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Keeping Track of the World’s Highest-Intensity Neutrino Beam

Fermilab uses Radian laser trackers to align its particle accelerator

Published: Tuesday, August 29, 2017 - 11:01

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Scientists at the Fermi National Accelerator Laboratory (Fermilab) are working on research projects that aim to answer fundamental physics questions. How did the universe begin? What are dark matter and dark energy? What is the mass hierarchy of neutrinos? Are there other undiscovered particles beyond the currently known Standard Model of Particle Physics?

To address these questions, Fermilab—the premier high-energy particle physics laboratory in the United States—operates some of the world’s most advanced particle accelerators. Fermilab’s 6,800-acre facility is located in Batavia, Illinois, and its particle accelerator chain—with a total length of more than 10 miles—resides in tunnels 25 ft or more below ground.

Fig 1: Fermilab’s accelerator chain lies 25 ft below ground and includes more than 10 miles of tunnels.

Recently, Fermilab has left its history as a collider physics laboratory behind and transitioned into the world’s highest intensity neutrino facility in support of international research into particles called neutrinos. In order to create the lab’s particle beam, a large number of protons must be accelerated to very high energies. The charged protons are guided by powerful magnets on a circular path before striking a graphite target, which generates secondary particles. These particles decay into neutrinos and other short-lived by-products.

When upgraded for the Deep Underground Neutrino Experiment (DUNE), Fermilab’s accelerator complex will deliver 1.2 MW of proton beam power to a graphite target at an energy of 120 GeV, creating the world’s highest-intensity neutrino beam. That beam will travel 800 miles through the earth to a detector filled with liquid argon, located at the Sanford Underground Research Facility in South Dakota.

Fig. 2: The Deep Underground Neutrino Experiment (DUNE) will deliver 1.2 MW of proton beam power to a graphite target 800 miles away.

Magnet alignment

The alignment of the magnets is critical for the optimal operation of the facility. Fermilab uses Radian laser trackers from Auomated Precision Inc. (API) during the installation and routine maintenance to position and inspect the dimensional integrity of the magnets in the tunnel. (See fig. 1, which shows the main injector tunnel.) A maintenance period can last up to three months and requires using laser trackers to facilitate a speedy alignment process. Fermilab requires the laser interferometer technology, as integrated into the laser tracker for precision distance measurements, to comply with the National Institutes of Technology Standard (NIST).

The API Radian trackers are also used to lay the foundation for the alignment of the magnets in the form of a large-scale control network throughout the accelerator tunnel infrastructure. These reference points allow the end user to relocate the tracker anywhere within the tight tunnel enclosure while maintaining a connection to the global control network. The API Radian produces the best results in the range of 0 m to 30 m, corresponding to the visible line of sight in many of the accelerator enclosures.

Fig. 3: A section of accelerator tunnel infrastructure

In addition, the API Radian is one of the most compact and least heavy instruments available. In many cases tunnel enclosures are only accessible through long and steep stairwells, so the equipment has to be hand-carried safely to the work site. Laser trackers are now commonly used at accelerator facilities around the world.

Locating ‘radiation hot spots’ in the vacuum tube

Fermilab already generates the most intense beam of neutrinos in the world, but the upcoming DUNE experiment will require a greater increase in beam power. This necessitates the upgrade of specific sections of the accelerator’s vacuum system. The existing vacuum infrastructure is not able to accommodate the increased beam size, and limits the machine operation. This puts a much higher demand on alignment requirements for the vacuum pipes, which do not have reference markers and can only be determined by feature measurements.

Fermilab recently purchased an API wireless I-Probe and I-Scan II to support the feature measurement process of beam pipes. The I-Probe/I-Scan II combo allows the teams to measure hidden points on the pipe and acquire a pipe cross-section with many data points in a very short time. This reduces the amount of time that alignment crews may be exposed to higher radiation levels in these areas. These accessories allow the users to navigate in tight spaces within the tunnel that they couldn’t access with just the API Radian and an SMR.


The backbone for most of the Fermilab alignment work is based on laser trackers, and Fermilab has been using the API Radian. With the recent acquisition of the I-Probe/I-Scan II, Fermilab enhanced its capabilities in the area of contactless measurements.


About The Author

Automated Precision Inc.’s picture

Automated Precision Inc.

Founded in 1987 by Kam Lau, Automated Precision Inc. (API) is the inventor and original patent holder on the first laser tracker systems. API develops and manufactures laser trackers; portable coordinate measuring machines (CMMs); laser tracker accessories, which include probes, sensors, targets, cameras, SMRs, and scale bars; and machine tool calibration products. API Technical Services include contract measurement equipment rental, onsite laser tracker calibrations, machine tool error mapping, machine tool alignment, and training for 3-D measurement systems and analysis software. With its world headquarters in Rockville, Maryland, API has offices in China, Germany, and India.