1. International Workshop on CEPC
Summary and Plan – CEPC
Weiren Chou
CEPC-SPPC Study Group
International Workshop on CEPC
November 6-8, 2017, IHEP, China

2. A Glorious History of e+e- Colliders 1961: 1st lepton collider AdA
W. Chou
CEPC Workshop, 11/8/2017

3. A Glorious History of e+e- Colliders
Lepton colliders had been built on schedule, on budget
W. Chou
CEPC Workshop, 11/8/2017

4. Four Lepton Colliders on the Horizon
ILC
CLIC
CEPC
FCC-ee
W. Chou
CEPC Workshop, 11/8/2017

5. Similar Cost for 3 of the 4 ILC (250 GeV) CLIC (380 GeV) CEPC (100 km)
CoM. Energy
250
500
Site Length
~21 31
Luminosity
0.82
1.8
AC Power
129
163
Value Cost in TDR
TBD
7.98
($5.5B)
($5 - 6B?)
No cost available for FCC-ee at this moment
W. Chou
CEPC Workshop, 11/8/2017

6. Two Different Timelines
ILC (2030)
CEPC (2030)
CLIC (2035)
FCC-ee (2039)
W. Chou
CEPC Workshop, 11/8/2017

7. CEPC CDR Goals Higgs: 1 million Higgs 10 years for L = 2 x 1034 Z:
1 year for physics
L as high as possible
W – same as Z
W. Chou
CEPC Workshop, 11/8/2017

8. CEPC Layout

9. CEPC Parameters Higgs W Z Number of IPs 2 Energy (GeV) 120 80 45.5
Higgs W Z
Number of IPs 2
Energy (GeV)
120 80
45.5
Circumference (km)
100
SR loss/turn (GeV)
1.68
0.33
0.035
Half crossing angle (mrad)
16.5
Piwinski angle
2.75
4.39
10.8
Ne/bunch (1010)
12.9
3.6
1.6
Bunch number
286
5220
10900
Beam current (mA)
17.7
90.3
83.8
SR power /beam (MW) 30
2.9
Bending radius (km)
10.9
Momentum compaction (10-5)
1.14
IP x/y (m)
0.36/0.002
Emittance x/y (nm)
1.21/0.0036
0.54/0.0018
0.17/0.0029
Transverse IP (um)
20.9/0.086
13.9/0.060
7.91/0.076
x/y/IP
0.024/0.094
0.009/0.055
0.005/0.0165
RF Phase (degree)
128
134.4
138.6
VRF (GV)
2.14
0.465
0.053
f RF (MHz) (harmonic)
650
Nature bunch length z (mm)
2.72
2.98
3.67
Bunch length z (mm)
3.48
3.7
5.18
HOM power/cavity (kw)
0.46 (2cell)
0.32(2cell)
0.11(2cell)
Energy spread (%)
0.098
0.066
0.037
Energy acceptance requirement (%)
1.21
Energy acceptance by RF (%)
2.06
1.48
0.75
Photon number due to beamstrahlung
0.25
0.11
0.08
Lifetime due to beamstrahlung (hour)
1.0
F (hour glass)
0.93
0.96
0.986
Lmax/IP (1034cm-2s-1)
2.0
4.1

10. CEPC vs FCC-ee: Higgs CEPC FCC-ee FCC-ee/CEPC Number of IPs 2
CEPC
FCC-ee
FCC-ee/CEPC
Number of IPs 2
Energy (GeV)
120
Circumference (km)
100
SR loss/turn (GeV)
1.68
1.72
Half crossing angle (mrad)
16.5 ?
Piwinski angle
2.75
Ne/bunch (1010)
12.9 15
1.16
Bunch number
286
393
Beam current (mA)
17.7 29
SR power /beam (MW) 30 50
1.7 (power ratio)
Bending radius (km)
10.9
Momentum compaction (10-5)
1.14
IP x/y (m)
0.36/0.002
0.3/0.001
1 mm / 2 mm (βy ratio)
Emittance x/y (nm)
1.21/0.0036
0.6/0.0013
Coupling 0.22% / 0.3%
Transverse IP (um)
20.9/0.086
13.4/0.036
3.7 (1/xy ratio)
x/y/IP
0.024/0.094
RF Phase (degree)
128
VRF (GV)
2.14
2.0
f RF (MHz) (harmonic)
650
Nature bunch length z (mm)
2.72
3.15
Bunch length z (mm)
3.48
4.9
1.4 (z ratio)
HOM power/cavity (kw)
0.46 (2cell)
Energy spread (%)
0.098
0.099/0.151
Energy acceptance requirement (%)
1.21
1.5
Energy acceptance by RF (%)
2.06
Photon number due to beamstrahlung
0.25
Lifetime due to beamstrahlung (hour)
1.0
42 min (total)
F (hour glass)
0.93
Lmax/IP (1034cm-2s-1)
7.8
3.9 (Lum ratio)

