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Title: Release mechanism of dust grains causing fast LHC beam losses
Plain: Micron-sized dust grains fall from the LHC vacuum chamber walls into the beam and cause sudden losses that can quench magnets; what makes them detach is unclear.
Precise: Fast loss events in the LHC (called UFOs, unidentified falling objects) last of order 1e-3 s and are modeled as micron-scale dust grains entering the proton beam, being ionized and repelled; this dust-beam dynamics was analyzed in 2020. Determine the release mechanism (electrostatic detachment driven by beam-induced charging or electron cloud, mechanical vibration, magnetic forces on ferromagnetic grains) and predict the event rate versus beam intensity, bunch spacing and cumulative beam time.
Settled by: Laboratory release tests on beam-screen surfaces under electron bombardment and electric field that reproduce the measured dependence of the event rate on intensity and conditioning time.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: partially-resolved
Status note: Dust-beam interaction dynamics were modeled and matched to loss signals in 2020 (Lindstrom et al., https://doi.org/10.1103/PhysRevAccelBeams.23.124501); the release step is not established.
Posed since: 2010