NEW DESIGN OF THE TESLA INTERACTION REGION WITH l*

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NEW DESIGN OF THE TESLA INTERACTION REGION WITH
l  5 m

• O. Napoly, J. Payet CEA/DSM/DAPNIA/SACM

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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
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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

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Main issues of the Design

• Final Focus Optics
• Extraction of Synchrotron Radiation from Final
  Doublet (i.e. check collimation depths)
• Extraction of Spent Beam from Final Doublet

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Final Focus Optics

• Matching conditions
• The R12, R34 terms of the transfert matrix
  between the paired sextupoles
• SV1, SV2 SH1,SH3 are set to zero
• Two approaches
• ?x and ?y corrections  à la NLC 
• Interleaved sextupole pairs
• Additional sextupole ( octupoles, decapoles not
  implemented)
• ?x correction  à la TDR  ?y correction  à
  la NLC 
• Non interleaved sextupole pairs

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NLC-like Optics
_at_ IP ?x 10 mrad
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NLC-like Beam sizes and Luminosity
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NLC-like Emittance growth with S.R.
Optimization with dipole locations
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Hybrid Optics
_at_ IP ?x 2.6 mrad
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Hybrid Beam sizes and Luminosity
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Hybrid Emittance growth with S.R.
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The collimation section

• We use the TDR collimation section with some
  changes
• Reverse the first
• dispersion bump
• Introduce a second
• energy spoiler
• (??x 2? between
• the 2 energy spoilers)

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NLC-like optics Central trajectories
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The collimation depths
The images of the slits are transported for
several energies to each relevant emission
positions in the Final Doublet. Their
intersection points define the collimated phase
space volume and are taken as origins of the
synchrotron radiation rays.
The emitted synchrotron radiation beam is
determined by the rays originating from all 4D
corners and all (discrete) energies.
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S.R. in FD 1st order transport
At 1st order transport, the aperture of the
collimators are in agreement with the on-momentum
predictions for the collimation depths
FFADA
Betatron spoilers gx 1.8 mm gy 0.7 mm
BETA
Energy spoilers gx 1.8 mm (NLC) gx 1.2 mm
(Hybrid)
Momentum acceptance 0.6 (NLC) 0.9
(Hybrid)
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S.R. in FD all d-order transport
NLC-like optics
All order momentum transport generates
distortions of the central orbits and beam
focusing. The energy spoiler apertures must be
reduced in order to keep a good synchrotron
radiation extraction.
-1.25 lt d lt 1.25
Hybrid optics
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S.R. in FD all d-order transport
NLC-like optics
Betatron spoilers gx 1.8 1.3 mm gy 0.7
mm
Energy spoilers gx 0.8 mm
Momentum acceptance -0.39 , 0.52
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Spent beam extraction
?
Angular acceptance of the final doublet as a
function of energy and angle ?
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Spent beam extraction
Better extraction of low energy charged
particles (ee- pairs, beam-beam bremsstrahlung)
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Conclusions

• Design of l 5 m new TESLA final focus is
  possible within the 600m TDR length constraint.
  Two solutions are investigated, using the NLC
  chromaticity correction scheme. For the both
  cases
• The momentum bandwidth is comparable or better
  than the TDR.
• The collimation requirements are about a factor
  2 tighter than the TDR.
• The code BETA develops a new tool to investigate
  the impact of off-energy particle collimation.
• The spent beam extraction through final doublet
  is roughly equivalent.
• Several optimizations are still needed