11. Can We increase Higgs Luminosity in CEPC?
Shall we increase bunch intensity (from 13 to 15)?
Larger beam-beam parameter y (from to 0.107)
Need larger momentum acceptance (from 1.2% to 1.5%)
Answer – No.
Shall we decrease β(y)* (from 2 mm to 1 mm)?
Would make already very difficult IR design more difficult
How about emittance?
ε(x) depends on cell length (CEPC: 71 m; FCC-ee: 55 m). But shorter length in creases cost (more magnets)
ε(y) depends on assumed x-y coupling (CEPC: 0.3%, FCC-ee: 0.22%). But smaller coupling is difficult or even not practical.
Answer – No change.
Conclusion – We will keep 2 x 1034 as the design goal.

12. CEPC vs FCC-ee: Z CEPC FCC-ee FCC-ee/CEPC Number of IPs 2 Energy (GeV)
CEPC
FCC-ee
FCC-ee/CEPC
Number of IPs 2
Energy (GeV)
45.5
45.6
Circumference (km)
100
SR loss/turn (GeV)
0.035
0.036
Half crossing angle (mrad)
16.5 ?
Piwinski angle
10.8
Ne/bunch (1010)
1.6 17
10.6
Bunch number
10900 (30 ns)
16640 (20 ns)
1.5
Beam current (mA)
83.8
1390
SR power /beam (MW)
2.9 50
17 (power ratio)
Bending radius (km)
10.9
Momentum compaction (10-5)
1.14
IP x/y (m)
0.36/0.002
0.15/0.0008
Emittance x/y (nm)
0.17/0.0029
0.27/0.001
Transverse IP (um)
7.91/0.076
6.36/0.089
x/y/IP
0.005/0.0165
RF Phase (degree)
138.6
VRF (GV)
0.053
0.1
f RF (MHz) (harmonic)
650
Nature bunch length z (mm)
3.67
3.5
Bunch length z (mm)
5.18
12.1
2.3 (z ratio)
HOM power/cavity (kw)
0.11(2cell)
Energy spread (%)
0.037
0.038/0.132
Energy acceptance requirement (%)
1.3
Energy acceptance by RF (%)
0.75
Photon number due to beamstrahlung
0.08
Lifetime due to beamstrahlung (hour)
70 min (total)
F (hour glass)
0.986
Lmax/IP (1034cm-2s-1)
1.0
230
230 (Lum ratio)

13. Can We increase Z Luminosity in CEPC?
Can we increase bunch intensity? (CEPC: 1.6, FCC-ee: 17)
Instability (microwave, TMCI, CBI) allows a factor of 2 increase
Beam-beam allows a factor of 3 increase (y from to 0.05)
Answer – can safely increase by a factor of 2 (from 1.6 to 3.1).
Can we reduce bunch spacing? (CEPC: 30 ns, FCC-ee: 20 ns)
SEY = 1.6 is too conservative, can be reduced to 1.2.
Answer – can safely reduce by 50%.
How about RF?
Power is no problem.
HOM and coupled bunch instability (CBI) allows an increase x7.
However, as small number of cavities will be used, coupler input power limit (300 kW) could be a bottleneck.
Answer – Under investigation.
Conclusion – If coupler power problem has solution, L can increase to 6 x 1034.

