1. 제2회 국제선형충돌가속기(ILC) Workshop
초전도 RF Cavity의 기술 및 ILC 건설에 한국의 참여방안, PAL의 관련 연구소개
손 영욱, 고 인수, 남궁 원
포항가속기연구소, 포항공과대학교
포항가속기연구소
Working Group 3: Accelerator Technology

2. Contents Activities of PAL in SC RF Technology - beam dynamics
- cavity design
- cryostat design
Technical Topics for SC RF Cavity Module
Proposal to Contribute ILC in Part of Cold Technology
1/22

3. Activities of PAL in SC RF
초전도 3rd Harmonic RF cavity의 feasibility study
- Beam dynamics 측면에서 필요성 연구 o Beam emittance의 개선으로 인한 빔수명단축을 개선
o Landau damping에 의한 빔안정화 개선
초전도 3rd Harmonic RF cavity의 Prototype 설계 Cavity shape 선정 및 field 해석
- Prototype 공학설계
초전도 Cavity 제작공정 연구 제작공정에 대한 외국사례연구
- 국내 업체의 제작능력 조사
2/22

4. Activities of PAL in SC RF
초전도 RF cavity 시험용 초저온 용기 설계
선진 연구 Group의 자문
- 일본 KEK 시설견학 (K,Saito Lab.) 및 자문
- 스위스 SLS 시설견학 및 자문
- 독일 BESSY SC cavity 설계자 자문
- 이탈리아 ELETTRA 설계자 자문
3/22

5. Feasibility Study of SC 3H Cavity for PLS in Beam dynamics
Fig. Potential well and longitudinal
bunch distribution of PLS
Fig. Lifetimes(□) and bunch
lengths(●) with 3rd harmonic
voltage
4/22

6. Preliminary Design of SC 3HC for PLS
Frequency MHz
Cavity type Elliptical
Diameter cm
Bore diameter 9.0 cm
Table. Material Properties
PARAMETERS VALUE
Material Niobium
Critical magnetic field mT
Critical temperature K
Resistivity x10-9  m
Residual resistance x10-6 
Operating temperature K
Fig. Cavity Geometry
5/22

7. Preliminary Design of SC 3HC for PLS
Table. RF characteristics
PARAMETERS VALUE
Averaged accelerating field MV/m
Frequency MHz
Stored energy Joules
Power dissipation W/cavity
Quality factor E+09
Shunt impedance MOhm/m
Rs*Q 
Z*T*T MOhm/m
Geometry factor(r/Q) Ohm
Ratio of peak fields Bmax/Emax mT/(MV/m)
Peak-to-average ratio Emax/E
Fig. Accelerating field
6/22

8. Conceptual Design of Cryomodule
Port for Instruments
Super-insulation
30 layers
50 layers
LN2 Tube
Port for Vacuum Pump
Port for RF Instruments
GHe Tube
LHe Tank
(Titanium)
Thermal Shield (30K)
Thermal Shield (77K)
External Vacuum Tank
(sus316)
SC RF Cavity
(Niobium)
Beam Tube
(SUS 316)
Port for Cryogenic Devices
1200
600
Fig. Conceptual scheme of cryomodule for SC cavity
7/22

9. Conceptual Design of Cryomodule
Table. Heat Loads of Cryogenic cooling system
HEAT SOURCES VALUE (W)
Dissipations in cavity
Conduction via warm flange of cryomodule
Conduction via feed-through of instruments 8
HOM couplers (or absorber) ?
Cryogenic losses in cryogenic supply system 30
Total 
()Total heat load depends on the scheme of HOM power removal and the piping distance between SC cavity and cold box of cryogenic system.
The refrigerator, of which capacity is more than 120 Watt, is required with consideration of capacity margin
8/22

10. Cryostat for Vertical Test
TEST PORT
LHe TUBE
LN2 TUBE
GHe TUBE
GN2 TUBE
He LEVEL
N2 LEVEL
INSULATION
PLUG
THERMAL
SHIELD (77K)
SUPER
INSULATING
VACUUM
VESSEL
TEST CRYOSTAT
2030
505
Prototype 3rd harmonic cavity
- Nb cavity with 2 volumes
- Test cryostat with multi-
purpose
- Cold test of SC cavity
- Design study
9/22

11. Design of Test Cryostat
Parameters
Values
Helium vessel neck diameter (mm)
505
Liquid helium volume (liter)
170
Liquid nitrogen volume (liter)
190
Working environment temperature (K)
helium vessel
nitrogen vessel
4.2
77.3
Liquid He consumption rate via cryostat (liter/hr)
0.7
Liquid He consumption rate via current leads (liter/hr)
2.4
Liquid nitrogen consumption rate (liter/hour)
Design pressure (Mpa)
0.25
Operation pressure
helium vessel (Mpa)
nitrogen vessel (Mpa)
thermal insulation space (pa)
0.1
<10-6
Cryostat height (mm)
2200
Cryostat diameter (mm)
800
Total weight (Kg)
~300
10/22

