Scientists at Fermi National Accelerator Laboratory successfully circulated proton beams for the first time in the lab’s FAST/IOTA test accelerator on March 9, 2026, completing a years-long effort to bring the compact storage ring into its full operating mode. The achievement gives U.S. physicists a dedicated proving ground for the beam-control techniques that will be needed to build the next generation of particle colliders, at a moment when American accelerator infrastructure is in transition.
Protons Now Circling a 40-Meter Ring
The milestone took place inside the Integrable Optics Test Accelerator, or IOTA, a roughly 40-meter-circumference ring housed within Fermilab’s FAST facility near Batavia, Illinois. According to a recent lab announcement, protons are now circulating the ring after being accelerated and stored for the first time. The ring is not designed to smash particles together and hunt for new physics directly. Instead, it exists to study the behavior of the beams themselves, amplifying subtle effects over many laps so researchers can test ideas that would be too risky or too slow to try on a full-scale machine.
IOTA first circulated electrons back in 2018, when the facility recorded its initial electron beam and began commissioning its research program. The ring was built from the start to switch between electron and proton modes, but adding protons required an entirely new injection system. That hardware, the IOTA Proton Injector, feeds 2.5 MeV protons into the ring through a chain of components: an ion source, a low-energy beam transport line (LEBT), a radio-frequency quadrupole (RFQ), and a medium-energy beam transport line (MEBT), as outlined on the injector project page. A 2023 conference paper on the beamline installation reports that the injector is designed to deliver pulses of roughly 20 mA at that energy, providing the intensity needed to explore collective effects in detail.
Bringing all of that hardware into coordinated operation required years of design, installation, and commissioning. Engineers had to thread the proton beam through tight apertures, match its optical parameters to the ring lattice, and synchronize timing systems so that injected bunches landed cleanly in IOTA’s RF buckets. The successful circulation of protons confirms that those systems are now working together and that the ring can store low-energy proton beams long enough for precision experiments.
Why Proton Beams Demand Different Tools
Electrons are relatively easy to steer. They are light, and when bent by magnets they shed energy as synchrotron radiation, which naturally damps unwanted oscillations. Protons, roughly 1,800 times heavier, do not cooperate as neatly. At low energies, the positive charges in a proton bunch repel one another through a phenomenon called space charge, distorting the beam and threatening to scatter particles into the walls of the accelerator pipe. Controlling those effects is one of the central engineering puzzles for any high-intensity proton machine.
IOTA’s research program targets exactly this problem. The facility is intended for studies in nonlinear beam dynamics, electron lens research, electron cooling, and other novel accelerator technologies. Each of these areas addresses a different piece of the beam-control puzzle. Nonlinear integrable optics, for example, aims to spread out the natural frequencies of particles in a beam so that destructive resonances cannot build up. Electron lenses use a low-energy electron beam threaded through the proton beam to compensate for space-charge forces. Electron cooling slows the random motion of protons by letting them transfer energy to a co-traveling electron stream. Testing all three in one compact ring, with the same diagnostics and the same lattice, is something no other facility in the United States currently offers.
With protons now circulating, the FAST/IOTA complex can begin the program of measurements that Fermilab officials have described as crucial for “transformative advances” in accelerator science. In a detailed overview of the test facility, the lab emphasizes that the ring is meant to bridge the gap between theory, simulation, and the realities of operating high-intensity machines. By deliberately pushing beams into regimes where space charge and nonlinearities dominate, researchers hope to map out the safe operating envelope for future accelerators and to discover techniques that can expand it.
Connecting IOTA to PIP-II and Future Colliders
The practical payoff of this work is tied to Fermilab’s largest ongoing construction project, the Proton Improvement Plan II, or PIP-II. The U.S. Department of Energy approved full construction of PIP-II in April 2022, clearing the way for a major upgrade of the lab’s proton complex. According to a DOE environmental assessment, the project centers on an 800 MeV superconducting linear accelerator, upgradable to 1 GeV, along with modifications to existing rings and transfer lines.
PIP-II is expected to provide the world’s most intense neutrino beam for the Deep Underground Neutrino Experiment, or DUNE, sending particles from Illinois to a detector located a mile underground in South Dakota. Delivering that beam will require unprecedented control over losses and halo formation in the upgraded accelerator chain. A 2024 Fermilab technical paper on PIP-II’s final physics design highlights the need to manage collective effects, resonances, and space-charge nonlinearities to maintain beam quality from the linac through the downstream rings.
IOTA offers a place to validate mitigation strategies before they are baked into hardware that costs hundreds of millions of dollars. Techniques such as integrable optics lattices or space-charge compensation with electron lenses can be tried in a flexible environment, with instrumentation tuned for detailed beam studies. The ability to run both electrons and protons in the same ring also opens the door to hybrid testing sequences, where researchers benchmark a technique with easy-to-handle electrons and then immediately stress-test it with protons under realistic conditions.
Fermilab leaders have framed the FAST/IOTA complex as part of a broader plan to sustain U.S. expertise in accelerator technology. In the lab’s description of the facility’s role in future high-power machines, officials note that insights from IOTA experiments are expected to feed directly into plans for increasing beam power in the lab’s existing accelerators and for designing any next-generation colliders or long-baseline neutrino facilities.
A Shifting U.S. Accelerator Map
IOTA’s proton milestone arrives as the American accelerator portfolio is contracting in some areas and expanding in others. While some long-running facilities are winding down, Fermilab is in the midst of building out a new flagship program centered on intense proton beams and precision detectors. Recent lab updates have pointed to progress on multiple fronts, including the move of the final subdetector for the Mu2e experiment and construction advances for DUNE, as described in a feature on current projects.
Within that landscape, FAST/IOTA plays a different but complementary role. Rather than chasing a single physics discovery, it functions as a technology incubator. Experiments in the ring are designed to answer cross-cutting questions that affect many machines: how to push beam intensities higher without unacceptable losses, how to design lattices that remain stable under large tune spreads, and how to integrate advanced diagnostics and feedback systems into complex accelerator chains.
The ability to circulate protons in IOTA also strengthens the case for U.S. participation in future international collider projects. As global plans for next-generation machines evolve, from high-energy proton colliders to advanced lepton factories, the techniques being tested at FAST/IOTA, particularly those aimed at taming intense proton beams, are likely to be in demand. Demonstrating those methods in a working ring gives U.S. researchers concrete results to bring to the table in design studies and collaboration talks.
Next Steps for the FAST/IOTA Program
With first proton circulation achieved, the immediate priority for the FAST/IOTA team will be to characterize the new beam in detail. That means measuring lifetimes, emittances, tune spreads, and loss patterns, and comparing them with simulation. Early runs are expected to focus on establishing stable operating points and verifying that the ring’s nonlinear elements behave as designed when space-charge forces are significant.
As the program matures, researchers plan to switch on more advanced configurations: inserting integrable optics elements, commissioning electron lenses, and eventually exploring electron cooling schemes tailored to low-energy protons. Each step will be accompanied by systematic scans of beam parameters to map out where instabilities arise and how they can be suppressed.
The March 2026 milestone does not mark the end of the IOTA story so much as the beginning of a new chapter. By adding protons to a ring that has already delivered results with electrons, Fermilab has turned FAST/IOTA into a uniquely versatile platform for accelerator R&D. In the years ahead, the data collected there are expected to inform upgrades to PIP-II, guide the operation of high-intensity beams for DUNE and Mu2e, and help shape the design of whatever ambitious machines come next in the global particle physics program.
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*This article was researched with the help of AI, with human editors creating the final content.