14. Highlight (1) – Dual Aperture D+S Magnet
Two types dual aperture dipole segments
The first and the last segments: sextupole combined
The three middle segments: dipole only
Beam center separation:
350mm
Trim coils:
For strength tapering
±1.5% adjustability
Radiation shielding:
30mm thickness

15. LEP Lead-Coated Vacuum Pipe
LEP acceptability criterion: Components fully operational after GeV
(i.e., 6 mA x 30,000 hrs)
Lead shielding (3 - 8 mm)
W. Chou
CEPC Workshop, 11/8/2017

16. Radiation Damage of LEP Magnet Coil
We obtained a large number of trim dipoles from LEP when it was decommissioned and used them in the MI-8 beam line and in the Recycler. From the darkening of the epoxy is was obvious that the coils had suffered radiation damage, and indeed we rejected a significant number of them for bad inductance measurements that we attributed to turn-to-turn shorts. More of them failed in operation. We eventually built all-new coils.
- D. Harding (Fermilab)
W. Chou
CEPC Workshop, 11/8/2017

17. CEPC
(100 km)
LEP1
LEP2

18. Dual Aperture D+S Magnet
Field optimization
For the dipole only segments
Pole shimming on the outer side to improve the uniformity
Better than
For sextupole combined segments
Tuning the pole surface profiles of each aperture
Further optimization is needed to make the dipole strength of two sides equal.
The sext. difference can be compensated by individual sext.
Adjusting the trim coil current in one aperture has no obvious effect to the field in the other aperture
Left aperture
Right aperture
Dipole T T
Quad.
T/m
T/m
Sext.
T/m2
T/m2

19. Dual Aperture Quadrupole
Polarity: F/D
Center separation:
350mm
Trim coils:
±1.5% adjustability
Gap between cores:
50mm
Magnetic shielding:
11.24mm
Radiation shielding:
30mm

20. New Lattice with Combined D+S Magnet
Five dipoles between two quadrupoles in the arc
Combined sextupoles are on the first and fifth dipoles (x,y >>y,x)
-- one dipole is cut into 6 slices
-- 7 thin sextupoles are insert in one dipole
No additional power sources for SF and SD SF SD

21. DA with Combined D+S Magnet
50% reduction
Optimization knobs: 234 K2s
Tracking 100 turns
20 seeds
Crab=1
phase=0
phase=/2
phase= 
phase=3/2

22. Radiation dose in Gy/Ah
Radiation damage
radiation damage in LEP
severed and degraded in Spring-8
Materials
Upper dose limit in Gy
Radiation dose in Gy/Ah
Time in h
Fiberglass
108
1.89×104
2.99×105
Semi-organic coating
Epoxy resin
2×107
5.98×104

23. Only 3% SR power escaped to the tunnel
Energy deposition
Only 3% SR power escaped to the tunnel
Total power 870 W/m
Beam direction: left W/m
Beam direction: right W/m
Al chamber
 199
186 
Cu chamber
 308
332
Dipole
 186
182
Lead A
 60.6
29.2 
Lead B
 33.5
80.0 
Lead C
 46.8
18.8 
Lead D
14.3
20.4 

24. RF Design and Optimization of 650MHz 2-cell cavity
Highlight (2) – Progress in SRF
RF Design and Optimization of 650MHz 2-cell cavity
The length of the cavity beam pipes and ports should be long enough to ensure negligible power dissipation on the gaskets and flanges surface, but cannot be too long to go beyond the critical temperature of Nb.
Special gapless gaskets will be considered to avoid the additional dissipation at different joints.
Cooling of cavity ports by extended helium vessel could be considered especially for the power coupler.
Copper plating is necessary for the bellows between cavities. RF shielded bellow might be needed.
Parameter
Unit
Value
Cavity frequency
MHz
650
Number of cells - 2
Cavity effective length m
0.46
Cavity iris diameter mm
156
Beam tube diameter
Cell-to-cell coupling 3%
R/Q Ω
213
Geometry factor
284
Epeak/Eacc
2.4
Bpeak/Eacc
mT/(MV/m)
4.2
P (W) (U = 1J) Qe
Port 1
2.19E12
Port 2
3.02E12
Port 3
7.51E11
Port 4
1.19E12
Port 5
1.23E12

25. Cavity Fabrication Progress in SRF
Three 2-cell cavities with coaxial HOM coupler, one 5-cell cavity with waveguide HOM coupler will complete fabrication at the end of 2017.
Cavity with more cells (4 or 5-cell)
A must for higher energy operation, and low HOM power (due to low current)
Possible for H with shared cavity if the input coupler power capacity could be increased to 500 ~ 800 kW or use two couplers per cavity for same gradient. If same coupler power, the gradient will be too low and cost more, beam loading effect ... But 1.5 times more HOM power, HOM damping and trapping, cavity pretuning, handling and infrastructure...
Not suitable for high current W and Z

