Status of the TESLA Beam Delivery System Lattice Design. Deepa Angal-Kalinin Daresbury Laboratory, UK

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1 Status of the TESLA Beam Delivery System Lattice Design Daresbury Laboratory, UK

2 Lattice Design since TDR Collimation Comparison - TRC Modifications in TDR lattice and associated problems Extraction line issues Alternate geometries for extraction Ongoing studies Plans

3 What has happened since TDR? Local chromaticity correction FFS solution for TESLA : O. Napoly & J. Payet. Collimation task force TESLA, NLC and CLIC collimation was compared at 500 GeV using same set of codes. O. Napoly and J. Payet : introduced one more energy collimator to improve the performance. With TDR layout - MES section and the additional energy collimator machine protection issues. Spent Beam Extraction Seminar : Dec 02 Karsten Büßer: Average Beamstrahlung power deposited on the septum blade (~0.3W nominal beam, ~80W realistic beam) : Charged particle loss Electrostatic separators, R& D on septum, dump & other considerations

4 What has happened since TDR? R. Brinkmann suggested to include a small (~0.3mrad) vertical crossing angle to shine the beamstrahlung away from the septum blade. to reduce e-particle loss for the low energy tail particles split the final strong doublet into quadruplet optics solutions for incoming beam? Optics and collimation review meeting Zeuthen, January 04 to discuss the problems with TESLA BDS optics, collimation & extraction. Crossing angle meeting was held a day before to discuss the impact of crossing angle on physics.

5 What has happened since TDR? Final focus lattice with local chromaticity correction for L*= 3m, 4m,5m in TDR length constraint of 600m by O.Napoly & J. Payet 300 β 1/2 (m 1/2 ) η x (m) 0, SF β x 1/2 SF η x SD 2 Beamstrahlung Dump β z 1/ SF1, SD1 s (m) 0,10 0,05 0,00

6 2,0 1,5 σ u /σ u0, L/L 0 Horizontal Vertical Luminosity Beam sizes and Luminosity 1,0 E/E = 0.4 %, L/L0 = ,0 σ E /E 0,000 0,002 0,004 0,006 0,008 0,010 6,E-14 x (m.rad) Optimization with dipole locations Emittance growth with S.R. 4,E GeV??? x = m.rad s (m) 0,E

7 Collimation task force TRC Simulation (A. Drozhdin) of collimation with beam halo shows no hard edge for TESLA system some particles can reach IR Bad performance of TESLA system not due to scattering, but appears to be optics! (confirmed by results of G. Blair)

8 O.Napoly & J.Payet : proposed to include one more energy collimator to improve the performance. Used the TDR collimation section with some changes : 1,25E-03 x (m) Energy Spoilers Reverse the first 7,50E-04 dispersion bump Introduce a second 2,50E-04 energy spoiler ( x =2π between the 2 energy spoilers) -2,50E-04-7,50E-04-1,25E-03 1st Order δ=+.6 % All Orders δ=+.6 % All Orders δ=+.52 % All Orders δ=-.39 % s (m)

9 TDR BDS Layout

10 linear dispersion x ' = I K D δ x π/2 π/2 non-linear dispersion (3rd-order) K 2 K 3 K 2 x 2 = R 12 x ' 1 = ϕ = ( n x 1 + ) π 1 ϕ = ( n + ) π y 1 6 R K 3 D x δ x y skew-sextupole octupole skew-sextupole 2 2 collimator With TDR layout, this scheme doesn t work : one of the energy collimator comes before magnetic energy spoiler machine protection issues!

11 Energy Spoiler Protection & Fast Extraction -I π π/ octupole skew sextupole MES energy spoiler betatron spoilers Fast extraction kicker placed upstream of energy spoiler passive protection against fast energy errors assume pure -oscillations less likely

12 Halo Collimation VTX with r = 14 mm requires mask with r = 12 mm collimation required: x: 7.8σ [TDR 13σ] y: 42.4σ [TDR 81σ] Collimation requirements about a factor 2 tighter! Collimator wakefields? Reconsider choice of L* Tail folding octupoles

13 TDR Collimation ±45º lattice : some strange chromatic properties. Balancing the second order terms was difficult in TDR

14 Ideas presented by Nick Walker to change the TESLA BDS LINAC spectrometer undulator E coll β coll FFS e+ target Fast Emergency Extraction Line Move Fast Emergency Extraction Line to exit of linac upstream of e+ source on e- side Explore use of e+ target bypass arc for energy collimation re-design (re-think) betatron collimation current 45 lattice not good separate diagnostics station (emittance measurement) ideally also placed directly after linac Other options..

15 Extraction Line Issues. Small vertical angle solution to reduce beamstrahlung on septum. Split final doublet into quadruplet to reduce e-particle losses. Daresbury group found an optics solution to this problem. Final Focus Optics for L*=5m with quadruplet 1/2 (m 1/2 ) Horz Vert Dispersion m S(m) 0.00

16 L*=5m with final quadruplet 3 Beam Sizes and Luminosity 8.E-15 Emittance growth with S.R. u/ uo, L/L Luminosity Horizontal Vertical x(m.rad) 6.E-15 4.E-15 2.E E/E 0.E S(m) Further optimisations..may give better results!

17 L*=5m with final quadruplet Beam Sizes for 40% energy tail particles at MSEP (~50 m from IP) in the extraction line : x(m) x(m) With doublet y(m) With quadruplet x(m) y(m)

18 A small horizontal crossing angle (~2 mrad) is proposed by O. Napoly, J. Payet, Saclay & P. Bambade, B.Mouton, Orsay QD (r=24mm) 1.5m QF (r=7mm) L*=4.1m 1m π optical transfer 2 mrad

19 Luminosity loss without crab-crossing for 2 mrad horizontal crossing angle L/L 0 ~ 0.85 geometric formula θ[mrad]

20 Crossing Angle Choices for TESLA 300 µrad vertical crossing + quadruplet to reduce beam losses :Necessary R&D on reliable 50KV/cm, m long electro-static separators. 2 mrad horizontal crossing angle no electrostatic separators, 15% Luminosity loss without crab crossing, can be compensated by angular dispersion at IP. Large crossing angle like in NLC Crossing angle working group to recommend the detector and physics implications.

21 Summary TESLA BDS design is being improved for incorporating local chromaticity correction section, better collimation and machine protection issues. Re-iteration on L*. FFS to be optimised for third & higher order terms. Alternative solutions for beam extraction suggested by Saclay, Orsay and Daresbury groups. The details of these designs including beam diagnostics need to be worked out.