1. CEPC RF Power Source System
Zusheng Zhou
Institute of High Energy Physics, Chinese Academy of Sciences
CEPC international workshop
November 12-14, 2018

2. Outline Design consideration R&D Progress Summary Collider Booster
Linac injector
R&D Progress
Design goal
1st prototype fabrication
High efficiency design
Summary

3. Introduction Injector
10GeV
Energy Ramp
10-45/120GeV
Electron
High power RF sources are required to provide the energy needed to accelerate particles or keep particles energy stable.
Positron
Booster
C=100km
CEPC Booster
SppC
Three rings in the same tunnel：
Collider & Booster
SppC
Collider Ring
C=100km
CEPC Collider
45/120 GeV

4. Collider
The Collider beam power is more than 60 MW. The increase in efficiency of RF power sources is considered a high priority issue.
RF power sources - efficiencies
Tetrodes
IOTs
Klystrons
SSA
Magnetrons
DC–400MHz
(200–1500)MHz
300 MHz – 1 GHz
DC – 20 GHz
GHz range
1 MW
1.2 MW
1.5 MW
< 1MW
85% - 90% (class C)
70%
65%
60%
90%
Remark
Broadcast technology, widely discontinued
Oscillator, not amplifier!
High power klystrons are the more attractive choice because of their high efficiency, low cost and more stable than IOT and SSA for CEPC collider.

5. Much higher efficiency, less energy consumption.
Collider
System overall efficiency
CEPC Collider SRF Wall Plug Efficiency
Wall to PSM power supply/modulator
95%
Modulator to klystron
96%
Klystron to waveguide
70%
Waveguide to coupler
Coupler to cavity
~100%
Cavity to beam
Overall efficiency
~60.6%
The critical factor is klystron efficiency
Much higher efficiency, less energy consumption.

6. CEPC at 800 RMB/MWh and 6000 hours/year
Collider
Efficiency impact on operation cost (Only considering operation efficiency of klystrons)
CEPC at 800 RMB/MWh and 6000 hours/year
Save Money
130M RMB
1 year
90 M RMB
Excessive electricity bill, M RMB
NOW
Efficiency, %
COMING
FUTURE

7. Coupler input power(kW)
Collider
Transmission system
Superconducting Cavity power demands
Parameters
Value
Freq.(MHz)
650+/-0.5
Cavity No.
240
Coupler input power(kW)
300
Considering klystron lifetime, power redundancy and cost, the 2 cavities will be powered with one CW klystron capable to deliver more than 800 kW.
Distribution of RF power (800kW) to the cavities (300kW), including waveguide, power divider, phase shifter, circulator and load.
Other Auxiliary PS, Interlock and Controls, LLRF, Pre-amplifier.

8. Collider Transmission system
Schematic of the RF Transmission System (RFTS)

9. Collider High efficiency klystron
The vast majority of the existing commercial klystrons in the electronic efficiency range between 40% and 55 %. Only a few klystron available on the market are capable of operating with about 65 % efficiency or above.
In a recent theoretical calculation，more than 80% RF power conversion efficiency is achieved in CW klystron. Considering this recent high efficiency approach, our design goal is to achieve around 80% on saturation point.
CEPC Klystron Key Design Parameters
Parameters
Units
Values
Centre frequency
MHz
650±0.5
Output power kW
800
Efficiency(Goal) %
80(70 linear)

10. Collider PSM Power supply PSM Design Parameters Parameters Units
Values
High voltage kV
130
Current A 16
Module quantity
168
Module voltage V
800
Module switch frequency Hz 1k
Module number of redundancy 9
Voltage stability %
< 0.2
Efficiency
>95
Turn-off time us
<5
Stored energy J
<20

11. Collider Infrastructure Collider Power Source Gallery
Klystron and transmission system are placed underground. PSM high voltage power supply and related auxiliary power supply are on the ground.

12. Collider Infrastructure
For space savings, transmission system in part are placed in RF tunnel.

13. Booster
Introduction
The Booster RF system consists of 1.3 GHz superconducting RF cavities. There are 12 cryo-modules for Higgs operation, each containing eight 9-cell superconducting cavities.
These cavities need 96 set 1300 MHz power sources.

14. Booster Power source choice-SSA
Their capabilities extend from a few kW to several hundred kW, and from less than 100 MHz to above 1 GHz. Reasonable efficiency (~50%), high gain, and modular design provide high reliability.
High reliability for redundancy design, high flexibility for module design, high stability, low maintenance requirements, absence of warm-up time and low voltage operation and reasonable efficiency.
So the SSA has been chosen for the Booster RF power source system.

15. Booster Solid state amplifier 1.3 GHz/25kW SSA Specifications
Parameters
Values
Frequency
1.3 GHz
Power
25 kW
Gain
≥65 dB
Bandwidth (1dB)
≥ 1 MHz
Amplitude stability
≤0.1% RMS
Phase stability
≤0.1°RMS
Phase Variation
≤10°
Harmonic
< -30 dBc
Spurious
< -60 dBc
Efficiency at 25kW
≥45%
MTBF
≥30000 h
Redundancy
1 power module failure

16. Booster
RF Transmission system

17. Linac injector Introduction
The main high power RF components are 75 units of 80 MW S-band klystrons and conventional solid state modulators.
A waveguide system is used for power transmission from the klystrons to the accelerating structures, 75 klystrons are used to provide power for 288 accelerating structures.

