Shuichi Noguchi 、 KEK 6-th ILC School, November 20111 Superconducting Cavity Design ( RF, Mechanical, Thermal ) Material Fabrication Techniques

Shuichi Noguchi 、 KEK

6-th ILC School, November 2011 1

Superconducting Cavity Design ( RF, Mechanical, Thermal ) Material Fabrication Techniques Surface Treatment Surface Inspection Vertical Measurement Cavity Behavior Diagnostics

Part-1



SRF Cavity Peculiarities

Surface Condition is essential,　　 but is usually irregular and contaminated. No Theory except BCS Surface Resistance.

　　 RF Magnetic Field Limit ? Many Steps in Production & Clean Works to realize Ideal Surface



SRF Cavity PeculiaritiesProperty Reality Consequence

Superconducting Need Helium 　 Thin Wall for better Cooling

　 Nb , Type II Need Magnetic Shield Even Hext << Hc1 Multi Layer Structure

Material Not Uniform, Not Ideal Grain Boundary Large Grain ? 　

　 Contaminated Surface Irregularity, Contamination Lattice Orientation 　

　　 Field Enhancement, H & E 　

RF Superconductivity Not Lossless but Very Low Loss Residual Surface Resistance 0.3 nΩ/ mgauss

　 Maximum Field Limit 　 Smooth Shape, Less Holes

　 High Impedance 、 HOM 　 Need HOM Dumper

　　　　

Structure Material is Expensive Thin Wall Mechanical Stability, Coating

ProductionDeep Drawing + Machining + EBW

Defect 　 Quench 　

　　　　

Surface TreatmentChemical Treatment + Ultra pure Water Rinsing

Contamination Quench, Field Emission

Assembly Class 10 Clean Room 　 Scatter of Performance

　　　　

Peripheral Thermal Insulation in Vacuum 　　

　　　　

Many Critical Components 　 Ceramic Break 　　

Others Vacuum Seal 　

　　　　



Superconducting Cavity

Accelerator

Users

Cryostat

Refrigerator

High Power RF

Low Level RF

Input CouplerHOM Coupler

Tuner

Forming , EBWSurface Treatment

Particle PhysicsMaterial ScienceMedical Application

Design



Design ProcessDesign Parameters Input Constraints 　

　　　　

Frequency, Structure Accelerating, Deflecting,.... 　 Mode

　 Particle β 　 gap Length

　 Ring / Linac 　 Iris Aperture

　　　　

Operating Gradient Accelerator Scale, CW / Pulse Beam Power (Coupler) 　

　　　 Cooling Power 　

Material 　　　

　　　　

Operating Temperature Frequency, Structure, Gradient Cooling Power 　

　　　　

Cavity Unit Length Beam Current, Gradient Beam Power (Coupler) 　

　 Accelerator Scale HOM damping 　

　　　　

Module Length Accelerator Scale 　　

　　　　

If Pbeam>>Pcavity Normal 　　　



> 0.4 < 0.4

Particle e, Proton Proton, Ion

FrequencyRing 0.3~0.5 GHz

Linac 0.7~3 GHzLinac 50~300 MHz

Beam Current Ring >1 A Linac > 100 mA > 1mA < 1mA

Accelerating Elliptical Spoke,

Spoke, Half Wave, Quarter Wave

Deflecting Crab Cavities

Focusing RFQ

Structure Examples



Accelerating Gap

g

E

E

z

SpaceDistribution

g

tcz

dzztrzEZ

cos0,eGainEnergy



Accelerating Gap

g

g ~

Small enough g

Lower Frequency

-Mode

0-Mode



Eacc

Acceleration by RF Cavity

Frequency

Shape

Beam

RF Resonator, Strong E field on axis

Z

- Mode



Cavity RF Parameters

22

2

0

2

2

2

00

222

0

,

,

22,

2

Cavityacc

SCavity

accsh

S

S

LW

E

Q

R

R

G

Q

RL

P

ER

dSH

dVHG

R

G

P

WQ

dVEdVHWdSHR

P

dzztrzEL

EL

zCavity

acc cos0,1

0



General RF DesignPreference Compromise

Power Efficiency Higher Rsh Rsh of HOM

Aperture

Acceleration Efficiency

Enough Acceleration Gap Frequency Cavity Size

Multi-Gap/Cell

Beam Quality Enough Aperture Rsh



Q-E Curves 　（ Performance ）

Q0

Quench ?

