Overview of CLIC BDS

Frank Zimmermann, CLIC BDS Day, 22.11.2005

Overview of CLIC BDS

Frank ZimmermannCLIC BDS Day 22.11.2005


BDS tasks• focus beams to nm spot size• stably collide two beams• deliver target luminosity• dispose spent beam• ensure adequate background conditions• protect the machine against self-destruction• preserve polarization• control spin orientation• function at different beam energies• handle multiple bunches and nominal intensity• …


schematic view of beam delivery system


modular layout

energy collimationbetatron collimation

compact final focus

interactionregion exit line

IP switch?

dump


Raimondi FF ~0.5 kmCCS length ~2.0 km

nonzero D’at IP

only 1 stagemomentumcoll.

betatron coll.with low x,y

final focus.

optics

F.Z., CLIC-NOTE-551


c.o.m. energy 3 TeV

final-focus length 0.5 km

collimation length 2.0 km

hor.,vert. emittance x,y 0.68, 0.01 m

hor.,vert. beta function x,y* 7, 0.09 mm

core spot sizes x,y* 60, 0.7 nm

linear spot sizes 37, 0.5 nm

bunch length z 30.8 m

crossing angle c 20 mrad

bunch population Nb 2.56x109

# bunches / train nb 220

luminosity w/o pinch L0 3.6x1034 cm-2s-1

ideal luminosity w/o pinch L00 9.3x1034 cm-2s-1

beam delivery system & beam parameters

61%luminosityloss


horizontalphase-spacedistributionat the IPcalculatedwithMerlinfor a nominalbunch

particles arefound evenat amplitudes>1 m, while the beam sizeis about 40 nm

S. Redaelli et al, CLIC Note 577 (Nanobeam’02)

Merlin, x>3x: 6.7%, x>6x: 2.3%, y>3 y: 15.2%, y>6y: 7.7%, large tail population

IP distribution

→ for recent studies see talks by T. Asaka & J. Resta Lopez


x rms Gaussian fit

MAD 96.3+/-0.7 nm 55.39+/-0.07 nm

DIMAD 99.0+/-1.4 nm 54.59+/-0.17 nm

Merlin 129.7+/-1.5 nm 57.49+/0.13 nm

PLACET 99.3 +/1.3 nm 54.12+/0.17 nm

y rms Gaussian fit

MAD 3.05+/-0.04 nm 0.680+/-0.001 nm

DIMAD 3.35+/-0.06 nm 0.800+/-0.002 nm

Merlin 4.04+/-0.03 nm 0.688+/-0.002 nm

PLACET 3.42+/-0.03 nm 0.775+/-0.002 nm

what is x,y? S. Redaelli et al, CLIC Note 577 (Nanobeam’02)

linear ideal beam sizes:x=37.3 nm, y=0.49 nm Gaussian fit ‘loses’ particles


CLIC BDS “footprints” at 3 TeV and 500 GeV

F.Z., CLIC-NOTE-551


compact FF à la Raimondi & Seryi

advantages:larger free length l* from last quad to IP,wider momentum bandwidth,reduced beam tails

drawbacks:tighter collimation in x,sextupoles near final doublet (tuning knobs)


simulated luminosity w/o pinch & w/o hourglass as a function of full-widthenergy spread with & w/o synchrotron radiation for two different values ofx,y* and assuming y=10 nm; L0=4.6x1034 cm-2 s-1

luminosity losses:

SR in bends→L~-50%

momentum spread→L~-30%

SR in finalquad’s→L~-10%

luminosity performance

F.Z., CLIC-NOTE-551


system Length [m] Luminosity w/o pinch [1034 cm-2 s-1]

total BDS 2557 3.56

original long BDS 6186 3.92

final focus only 548 4.85

geometric luminosity without hourglass and without pinch (input distribution from PLACET for old linac pararameters, and taking x=6 mm, y=70 mm)

numbers refer to new beam parameters: 2.56e9, 150 Hz, 22 bunches/ train

28% luminosityloss fromcollimation system

CLIC-NOTE-551


O. NapolyCLIC Note 414, 1999

y~1 nm limitfor y~20 nm

dependence on as y~5/7

x ~30 nm limit

spot-size limit from SR in final quadrupoles (Oide effect)


top view of

CLIC IR

R. Assmann

crab cavity

crab cavity

CLIC-NOTE-551


final quadrupole study by M. Aleksa & S. Russenschuckindicated preference for permanent magnet

CLIC-NOTE-506

stability of magnetic center? asymmetric T=1 K (9 kJ/m)→ y=286 nm


or should we reconsider s.c.quadrupole?


synchrotron radiation in solenoid (fringe) field together with vertical dispersion due to crossing angle & solenoid causes vertical beam blow → crossing angle limited to 20 mrad

D. Schulte, F. Zimmermann, CLIC-NOTE-484


spent beam & exit line

at 3 TeV wide energy spread

conceptuallayout of quadrupole-lessexit line

F.Z., CLIC-NOTE-551

D. Schulte,CLIC-NOTE-391

water dump at 4oCB. Jeanneret & E. Wildner, CLIC-NOTE-421


polarizationspin rotation angle a~ 3404 times bend angle

polarizationvectormust bematched into theBDSto ensurelongitudinalpolarizationat the IP

