1. Philip Bambade / LAL-Orsay Sha Bai / IHEP-Beijing
Interaction point and machine-detector interface ) highlights of recent developments for ee colliders ATF2 – SuperKEKB – CEPC ) LAL-IHEP collaboration
Philip Bambade / LAL-Orsay
Sha Bai / IHEP-Beijing
9th FCPPL workshop IPHC-Strasbourg /3-1/4 2016

2. Collaborating teams LAL-Orsay IHEP SuperKEKB CEPC
Philip Bambade – SuperKEKB & ATF2
Cécile Rimbault – SuperKEKB
Viacheslav Kubytskyi – SuperKEKB & ATF2
Shan Liu – student/CSC 
Dima El Khechen – student/ED517
Renjun Yang – student/CSC
Pang Chengguo – student/CSC (tbc)
IHEP
Jie Gao – CEPC
Sha Bai – CEPC (+ ATF2)
Dou Wang – CEPC (+ ATF2/ILC)
Yiwei Wang – CEPC (+ CLIC/ILC + SuperKEKB)
SuperKEKB CEPC
Related collaborations:
- KEK (S. Uehara, Y. Funakoshi et al.): luminosity monitoring&feedback for SuperKEKB
- KEK (N. Terunuma, T. Tauchi et al.): ATF2 final focus prototype for linear collider
- IPHC-Strasbourg (I. Ripp-Baudot et al.): characterize beam backgrounds in Belle-II
- BINP (E. Levichev et al.): collaboration on CEPC design

3. LAL/France and IHEP/China collaborate since 2007
PhD Students :
Sha BAI ( )  ATF2
Shan LIU ( )  ATF2
Renjun YANG ( )  ATF2
Pang CHENGGUO tbc ( )  SuperKEKB
Publications :
1) In vacuum diamond sensor scanner for beam halo measurements in the beam line at the KEK Accelerator Test Facility, by S. Liu et al.: arXiv: ,submitted to NIMA (December 2015)
2) Study of alternative ILC final focus optical configurations, by D. Wang et al.: Nucl.Instrum.Meth. A781 (2015) 14-19
3) Analytical Estimate of ATF Beam Halo Distribution, by D. Wang et al.: Chinese Physics C 2014 Vol. 38(12):
4) Experimental Validation of a Novel Compact Focusing Scheme for Future Energy-Frontier Linear Lepton Colliders, by G. White et al. (ATF2 Collaboration): Physical Review Letters 112, (2014)
5) Propagation of a beam halo in accelerator test facility 2 at KEK , by S. Bai et al.: Chinese Physics C 2013 Vol. 37(5):
6) Mitigating the effects of higher order multipole fields in the magnets of the Accelerator Test Facility 2 at KEK, by S. Bai et al.: Chinese Physics C 2012 Vol. 36(8):
7) Simulation of beam size multiknobs correction at the Accelerator Test Facility 2 at KEK, by S. Bai et al.: Chinese Physics C 2011 Vol. 35(4):
8) First beam waist measurements in the final focus beam line at the KEK Accelerator Test Facility, by S. Bai et al.: Physical Review Special Topics - Accelerators and Beams 13, (2010)
9) Present status and first results of the final focus beam line at the KEK Accelerator Test Facility, by P. Bambade et al. (ATF Collaboration): Physical Review Special Topics - Accelerators and Beams 13, (2010)
Conference reports : Technical reports : 4

4. ATF2 final focus prototype for linear colliders see talk by Shan LIU

5. Measuring nanometre beam sizes at ATF2
 37 nm vertical size
Modulation of Compton scattered photon rate from beam interaction with laser interference fringe pattern
Laser wavelength 532 nm

6. Vertical feedback stabilization of 2nd bunch
Preliminary : y  41 nm
smallest vertical beam size ever achieved
Kano, Okugi, Kraljevic,…

7. Collimator for beam halo & background control
Diamond Sensors x/y
Beam size monitor
Last bend magnet
Transition foil (elastic part)
Transition pipe
Vacuum chamber
600 mm
Fuster, Wallon,…

8. Beam halo & background control – first results
Bremstrahlung background near IP
Background rate beam size monitor  collimator efficiency study
Beam halo near IP
Vertical halo symmetric cut
Horizontal halo reduction (secondaries)
 GEANT4
[mm]
Horizontal beam halo distribution
[mm]
Fuster, Yang,…

9. SuperKEKB asymmetrical very high luminosity B-meson factory

10. SuperKEKB / Belle-II Machine-Detector Interface
Luminosity monitoring & tuning
Control beam induced backgrounds
1) Phase 1 : 2016/Feb.  Jun.
- single beam commissioning, vac. scrubbing
- no luminosity (no final focus), no detector
2) Phase 2 : 2017/Nov.  2018/Mar.
- colliding beam commissioning, no vertex detector
3) Phase 3 : from 2018/autumn
- full luminosity for physics running
βy = 300 m
d  300 m
 mitigates beam-beam and hour-glass effects…
 Lumi  40

11. Beam background at SuperKEKB
At SuperKEKB with x 40 larger luminosity, beam background will also increase drastically
Touschek scattering
Beam-gas scattering
Synchrotron radiation
Radiative Bhabha event: emitted g
Radiative Bhabha event: spent e+/e-
2-photon process event: e+e-e+e-e+e-
etc…
Beam-origin
Luminosity dependent
In this slide, I have listed up variety of possible beam background sources at SuperKEKB.
Among these background sources, so-called “Touschek scattering” will be the most difficult one to cope with, which I will explain in more detail in the following slides. e- e+
Nakayama,…

