1. SuperB ARC Lattice Studies
P. Raimondi
LNF December,2009

2. 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

3. 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

5. 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

7. 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

8. 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

9. 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

11. 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
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= for dE/E=+/-1%

12. 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

15. 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%

16. 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