Update on design of final TALs in the CLIC Drive Beam

R. Apsimon, J. Esberg

Optimisation techniques

• Local optimisation– Each cell optimised separately• Easy to tune• Poor energy acceptance

– Sextupoles don’t help a lot

• Global optimisation– Match all sextupoles and quadrupoles• Very good energy acceptance• Very weak sextupoles needed

• 20 sextupoles used– 4 sextupoles per arc cell– Maximum pole-tip field ~0.018 T

Locally optimised solution

Globally optimised solution

Dispersion energy dependence

R56 energy dependence

Emittance growth vs sextupole strength: PLACET tracking

Emittance growth vs sextupole strength: PLACET tracking

Emittance growth vs sextupole strength: PLACET tracking

Emittance growth vs sextupole strength: MADX-PTC tracking

HorizontalVertical

Longitudinal

PLACET tracking: longitudinal phase space: no synchrotron radiation

Emittance growth vs sextupole strength: PLACET tracking

HorizontalVertical

Longitudinal

PTC tracking emittance growth

Horizontal Vertical LongitudinalLocal optimisation 138 μm.Rad 2.2 μm.Rad 1.8 μm.GeV

Global optimisation 3.0 μm.Rad 2.0 μm.Rad -0.0012 μm.GeV

PLACET 0.67 s.f. 3.0 μm.Rad 0.85 μm.Rad 0.0 μm.GeV