CEPC MDI Issues Sha Bai for CEPC MDI

CEPC MDI Issues Sha Bai for CEPC MDI group IAS Program on High Energy Physics, Hong Kong, Jan 19 -21, 2021 -01 -21

Outline v MDI design for High Luminosity Higgs v CDR TDR optimization for MDI v MDI mechanics and integration v Summary

MDI layout and IR design • • The Machine Detector Interface (MDI) of CEPC double ring scheme is about 7 m long from the IP. The CEPC detector superconducting solenoid with 3 T magnetic field and the length of 7. 6 m. The accelerator components inside the detector without shielding are within a conical space with an opening angle of cosθ=0. 993. The e+e- beams collide at the IP with a horizontal angle of 33 mrad and the final focusing length is 1. 9 m.

MDI parameters range L* 0~1. 9 m Crossing angle 33 mrad MDI length Detector requirement of accelerator components in opening angle Peak filed in coil Central filed gradient Bending angle length Beam stay clear region Minimal distance between two aperture Inner diameter Outer diamete r Critical energy (Horizonta l) Critical energy (Vertical ) SR power (Horizont al) SR power (Vertica l) 1. 9 m 7 m 8. 11˚ 3. 2/2. 8 T 141/84. 7 T/m 1. 21 m 15. 2/17. 9 mm 62. 71/105. 28 mm 48 mm 59 mm 724. 7/663. 1 ke. V 396. 3/26 3 ke. V 212. 2/239. 23 W 99. 9/42. 8 W 3. 3 T 94. 8 T/m 1. 5 m 24. 14 mm 155. 11 mm 56 mm 69 mm 675. 2 ke. V 499. 4 ke. V 472. 9 W 135. 1 W 0. 16 m 57 mm 200 mm 8. 2 T 1. 1 m 120 mm 390 mm Anti-solenoid QD 0 3 T 2. 5 m 120 mm 390 mm Anti-solenoid QF 1 3 T 1. 5 m 120 mm 390 mm 120 mm 28 mm QDa/QDb QF 1 Lumical 0. 95~1. 11 m Anti-solenoid before QD 0 Beryllium pipe Last B upstream First B downstream 64. 97~153. 5 m 0. 77 mrad 88. 5 m 33. 3 ke. V 44. 4~102 m 1. 17 mrad 57. 6 m 77. 9 ke. V 1. 21 m 1. 19/1. 31 W Beampipe within QF 1 1. 5 m 2. 39 W Beampipe between QD 0/QF 1 0. 3 m 26. 5 W Beampipe within QDa/QDb

QDa/QDb, QF 1 physics design parameters βy*=1 mm, βx*=0. 33 m QDa/QDb Horizontal BSC 2（18 x+3） Entrance 9. 15/12. 41 mm Middle Exit Good field region Effective length Distance from IP Gradient Vertical BSC 2（22 y+3） e+e- beam center distance 12. 89/15. 22 62. 71/105. 2 mm 8 mm 10. 37/14. 84 14. 61/14. 88 82. 84/125. 4 mm mm 12. 13/17. 92 15. 21/13. 87 102. 64/145. mm mm 21 mm Horizontal 12. 13/17. 92 mm; Vertical 15. 21/15. 22 mm 1. 21 m 1. 9/3. 19 m 141/84. 7 T/m QF 1 Horizontal BSC 2（18 x+3） Vertical BSC 2（22 y+3） e+e- beam center distance Entrance 19. 66 mm 13. 21 mm 155. 11 mm Middle 23. 02 mm 12. 00 mm 179. 87 mm Exit 24. 14 mm 11. 60 mm 204. 62 mm Good field region Effective length Distance from IP Gradient Horizontal 24. 14 mm; Vertical 13. 21 mm 1. 5 m 4. 7 m 94. 8 T/m

