1. NEW DESIGN OF THE TESLA INTERACTION REGION WITH l* = 5 m
O. Napoly, J. Payet CEA/DSM/DAPNIA/SACM

2. 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 l*
IP waist β*
chromaticity : ξ = l* / β*

3. 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

4. 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

5. Final Focus Optics Matching conditions : Two approaches :
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

6. NLC-like Optics
@ IP ’x = 10 mrad

7. NLC-like : Beam sizes and Luminosity

8. NLC-like : Emittance growth with S.R.
Optimization with dipole locations

9. Hybrid Optics
@ IP ’x = 2.6 mrad

10. Hybrid : Beam sizes and Luminosity

11. Hybrid : Emittance growth with S.R.

12. The collimation section
We use the TDR collimation section with some changes :
Reverse the first
dispersion bump
Introduce a second
energy spoiler
(ΔΨx =2 between
the 2 energy spoilers)

13. NLC-like optics : Central trajectories

14. 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.

15. S.R. in FD : 1st order transport
FFADA
At 1st order transport, the aperture of the collimators are in agreement with the on-momentum predictions for the collimation depths
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)

16. S.R. in FD : all δ-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 % < d < %
Hybrid optics

17. S.R. in FD : all δ-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 % , %
Betatron spoilers :
gx = 1.8 & 1.2 mm
gy = 0.7 mm
Energy spoilers :
gx = 0.9 & 0.7 mm
Hybrid optics
Momentum acceptance :
-0.42 % , %

18. Spent beam extraction 
Angular acceptance of the final doublet as a function of energy and angle 

19. Spent beam extraction Better extraction of
low energy charged particles
(e+e- pairs, beam-beam bremsstrahlung)

20. 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