Machine Detector Interface for CEPC Sha Bai Chenghui

Machine Detector Interface for CEPC Sha Bai, Chenghui Yu, Yiwei Wang, Yuan Zhang, Dou Wang, Mike Sullivan, Huiping Geng, Na Wang, Yingshun Zhu, Jianli Wang CEPC CDR review 2018 -06 -28

Outline v MDI layout and IR design v IR superconducting magnets v Solenoid compensation v Synchrotron radiation and mask design v Beam loss background and collimator design v Mechanics and assembly v Summary 2

MDI layout and IR design Without Detector solenoid ~cryostat in detail With Detector solenoid • • • 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 2. 2 m Lumical will be installed in longitudinal 0. 95~1. 11 m, with inner radius 28. 5 mm and outer radius 100 mm. • • 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. 3

The design of interaction region The definition of beam stay clear • To satisfy the requirement of injection: BSC > 13 x • To satisfy the requirement of beam lifetime after collision BSC > 12 y Beam tail distribution with full crab-waist BSC>13 x BSC>12 y BSC_x = (18 x +3 mm), BSC_y = (22 y +3 mm), While coupling=1% 4

The design of interaction region The inner diameter of the beryllium pipe is 28 mm with the length of 7 cm. Without tungsten shield. 5

IR Superconducting magnets Superconducting QD coils Rutherford Nb. Ti-Cu Cable Room-temperature vacuum chamber with a clearance gap of 4 mm Magnet Central field gradient (T/m) QD 0 136 Magnetic Width of Beam stay length (m) clear (mm) 2. 0 19. 51 4 Single aperture of QD 0 (Peak field 3. 2 T) *10 - Field cross talk of two coils Min. distance between beams centre (mm) 72. 61 6

IR Superconducting magnets Superconducting QF coils There is iron yoke around the quadrupole coil for QF 1. Since the distance between the two apertures is larger enough and there is iron yoke, the field cross talk between two apertures of QF 1 can be eliminated. One of QF 1 aperture (Peak field 3. 8 T) Rutherford Nb. Ti-Cu Cable Room-temperature vacuum chamber with a clearance gap of 7 mm Magnet Central field gradient (T/m) QF 1 110 Magnetic Width of Beam stay length (m) clear (mm) 1. 48 27. 0 Min. distance between beams centre (mm) 146. 20 Integral field harmonics with shield coils（× 10 -4） n 2 6 10 14 Bn/B 2@R=13. 5 mm 10000 1. 08 -0. 34 0. 002 8

Solenoid compensation 3 T & 7. 6 m Specification of Anti-Solenoid Anti-solenoid Central field（T） Magnetic length（m） Conductor (Nb. Ti-Cu, mm) Coil layers Excitation current（k. A） Inductance（H） Peak field in coil (T) Number of sections Solenoid coil inner diameter (mm) Solenoid coil outer diameter (mm) Total Lorentz force F z (k. N) Cryostat diameter (mm) Before QD 0 7. 2 1. 1 16 7. 7 4 -75 Within QD 0 2. 8 2. 0 2. 5× 1. 5 8 1. 0 1. 2 3. 0 11 120 390 -13 500 After QD 0 1. 8 1. 98 4/2 1. 9 7 88 Ø Bzds within 0~2. 12 m. Bz < 300 Gauss away from 2. 12 m Ø The skew quadrupole coils are designed to make fine tuning of Bz over the QF&QD region instead of the mechanical rotation. 10

Solenoid compensation Emittance growth caused by the fringe field of solenoids Design emit. Y/emit. X H: 3. 6 pm/1. 21 nm (0. 3%) W: 1. 6 pm/0. 54 nm (0. 3%) Z: 1. 0 pm/0. 17 nm (0. 5%) expected contribution 0. 36 pm 0. 16 pm 0. 09 pm real contribution 0. 14 pm (0. 01%) 0. 47 pm (0. 09%) 2. 9 pm (1. 7%) 11

Solenoid compensation Coupling=1. 7% + 0. 3~0. 5% Large beam size & serious bunch lengthening • Set the detector solenoid at 2 T Higher luminosity & Lower difficulty of SC magnet & More free space nearby IP • Only set the detector solenoid at 2 T or < 2 T during Z operation Only higher luminosity @ Z 12

