infn school on electron accelerators · electron accelerator school, lect. 4b, pisa, 13 sep 2007...

Carlo PaganiUniversity of Milano

INFN Milano-LASA & GDE

High Gradient SRF Cavities,Tuners, Couplers and HOMs

INFN School on Electron Accelerators12-14 September 2007, INFN Sezione di Pisa

Lecture 4b

Electron Accelerator School, Lect. 4b, Pisa, 13 Sep 2007

Carlo Pagani 2

High Gradient Cavity Requirements

Cavity DesignNiobium materialMechanical fabrication: forming and weldingSurface treatments–Damaged layer removal–Surface smoothening–Cleaning residuals

Clean assemblyAll the above following a proven process and under the highest possible level of Quality Control, QC, and Quality Assurance, QA.


Carlo Pagani 3

Cavity Design


Carlo Pagani 4

Cell Shape Parametrization

Full parametric model of the cavity in terms of 7 meaningful geometrical parameters:

Ellipse ratio at the equator (R=B/A)Ruled by MechanicsEllipse ratio at the iris (r=b/a)EpeakSide wall inclination (α) and position (d)Epeak vs. Bpeak tradeoff and coupling kCavity iris radius RirisCoupling kCavity Length L βCavity radius Dused for frequency tuning

Behavior of all e.m. and mechanical properties has been found as a function of the above parameters


Carlo Pagani 5

Tools used for the parametrization

We built a parametric tool for the analysis of the cavity shape on the electromagnetic (and mechanical)parameters

– All RF computations are handled by SUPERFISH

– Inner cell tuning is performed throughthe cell diameter, all the characteristic cell parameters stay constant: R, r, α, d, L, Riris

– End cell tuning is performed through the wall angle inclination, α, or distance, d. R, L and Riris are independently

settable. All e.m. cavity results are stored in a database for futher parametricinvestigations.A multicell cavity is then built to:

– minimize the field unflatness– compute the effective β– Compute the final cavity performances

A proper file to transfer the cavitygeometry to ANSYS is then generated

Inner cell data

L = 56.8 mmR = 1.5r = 1.4α = 7°d = 8 mmRiris = 41 mm


Carlo Pagani 6

Good results from basics concepts

β = 0.61 SNS 6-cell cavity β = 0.81 SNS 6-cell cavity


Carlo Pagani 7

The TESLA/ILC/XFEL Cavity


Carlo Pagani 8

Alternative Cell Design for the ILC


Carlo Pagani 9

Niobium Material


Carlo Pagani 10

Niobium (1)

Niobium is the elemental superconductor with the highest critical temperature and the highest critical fieldFormability like OFHC copperReadily available in different grades of purity (RRR > 250)Can be further purified by UHV heat treatment or solid state gettering

High affinity to interstitial impurities like H, C,N,O ( in air T < 150 C )Joining by electron beam weldingMetallurgy not so easyHydrogen can readily be absorbed and can lead to Q-degradation in cavities


Carlo Pagani 11

Niobium (2)

Quality/purity of niobium used for accelerator application is specified by the RRR ratioRRR = R(300)/[R(10) +Σ δRi/δCi ]

δRi/δCi are the contributions by interstitial impurities such as H,C,N,O and Ta

H: 0.8 x 10-10 Ωcm/at ppmC: 4.3 x 10-10 Ωcm/at ppmN: 5.2 x 10-10Ωcm/at ppmO: 4.5 x 10-10 Ωcm/at ppmTa: 0.25 x 10-10 Ωcm/at ppm

K.Schulze,Journal of Metals, 33 (1981), p. 33ff

Typical specifications for impurities ( wt ppm)

H < 2C < 10N < 10O < 10Ta < 500

RRR > 250Grain size 50 μmYield strength > 50 MpaTensile strength > 100 MpaElongation > 30 %VH < 50Thermal conductivity at 4.2K

λ(4.2Κ) ∼ RRR/4


Carlo Pagani 12

BB Electron Beam Melting Scheme

1 Gun2 Electrode3 Vacuum Chamber4 Water Cooled Mold5 Retractable Ingot

[from H.R.S. Moura, “Melting andPurification of Niobium” ,p. 147 inProc. of Int. Symposium Niobium 2001]


