Beam-beam instabilities in large Piwinski angle crab-waist collisions · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
Beam-beam instabilities in large Piwinski angle crab-waist collisions
Plain
New colliders cross very flat beams at a large angle with a special focusing scheme, the crab waist, to reach high collision rates. Unexpected instabilities, some involving the beam's interaction with its surroundings, have kept performance below design.
Precise · changed · core
Revision 1: In crab-waist schemes with Piwinski angle $\phi >> 1$, strong-strong simulations predict coherent X-Z instabilities and interplay with longitudinal and transverse impedance. Determine the stability boundary in $(\xi_x,\xi_y,\nu_s,\mathrm{impedance})$ and whether it explains the luminosity shortfall of SuperKEKB relative to its design value of $8e35\ \mathrm{cm}^{-2}\ \mathrm{s}^{-1}$ (later target about $6.5e35$).
Revision 2: In crab-waist schemes with Piwinski angle $\phi >> 1$, strong-strong simulations predict coherent X-Z instabilities and interplay with longitudinal and transverse impedance. Determine the stability boundary in $(\xi_x,\xi_y,\nu_s,\mathrm{impedance})$ and whether it explains the luminosity shortfall of SuperKEKB relative to its design value of $8 \times 10^{35}\ \mathrm{cm}^{-2}\ \mathrm{s}^{-1}$ (later target about $6.5 \times 10^{35}$).
Settled by
Strong-strong simulations including impedance that reproduce measured SuperKEKB blow-up and luminosity, and machine experiments that confirm the predicted cures.
Kind
phenomenon
Answer type
mechanism
References
(empty)
Literature status
open
Status note · changed
Revision 1: SuperKEKB set a world-record peak of about $5.1e34\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}$ in December 2024, roughly 6 to 8 percent of its design and later target values; vertical blow-up, a vertical instability linked to collimator impedance and sudden beam losses are the identified limits.
Revision 2: SuperKEKB set a world-record peak of about $5.1 \times 10^{34}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}$ in December 2024, roughly 6 to 8 percent of its design and later target values; vertical blow-up, a vertical instability linked to collimator impedance and sudden beam losses are the identified limits.
Posed since
(empty)

Decisions