SRF%20Cavity%20Technology

1
SRF Cavity Technology

• Peter Kneisel
• Jefferson Lab

2
General Remarks

• SRF technology is a difficult technology and it
  is not very
• forgiving, if mistakes are made.However, it is
  very challenging
• It involves many areas of physics and technology
  such as
• Surface science, vacuum technology, metallurgy,
  chemistry,
• rf engineering, cryogenics, clean room
  technology,
• contamination control, cleaning
  technology,quality control
• Much attention has to be paid initially to the
  design of the
• cavities and during manufacturing to material,
  cleaning,
• electron beam welding, tolerances, tuning, heat
  treatments,
• surface preparation, control of contamination.
• It is one thing to achieve good performance of
  cavities in a
• laboratory environment ( vertical dewar tests,
  ILC goals are
• Eacc 35 MV/m at a Q-value of Q 8x 109 at 2K)
  and another to
• consistantly produce in an production environment
  over several years 20
• km of cavity strings with the design parameters

3
General Remarks(2)

• Stringent adherence to clever procedures and
• processes and robust designs are an absolute
• must for a successful implementation of an as
• large a machine as the ILC.
• The installation of the X-FEL at DESY,
• starting next year, will be a good demonstration
• project to see the difficulties of the
• implementation of a very large scale SRF
• accelerator.

4
Acknowledgement

• For this presentation I used freely material
• from presentations of colleagues, whom I
• want to thank
• J. Sekutowicz, DESY S. Noguchi, KEK
• I. Campisi, SNS V. Palmieri, INFN
• W. Singer, DESY A. Matheisen, DESY
• G. Ciovati, Jlab D. Reschke, DESY
• K. Saito, KEK T. Garvey, Saclay
• W.-D. Moeller, DESY T. Saeki, KEK
• M. Liepe, Cornell Uni L.Lilje, DESY

5
Recommended Literature

• H.Padamsee, J. Knobloch, T. Hays
• RF Superconductivity for Accelerators, John
  WileySons, Inc ISBN 0-471-15432-6
• Proceedings of the Workshops on RF
  Superconductivity 1981 2005
• A.W.Chao, M. Tigner
• Handbook of Accelerator Physics and
  Engineering, World Scientific PublishingCo,
  P.O.Box 128, Farrer Road, Singapore, ISBN
  9810235003

6
Recent Conferences/Workshops

• First ILC Workshop at KEK,Japan, Dec. 2004
• http//lcdev.kek.jp/ILCWS/
• ILC Workshop at Snowmass, Col., Aug. 2005
• http//wwwconf.slac.stanford.edu/snowmass05/procee
  dings/
• proceedings.html
• TTC Workshop at Frascati, Dec.2005
• https//ilcsupport.desy.de/cdsagenda/fullAgenda.ph
  p?idaa0561s4
• SRF 2003, Travemuende, Germany
• http//srf2003.desy.de/
• SRF 2005, Cornell Uni, Ithaca,NY
• http//www.lns.cornell.edu/public/SRF2005/
• CARE Meeting, INFN Legnaro, 2005
• https//ilcsupport.desy.de/cdsagenda/fullAgenda.p
  hp?idaa062

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SNS Medium Beta Cavity
8
SNS Titanium Helium Vessel
Stiffening Rings
Titanium Bellows
2 - Phase Return Header
NbTi Dished Head
NbTi Dished Head
HOM Coupler
Field Probe
HOM Coupler
Fundamental Power Coupler
Medium Beta Cavity
9
Topics

• Cavity Fabrication
• Material
• Fabrication Methods
• Cavity Treatment
• Fundamental Power Couplers
• Requirements, beam loading
• Higher Order Mode Couplers
• Integrated Helium Vessel/Tuners
• Coarse tuners, fine tuners
• String Assembly
• Testing/Results

10
NIOBIUM
11
Niobium (1)

• Niobium is the elemental superconductor with
  the highest critical temperature and the highest
  critical field
• Formability like OFHC copper
• Readily available in different grades of purity
  (RRR gt 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 lt 150 C )
• Joining by electron beam welding
• Metallurgy not so easy
• Hydrogen can readily be absorbed and can lead to
  Q-degradation in cavities

12
Niobium (2)

• Typical specifications for impurities ( wt ppm)
• H lt 2
• C lt 10
• N lt 10
• O lt 10
• Ta lt 500
• RRR gt 250
• Grain size 50 mm
• Yield strength gt 50 Mpa
• Tensile strength gt 100 Mpa
• Elongation gt 30
• VH lt 50
• Thermal conductivity at 4.2K
• l(4.2K) RRR/4

• Quality/purity of niobium used for accelerator
  application is specified by the RRR ratio
• RRR R(300)/R(10) S dRi/dCi
• dRi/dCi are the contributions by interstitial
  impurities such as H,C,N,O and Ta
• H 0.8 x 10-10 Wcm/at ppm
• C 4.3 x 10-10 Wcm/at ppm
• N 5.2 x 10-10Wcm/at ppm
• O 4.5 x 10-10 Wcm/at ppm
• Ta 0.25 x 10-10 Wcm/at ppm
• K.Schulze,Journal of Metals, 33 (1981), p. 33ff

13
NiobiumElectron Beam Melting

• High Purity Niobium(RRRgt250) is made by multiple
  electron beam melting steps under good vacuum,
  resulting in elimination of volatile impurities
• There 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)

