Tune and Tune Plane
We define the “tune” Q (or n) as the number of complete betatron oscillations around the ring.
For example, the horizontal tune of the Booster is about:
6.7
Magnet Count/Aperture optimization
Beam Stability
In general…
“small” integers
fract. part of X tune
fract. part of Y tune
Many deviations from the ideal lattice are characterized in terms of their resulting “tune-shift”.  In general, the beam will become unstable if it shifts onto a resonance.