the 2mrad horizontal crossing angle ir layout for the ilc
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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)
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
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
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
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