Global Heating

Q Switch

Field Emission

Ideal (Constant Q = Constant Rs, T)

5.15.2 exp SP

SP EEI

Quench

Quench

Multipacting

Q Slope

H Q-Dieses

Eacc



RFQINFN-Legnaro

DifficultyHigh Power CouplerEnd Flange ContactFrequency Tuning



Quarter Wave (/4) & Split Ring

ANLCoaxial Resonator

Mechanical Vibration, High Power Coupler



Half

Beam



Half to SpokeBy Squeezing the Height



Multicell Spoke



Two Axis Coupled Cavity

Acceleration Beam

Coupler

Drive Beam



f

1

Smaller Riris

R / Q ; LargerEsp / Eacc ; SmallerHsp / Eacc ; SmallerCell Coupling ; SmallerCleaning ; More DifficultAlignment ; Tight

RF Design, = 1



The mechanical design of a cavity follows its RF design:

Lorentz Force Detuning

Mechanical Resonances

Mechanical Design Cavities

-0.006

-0.003

0

0.003

0 20 40 60z [mm]

P [N

/mm

^2]

Lorentz Force Detuning

E and H at Eacc = 25 MV/m in TESLA inner-cup

50 MV/m

92 kA/m

Mechanical Design



Surface deformation without and with stiffening ring (courtesy of I. Bonin, FERMI)

Mechanical Design Cavities

10-4m 3∙10-5m

No stiffening ringWall thickness 3mm

Stiffening ring at r=54mmWall thickness 3mm

kL = -1 Hz/(MV/m)2Essential for the operation of a pulsed acceleratorΔf = kL(Eacc)2

Lorentz Force Deformation

- df

- df



Lorentz ( Maxwell ) Detuning Ｋｊａｃ

ｋｅｔ

Ｋ tuner

Ｋ cavityFZ FZ

Ｆｚ

Ｆｒ

42 N

135 N

Eacc = 35MV/m

　　 TTF Saclay-I STF Slide Jack Blade

A Hz / (MeV/m)2 0.37(TESLA) 0.37(TESLA) 0.37(TESLA)

B N / (MeV/m)2 0.034 0.034 0.034

df / dl Hz /μm 300 300 300

KS N /μm 20 72 22

Kjacket N /μm 50 95 40

Ktuner N /μm 30 290 50

Stationary Δf (31.5 MV/m) Hz 880 510 800

f (Compensation) Hz 510 140 460

Necessary Tuning Stroke μm 1.7 0.5 1.5



k

kkk

k

k

kk

kk

kk

m

Fx

td

xd

Qtd

xd

FFtsxtsx

2

2

2

;,,

Deformation is the Sum of all the Mechanical Modes



Two Dominant Mechanical ModesSingle –Cell

~ +

~2500Hz~200Hz

Need Stiff Cavity

Need Stiff Jacket-Tuner System

2-nd order mode Fundamental mode

F(H2)

F(E2)



1/9 mode 204Hz

2/9 mode 376Hz

3/9 mode 548Hz

FixFree

Longitudinal Modes

9000N by Tuner



Transverse Modes

1/9 56Hz

2/9 141Hz

3/9 251Hz



Material

High Purity Niobium is almost an unique

Choice at the moment. RRR~300

Pb ( Plating ) was used for some Application.

Nb3Sn (Vapor Deposition + Heat Treatment)

NbTiN (Sputtering)

High Tc Materials are still very difficult.



