Revision 1

Accepted · first revision · record

Title: Instabilities that appear minutes after a beam is predicted stable
Plain: 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: 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.
Settled by: Controlled noise-injection experiments in which measured latency versus noise level matches a diffusion model with no fitted parameters.
Kind: well-posed
Answer type: mechanism
References: (empty)
Literature status: partially-resolved
Status note: 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.
Posed since: (empty)