Physicists Isolate a Resonant “Ghost” Inside CERN’s Super Proton Synchrotron

Physicists Isolate a Resonant “Ghost” Inside CERN’s Super Proton Synchrotron

Researchers at CERN and Goethe University Frankfurt report in Nature Physics that they have identified a resonant “ghost” — a subtle, recurring dynamical feature — influencing particle motion inside the Super Proton Synchrotron (SPS).

What the Ghost Is

The anomaly behaves like a three-dimensional structure that evolves over time, so the team models it as a four-dimensional phenomenon to capture its temporal changes. The effect arises from resonance: interacting oscillations that locally amplify motion. Analogies include sloshing coffee spilling when waves meet or one jumper boosting another on a trampoline.

Why the SPS Matters

The SPS is a key CERN machine built in the 1970s; it remains central to many experiments and tests and measures about four miles in circumference. In 2019 the facility received an upgraded beam dump — a safety system comparable to a runaway-truck ramp for high-powered beams — and the discovery of this resonant feature prompted scientists to map and model it so future operations and upgrades can mitigate its impact.

How Small Imperfections Grow

Resonances matter because they amplify small imperfections. Magnets that steer and focus the beam are never perfectly uniform; tiny field fluctuations create harmonic components that interact. In the SPS those interactions can cause beam degradation: particles (and associated photons) are scattered or lost, reducing beam quality and experimental sensitivity.

Degrees Of Freedom And Particle Motion

Although particles in the SPS primarily move along a defined path, they also execute small transverse oscillations within the thickness of the beam pipe. These “bounces” are perturbed by the facility’s imperfect hardware and by the interplay of multiple harmonic components, producing complex dynamical patterns that repeat around the closed ring.

Measurements And Mathematical Modeling

To quantify the effect, the researchers collected detailed measurements around the ring and constructed a Poincaré section: a mathematical map built by fixing one element of the system and recording the intersections of the remaining variables step by step. The resulting surface represents the system’s dynamics; because the SPS is a closed, repeating system, that 4D surface loops in time much like a repeating animation.

“Fixed lines” in the Poincaré analysis correspond to loci where particles tend to cluster and where resonant amplification occurs. The team showed these structures can predict where losses are likely to appear.

Practical Consequences

With this predictive power, accelerator physicists can design damping strategies to reduce losses in existing machines and avoid creating similar magnet “ghosts” when building new accelerators. Reducing resonant-driven degradation preserves beam quality, improves experimental sensitivity, and can save time and resources in upgrades and future facilities.

Broader Relevance

Harmonic interference and resonance are not unique to particle accelerators. Similar phenomena complicate magnetic-confinement fusion experiments in tokamaks, where standing waves and resonant dead zones can rob a system of heat and energy needed for productive fusion. The methods used here — combining careful measurement with dynamical-systems mathematics — can inform other precision experiments that must manage subtle resonant effects.

In short: by measuring and modeling a 3D resonant structure that evolves in time, scientists have made a practical step toward predicting and damping a previously elusive source of beam degradation inside one of the world’s most important accelerators.