Instabilities that appear minutes after a beam is predicted stable
In plain words
In the LHC, beams calculated to be stabilized by octupole magnets sometimes become unstable after minutes, suggesting slow erosion of the stabilizing frequency spread.
Precise statement
LHC transverse instabilities appeared with latencies of minutes at octupole strengths predicted stabilizing by linear Landau-damping theory. Determine whether diffusion driven by transverse-feedback and external noise, which flattens the tails of the particle distribution and shrinks the stability diagram, accounts quantitatively for measured latencies and octupole thresholds.
What would settle it
Controlled noise-injection experiments in which measured latency versus noise level matches a diffusion model with no fitted parameters.
Status in the literature
Noise-driven erosion of Landau damping was proposed and supported by simulations and dedicated LHC experiments around 2019-2021; predictive accuracy for operation is limited.