SR on IR beam pipe from last bend upstream and Final Doublet • There is no SR photons hitting the central beam pipe in normal conditions. • Single layer beam pipe with water cooling, SR heat load is not a problem. QF 1 QDa QDb Region SR heat load SR average power density 0~805 mm 0 0 805 mm~855 m m 12. 5 W 69. 4 W/cm 2 855 mm~1. 9 m( QDa entrance） 1. 06 W 0. 28 W/cm 2 QDa 1. 19 W 0. 27 W/cm 2 QDa~QDb 3. 73 W 12. 95 W/cm 2 QDb 1. 31 W 0. 3 W/cm 2 QDb~QF 1 26. 5 W 4. 9 W/cm 2 QF 1 2. 39 W 0. 44 W/cm 2

SR from last bending magnet upstream of IP Abnormal condition Ø SR photons hitting the bellows under the extreme beam conditions, temperature rise ~10 C v Extreme condition, eg, if a magnet power is lost, a large distortion will appear immediately for the whole ring orbit. The beam will be lost when exceeded. v In extreme cases ~ at least 10 times per day. The beam will be stopped within 0. 5 ms when abnormal. It is not afraid of this 0. 5 ms for other material beam pipe except beryllium pipe. v The background of the detector should not be considered under abnormal conditions. v It is not necessary to care about whether the beam orbit deviation will affect detector operation, since the high background part will be removed when data analysis is carried out. SR will enter into the bellows (no cooling): Ø IP~677 mm, no SR heat load. Ø -677~-805 mm beam pipe, SR power ~14. 65 W, APD~ 31. 8 W/cm 2. Ø -805~855 mm beam pipe, SR power~12. 96 W, APD~72 W/cm 2. Ø Temperature rise ~10 C

Beam loss from RBB and BS Without collimator With collimator Radiative Bhabha scattering Without collimator With collimator Beamstrahlung

Beam loss from Beam-gas bremsstrahlung and Beam thermal photon scattering events Without collimator With collimator BG events Without collimator With collimator BTH

Collimator design Beta function/m Horizontal Dispersion/m Phase BSC/2/m Range of half width allowed/mm name Position Distance to IP/m APTX 1 D 1 I. 785 2388. 31 100. 99 0. 2 384. 11 0. 00181 1. 81~8. 42 APTX 2 D 1 I. 787 2325. 75 100. 99 0. 2 384. 36 0. 00181 1. 81~8. 42 APTY 1 D 1 I. 791 2075. 48 19. 52 0. 1995 387. 46 0. 003348 0. 079~3. 3 APTY 2 D 1 I. 793 2012. 92 19. 52 0. 1995 387. 71 0. 003348 0. 079~3. 3 APTX 3 D 1 O. 5 1856. 35 101. 95 0. 20 6. 877 0. 00182 1. 82~8. 45 APTX 4 D 1 O. 7 1918. 92 101. 95 0. 20 7. 127 0. 00182 1. 82~8. 45 APTY 3 D 1 O. 10 2075. 33 101. 95 0. 1 7. 75 0. 00182 0. 182~3. 67 APTY 4 D 1 O. 16 2388. 17 101. 95 0. 1 9. 00 0. 00182 0. 182~3. 67 Ø horizontal collimator half width 4 mm(13 x), Vertical collimator half width 3 mm (22 y) Ø The collimators will not have effect on the beam quantum lifetime.

Radiation background Ø Including Radiative Bhabha, Beam-Gas, Beam Thermal Photon. Almost No Beamstrahlung. Ø Normalized to loss power in m. W(one beam). Ø Higgs mode in CDR. Ø Higgs Backgrounds on 1 st layer of Vertex. Ø With a safety factor of 10. Background type Pair production 1. 91 526. 11 Synchrotron Radiation 0. 026 15. 65 Radiative Bhabha 0. 34 592. 66 Beam Gas 0. 9607 1235. 9 Beam Thermal Photon 0. 02 22. 31 Total 3. 2567 2392. 63