Niobium Sheet Fabrication



Niobium Insufficient recrystallization,formability and mechanicalproperties are effected

Fully recrystallized material after appropriate heat treatment (after rolling operation)X. Singer, DESY



Large Grain directly from Ingot

Lattice Orientation, Slippage at Boundary



Property of Nb2~5k Room Temperature

Density 8.57

Lattice Structure B.C.C

Melting Temperature 2468℃

Conductivity ~ 2x109 ・ m

Thermal Conductivity 20 ~ 50 W / m ・k

Yield Strength ~ 600 MPa ~ 40 MPa

Tensile Strength ~ 900 MPa ~ 160 MPa

Elongation ~ 15% ~ 40%

Yang Module ~ 100 GPa

Vickers Hardness ~ 500 MPa



Niobium Thermal Conductivity Post-Purification Treatment (G.R.Myneni, Jlab)

RRR ; Residual Resistance Ratio

Wiedemann-Franz

k2.4

k2.4k300

RRR

Tres

TL



Cooling Efficiency

0

10

10

10

Q

100 10 20 30 40

Eacc [MV/m]

K-14　Cavity

1.8 K4.2 KE-quench (T)E-rf limit2.17 K

50

11

10

9

8

He-II

He-I

0

0.05

0.10.15

0.2

0.25

Q,

Hea

t flu

x [

W/c

m ]

0.3

0.35

0.4

1.5 2 2.5 3He - Temperature [K]

K-14　Cavity

Heat flux -QuenchHeat flux -rf power

3.5 4 4.5

2

.

(no Quench)

0

10

20

30

40

50

1.5

Eac

c-qu

ench

[M

V/m

]

2 2.5 3 3.5 4 4.5

-point

He - Temperature [K]

K-14

C-3

MK-0

M-1

He-IHe-II

(SRF93’)

TemperatureMappingSystem

Quench Limit Heat Flux

He-I / He-II

1.8K

4.2K

(EPAC96’)

2.17K



Cavity Fabrication



Cavity (9 Zeller)

Endhalbzell-Endrohr- Einheit

kurz

Endhalbzell- Endrohr- Einheit

lang

Flansch(Hauptkoppler-

Stutzen)

Flansch(Endflansch)

HOM-Kopplerkurze Seite

Rippe RippeAnbindung(end-kurz-lang)

Endhalbzellekurz

AntennenflanschNW 12

HOM-KopplerDESY

End-kurz-lang

Formteil F

Bordscheibelange Seite

Endhalbzellelang

Flansch(end-kurz-lang)

HOM-Kopplerlange Seite

Flansch(Endflansch)

Antennenstutzenlang

Endrohrlang

AntennenflanschNW 12

Formteil Flang

HOM-KopplerDESY

End-kurz-lang

Hauptkoppler-stutzen

Endrohrkurz

Cavity (9 cell TESLA / TTF design)

End group 1 End group 2Hantel

Normalhalb-Zelle

Normalhalb-Zelle

Stützring

Nb-BlechNormalhalelle

Nb-BlechNormalhalbzelle

Dumb-bell

Overview over cavity fabrication



Fabrication of STF Baseline CavitiesCenter-cells

(Tokyo Denkai ; RRR~300 Nb)

End-groupsHOM coupler

Magnetic Shield



Half Cell Press Forming

Iris ThinnerEquator Thicker



Fabrication



Beam Pipe & HOM Coupler

Wire cutting of Nb BrockBeam tube

HOM Coupler



Deepdrawing & Port Forming



End GroupTi End Plate

End cell & End group



Electron Beam Welding (Jlab)Dumbbells Stiffening Rings



Dumbbells

With Stiffener





Electron Beam Welding (Jlab)



STF Baseline Cavity



Other Fabrication Technique Hydro forming (W.Singer,DESY) Spinning (V.Palmieri,INFN

Legnaro)



Thin Niobium Films Sputtering

Documents

Shuichi Noguchi 、 KEK 6-th ILC School, November 20111 Superconducting Cavity Design ( RF, Mechanical, Thermal ) Material Fabrication Techniques