Overall Design of the CEPC Injector Linac

Jingru Zhang
On behalf of CEPC linac teamInstitute of High Energy Physics, CAS
2018.11.22

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Outline

1 CEPC layout
2 CEPC linac design
3 CEPC linac key technologies development
4 Summary

2018.11.22

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CEPC layout• CEPC (Circular Electron-Positron Collider)
was proposed by Chinese Scientists in Sep.
2012
• It is a Higgs Factory• There will be two detectors in the mainring• The CDR has been official released in Nov
14, 2018• From 2018-2022, finish TDR
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CEPC layout• The circumference of the collider is 100 km(120Gev)l
The booster circumference is 100 km.
l
The total length of the linac is about 1.2 km
10GeV

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Outline

1 CEPC layout
2 CEPC linac design
3 CEPC linac key technologies development
4 Summary

2018.11.22

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CEPC linac designl

The requirements of the booster to the linac
Parameter

Symbol

Unit

Value

e- /e+ beam energy

Ee-/Ee+GeV

10Repetition rate

frepHz100

Bunch numbers per pulse
e- /e+ bunch population

1Ne-/Ne+nC

Energy spread (e- /e+ )σEEmittance (e- /e+ )εr

2018.11.22>9.4109>1.5<210-3nm<1206CEPC linac designlLinac design goals

Should provide beams that can meet requirements ofBoostern Top-up injection can be implemented
n Should have the high availability and reliability
nThermionic electron gun (High charge)u Normal conducting structures and mature technologiesu ~ 15% backups for linac RF units
unShould have the potential to meet the higher
requirements and updates in the future, such as
Two bunches accelerating modeu Increasing of charge quantity
u …...
u2018.11.227

CEPC linac designl

Layout of the linac
nElectron linacnPositron linac

ElectronSource andBunching
SystemElectron Bypass
Transport Line(EBTL)

Section 1PSPAS(ESBS)
50MeV

4GeV

200MeV

Positron Source andPre-Accelerating
Section (PSPAS)
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Section 3DR

1.1GeV

4GeV

10GeV

Section 28

CEPC linac design

80MW klystron2018.11.22

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CEPC linac designlElectron linac (source)

S.L. Pei

ParmelaThermionic triode electron gun
n Sub-harmonic pre-buncher
n143 MHzu 572 MHzunBuncher & A0un

Emittanceun2860 MHz<100 mm-mrad (Norm.Rms)

Transmission efficiencyu

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~90%

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CEPC linac design
lElectron linac

Section 1Section 3

10 GeV with 3nC chargen Energy spread (rms): 0.15%
n Emittance (rms): 5nm
nC. Meng
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11CEPC linac designlPositron linac (Source)
Target (conventional)n Adiabatic Matching Device (AMD)n Capture sectionn Pre-accelerating sectionn Chicane (Deflecting the useless electrons andphotons)n2018.11.22

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CEPC linac designlPositron linac (Source :Target )nElectron beam

4 GeV/10 nC/100 Hz
u Beam size (Rms): 0.5 mm
u Beam power: 4 kW
unTargetTungsten
u Thickness 15 mm
unEnergy deposition
0.784 GeV/e- @ FLUKA
u 784 W à water coolingun

Support && coolingu

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Copper13

CEPC linac designlPositron linac (Source :AMD)

Length: 100 mm
n Aperture: 7 mmà52 mm (accelerating structureaperture is 25mm)
n Magnetic field: (5.5 Tà0 T) + 0.5 Tn

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CEPC linac designlPositron linac (Source: AMD)
nLonger bunch length

Different energy
u Different horizontal momentum
uDistribution before and after AMD
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15CEPC linac designlPositron linac (Source: Capture section)nCapture structure

Length:2 mu Aperture: 25 mm
u Gradient: 22 MV/mun

The capture RF phase

Capture efficiency VS. input RF phase2018.11.22

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CEPC linac designlPositron linac (Source: Capture section)n

