Past exam of the short options paper shared by Prelims and Parts A and B of the physics course of the University of Oxford / 2017 / S19 / 2 / c

Equilibrium emittance obeys ${ϵ}_x=C_q{\gamma }^2{I}_5/(J_x{I}_2)$, with $I_5=\oint H(s)|\rho {|}^{-3}ds$, $H={\gamma }_x{\eta }^2+2{\alpha }_x\eta {\eta }^{\prime }+{\beta }_x{\eta }^{\prime 2}$. Thus reduce both bend angles and the dispersion invariant inside bends, rather than merely focusing to a small beam size elsewhere. The damping partition can also be adjusted within stability constraints.

A DBA uses two bends and quadrupoles to return dispersion and its slope to zero at the cell boundaries; this provides dispersion-free insertion straights, at some emittance cost. A multi-bend achromat distributes the total angle over more weak bends and carefully controls the interior dispersion. A non-achromatic theoretical-minimum-emittance cell permits nonzero boundary dispersion and chooses the beta function and dispersion near a bend's optimum; longitudinal-gradient or reverse bends offer further control of radiation integrals. Strong focusing and dispersion suppression can increase natural chromaticity and sextupole demands, compromising dynamic aperture and momentum acceptance.