18. R&D Progress Strategy and plan Progress of 1st prototype fabrication
650MHz/800kW meets CEPC project demands
>80% efficiency
Progress of 1st prototype fabrication
Beam dynamic, beam optics and cooling system
Mechanical design, infrastructure preparation
Design progress on high efficiency klystron
Optimization using different methods
Multi-Beam Klystron consideration

19. Strategy and plan (2016 to 2021) 3 or more klystron prototypes 2016
2017
2018
2019
2020
2021
Prototypes
Step1
1st
4th
Step2
2nd
5th
Step3
3rd
6th
more

20. Progress of 1st prototype development
Conventional method based on 2nd harmonic cavity in order to investigate the design and manufacture technologies for high power CW klystron
Design Parameters
Main parameters
Goal
Freq. (MHz)
650
Vk (kV)
-81.5
Ik (A)
15.1
Perveance (µP)
0.65
Efficiency (%)
>60
Output power (kW)
800
1dB bandwidth (MHz)
±0.5

21. Dynamics for 1st tube
1D optimization on the dynamics and cross checked by 2D &3D
1D AJDISK
73% efficiency
2D EMSYS
68% efficiency
3D CST
65% efficiency

22. Electron beam trajectory without RF drive
Gun design
Results for beam optics using different codes and thermal-structure analysis using ANSYS
Main parameters
DGUN
EGUN
MAGIC2D
CST
Design goal
Beam waist radius (mm)
17.8
17.48
17.64
17.5
Perveance (µPerv)
0.64
0.65
Current density
<0.45
0.39~0.43
<0.5
Current uniformity
9.8%
<10%
Beam optics
Thermal deformation
Electron beam trajectory without RF drive
Beam profile shows laminar flow
Ripple rate < 5%

23. On-axis magnetic field
Focusing coils
Designed by 2D and cross checked by 3D, very good consistency obtained
15 regular coils with 1 bucking coil near the gun
2D solenoid model
3D solenoid model
On-axis magnetic field

24. Cavity chain and it’s cooling system
RF design and cooling analysis conducted
Grooved nose cone for each cavity to suppress the multipacting effect
Grooved nose cone
Cavity chain
Cooling pipes distribution
Temperature distribution
cavity chain cooling scheme

25. Collector and window
~2m long collector to sustain 1.23MW full beam power
Thermal load distribution
Temperature distribution
Mechanical design
>800 kW sustainable CW RF power and < ±0.5MHz
Temperature distribution
Mechanical design

26. Mechanical design progress
3D model and 2D drawings are ready for manufacturing
3D model
2D drawings

27. 165 pages
Klystron body

28. Collector
Oil tank
Coils

29. Infrastructure preparation
The contract of new big furnace has been signed last month and construction period is less than 8 month.
All the procedures for the construction of the plant have been completed.
Construction period is less than 4 month.
Dimension of main building

30. High efficiency design
Schemes of 3 designs
Scheme 1：Optimize cavity chain by using the same gun as 1st tube
Scheme 2: With high voltage gun (110 kV/9.1 A), low perveance
Scheme 3：MBK, 54 kV/20 A electron gun
Parameter
Scheme1
Scheme2
Scheme3
Freq. (MHz)
650
Voltage (kV)
81.5
110 54
Current (A)
15.1
9.1
20(2.5×8)
Beam No. 1 8
Perveance (µP)
0.65
0.25
1.6(0.2×8)
Efficency (%)
>70
~80
>80
Power(kW)
800
800(100×8)

31. Tentative Scheme 1 Same gun with the 1st tube Optimization
8 CAV/1 2nd harmonic CAV/80%/3.1m
10 CAV/2 2nd harmonic CAV/80%/2.9m
8 CAV/2 2nd harmonic CAV and 1 3rd harmonic CAV/80%/2.2m

32. Tentative Scheme 2 Based on CSM，with 2nd and 3rd harmonic cavities
Better bunching with shorter length
AJDISK/EMSYS/CST 86%/81%/77%
Reduce beam aperture and beam size
KLYC 1D/ KLYC 2D/ EMSYS 82.6%/80.8%/81%

33. Tentative Scheme 3 Based on CSM, with 2nd and 3rd harmonic cavities
Perveance is 0.2 µPerv
CSM: 8 CAV / 2.4m / 88.5%
CSM: 7 CAV / 1.8m / 87.6%
650MHz
1300MHz
1950MHz

34. Summary
Design of RF power sources for collider, booster and linac is showed;
The increase in efficiency of RF power sources is considered a high priority issue;
All drawings of the 1st prototype has finished and it is being processed and manufactured in the machine shop;
The three different schemes for the high efficiency klystron design are ongoing simultaneously and more prototypes will be manufactured in the near future.

35. Thanks for your attention!