Carlo Pagani 13

From the Mine to the pure IngotHigh Purity Niobium(RRR>250) is made by multiple electron beam melting steps under good vacuum, resulting in elimination of volatile impuritiesThere are several companies, which can produce RRR niobium in larger quantities:Wah Chang (USA), Cabot (USA), W.C.Heraeus (Germany), Tokyo Denkai(Japan), Ningxia (China), CBMM (Brasil)

Nb Mine Nb IngotsEB Melting


Carlo Pagani 14

Nb Fabrication at Tokyo Denkai


Carlo Pagani 15

Insufficient recrystallization,formability and mechanicalproperties are effected

Fully recrystallized material after appropriate heat treatment (after rolling operation)

Non Uniform quality


Carlo Pagani 16

Check for inclusions and defects

Eddy Current Scanning system for SNS highpurity niobium scanning


Carlo Pagani 17

Mechanical Fabrication


Carlo Pagani 18

Cavity fabrication was set up in close connection with industrial companies

Each company had its characteristic in manufacturing and specially in welding technique

TTF Cavity fabrication


Carlo Pagani 19

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-langFormteil 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


Carlo Pagani 20

Cavity Fabrication at KEK


Carlo Pagani 21

Frequency measurement of dumbbell

Frequency measurement of half cell

Cavity Tuning during fabrication

Computerized tuning machine at DESY• Equalizing stored energy in each cell by

squeezing or pulling• Straightening of cavity


Carlo Pagani 22

Field Flatness after pre-tuning


Carlo Pagani 23

H.Padamsee et al; ”RF Superconductivity for Accelerators”

Set-up for field profile measurements: a metallic needle is perturbing the rf fields while it is pulled through the cavity along its axis; the stored energy in each cell is recorded.

Field Flatness Tuning


Carlo Pagani 24

Surface Treatments


Carlo Pagani 25

Eddy CurrentScanning, Squid Scanning(successfully used at DESY on TTF cavities)Degreasing ( ultrasound + soap+water, solvents)BCP ( HF:HNO3 :H3PO4 as 1:1:1, 1:1:2,1:1:4)(room temperature or below to avoid excessive hydrogen pick-up)Electropolishing (HF/H2SO4 Siemens-KEK-Recipes)Barrel PolishingHigh Pressure Ultrapure Water Rinsing (HPR)High Temperature Heat Treatment (600C to 1400C for Hydrogen degassing, Post Purification)“In-situ” baking ( typically 120C for> 24 hrs)Alternative Cleaning:CO2 Snow, Megasonic, UV Ozon..

Surface Treatment Procedures


Carlo Pagani 26

Electro Polishing, EP, scheme


Carlo Pagani 27

R.Geng(2004)Vertical system for single cellsCornell

Implemented and commissioned system in 2003/2004, starting to develop parameters

Jlab

CARE 2004-Meeting

Implemented,commissioned and uses system for multi-cell EPCARE: optimizing parameter (Saclay)

industrializing/automating (INFN)

DESY/TTF

K.Saito(1991)T.Higuchi,K.Saito(2003)

Developed EP based on Siemens RecipeSuccessfully applied to Tristan & B-factory cavitiesDeveloped Hydrogen –free EP: HNO3 add

KEK/Nomura Plating

ReferenceWhat has been done/is being done?Lab

Different processes in the Labs


Carlo Pagani 28

INFN

11.03.2005Lutz Lilje DESY -MPY-

KEK/Nomura Plating DESY

Cornell

JLab

EP Systems


Carlo Pagani 29

Universally used as last step in surface preparationWater: ultrapure, resistivity > 18 MΩcmPressure: ~ 100 bar ( 1200 psi)Nozzle configuration: varying, SS or sapphire“Scanning”: single or multiple sweep, continuous rotation + up/downAdd. HPR after attachment of auxiliary components