Heat load in IR from beam loss Region SR heat load from RBB SR heat load from BS SR heat load from BG SR heat load from BTH Berryllium pipe 6. 7 m. W 0 0 0 Detector beam pipe 0. 024 W 0 4. 8 u. W 1. 2 u. W Accelerator beam pipe before QDa 0. 17 W 0 4. 2 u. W 1. 2 u. W QDa~QDb 2. 13 W 3. 8 u. W 5. 9 u. W 1. 8 u. W QDb~QF 1 0. 01 W 3. 8 u. W 0. 5 u. W 0. 6 u. W QF 1 0. 26 m. W 0 3. 7 u. W 0. 66 u. W Heat load in IR from beam loss background is so small, compared to synchrotron radiation and HOM.

HOM power distribution

Beam pipe structure Ø Berryllium (central) and Aluminum(forward) beam pipes From IP(mm) Shape Inner diameter(mm ) 0 -120 Circular 28 Be 10556 120~205 Circular 28 Al 7477 205~655 Cone 28~40 Al 48071 655~700 Circular 40 Al 5655 Material Inner surface area(mm 2) Marker Taper: 1. 75

Beam pipe thermal analysis With the heat deposition in High Luminosity Z mode, it becomes impossible to cool the Be beam pipe with oil. Water is chosen as the coolant for the demonstration purpose. • Water flow rate for Be: 3. 4 L/min • Water inlet temperature: 230 C • Other calculation condition is the same as before CDR Z parameters High Lumi Z parameters

Movable collimators Ø Located in straight section between two dipoles, the length is 800 mm. Ø SR power: 7700 W @120 Ge. V, 30 MW Highest temperature: 148 ℃ Loss-Factor: 0. 045 V/p. C Ploss: 18. 8 w(Higgs)/76. 1 w(W)/265. 8 w(Z)

MDI integration and alignment Alignment scenario: Ø Pre-align the SC magnets using vibrating wire system to “certain location” to compensate the effect of loads. Ø Align the SC magnets in two cryostats using optical system. Ø Measure misalignment using SSW and adjust by corrector magnets meet the alignment requirements. VWS is a candidate pre-alignment method, accuracy of magnet centers: ≤ 10 μm

Remote vacuum connector • Difficulties: • Transversal space: All the structure should be within detection angle. • Leak rate requirement: Ultra-high vacuum. Leak rate requirement: ≤ 2. 7 e-11 Pa. m 3/s • Longitudinal space: Bellows should absorb deformation when baking. Add Z-direction support, length has been decreased to 83 mm. • Minimize thermal loads: The thermal loads mainly includes SR power and HOM power. Avoid SR power by layout design, and decrease HOM power by RF finger. • Cooling: It is hard to dissipate the heat at RF finger which is thin, low thermal conductivity and far from the coolant. FEA

SC magnet supports Key points Ø Ø Stability (static and modal) Accuracy Easy-operating Dimensions Ø High stiffness for stability conflict Flexibility for high accuracy. Ø Studies on support stiffness is on-going. Ø Motor driven wedges jacks for high stiffness and accuracy. Ø Auxiliary support, high damping material/structure also in consideration

Summary Ø Ø Ø The final focusing length has changed from 2. 2 m to 1. 9 m in High Luminosity Higgs. There is no SR photons hitting the central beam pipe in normal conditions. Single layer beam pipe with water cooling, SR heat load is not a problem. SR photons hitting the bellows under the extreme beam conditions, temperature rise ~10 C Beam loss background in High luminosity Higgs with collimators can be reduced to the same level in CDR. Hit density on first layer of vertex detector is low from radiation background. Heat load in IR is mainly from HOM, especially in High luminosity Z mode. With the heat deposition in High Luminosity Z mode, it becomes impossible to cool the Be beam pipe with oil. Water is chosen as the coolant for the demonstration purpose. Highest temperature on collimators from SR and HOM is 148 ℃ MDI alignment system is preliminary considered and designed. Replace the sealing membranes by two layers of edge sealing.

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