The 2mrad horizontal crossing angle IR layout for the ILC

The 2mrad horizontal crossing angle IR layout for the ILC

Rob Appleby

Daresbury Laboratory

MDI workshop at SLAC - 07/01/05

D. Angal-Kalinin (DL),

P. Bambade, B. Mouton (Orsay),

O. Napoly, J. Payet (Saclay)

Could this be used for the ILC?

Rationale(cold ILC bunch-spacing no multi-bunch kink instability)

• only ~15% luminosity loss without crab-crossing (2 mrad) • correction possible without cavities exploiting the natural ’ in the local chromatic correction scheme used

• no miniature SC final doublet needed• no strong electrostatic separators needed, and no septum• both beams only in last QD more freedom in optics

• negligible effects on physics• spent beam diagnostics may be easier compared to head-on

(see CARE/ELAN Document 2004-20)

Possible doublet parameters for 0.5-1 TeV

(consistent with global parameter sets as in TESLA TDR)

l*=4.1m

1.3-2.3m

3m

optical transfer

SC QD (r 35mm)214-228 T/m

warm QF (r ~ 10mm)140-153 T/m

< 2 mrad

R22 ~ 2.84 from IP to QD exit

~ 6 mrad

1-1.9m

to beam diagnostics

LHC NbTi IR quads

Tolerable beam power losses in SC QD

• gradient for 0.5 TeV : 215 T/m, • radius 35mm (effective = 31mm)• higher gradients are studied for LHC upgrades using NbTi(Ta), Nb3Sn

US-cold design parameters assumed at IPlocal & integral LHC spec: 0.4 mW/g & 5 W/m

Ne 2 1010 per bunch x=543(489) nm y=5.7(4) nm z=0.3 mmEbeam = 250(500) GeV x=15(24.2) mm y=0.4 mm

Beamstrahlung clearance at QF

Calculated need of 0.5mrad around beam direction at IP in realistic beam conditions & beam pipe with r = 10mm in QF

Horizontal cone half-opening angle Vertical cone half-opening angle

CARE/ELAN document 2004-21 (A+B)

0.5 TeV doublet c 1.7mrad 1 TeV doublet c 1.6mrad

Beam power losses in QD

0.5 TeV doublet

0.5 TeV using 1 TeV doublet1 TeV doublet for Ne 1010 per bunch

1 TeV doublet for Ne 2 1010 per bunch

without beam size effect

with beam size effectwith beam size effect

Compton tail

Beamstrahlung tail

Beamstrahlung extraction

incoming, outgoing and beamstrahlungclose together at QF

plan common beampipe, with separation later

Simultaneous charged beam and beamstrahlung extractionfeasible at 0.5 TeV (2mrad)

Harder at 1 TeV - c=1.6mradseems favoured(benefit from SCQ grad. R+D)

Clearance at QF for synchrotron radiation emitted in QD & QF

(x - c zQF)2 x2 + y2 y

2 = 1 x,y = core (1-) photons at QF (estimated from CS paras.)

need to collimate to nx,yx,y

nx,y=5.9, 49

If the photon rate reflected off QF and transmitted back to the VD results intoo tight collimation requirements(recent work by T. Murayama OK)

• can increase c

• specially shape QF magnet poles• use smaller beam pipe radius

zIP

Luminosity loss without crab crossing

L/L0

c[mrad]geometric formula 0.88

~ 0.85

Extraction line for disrupted beam

Transport spent beam with controlled losses, both under disrupted and undisrupted conditions.

Constant geometry up to 1 TeV use 1 TeV doublet design Diagnostics on disrupted beam

Compton polarimeter (need chicane and zero net bend) Energy measurement (energy chicane) WISRD-style spectrometer image beam

Choose 10W in QD, requiring c=1.6mrad

Study for 1 TeV machine and Ne=2 1010 (hardest case!)

Extraction line geometry fixed: R22c=4.544mrad

Initial achromat to cancel dispersion

Off-axis beam in QD produces horizontally dispersed beam Initial extraction line achromat designed to cancel this Horizontally focussing quad QFX produces phase advance

QFX very close to incoming beamline (50mm) use current-sheet quadrupoleand 8m drift QD->QFX

BPT=1.3T (g=26 T/m) aperture radius 5cm l=5.8m (1 TeV) Designed and costed for

TESLA TDR (2001-21)

Initial achromat to cancel dispersion II

Power loss for aperture r=5cm, scaling r For 1 TeV, lose 3.1kW for =1, 350W for =1.5 and 69kW

for =0.5 Ne=1 1010, lose 10W; 500 GeV 80W (=1) Use Tungsten collimator need to check VXD backsplash

QFX becomes weaker doublet; reduce over focussing

Achromat completed by 14m drift and 2.5mrad bend Inherent flexibility - optimise strengths, lengths and

apertures

r

QFX

Linear dispersion for the 1 TeV lattice

point-focus and chicane

achromat

"bend back"

-functions for the 1 TeV lattice

point-focus and chicane

"bend back"achromat

Some on-going studies

• Increase BeamCAL aperture to 2cm to relax collimation? K. Büsser: rate in VXD increases - origin from inside of BeamCal or QD. Reduce by High Z material on BeamCAL and (early) QD surface? • Further study of post-IP beam transport beyond QFX to limit beam losses to acceptable levels and allow post-IP beam instrumentation. Possible reduction using chromatic correction scheme; inclusion of the detailed B field map in the half-quadrupole QFX

• Feasibility of collimator for kW power loss for the case of TeV machine - backgrounds in the detector?

• Beam dumps? incoming beam to -dump separation 0.62m, -dump to disrupted beam separation 0.54m