collimation depth calculations for ilc bds
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Collimation Depth Calculations for ILC BDS
Frank Jackson
Latest Versions ILC-BDS
• ‘FF9’ deck available at SLAC– http://www.slac.stanford.edu/~mdw/ILC/Beam_Delivery/20050316/
• 20 mrad and 2 mrad x-ing angle schemes
• Include energy spectrometers
• Bandwidth has been optimised
• Different designs for 2 mrad extraction– SLAC-EU collaboration, under development
Collimation Depth Calculation
• SR must pass through all apertures close to IR– IP beampipe, extraction quadrupoles or the
facing final doublet
• Use semi-analytic linear calculation routine DBLT by Oliver Napoly (SACLAY)– Calculates SR fan as function of collimation
depth– Constrain the fan to pass through IR
apertures, solve for collimation depth
DBLT (O. Napoly) Assumptions and Method
• Assumes minimal 2-phase collimation– Collimators in phase and
90O out of phase with IP• Assumes mono-
energetic halo particles• Track corners of
collimated phase space at IP back through final doublet
• Use many SR emission points in final doublet
x
x’
Collimated halo phase space at IP
DBLT Solutions
• Aperture constraint satisfied by ellipse of solutions in Nx, Ny space
• A different ellipse for every SR emission point in FD
• ‘Smallest’ ellipse defines collimation depth
Possible coll. depth solutions for one emission point
Aperture
SR profiles
x
y
Nx
Ny
X marks solution for square SR profile at
apertureFor more details see 15 Oct 04 talk
http://www.astec.ac.uk/ap/collider/collimmeet05Oct04/index.html
20 mrad Collimation IssuesAperture list
http://www.slac.stanford.edu/xorg/lcd/ipbi/lcws05/maruyama_backgrounds.ppt
Component Aperture (radius, mm)
S(entrance) (wrt IP)
S(exit)
(wrt IP)
IP 12 -0.06 0.06
QFEX1A 12 3.51 5.71
QFEX1B 17 6.01 7.72
QFEX1C 24 8.02 9.73
QDEX2A 30 10.03 11.50
QDEX2B 43 13.25 16.72
QDEX2C 43 17.03 20.51
QFEX3A 43 20.81 24.08
QFEX3B 46 24.38 27.66
QFEX3C 58 27.96 31.23
Last extraction quad is at 47m from IP, 71 mm aperture.
20 mrad Collimation Issues
• Extraction quads extend to ~50m from IP.• How far from IP should SR cleanly pass?
– Don’t have good feeling for background effects/back scattering
• For depth calculation choose 3 apertures for SR clearance– VTX beampipe at IP– QFEX1A exit (12mm, 5.71 m from IP)– QFEX1C exit (24mm, 9.73 m from IP)
20 mrad Collimation Solutions
VTX beampipe QFEX1A exit QFEX1C exit
QFEX1A exit solution Nx = 8.82 x Ny= 68.89 y
Compare with estimation by optics rescaling from NLC (A. Drozhdin), Nx = 8 x Ny = 57 y
Corresponds to spoiler gaps of ax = 1mm, ay = 0.5 mm
20 mrad SR Fan Envelope• Plot SR fan
envelope for 8.82x x 68.89y collimated halo
• Demonstrates SR clearance of constraining aperture
• Rays are not straight lines in r vs. s space!
FD VTX QFEX1-5
• Now non-symmetrical problem
• SR fan passes through one or more non-symmetrical apertures, then will hit beam pipe eventually
2mrad Collimation Depth
QD0
SR fan centroid
IP
QD0
Extracted Beam
2mrad Extraction (Daresbury/Orsay) 500 GeV
• What collimation depth to clear QD exit?
• Treat as symmetric problem and constrain SR fan with 22 mm symmetrical aperture – to do
QD
QD
1.6 mrad
5.4 m
8.8mm
31 mm
Distance of closest approach ~ 22 mm
Ignore everything afterwards
SR fan centroid
Other Issues
• SR from last bend before final focus may also constrain coll. depth
• Have been ignoring effect of local chromaticity correction sextupole
• Have been ignoring energy spread of beam halo
Conclusion and Future Work
• DBLT gives quick evaluation of collimation depth– Can use as first approximation for spoiler gaps
• Fine tuning of collimation depth requires simulation– For example, BDSIM cross check of DBLT
incorporating halo energy spread
• Broader collimation questions– Collimation performance of whole lattice
(STRUCT/BDSIM) – Machine protection issues
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