26. N-doped 650 MHz Single Cell Cavity
Progress in SRF
N-doped 650 MHz Single Cell Cavity
FNAL PIP-II
A. Rowe. LINAC2016

27. 1.3 GHz SRF Technology for CEPC Booster
Progress in SRF
1.3 GHz SRF Technology for CEPC Booster
XFEL and LCLS-II type cryomodule, without SCQ. Technology R&D in synergy with Shanghai XFEL (SCLF). No big challenge.
TESLA cavity. Nitrogen-doped bulk niobium and operates at 2 K. Q0 > 3 × 1010 at 24 MV/m for the vertical acceptance test. Q0 > 1×1010 up to 20 MV/m for long term operation.
XFEL/ILC/LCLS-II or other type variable power coupler. Peak power 30 kW, average 4 kW, Qext 1E7-5E7, two windows.
XFEL/LCLS-II type end lever tuner. Reliability. Large stiffness. Piezos abundance, radiation, overheating. Access ports for easy maintenance.

28. IHEP New Large SRF Facility
Progress in SRF
IHEP New Large SRF Facility
4500 m2 SRF lab in the Platform of Advanced Photon Source Technology R&D (PAPS), Huairou Science Park, Beijing.
Mission: World-leading SRF Lab for Superconducting Accelerator Projects and SRF Frontier R&D.
Mass Production: 200 ~ 400 cavities (couplers) test per year, 20 cryomodules assembly and horizontal test per year.
Construction:

30. MODE: Multi-Objective optimization by Differential Evolution
Highlight (3) – Simulation Code Development
MODE: Multi-Objective optimization by Differential Evolution
The parallel algorithm is referencing to J. Qiang(IPAC’13)
Initialize the population of parameter vectors
Generate the offspring population using the above differential evolution algorithm
Find the non-dominated population, which are treated as the best solutions in DE to generate offspring
Sorting all the population, select the best NP solution as the parents
Return to step 2, if stopping condition not met

31. On Momentum Dynamic Aperture (CEPC-Higgs)
Simulation Code Development
On Momentum Dynamic Aperture (CEPC-Higgs)
Initial Phase: 0
Initial Phase: Pi/2
100 samples are tracked. 200 turns are tracked.
Synchrotron motion, synchtron radiation in dipoles, quads and sextupoles, tapering, Maxwellian fringes, kinematical terms, crab waist are included.

32. Off momentum Dynamic Aperture
Simulation Code Development
Off momentum Dynamic Aperture
W/O Optimization
Momentum Acceptance: 0.017
Error bar means min and max
90% survival
100 samples. Radiation fluctuation is included. 0.3% emittance coupling. 200 turns are tracked.

33. Challenge (1) – Machine-Detector Interface
MDI layout
The Machine Detector Interface of CEPC double ring scheme is about 7m long from the IP.
The CEPC detector superconducting solenoid with 3 T magnetic field and the length of 7.6m.
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 33mrad and the final focusing length is 2.2m
Lumical will be installed in longitudinal 0.95~1.11m, with inner radius 28.5mm and outer radius 100mm.

34. IR superconducting magnets
Machine-Detector Interface
IR superconducting magnets
Both of QD0 and QF1 are double aperture superconducting magnets.
QD0/QF1 and anti-solenoid are all in a cryogenics system.
QD0/QF1 peak field in coil 3.5T/3.7T.
Peak field in coil of Anti-solenoid is 7.4T before QD0, 2.9T within QD0 and 1.9T after QD0.

35. Solenoid compensation
Machine-Detector Interface
Solenoid compensation
Anti-solenoids are designed to compensate the solenoid field from the detector.
The integral longitudinal field Bzds within 0~2.12m is 0 and Bz is less than 460Gauss after 2.12m away from the IP.
The skew quadrupole coils are designed to make fine tuning of Bz over the QF1 and QD0 region instead of the mechanical rotation.

36. SuperKEKB Final Focus Magnets & Cryostat
W. Chou
CEPC Workshop, 11/8/2017
(Courtesy Norihito Ohuchi)

37. MDI
W. Chou
CEPC Workshop, 11/8/2017

38. QCS-L Magnets & Cryostat (real)
QC1LP
(no yoke)
QC2LP
Octupole corrector
Anti-solinoid
Permendur e+
Ø820
Ø1100
Ø500
Ø653
Ø405 e-
Permendur
Tungsten
QC2LE
QC1LE
W. Chou
CEPC Workshop, 11/8/2017

39. Challenge (2) – Booster Low Field Magnet
The core dilution technology of the CEPCB’s dipole magnet.
In transversal direction, by making the return yokes of the cores as thin as possible and by stamping holes in the pole areas, the weight of the cores can be reduced dramatically.
In longitudinal direction, the cores were made by 40% steel laminations and 60% aluminium laminations. The weight of the cores can be reduced further.