The capture phase

Accelerating modeu better moment chipu small phase spreadu

Deceleration mode (D1)

Acceleration mode (A1)

Distribution of different mode
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CEPC linac designlPositron linac (Source: The preaccelerating structure)nn

Different modes have different optimal
accelerating phases
Acceleration mode have higher positron yieldu

Stray bunches should be considered
Deceleration mode (D1)

Acceleration mode (A1)

Ne+/Ne-[-10,10,230 MeV,260 MeV]=0.4

Ne+/Ne-[-8,12,235 MeV,265 MeV]=0.55

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CEPC linac designlPositron linac (Source)nNorm. RMS. Emittance is about 2500
mm-mradnEnergy: >200 MeVnPositron yieldu

Ne+/Ne- ~=0.55

u[-8,12,235 MeV,265 MeV]
XPhaseEnergy
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CEPC linac designlPositron linac (Damping ring)

DR V2.0Energy
Circumference
Storage time
Bending radius
Dipole strength B0U0
Damping time x/y/z
d0e0UnitGeVmmsMTkeV
ms%
mm.mradszinjmm
Nature szmm
einjmm.mrad
eext x/ymm.mrad
dinj /dext%
Energy acceptance by RF%
fRF
MHzVRFMV

2018.11.22

D, Wang

Value
1.1
75.4
20
3.565
1.03
36.3
15.2/15.2/7.6

0.05
376.7
5.0
7.5
2500
530/180
0.2/0.05
1.0
650
2.020

CEPC linac design
lPositron linac

10 Gev with 3 nC chargen Energy spread (rms): 0.16%n Emittance with DR (rms): 30(H)/10nm(V)n2018.11.22

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Outline

1 CEPC layout
2 CEPC linac design
3 CEPC linac key technologies development
4 Summary

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CEPC linac key technologies development
lS-band accelerating structurelFlux concentrator

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CEPC linac key technologies developmentlS-band accelerating structure design
nMotivation: The total energy of the main Linac is 14 GeV.

nGoal: For the 3 meters long accelerating structure, about 30
MV/m@1S (without beam) is expected.

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CEPC linac key technologies development
lS-band accelerating structure design
nCavity shape optimization

Superfish is used to optimize the single cell.
u Rounding the cell improves the quality factor by >12%and reduces the wall power consumption. At the sametime, the shunt impedance increases by ~10.9%.
u Irises with elliptical shape (r2/r1=1.8) can reduce thepeak surface field by 13%.
uDisc-loaded cavity

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Rounding shape25

CEPC linac key technologies development

151052a2b015350

050
Cell number

0.02

600.015400.01

Shunt impedance

200.005

0001540015300

S-band travelling wave accelerating structure
design0.025

80204060Cell number

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15450

80

80
Power flowMW

Shunt impedance MΩ/m

0S-band travelling wave accelerating structure
design50
Cell number

S-band travelling wave accelerating structure
design
35

75MV

3060

25
2040
Power flow

20

15

Gradient

1050

GradientMV/m

2015500

Unloaded Q

25

89.8
89.6
89.4
89.2
8988.8
88.6
88.4
88.2

relative group velocity

30

S-band travelling wave accelerating structure
designCavity diameters 2b (mm)S-band accelerating structure design
Beam diameters 2a(mm)l00204060
Cell number

8026

CEPC linac key technologies development
lS-band accelerating structure design
Parameters
No. of Cells
Phase advance
Total length
Length of cell (d)Disk thickness (t)Shunt impedance (Rs)
Quality factor
Group velocity: Vg/c (%)
Filling time (tf )Attenuation factor (τ)

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Values84+2*0.52π/3
3.134.9885.5
60.3~67.8
15465~15373
2% ~ 0.94%
784
0.46

