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BJ material for Roberto at ACE, 20 sep 08

BJ material for Roberto at ACE, 20 sep 08. Worked-out set : DB long Transfer Line, see below Combiner rings : My set of slides ‘CR1_status.ppt’ at last beam_dyn meeting Aim was to fix the momentum band from 2% down to 1% This was felt premature to discussit ACE

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BJ material for Roberto at ACE, 20 sep 08

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  1. BJ material for Roberto at ACE, 20 sep 08 • Worked-out set : DB long Transfer Line, see below • Combiner rings : • My set of slides ‘CR1_status.ppt’ at last beam_dyn meeting • Aim was to fix the momentum band from 2% down to 1% • This was felt premature to discussit ACE • No ‘positive results’ yet , see the slides • Roberto may decide to just say that I am at work on this from now on. • Turn-Around : • Missing in the ACE agenda • I proposed that Frank could provide Roberto with a few slides (from his forthcomimg EuroTeV talk)

  2. DB long transfer line : simple optics but 21 km long • Optics • Parasitic dispersion + |dp|=2% => emittance dilution • Logistics • Beam line suspended to the ceiling • Light & transversely thin magnets preferred • Cost & power • Weak magnets preferred • Collective effects • Trains : 100 A , 73 m long • Strong transverse multi-bunch resistive wake-fields • Ions => detuning & instabilities Deserves global optimisation

  3. Optics & logistics : Optimisation • Use thin FODO formalism • All functions can be expressed as a.u. a.u. See: CLIC Note 760 BJ+HB Paras. dispersion Paras. kicks Phase advance: 45o looks good (also better for correction schemes) Number of cells µ µ a.u. Power Max beta and cell length : As large as possible µ a : vacuum chamber aperture

  4. Parasitic dispersion andChromatic phase error • With a rms relative offset beam/quadrupole dx = 0.1 mm • With p = 2%, n=10-4 mrad, max=195 m => Dpar p / beta = 1.8 • Still not adequate, need either • BPM resolution dx < 0.03 mm • Or Beam-based alignment • Chromaticity : with Lcell=100m, Cline = -28 •  = -200o at p = 2% • Normalised injection will add quadratically to emmitance • Either • Work-out a precise injection scheme (reliable to < 0.1 beta) • Or implement a chromatic correction (worked-out but complicates the line)

  5. Transverse multi-bunch resistive wake-fields • A bunch displaced by (s) at s leaves a dipole field which decay slowly with 1/t-1/2 or 1/z-1/2 • With double-summing over n-bunches and segments l where  ~const : • Large effect & no feed-back possible on a straight beam line • Small chambers and stainless steel ruled-out • Use copper, large radius • Drive Beam : a = 100 mm • Main Beam : a = 60 mm See CLIC Note 761, BJ et al.

  6. Results for Wperp • With Cu chamber, radius a=100 mm • Norm. emittance growth ~ 5% with misalignments • Injection errors amplified by 10%

  7. Ion effects See CLIC Note 761, BJ et al. TOR+DS, unpublished Clic note,1999. • Electrons will ionize the residual gas • Positive ions will be trapped in the train (but not between trains) • They induce detuning • And beam-ion instabilities A~0.1 : frequency factor Qi=1 : ion charge OK with the quoted pressure => Need getter+bake-out Factor 3 for uncertainty of the model

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