R. Assmann, F. Zimmermann,CLIC-NOTE-501


collimation requirements:

• remove beam halo to suppress detector background arising from synchrotron radiation and beam loss

• provide minimum distance from collimators to collision point for muon suppression

• ensure collimator survival and machine protection against errand beam pulses

• not be excessively long

• not amplify incoming trajectory fluctuations via collimator wake fields


SR fans with beam envelopes at 14 x & 83y

O. Napoly

CLIC-NOTE-446


collimator survival? surface of 20-m gold-plated Ti-alloycollimator at the endof SLC linac after damage; CLIC beam is ~104 times more intense!


LC collimation concept: thin spoilers followedby thick absorbers [H. DeStaebler & D. Walz];spoiler increases angular divergence, reducesrisk of fracture and/or melting


nominal beam sizes at CLICspoilerssuperposedon ‘FJP’ damagethresholddiagram

‘FJP’ = S. Fartoukh, B. Jeanneret & J. Pancin CLIC-NOTE-477


CLIC failure modes & machine protection

• large betatron oscillations are not easily generatedfrom pulse to pulse; and in the linac they rapidly filament& emittance increases by ~2 orders of magnitude

• energy errors will occur much more frequently, e.g., due to missing or mis-phased drive beams, injection phase errors, or charge fluctuation

CLIC philosophy: demand passive survival for momentum errors; but allow sacrificial betatron collimators

failure mode study by Daniel Schulte & F.Z. at PAC2001

(shorter length)


simulated effective beam size r=(x y)1/2 at 1st spoiler; error bar indicates minimum and maximum over 10 random seeds

CLIC-NOTE-492

various failure modes


simulated centroidbetatron oscillationamplitudes at the first spoiler, norma-lized to unperturbedrms beam sizes; error bars showmin. and max. over10 random seeds

these pulses would destroythe betatron collimatorsthese pulses might destroy

the betatron collimators

tighten momentum collimation depth to intercept all dangerous pulses by the momentum spoiler!

various failure modes

CLIC-NOTE-492


momentum collimation depth: failure modes & machine protection from linac failure modes: about +/- 1.5%

transverse collimation depth: from synchrotron radiation & beam loss in final quadrupoles on incoming side onlyx from SR fan in final doublet: about +/- 10 x

y from SR fan in final doublet: about +/- 80 y


cm energy 3 TeV 500 GeV

spoiler gap +/- 4 mm (1.5%) +/- 4.8 mm (1.5%)

x spoiler gap +/- 80 m (10 x) +/- 300 m (9 x)

y spoiler gap +/- 104 m (80 y) +/- 215 m (69 y)

spoiler material Be Be

spoiler length 177 mm (0.5 r.l.) 177 mm (0.5 r.l.)

absorber material

Ti (Cu coated) Ti (Cu coated)

absorber length 712 mm (20 r.l.) 712 mm (20 r.l.)

no. of spoilers 1 1

no.x,y spoilers 4, 4 4, 4

collimator parameters

scattered beam size on -absorber: r ~1.1 mm!?should r>r.l.?


unmagnetized cyl.radius 20 cmunmagnetized cyl.& only 1st photon

magnetized cyl.

unmagnetized cyl.radius 50 cm

Geant-4simulationfor 10000 e- lost on first spoiler(H. Burkhardt)

size of magnetsmatters!

(H. Burkhardt, Nanobeam 2002)

muon background

Frank Zimmermann, CLIC BDS Day, 22.11.2005nominal

max. jitter enhancement from collimator wake

carbon spoilerseems not acceptable;Be spoilerpossible;absorbers fromCu-coatedTi & pureCu both ok

4 spoilers & 4 absorbers(Redaelli)CLIC-NOTE-579


alternative nonlinear collimation system

basic scheme

→ talks by A. Faus-Golfe & J. Resta Lopez

better optical performancereduced wake fieldsshorter?


energy distribution alongold CLIC BDS from 1000laser-wire Compton scatters

total energy loss per bunchtrain along the CLIC BDSdue to 0.1% flat halo

backgrounds completely swamp laser-wire signal!G.A. Blair, BDSIM simulation, Nanobeam2002

laser wire as beam-size monitor?


margins & overheads?

S. Redaelli’s simulations indicate 25-30% luminosity loss due to fast ground motion

1996 NLC ZDR estimated 20% luminosity loss due to limited beam-based tuning precision for 16 important IP aberrations (Irwin et al)

we could expect a total luminosity loss >50% due to these effects


simulate luminosity performance with errors, ground motion, component jitter, feedback, and realistic tuning, and noisy diagnostics integrated simulation, including realistic beam distribution from linac with its own errors and tails improve performance of present system, especially collimation (→shorter, wider bandwidth, higher luminosity), characterize collimation efficiency fully master design of compact final focus Be spoilers acceptable? beam size at absorber? wake field effects, electron cloud, etc.

open questions & outstanding tasks


thank you for your attention!

Overview of CLIC BDS

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