High Pressure Water Rinsing


Carlo Pagani 30

High Pressure Rinse Systems

Jlab HPR Cabinet

DESY-System

Variety of nozzles

KEK-System


Carlo Pagani 31

Clean Room Assembly


Carlo Pagani 32

Typically, the cavities of a cavity string are assembled in a class 10 or class 100 clean room on an assembly bench over a period of several days after they have been qualified in a vertical or horizontal (“Chechia –test” at DESY) test.They are high pressure rinsed for several hours, dried in a class 10 clean room, auxiliary parts are attached, high pressure rinsed again, dried and mounted onto the assembly bench.The most critical part of the assembly is the interconnection between two cavities, monitored by particle counting

Cavity String Assembly


Carlo Pagani 33

Hints from assembly experience - 1


Carlo Pagani 34

The inter-cavity connection isdone in class 10 cleanrooms

TTF String Assembly overview


Carlo Pagani 35

Some Remarks

To transform the impressive results on prototypes into a stable, fully controlled, Industrial production of SCRF:

– Large investments in infrastructure are required– Industry and industrial stile have to be integrated for an higher level of Quality Control and Quality Assurance

This effort, mandatory for ILC, is needed for the extended application of SCRF foreseen The European XFEL could be the required infrastructure.

– XFEL needs to transfer to industry the reliable production, at a moderate and controlled cost, of:

• 120 Cryomodules• 1000 Cavities at 28 MV/m on average• All cavity ancillaries• Few tens of 10MW klystron and modulators• Etc.

XFEL will be a very effective 6% prototype for ILC and possibly the best SCRF large infrastructure for ILC


Carlo Pagani 36

European XFEL Layout and Site


Carlo Pagani 37

Regional Infrastructures for ILC

TESLA Test Facility (TTF) @ DESYcurrently unique in the worldFLASH as VUV-FEL user facilitytest-bed for both XFEL & ILCCMTB for independent cryomodule test

SMTF @ FNALSupported by: Cornell, JLab, ANL, FNAL, LBNL, LANL, MIT, MSU, SNS, UPenn, NIU, BNL, SLAC + DESY, INFN & KEKTest Facility for ILC and other projects

STF @ KEKTo set up the ILC technology in Japan and Asia

Others: JLab, CERN ?, R&D Infrastructures


Carlo Pagani 38

CMTB & DESY as in fall 2006

6 cool-down warm-up cycles successfully performed

Test of module 6 started end October2006


Carlo Pagani 39

SMTF @ FNAL as presented to DOE

“The SMTF proposal is to develop U.S. Capabilities in high gradient and highQ superconducting accelerating structures

in support of

International Linear ColliderProton Driver

RIA 4th Generation Light Sources

Electron coolers lepton-heavy ion colliderand other accelerator

projects of interest to U.S and the world physics

community.”


Carlo Pagani 40

Fermilab and Argonne are jointly building a surface processing facility for ILC Cavity R&D.

The facility will have capability to perform BCP, EP and HPR.

The BCP Facility is under final phase of construction and will be safety reviewed by Spring of 07.

Design of the EP facility is progressing with plans to be commission with 9 Cell 1.3 GHz Cavities by the end of FY07.

Surface Processing at ANL/FNAL


Carlo Pagani 41

STF @ KEK


Carlo Pagani 42

clean room for cavity assembly 5MW power source and coupler test stand

5m cryomodule vacuum vessels

TESLA-like cavities Disk Input Coupler LL shape cavities Capacitive Couplers

KEK STF Highlights


Carlo Pagani 43

Cavity Major Ancillaries

Power coupler Frequency Tuner: slow and fastHOM (High Order Mode) CouplersBut also:– Helium vessel– Magnetic shielding


Carlo Pagani 44

Ancillaries: Power Coupler

bias voltage, suppressing multipactingisolated inner conductor6 W70 K heat load

sufficient for safe operation and monitoringdiagnostic

0.5 W4 K heat load0.06 W2 K heat load

safe operationclean cavity assembly for high Eacc

two windows, TiN coated

pulsed: 500 µsec rise time,800 µsec flat top with beam

operation

1.3 GHzfrequency

• TTF III Coupler has a robust and reliable design.

