J. Payet, O. Napoly

1
Design of a new Final Focus System with l 4,5
m

• J. Payet, O. Napoly
• CEA/Saclay

2
New Final Focus NLC(P.Raimondi, A.Seryi)
Two optics with angular dispersion Dx at the
IP 1)  Long doublet  3 cm radius
aperture with 72 T/m, Dx 5 mrad 2)
 Short doublet  (not published) 1 cm
radius aperture with 140 T/m, Dx 9
mrad
3
New Final Focus NLC Chromatic correction
For both optics, ß-bandwidth gt 1 (TESLA
parameters)
ßx 15 mm
ßy 400 µm
4
New Final Focus NLC IP spot sizes
energy offset
energy offset
5
New Final Focus à la NLC

• Advantages from the machine point-of-view
• Better chromaticity correction ? larger l
• l 5m ? final doublet moved out of the
  detector solenoid

chromaticity ? l / ß
6
New Final Focus with l 5m

• Advantages from the detector point-of-view
• Larger forward acceptance at low angles
• Final doublet moved out of the calorimeter
• ? less e.m. showers in the detector
• Lighter Tungsten-mask and simpler support

7
Main issues of the Design

• Extraction of Beam after the interaction
• Extraction of Synchrotron Radiation from Final
  Doublet (i.e. check collimation requirements)
• 3. Final Focus Optics

N.B. First two issues, independent of the FF
optics, depend only on l and on the
final doublet apertures F.
8
Beam Extraction

• Final doublet acceptance
• Tmax (E, f)
• with
• l 5m
• F 48 mm
• Solenoid BS 4 T

9
Comparison of horizontal acceptances (f 0) for
l 3,4,5 m
l5m acceptance better for lower
energies worse for high energies
Differences are small. Tracking simulations are
needed
10
Synchrotron Radiation Extraction

• Collimation
• requirements
• for
• l 5m
• F 48 mm
• inner mask
• - s 4 m
• - F 24 mm

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Collimation Requirements
l m smask m Nx Ny
TDR 3 2 13 81
New FF 5 2 10 48
New FF 5 4 7.8 42

• new collimation section required
• with tail folding by octupoles

12
NLC type correction, l5m
Beamstrahlung Dump
SF3
SF2
SF1, SD1
SD2
IP angular dispersion Dx 10 mrad
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NLC type correction, l5m
ex _at_ 400 GeV 10-11 m.rad
Emittance growth minimized by fine tuning of
dipoles
14
NLC type correction, l5m
IP spot sizes
15
Correction type NLC, l5m
L/L0 0.86 for sE/E 0.4 ,
IP spot sizes and luminosity
16
Hybrid Correction, l5m
Beamstrahlung Dump
SH
SH
SV2
SV1
IP angular dispersion, Dx 2.6 mrad
17
Hybrid correction, l5m
ex _at_ 400 GeV 10-11 m.rad
Emittance growth at 400 GeV
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Chromatic Acceptance IP Spot sizes
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Correction hybride, l5m
L/L0 0.70 for sE/E 0.4
Dimensions rms et luminosité _at_ IP
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Optics Summary
The ideal solution is surrounded, but not yet
found
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Conclusions

• Design for l 4,5 m new optics is possible
  within the TDR length constraint, about 600 m
• Momentum bandwith already better than TDR
• Several optimisations are still needed (w.r.t.
  to dispersion, emittance growth, octupoles, )
• Beam extraction through final doublet OK
• Collimation requirements about a factor 2 tighter