12. Technical Topics for SC RF Cavity Module
Superconductivity of Niobium
Critical magnetic field
Penetration depth, coherence length, G-L parameter, RF critical magnetic field
Thermal conductivity
RRR measurement
Surface resistance in AC application
11/22

13. Technical Topics for SC RF Cavity Module
Design of SC RF Cavity
Cavity shape
Characteristic parameters of RF cavity
Analysis of electromagnetic fields
Engineering design
Planning fabrication and tests & measurements
12/22

14. Technical Topics for SC RF Cavity Module
Fabrication of SC RF Niobium Cavity
Forming (deep drawing, spinning, hydroforming)
Coated cavity with Nb film
Trimming
Correcting machining error
Beam tube fabrication
Electron Beam Welding (EBW)
Bonding technology
13/22

15. Technical Topics for SC RF Cavity Module
Cleaning & Conditioning
Mechanical grinding
☞ Centrifugal barrel polishing (CBP)
Chemical polishing (CP)
Electropolishing (EP)
Heat treatment
High pressure rinsing with ultra-pure water (HPR)
Ultrasonic rinsing
Assembly in clean room
14/22

16. Technical Topics for SC RF Cavity Module
Test & Measurements in Vertical Cryostat
Theory of RF measurement of SC cavities
RF measurement system for vertical test;
electronic devices, monitoring sys., controller, etc
Cryogenics for cooling
RF accessories;
pickup/input coupler, RF generator, vacuum devices, etc
15/22

17. Technical Topics for SC RF Cavity Module
Final Cavity Assembly Method with Cleanness
Cavity disassembly after vertical test;
- preventing large degradation from exposure to air
- baking to recover performance
- removing indium sealing
Assembly in horizontal cryostat
16/22

18. Technical Topics for SC RF Cavity Module
Cryogenics
Design of horizontal cryostat for SC cavity modules
- horizontal test cryostat
- real cryostats for installation
Fabrication of horizontal cryostat
Test of cryostat performance
Assembly cryomodules with SC cavity
Design of cryo-plant
17/22

19. Advanced Technical Issues (Challenges)
High gradient SC cavity, Eacc > 45 MV/m
- High pure niobium material, RRR~250
- Electropolishing (EP)
- High Pressure Water Rinsing (HPR)
- Baking (70~140oC)
Degradation-free final cavity assembly
- Opening vacuum with argon gas
- Simple aluminum vacuum sealing
Cost-effective cavity production method
- Nb/Cu clad seamless cavity
- Simplified surface treatment
18/22

20. Proposal to contribute ILC in part of SC RF Cavity
Work Process: Superconducting RF cavity
Establishment of technology for high gradient accelerating field, Eacc  35 MV/m
- 일본 KEK, 미국 FNAL 등에서 기술개발 주도
- 한국의 PAL, … 등에서 공동참여 및 인력 training
Preliminary development of prototype cavity modules
- 설계, 제작, 시험 등 KEK, FNAL 등에서 개발 주도
- 한국의 PAL, … 등에서 인력지원 및 training
19/22

21. Proposal to contribute ILC in part of SC RF Cavity
Work Process: Superconducting RF cavity
Calculation & design of production cavities
- KEK, FNAL 등에서 개발 주도
- 한국의 PAL, … 등과 설계참여 및 training
Fabrication, cleaning & conditioning
- 국내 제작을 위한 시설확보 (PAL, …, 참여기업)
- 제작후 processing을 위한 시설확보 (PAL, 참여기업)
- 국내 지분율에 해당하는 cavity제작 (PAL, …, 참여기업)
: 9-cell cavity 약 2,000 set
20/22

22. Proposal to contribute ILC in part of SC RF Cavity
Work Process: Superconducting RF cavity
Vertical test of 9-cell cavity
- Vertical test를 위한 시설확보 (PAL, …)
- 9-cell cavity에 대한 상온 및 저온상태에서 시험
(PAL, …)
21/22

23. Proposal to contribute ILC in part of cold technology
Work Process: Cryogenics, Test & Measurement
in Cryomodule
Assembly of cryomodule with 9-cell cavities
- 시험용 horizontal cryostat 설계, 제작 (KBSI, 참여기업)
- Test facility 구축 (KBSI, 참여기업)
- 양산용 cryostat 설계, 제작 (KBSI, 참여기업)
- 9-cell cavity 12 set로 구성된 cryomodule 조립
Test & measurements with horizontal cryomodule
- Test & measurements (KBSI)
- Data analysis (KBSI, PAL)
22/22

24. 감사합니다.