g-2, when I’m in the experiment, our meetings may be about how to get this particular capacitor we need, but everyone is still very motivated and focused on the same end goal. I think that’s the best thing about it.

What about your current work at Fermilab differs from your previous Ph.D. work?

Oh, so many things. I used to work on the tracking detectors, but now I work on a completely different system, the kicker, which forces the muons onto their correct path inside the large, magnetic ring. I’m still working on hardware and data analysis, but now I get to work on some electronics, readout systems and build circuit boards too. It is just completely new.

During my Ph.D., I did hands-on work, too, but I was a student, so there were other people deciding what to do. But now it’s like, “Great! Get this data acquisition system to work.” That is definitely new to me.

What do you enjoy outside of work?

I really like soccer, but only watching it. Everyone knows that because the World Cup just happened, and I was very vocal about supporting England. I also like swimming and playing the piano.

What do you enjoy about Fermilab?

I like loads of things about it, which is why I wanted to stay here. It’s such a beautiful place to work, and I like seeing all the animals on site. I had never seen a bison before I came here.

Sometimes I try to run around the site, but usually it turns into more like walking around the site.