Unitradm
mmmm
MΩ/mnsNp27

CEPC linac key technologies development
lS-band accelerating structure designnCoupler design
The asymmetry of the coupling
cavity will cause emittance growth.
u The shape of the coupling cavity is
racetrack dual-feed type.
u Kyhl method is used to match thecoupler.
u!"#$%"&' =4∆567∆3- =-*8&*!"#%"%)%&'+ ,-*[∆9 ∗ ;<=> −∆667,∆/012The calculation model*The distribution of the electric field on axiscos>]
Phase advance per cell2018.11.22

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CEPC linac key technologies development
lFactors to limit the gradient:nPeak surface electric field (E_peak)un

1 62 M+/ = 2C - 32 5

Peak surface magnetic field (H_peak)u, 6562C$
C6= "6││2C %&6!
'( )*+,n62626

5C 6Modified Poynting vector(Sc),78 8un6 6 C
6 2C C 6- 32 5 .M-+ ./ 1̅
3 62 5I

Pulse length

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23 4̅
52C6
6 6 C

1IS6+ %9:;<C * C 6 362=
3= C 6 2 6 E2 6+0 ==29

CEPC linac key technologies development
lFactors to limit the gradient:

3D program HFSS is used to confirm the design.
n The 1st cell adjacent the input coupler is simulatedfor Pin=75 MW.
n The values are safe. Both E_peak and Sc locates at
the irisMV/m.
area.
E_peak=73
H_peak=86 kA/m.
Sc_max=0.59 MW/mm2.
nSurface electric field
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Surface magnetic field

Modified Poynting vector
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CEPC linac key technologies development
lFactors to limit the gradient:

To reduce the pulsed heating, the coupler windowedge is rounded.
40c]=127 - [/0/2]![
5. 7-8 . 9: [;<]n For S-band copper:n For 75 MW input power, the maximum value of thepeak surface magnetic field is 2.1*105 A/m. for 1 S
pulse length, Δ!=9.40C.
n││!

2018.11.22"││$%&'( )*+,

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CEPC linac key technologies developmentlS-band accelerating structure designnMechanical design
Inner water-cooling has been adopted. 8 pipes arearound the cavity.
u Compact coupler arrangements. The splitter is milling
together with the coupling cavity.
u Two tuners are outside the cavity.
u2018.11.22

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CEPC linac key technologies developmentlMechanical design

Accelerating structure under cold test

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CEPC linac key technologies development
lS-band accelerating structure designnHigh power test bench
The power source is available at IHEP.
u The faraday cup and magnet has been
designed in order to diagnostic the darkcurrent.
u The high power test will begin recently.
uModulator and klystron

Test bench upgrade2018.11.22

Analyzing Magnet

Faraday Cup34

CEPC linac key technologies developmentlFlux concentrator design

The FLUX concentrator produces a pulsed
magnetic field of 6 T to 0.5 T and It is difficult tomachining.
n An MOU was signed with KEK to assist us in thespiral wire cutting process.
n2018.11.22

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CEPC linac key technologies developmentlFlux concentrator design
nsolid-state pulsed power generator
The maximum output value is 15 kA / 15 kV / 5 µs;
u Solid state IGCT discharge switch module is used;
u The 10 kA output power has tested successfully;
u Full output power 15 kA will be tested in the near future.
uParameters

Value

Unit

≥15kA

5 0.5

us

Half sine wave-Repetition frequency

50HzLong term stability

0.5%-Peak voltage of charging
The type of discharge
switch15kV

IGCT-Peak pulse current
Pulse width (bottomwidth)
Pulse waveform

0 0 -1

2018.11.22-010-101036

Summary
The linac provides 10 GeV electron and positron beamwith single bunch mode to the Booster.
l A bypass section has been designed for the e- to makethe e+ target simple.
l A fixed tungsten target is used in the positron source
system. The e- beam on the target is 4 GeV & 10 nC.
l A damping ring is in the position of 1.1 GeV to reduce
the positron emittance.
l An
S-band accelerating structure and A FLUX
concentrator are designed andfabricated. The
prototypes are under test.
l

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Thank you for your attention!

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