12. Fast & slow variations at IP require feedback corrections
Beam-beam deflection (SLC, KEKB) for fast vertical motion
Luminosity feedback by “dithering” (PEP-II) for slower horiz. motion
Luminosity tuning with optical knobs (SLC, FFTB, ATF2) to maintain small spot sizes ( time scales of  hours ? )
Dy at IP=
 5nm  1/10sy*
BPM IP
Dy at BPM=  1.3mm
Vertical vibration  Hz
Sampling (BPMs)  32 kHz 
2f0
Horizontal motion  few Hz
Modulation freq. f  77 Hz
Sampling (lumi. meas.)  1 kHz
 minimize f0 output component 
Luminosity f0 x

13. Radiative Bhabha (“Compton”) process
  250 mbarn (E > 1% Ebeam )
major background source from induced particle losses after IP
use for luminosity monitoring
Luminosity monitoring specs
Relative measurements
10-3 in 1 ms over all bunches
10-3 in  1 s for each 2500 bunch  4ns
(for nominal luminosity)
Non luminosity scaling contamination < 1% (e.g. beam gas bremstrahlung and Touschek losses)
Should also work for initial luminosity
Macroscopic QED effect…
Y. Funakoshi (KEK), background workshop, Feb. 2012

14. LER & HER measurement stations
Recoil electron
Outside
g from positron
 from  30 m
Recoil 11 m
2 diamonds + 1 Cherenkov + 1 Scintillator
2 diamonds + 1 Cherenkov + 1 Scintillator

15. SuperKEKB single beam commissioning  1st signals from beam gas bremstrahlung
coincidence…
HER diamond and Cherenkov…
Injection noise…
Coming soon :
- beam particle loss analysis
- studies w.r.t. beam conditions
Uehara, Kubytskyi, El Khechen, Jehanno,…
Signal distribution along 10 s revolution time…

16. CEPC High luminosity Higgs & Z boson factory
Parameters and layout
Machine Detector Interface
Background
Collimators
Shielding
Solenoid compensation
Fast luminosity measurement & feedback
What CEPC can learn from SuperKEKB

17. Advantage: Avoid pretzel orbit Accommodate more bunches at Z/W energy
Reduce AC power with crab waist collision
bypass (pp)
bypass (pp)

18. Basic parameters for CEPC double ring（wangdou20160219）
Pre-CDR
H-high lumi.
H-low power Z
Number of IPs 2
Energy (GeV)
120
45.5
Circumference (km) 54
SR loss/turn (GeV)
3.1
2.96
0.062
Half crossing angle (mrad)
14.5 15
11.5
Piwinski angle
2.5
2.6
8.5
Ne/bunch (1011)
3.79
2.85
2.81
2.67
0.46
Bunch number 50 40 44
1100
Beam current (mA)
16.6
16.9
10.1
10.5
45.4
SR power /beam (MW)
51.7 30
31.2
2.8
Bending radius (km)
6.1
6.2
Momentum compaction (10-5)
3.4
3.0
2.2
3.5
IP x/y (m)
0.8/0.0012
0.306/0.0012
0.25/
0.22/0.001
0.268 /
0.08/0.001
Emittance x/y (nm)
6.12/0.018
3.34/0.01
2.45/0.0074
2.67/0.008
2.06 /0.0062
0.62/0.002
Transverse IP (um)
69.97/0.15
32/0.11
24.8/0.1
24.3/0.09
23.5/0.088
7/0.046
x/IP
0.118
0.04
0.03
0.032
0.005
y/IP
0.083
0.11
0.084
VRF (GV)
6.87
3.7
3.62
3.6
3.53
0.12
f RF (MHz)
650
Nature z (mm)
2.14
3.3
3.2
3.9
Total z (mm)
2.65
4.4
4.1
4.2
4.0
HOM power/cavity (kw)
1.5
1.3
0.99
Energy spread (%)
0.13
0.05
Energy acceptance (%)
Energy acceptance by RF (%) 6
2.1
1.1 n
0.23
0.49
0.47
0.27
Life time due to beamstrahlung_cal (minute) 47 53 36 41 32
F (hour glass)
0.68
0.73
0.82
0.69
0.81
0.95
Lmax/IP (1034cm-2s-1)
2.04
2.97
2.03
2.01
3.61

19. MDI layout and issues : single  local double ring
Beam background
Shielding design
Collimator design
SC magnet design
Beam pipe
Solenoid compensation
Lumical & fast lumi measurement & feedback
……..

20. CEPC Background Synchrotron radiation background
a) from the last bend magnet
b) from the quadrupole in the IR
Lost particles background
a) radiation Bhabha scattering
b) beamstrahlung
Generator
Geant4(Mokka)
Analysis(Marlin)
Accelerator
Simulation

21. Proposed exchange & collaboration
IHEP : Use CEPC simulation tool to evaluate beam losses at SuperKEKB
 benchmarking of simulation tool
 validation on real system
LAL : Conceptual design of fast luminosity monitoring for CEPC
 apply experience from SuperKEKB
Application to FCPPL for support:
1-2 visits each way for face to face discussions and exchanges