SuperB ARC Lattice Studies P. Raimondi LNF December,2009

Lattice for tau-charm run Simply scaling the ring energy makes - Emittance very small - Damping time very long Aiming to something around 10^35: Damping time about 2 times nominal Emittance about 2 times nominal IP Y-Beta about 2 times nominal Bunch charge about 2 times smaller

Two possibility checked so far: a) Add short bends (about 15cm long) at the edges of the existing ones Ramping down the rings we turn down the main dipoles and up the short ones. The length of the dipoles matches the requirements for damping and emittance Advantage: Optic unchanged, no need for wigglers About 10% smaller emittance at nominal energy About 10% less synchrotron radiation at nominal energy Disadvantages: - Very short dipoles are ok? - Horizontal Orbit change in the dipoles is about 37mm

b) Add wigglers in the ARCs (6) and in the Straights (2) About 8 wigglers 2m long with 1.2T peak field Advantage: Flexibility in changing the emittances trading ARCs vs Straights wigglers Possible to use the Dafne (and PEP) ones Disadvantages: - Some rematchiong needed - Synchrotron radiation absorbtion needs engineering work

Decreasing the emittance for the nominal lattice HER emittance is about 2nm To decrease it there are several possibilities 1) Add wigglers => Wall plug power direct increase 2) Add cells => Wall plug power decreases Momentum compaction decreases Beam more unstable longitudinally RF system harder to match (Lower RF voltage) Collective effects worst

3) Change the partition number Jx>1 Jz<2 Momentum compaction unchanged Horizontal damping decreases Energy spread and natural bunch length increase Beam more stable longitudinally RF system simpler to match (Higher RF voltage) Collective effects better

Partition number could be changed by: a) Offset the QDs Less SR (about 5%) Loss in flexibility (hard to change Jx and QDs gradients) b) Adding Robinson Wigglers (Pavel suggestion) (RW) (8 * 1.5m long) 2% more SR for Jx=2 Possible to change Jx from 1 to 2 anytime Horizontal emittance can be varied from 2nm to 1nm (Luminosity with LPA&CW goes with 1/emi_x) Very small readjustment of the quads in the cells with RWs

ARCs optimization Present cells do provide very large transverse acceptance but somewhat smaller energy acceptance w.r.t. lattice with alternating mux phase advance cells 0.5-0.75 Transverse is better because all sexts are at –I in both planes Energy is worst because the missing sextupoles (the ones not at –I) do generate second order dispersion (about 5-10m) that leads to a negative quadratic tunes dependence vs energy. With some adiabatic reoptimization of the cells (betas and drift spaces), this dependence has been reduced to: dmux=-0.03, dmuy=-0.025 for dE/E=+/-1%

ARCs optimization Octupoles do not help, they cure the quadratic term but decrease the transverse acceptance since the do not cancel like the Sextupoles do. Adding the missing sextupoles has the same problem By playing with Sextupoles families the quadratic term could be further reduced (hopefully down to 0.02 in x). Work in progress, ideas and suggestions welcome

X dE/E = 0 Y dE/E = 0 Mux=0.575 10 sigmas full coupled rings X dE/E = -1.3% Y dE/E = -1.3%

Conclusions - Tau/Charm looked at and seems “easy” - Flexibility for emi_x seems straightforward - Better longitudinal dynamic - Adiabatic and Quasi-Adiabatic optimization done - All knobs not yet exausted