• Extensively power tested with significant margin

• New Coupler Test Stand at LAL, Orsay

Pending Problems• Long processing time: ~ 100 h• High cost (> cavity/2)• Critical assembly procedure


Carlo Pagani 45

Coupler Development at LAL-Orsay

TTF III

Clean room assemblyHigh Power Coupler Test Stand

Alternative Designs


Carlo Pagani 46

Ancillaries: Cavity Tuners

The Saclay Tuner in TTF The INFN Blade-Tuner

Successfully operated with superstructures


Carlo Pagani 47

Lorentz Force Detuning

High magnetic field and high currents on the cavity surface produce a Lorentz force

At each RF millisecond power pulse the Lorentz force produces a cavity deformation at the micrometer level

Due to the high Q and the consequent small frequency band, ~ 400 Hz over 1.3 GHz, the cavity moves from the original tuningAt 35 MV/m the Lorentz force detuning is ~ 1000 Hz

magelLorentzem FFBvEqdtpdFF

rrrrrrrr+=×+=== )(

ANSYS 5.6APR 4 200018:51:21PLOT NO. 3NODAL SOLUTIONSTEP=1SUB =1TIME=1USUM (AVG)RSYS=0PowerGraphicsEFACET=1AVRES=MatDMX =.155E-05SMN =.567E-07SMX =.155E-05

1

MN

MX

0.278E-06.556E-06.833E-06.111E-05.139E-05.167E-05.194E-05.222E-05.250E-05


1

MN

MX

0.278E-06.556E-06.833E-06.111E-05.139E-05.167E-05.194E-05.222E-05.250E-05


1

MN

MX

0.278E-06.556E-06.833E-06.111E-05.139E-05.167E-05.194E-05.222E-05.250E-05


1

MN

MX

0.278E-06.556E-06.833E-06.111E-05.139E-05.167E-05.194E-05.222E-05.250E-05

Cavity deformation for different stiffening ring radial position

1

Slater integral for a unitary displacement


Carlo Pagani 48

Successful Compensation @ 35 MV/m

Cavity detuning induced by Lorentz force during the tests performed in Chechia at TESLA-800 specs

Piezo-compensation on: just feed-forward resonant compensationPiezo-compensation off


Carlo Pagani 49Status as on February 1st, 2005

The Blade-Tuner for ILC

• Integration of piezos for Lorentz forces and microphonics completed.

• Two prototype, including the modified helium tank, are being build for cold qualification

• Successful Tests under way at DESY, soon at Fermilab


Carlo Pagani 50

Damping of Higher Order Modes (HOMs)

1 10

100 1000 f [GHz]

0.4 W 0.8 W 2.6 W

1.6 W

modes below cut-off

modes above cut-off (propagating modes)

1.3 GHzThe spectrum of the XFEL electron bunch (σz = 25 µm) reaches high frequencies up to 5 THz.

The standard accelerator module has an integrated loss factor of 135 V/pC.

The total power deposited by the nominal beam is 5.4 W per module.

capacitor of notch filter

superconducting pick-up loop

capacitive coupling

output

HOM coupler

bellows

to 70 K

beam

ceramic

copper stub

beam pipe absorber

The ILC should have a little less HOM power at high frequencies.

Nevertheless, HOM couples and absorbers are required. The XFEL version is available.


Carlo Pagani 51

HOM couplers and Beam Line Absorbers HOM

The coupler is designed as a filter rejecting the fundamental mode and minimizing the

Electric field at the pick-up probe

2 HOM couplers <PHOM> ~ few watts

outputTESLA 1.3 GHz

Couplers are assembled outside the LHe vessel !!

FM rejection filter

TTF Low Frequency HOM Coupler


Carlo Pagani 52

HOM couplers and Beam Line Absorbers HOM

Cs

Cf

Co

L1 L2

Ro

x1, z1 x2, z1

TTF LF HOM Coupler Performances


Carlo Pagani 53

HF HOM Coupler

In the XFEL the HOM Couplers for frequencies above cut-off are placed at each module interconnection. The power extracted from the beam is dissipated at the 40-70 K level.


Carlo Pagani 54

3D Model of a dressed cavity

infn school on electron accelerators · electron accelerator school, lect. 4b, pisa, 13 sep 2007...

Documents