1. 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)

2. Could this be used for the ILC?

3. (cold ILC bunch-spacing  no multi-bunch kink instability)
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 )

4. Possible doublet parameters for 0.5-1 TeV
SC QD (r  35mm)
T/m
warm QF (r ~ 10mm)
T/m
1-1.9m 3m
< 2 mrad
l*=4.1m
~ 6 mrad m
 optical transfer
R22 ~ 2.84 from IP
to QD exit
to beam diagnostics
(consistent with global parameter sets as in TESLA TDR)

5. Tolerable beam power losses in SC QD
LHC NbTi IR quads
• gradient for 0.5 TeV : 215 T/m,
• radius  35mm (effective = 31mm)
• higher gradients are studied for LHC
upgrades using NbTi(Ta), Nb3Sn
Tolerable beam power losses in SC QD
local & integral LHC spec: 0.4 mW/g & 5 W/m
US-cold design parameters assumed at IP
Ne  per bunch x=543(489) nm y=5.7(4) nm z=0.3 mm
Ebeam = 250(500) GeV x=15(24.2) mm y=0.4 mm

6. 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 (A+B)
0.5 TeV doublet  c  1.7mrad
1 TeV doublet  c  1.6mrad

7. 1 TeV doublet for Ne  2 1010 per bunch 0.5 TeV doublet
Beam power losses in QD
without beam size effect
with beam size effect
with beam size effect
Compton tail
Beamstrahlung tail
1 TeV doublet for Ne  per bunch
0.5 TeV doublet
1 TeV doublet for Ne  1010 per bunch
0.5 TeV using 1 TeV doublet

8. Beamstrahlung extraction
Simultaneous charged beam
and beamstrahlung extraction
feasible at 0.5 TeV (2mrad)
Harder at 1 TeV - c=1.6mrad
seems favoured
(benefit from SCQ grad. R+D)
incoming, outgoing
and beamstrahlung
close together at QF
 plan common
beampipe, with
separation later

9. Clearance at QF for synchrotron radiation emitted in QD & QF
x,y = core (1-) photons at QF
(estimated from CS paras.)
(x - c zQF)2  x2 + y2  y2 = 1
 need to collimate to nx,yx,y
nx,y=5.9, 49
• can increase c
• specially shape QF magnet poles
• use smaller beam pipe radius
If the photon rate reflected off QF and
transmitted back to the VD results in
too tight collimation requirements
(recent work by T. Murayama  OK) IP z

10. Luminosity loss without crab crossing
L/L0
~ 0.85
geometric formula  0.88
c[mrad]

11. 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= (hardest case!)
Extraction line geometry fixed: R22c=4.544mrad

12. 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 quadrupole
and 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 ( )

13. Initial achromat to cancel dispersion II
QFX becomes weaker doublet; reduce over focussing
Achromat completed by 14m drift and 2.5mrad bend
Inherent flexibility - optimise strengths, lengths and apertures r
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

14. Linear dispersion for the 1 TeV lattice
 point-focus and chicane
"bend back"
achromat

15. -functions for the 1 TeV lattice
 point-focus and chicane
achromat
"bend back"

16. 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