SR from bends of IR Surface Power (W) SR photons > 1 ke. V Under QF 1 2. 51 1. 01× 109 Between QF 1 and QD 0 40. 04 1. 63× 1010 Under QD 0 In front of QD 0 8. 08 4. 45 3. 26× 109 1. 80× 109 ü A significant fraction of these incident photons will forward scatter from the beam pipe surface and hit the central Be beam pipe (a cylinder located ± 7 cm around the IP with a radius of 14 mm). ü Masks are needed. ü IP upstream: Ec < 120 ke. V within 400 m. Last bend(66 m)Ec = 45 ke. V ü IP downstream: Ec < 300 ke. V within 250 m, first bend Ec = 97 ke. V 13

Mask design of IR 3 mask tips are added to shadow the beam pipe wall reduces the number of photons that hit the Be beam pipe from 2 104 to about 200 (100 times lower). The number of scattered photons that can hit the central beam pipe is greatly reduced to only those photons which forward scatter through the mask tips. The optimization of the mask tips (position, geometry and material) is presently under study. photon trajectories from the mask tips that can still hit the central beam pipe 14

SR from Final doublet quadrupoles 15

Beam loss Backgrounds at CEPC Beam-Thermal photon scattering IP 1 Beamstrahlung Beam Lost Particles Energy Loss > 1. 5% (energy acceptance) IP 3 Radiative Bhabha scattering Beam-Gas Scattering 16

CEPC beam lifetime Beam lifetime Quantum effect >1000 h Touscheck effect >1000 h Beam-Gas（Coulomb scattering） >400 h others Residual gas CO，10 -7 Pa Beam-Gas（bremsstralung） 63. 8 h Beam-Thermal photon scattering 50. 7 h Radiative Bhabha scattering 100 min Beamstrahlung 60 min 17

Loss particles due to RBB 7000 6000 5000 Counts 4000 downstream 3000 upstream 2000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 0 turns Ø Most the events lost in the detector immediately. A few particles with high energy will lost near the IP after one revolution for a small energy loss. Ø Although pretty large fraction of events lost in the downstream region, the radiation damage for detector component is tolerable. Ø Compared to the one turn’s tracking, more particles get lost in the upstream region of the IR. Ø The events lost in the upstream region are more dangerous for they are likely permeate into the detector components, even with the small flying angle respect to the longitudinal direction considered. Ø Collimators are needed. 18

Loss particles due to BS 4000 3500 3000 Counts 2500 2000 downstream 1500 upstream 1000 500 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 0 turns Ø Energy spread distribution close to the energy acceptance, the beam loss particles not appeared in the downstream of first turn. Ø Compared to the one turn’s tracking, more particles get lost in the upstream region of the IR. Ø The events lost in the upstream region are more dangerous for they are likely permeate into the detector components, even with the small flying angle respect to the longitudinal direction considered. Ø Collimators are needed. 19

Collimator design in ARC for Higgs Horizontal Dispersion /m Phase BSC/2/m Range of half width allowed/m m name Position Distance to IP/m Beta function/ m APTX 1 D 1 I. 1897 2139. 06 113. 83 0. 24 356. 87 0. 00968 2. 2~9. 68 APTX 2 D 1 I. 1894 2207. 63 113. 83 0. 24 356. 62 0. 00968 2. 2~9. 68 APTX 3 D 1 O. 10 1832. 52 113. 83 0. 24 6. 65 0. 00968 2. 2~9. 68 APTX 4 D 1 O. 14 1901. 09 113. 83 0. 24 6. 90 0. 00968 2. 2~9. 68 20

RBB and BS loss with horizontal collimator half width BS loss upstream vs horizontal collimator half width RBB loss upstream vs horizontal collimator half width 2500 12000 10000 2000 RBB loss no vertical collimator y=3. 3 mm 1000 y=3 mm 500 0 BS loss 8000 1500 no vertical collimator 6000 y=3. 3 mm y=3 mm 4000 2000 9 8 7 x(mm) 6 5 Ø Only horizontal collimator are selected, vertical collimators are not needed. Ø Vertical collimators are usually placed very close to the beam, no vertical collimators to avoid transverse mode coupling instability. 21

RBB and BS loss with collimators for Higgs Lost particles due to RBB in turns with collimators half width x=5 mm for Higgs Lost particles due to BS in turns with collimator half width x=5 mm for Higgs 8000 1 7000 0, 9 0, 8 6000 Counts 4000 downstream 3000 upstream 2000 0, 6 0, 5 downstream 0, 4 upstream 0, 3 0, 2 1000 0 Counts 0, 7 5000 0, 1 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 turns 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 turns Ø horizontal collimator half width 5 mm(13 x) Ø The collimators will not have effect on the beam quantum lifetime. Ø The lost particles has been reduced to a very low level with the system of collimators, especially in the upstream of the IP. Ø Although the beam loss in the downstream of the IP is still pretty large in the first turn tracking, the radiation damage and the detector background are not as serious as the loss rate for the relative small flying angle to the ideal orbit. 22

