Technical Status of Superconducting RF Cavity in Particle Accelerators

제 2 회 국제선형충돌가속기 (ILC) Workshop

초전도 RF Cavity 의 기술 및 ILC 건설에 한국의 참여방안 , PAL 의 관련 연구소개

포항가속기연구소 , 포항공과대학교

Working Group 3: Accelerator Technology

손 영욱 , 고 인수 , 남궁 원

2004. 12. 28-29 포항가속기연구소

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

Activities of PAL in SC RF

초전도 3rd Harmonic RF cavity 의 feasibility study - Beam dynamics 측면에서 필요성 연구

o Beam emittance 의 개선으로 인한 빔수명단축을 개선 o Landau damping 에 의한 빔안정화 개선

초전도 3rd Harmonic RF cavity 의 Prototype 설계 - Cavity shape 선정 및 field 해석

- Prototype 공학설계

초전도 Cavity 제작공정 연구 - 제작공정에 대한 외국사례연구

- 국내 업체의 제작능력 조사

2/22

초전도 RF cavity 시험용 초저온 용기 설계

선진 연구 Group 의 자문 - 일본 KEK 시설견학 (K,Saito Lab.) 및 자문 - 스위스 SLS 시설견학 및 자문 - 독일 BESSY SC cavity 설계자 자문 - 이탈리아 ELETTRA 설계자 자문

Activities of PAL in SC RF

3/22

Feasibility Study of SC 3H Cavity for PLS in Beam dynamics

Fig. Lifetimes(□) and bunch lengths(●) with 3rd harmonic voltage

Fig. Potential well and longitudinal bunch distribution of PLS

4/22

Frequency 1500 MHz Cavity type Elliptical Diameter 19.2 cm Bore diameter 9.0 cm

PARAMETERS VALUE Material NiobiumCritical magnetic field 190 mTCritical temperature 9.2 KResistivity 1.724x10-9 mResidual resistance 1.077x10-6 Operating temperature 4.5 K

Table. Material Properties

Fig. Cavity Geometry

Preliminary Design of SC 3HC for PLS

5/22

Preliminary Design of SC 3HC for PLS

PARAMETERS VALUEAveraged accelerating field 4.20 MV/mFrequency 1499.99 MHzStored energy 0.1012 JoulesPower dissipation 15.88 W/cavityQuality factor 0.2403E+09 Shunt impedance 243671.03 MOhm/mRs*Q 258.95 Z*T*T 41505.11 MOhm/mGeometry factor(r/Q) 34.54 Ohm Ratio of peak fields Bmax/Emax 3.32 mT/(MV/m)Peak-to-average ratio Emax/E0 2.84

Table. RF characteristics

Fig. Accelerating field6/22

Conceptual Design of Cryomodule

Fig. Conceptual scheme of cryomodule for SC cavity

Port for Instruments Super-insulation30 layersSuper-insulation50 layers

LN2 TubePort for Vacuum PumpPort for RF Instruments

GHe Tube

LHe Tank(Titanium)

Thermal Shield (30K)

Thermal Shield (77K)

External Vacuum Tank(sus316) SC RF Cavity

(Niobium)Beam Tube(Niobium)

Beam Tube(Titanium) Beam Tube

(SUS 316)

Port for Cryogenic Devices

1200

600

7/22

Conceptual Design of Cryomodule

HEAT SOURCES VALUE (W)Dissipations in cavity 32 Conduction via warm flange of cryomodule 11 Conduction via feed-through of instruments 8 HOM couplers (or absorber) ?Cryogenic losses in cryogenic supply system 30 Total 81+

Table. Heat Loads of Cryogenic cooling system

()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

Prototype 3rd harmonic cavity - Nb cavity with 2 volumes - Test cryostat with multi- purpose - Cold test of SC cavity - Design study

Cryostat for Vertical Test

TEST PORTLHe TUBE

LN2 TUBE

GHe TUBE

GN2 TUBE

He LEVEL

N2 LEVEL

INSULATION PLUG

THERMALSHIELD (77K)

SUPERINSULATION

INSULATINGVACUUMVESSEL

TEST CRYOSTAT

2030

505

9/22

Parameters Values

Helium vessel neck diameter (mm) 505Liquid helium volume (liter) 170Liquid nitrogen volume (liter) 190Working environment temperature (K) helium vessel nitrogen vessel

4.277.3

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) 0.7Design pressure (Mpa) 0.25Operation pressure helium vessel (Mpa) nitrogen vessel (Mpa) thermal insulation space (pa)

0.10.1

<10-6

Cryostat height (mm) 2200Cryostat diameter (mm) 800Total weight (Kg) ~300

Design of Test Cryostat

10/22

Critical magnetic fieldPenetration depth, coherence length, G-L parameter, RF critical magnetic fieldThermal conductivityRRR measurementSurface resistance in AC application

1. Superconductivity of Niobium

Technical Topics for SC RF Cavity Module

11/22

Cavity shapeCharacteristic parameters of RF cavityAnalysis of electromagnetic fieldsEngineering designPlanning fabrication and tests & measurements

2. Design of SC RF Cavity

Proposed 3rd Harmonic cavity for PLS F = 1499.994 MHz

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12/22

Forming (deep drawing, spinning, hydroforming)

Coated cavity with Nb film

Trimming

Correcting machining error

Beam tube fabrication

Electron Beam Welding (EBW)

Bonding technology

3. Fabrication of SC RF Niobium Cavity


13/22

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

4. Cleaning & Conditioning


14/22

Theory of RF measurement of SC cavities RF measurement system for vertical test;

electronic devices, monitoring sys., controller, etcCryogenics for coolingRF accessories;

pickup/input coupler, RF generator, vacuum devices, etc

5. Test & Measurements in Vertical Cryostat


15/22

Cavity disassembly after vertical test; - preventing large degradation from exposure to air - baking to recover performance - removing indium sealing

Assembly in horizontal cryostat

6. Final Cavity Assembly Method with Cleanness


16/22


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

7. Cryogenics

17/22

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

Proposal to contribute ILC in part of SC RF Cavity

1. 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

2. Preliminary development of prototype cavity modules

- 설계 , 제작 , 시험 등 KEK, FNAL 등에서 개발 주도

- 한국의 PAL, … 등에서 인력지원 및 training

Work Process: Superconducting RF cavity

19/22


3. Calculation & design of production cavities

- KEK, FNAL 등에서 개발 주도

- 한국의 PAL, … 등과 설계참여 및 training

4. Fabrication, cleaning & conditioning

- 국내 제작을 위한 시설확보 (PAL, …, 참여기업 )

- 제작후 processing 을 위한 시설확보 (PAL, 참여기업 )

- 국내 지분율에 해당하는 cavity 제작 (PAL, …, 참여기업 )

: 9-cell cavity 약 2,000 set


20/22


5. Vertical test of 9-cell cavity

- Vertical test 를 위한 시설확보 (PAL, …)

- 9-cell cavity 에 대한 상온 및 저온상태에서 시험

(PAL, …)


21/22

Proposal to contribute ILC in part of cold technology

1. 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 set 로 구성된 cryomodule 조립

2. Test & measurements with horizontal cryomodule - Test & measurements (KBSI) - Data analysis (KBSI, PAL)

Work Process: Cryogenics, Test & Measurement in Cryomodule

22/22

감사합니다 .

Technical Status of Superconducting RF Cavity in Particle Accelerators

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