40. Challenge (3) – Power Consumption Location and electrical demand(MW)
Electric power demand estimated for CEPC
System
Location and electrical demand(MW)
Total (MW)
Ring
Booster
LINAC
BTL IR
campus
RF power source
160
7.68
1.75
169.43
Cryogenics
16.8
Converter for magnets
98.5
10.5
5.7 2
116.7
Experimental devices 14
Dedicated services 6 3 1
0.5
Utilities 40
45.5
General services 13
0.3 12
27.3
Total
334.3
20.18
11.45
3.3 18
400.23

41. FCC-ee

42. New Idea (1) – Linac Afterburner (W. Lu)

43. New Idea (2) – PWFA for Injector (J. Seeman)
PWFA or DWA Overview
New Idea (2) – PWFA for Injector (J. Seeman)
1.4 km
Main FCCee Ring Straights
175 GeV e+
175 GeV e-
Plasma cells or DWA cells
280 m radius
~500 m
6 total arcs
0.5m apart
6 total arcs
0.5 m apart … …
e- arcs
e+ and e- drive arcs
e+ one bunch
Bunch
compress
in arcs.
e- 5 bunches
e- 6 bunches
Kicker is a linear ramp.
Linac (30 GeV)

44. New Idea (3) – CEPC as a  Collider
Goal: 10,000 Higgs/year
RF (650 MHz, 8 sets, 0.5 GV /set) RF RF
e‒ (80 GeV)
Fiber Laser
(0.351 μm, 5 J, 3 kHz)
γγ collision
(125 GeV)
e‒ (80 GeV) RF RF e‒
80 GeV Booster
E = 80 GeV
ρ= 6000 m
U = 0.6 GeV/turn
I = 48 mA x 2
P(rf) = 58 MW e‒ RF RF RF

45. CDR Table of Contents

46. CDR Table of Contents (cont’d)

47. Summary
CEPC has made good progress in the design study as well as in R&D since the Pre-CDR. It is now ready for a CDR.
The accelerator community in China has built a young, talented and well-motivated team, which is eager to take up a big construction project.
2018 will be an important year for world HEP:
CEPC CDR will be published in April
FCC CDR will be published in November
Japanese government is expected to make a decision on ILC
LHC Run2 final result will be available
W. Chou
CEPC Workshop, 11/8/2017

48. “Dad, tell me one thing you did in your lifetime.”
A Scientist’s Dream
“Dad, tell me one thing you did in your lifetime.”
“I helped build the largest accelerator in the world.”
W. Chou
CEPC Workshop, 11/8/2017

49. Questions?

50. CEPC Magnet Radiation Dose (Gy/A-hr, Yadong Ding)
At 120 GeV:
A: 6.94×105
B: 2.39×105
C: 3.59×105
D: 3.59×105
E: 2.87×104
F: 2.13×103
G: 5.74×103
Unacceptable!
Insulation material
Upper dose limit (GY)
Radiation lifetime at 2 x 16.6 mA
Epoxy resin (coil)
2 x 107
2,500 hrs
Fiber glass (coil)
1 x 108
13,000 hrs
Semi-organic coating
(lamination)
8,400 hrs
W. Chou
CEPC Workshop, 11/8/2017

51. Electricity Bill For a 500 MW collider in China:
Fermilab:
$ 440k per MW-year
$ 20M a year (~5% of lab budget)
(5 US cents per kWh)
CERN:
1,200 GWh /year
CHF 65M a year (~5% of lab budget)
(5 Swiss cents per kWh)
BEPC II: (Qing Qin)
Annual machine operation: 100M yuan
Electricity: 40M yuan a year (US$ 6M)
(~3% of lab budget)
For a 500 MW collider in China:
To reach the required integrated luminosity, we need at least 4,400 hours for operation each year:
500 MW x 4,400 hours = 2.2 x 109 kW-hr
Annual electricity cost: RMB 2.2B (US$ 320M)
(RMB 1 yuan per kWh for industry, 3 times higher than in the US or France)
W. Chou
CEPC Workshop, 11/8/2017