Beam-Gas bremsstrahlung loss particles Without collimators With collimators Ø The lost particles has been reduced to a very low level with RBB collimators, especially in the upstream of the IP, can be accepted by the detector. Ø Although the beam loss in the downstream of the IP is still remained, the radiation damage and the detector background are not serious, since the direction is leaving the detector. 23

Beam-Thermal photon scattering loss Without collimators With collimators Ø The lost particles has gone with RBB collimators in the upstream of the IP, can be accepted by the detector. Ø Although the beam loss in the downstream of the IP is still remained, the radiation damage and the detector background are not serious, since the direction is leaving the detector. 24

Collimator design in ARC for Z 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. 1897 2139. 06 113. 83 0. 24 357. 36 0. 00323 0. 83~3. 23 APTX 2 D 1 I. 1894 2207. 63 113. 83 0. 24 357. 11 0. 00323 0. 83~3. 23 APTX 3 D 1 O. 10 1832. 52 113. 83 0. 24 6. 876 0. 00323 0. 83~3. 23 APTX 4 D 1 O. 14 1901. 09 113. 83 0. 24 7. 126 0. 00323 0. 83~3. 23 Ø According to the off-momentum dynamic aperture after optimizing the CEPC lattice, and considering the beam-beam effect and errors, the energy acceptance is about 1. 0%. Ø For Z lattice, the emittance is about 7 times lower. So BSC is smaller. 25

RBB loss with collimators for Z Lost particles due to RBB in turns with collimators half width x=2. 5 mm for Z 6000 5000 Counts 4000 3000 downstream upstream 2000 1000 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 turns Ø Ø No beamstrahlung in Z horizontal collimator half width 2. 5 mm(17 x) The collimators will not have effect on the beam quantum lifetime. The lost particles has been reduced to a very low level with the system of collimators, especially in the upstream of the IP. Ø Although the beam loss in the downstream of the IP is still pretty large in the first turn tracking, the radiation damage and the detector background are not as serious as the loss rate for the relative small flying angle to the ideal orbit. 26

Beam-Gas bremsstrahlung in Z Without collimators With collimators Ø Beam-Gas bremsstrahlung is important effect due to beam lifetime caused by it ~ 57. 26 hours. Ø With collimators design half width x=2. 5 mm, the beam loss caused by beam-gas bremsstrahlung has disappeared in upstream of the IP. Although the beam loss in the downstream of the IP is still pretty large in the first turn tracking, the radiation damage and the detector background are not as serious as the direction is leaving the detector. 27

Beam thermal photon scattering in Z Without collimators With collimators Ø Beam thermal photon scattering is important effect due to beam lifetime caused by it ~ 70. 17 hours. Ø With collimators design half width x=2. 5 mm, the beam loss caused by beam thermal photon scattering has disappeared in upstream of the IP. Although the beam loss in the downstream of the IP is still pretty large in the first turn tracking, the radiation damage and the detector background are not as serious as the direction is leaving the detector. 28

Assembly nearby the IP 1, IP Chamber (supporting) 3, SC Magnet and Vacuum chamber (remotely) 2, Bellows and Lumical (remotely) 4, Move Lumical back and attach to the cover of cryostat by alignment holes (remotely) (supporting system) 29

Assembly nearby the IP We are studying the special installation tools for the remote connection of bellows. 30

Assembly nearby the IP If the space is large enough, Lumical will be connected together with the SC magnet. The boundary between accelerator and detector is still not clear. The design of HOM absorber and the special tool can’t be confirmed in short period. 31

Assembly nearby the IP Crotch region Helicoflex 32

Summary Ø The finalization of the beam parameters and the specification of special magnets have been finished. The parameters are all reasonable. Ø The detector solenoid field effect to the beam can be compensated. Ø HOM of IR beam pipe has been simulated and water cooling was considered. Ø Beam lifetime of CEPC double ring scheme is evaluated. Ø The most importance beam loss background is radiative Bhabha scattering and beamstrahlung for the Higgs factory. Ø Collimators are designed in the ARC which is about 2 km far from the IP to avoid other backgrounds generation. Beam loss have disappeared in the upstream of IP for both Higgs and Z factory. Ø Preliminary procedures for the installation of IP elements are studying. The boundary between detector and accelerator is still not clear. Very long time is needed to confirm the final scheme. 33

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