EBM Ingots at CBMM
CBMM deposit in Araxa, Brasil
EBM furnace at Tokyo Denkai
14
Niobium Production

• Niobium Ore in Araxa mine (open air pit) is
  Bariopyrochlor with 2.5 Nb2O5
• The ore is crushed and magnetite is magnetically
  separated from the pyrochlor.
• By chemical processes the ore is concentrated in
  Nb contents (50 60
• of Nb2O5
• A mixture of Nb2O5 and aluminum powder is being
  reacted to reduce the oxide to Nb
• This Nb is the feedstock for the EBM processes

• H.R.Salles Moura,Melting and Purification
• of Nb, Proc.Intern.Sumposium Niobium
• 2001,Dec 2-5, 2001, Orlando Fl, p.147
• CBMM Plant Araxa, Brasil

15
Electron Beam Melting

• 1 Gun
• Electrode
• Vacuum Chamber
• Water Cooled Mold
• Retractable Ingot
• from H.R.S. Moura, Melting and
• Purification of Niobium ,p. 147 in
• Proc. of Int. Symposium Niobium 2001

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Niobium (3)
17
Niobium (4)
18
Niobium (5)
19
Niobium (6)

• Insufficient recrystallization,
• formability and mechanical
• properties are effected

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

20
Niobium (7)

• Post Purification of niobium in presence of Ti
  as a solid state getter material
• H.Padamsee,J.Knobloch,T.Hays,
• RF Superconductivity for Accelerators, J.Wiley
  and Sons

• During the purification process the interstitial
  impurities ( O,N,C) diffuse to the surface and
  react with the evaporated Ti atoms Ti has a
  higher affinity to these impurities than Nb
• W. Singer, Material properties of High Purity Nb
  for SC cavities, FNAL Workshop, June 2002

21
Niobium (8)

• Post-Purification Treatment (G.R.Myneni, Jlab)

22
Q - Disease
23
Procedures

• Eddy Current Scanning system for SNS high
• purity niobium scanning

24
Cavity Fabrication for TESLA/ILCStandard (A.
Matheisen, DESY) Seamless (W. Singer, DESY
V.Palmieri, INFN)Super-Structure (J.
Sekutowicz, DESY)
25
Cavity fabrication and preparation sequences
for the TESLA / TTF cavities at DESY 1st ILC
workshop at KEK Tsukuba Japan A.Matheisen for
DESY and the TESLA Collaboration
26
Overview over cavity fabrication
Cavity (9 cell TESLA /TTF design)
Cavity (9 Zeller)
Endhalbzell- Endrohr- Einheit lang
Endhalbzell- Endrohr- Einheit kurz
End group 1
End group 2
Flansch (Hauptkoppler- Stutzen)
Endhalbzelle kurz
Flansch (Endflansch)
Hauptkoppler- stutzen
Bordscheibe lange Seite
Endhalbzelle lang
Flansch (end-kurz-lang)
Antennenstutzen lang
HOM-Koppler kurze Seite
Rippe
Rippe
Anbindung (end-kurz-lang)
Endrohr kurz
HOM-Koppler lange Seite
Flansch (Endflansch)
Endrohr lang
Antennenflansch NW 12
HOM-Koppler DESY End-kurz-lang
Formteil F
Antennenflansch NW 12
Formteil F lang
HOM-Koppler DESY End-kurz-lang
27
Cavity fabrication Example dumb bell / Cavity

1. Mechanical measurement
2. Cleaning (by ultra sonic us cleaning
   rinsing)
3. Trimming of iris region and reshaping of cups
   if needed
4. Cleaning
5. Rf measurement of cups
6. Buffered chemical polishing Rinsing (for
   welding of Iris)

7. Welding of Iris 8. Welding of stiffening
rings 9. Mechanical measurement of
dumb-bells 10. Reshaping of dumb bell if
needed 11. Cleaning 12. Rf measurement of
dumb-bell 13. Trimming of dumb-bells ( Equator
regions ) 14. Cleaning 15. Intermediate chemical
etching ( BCP /20- 40 µm ) Rinsing 16. Visual
Inspection of the inner surface of the
dumb-bell local grinding if needed (second
chemical treatment inspection )
Dumb- bell
Dumb-bell ready for cavity
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Overview over cavity fabrication
Cavity (9 Zeller)
Cavity (9 Zeller)
29
Mechanical Design
Cavities

• The mechanical design of a cavity follows its RF
  design
• Lorentz Force Detuning
• Mechanical Resonances

Lorentz Force Detuning
92 kA/m
50 MV/m
E and H at Eacc 25 MV/m in TESLA inner-cup
30
Mechanical Design
Cavities
Surface deformation without and with stiffening
ring (courtesy of I. Bonin, FERMI)
10-4m
310-5m
Stiffening ring at r54mm Wall thickness 3mm
No stiffening ring Wall thickness 3mm
kL -1 Hz/(MV/m)2
Essential for the operation of a pulsed
accelerator ?f kL(Eacc)2
31
Lorentz Force Detuning HG shape
32
Mechanical Design
Cavities
Mechanical Resonances of a multi-cell cavity
60 Hz
Transverse modes
152 Hz
250 Hz
Longitudinal mode
TESLA structure
The mechanical resonances modulate frequency of
the accelerating mode. Sources of their
excitation vacuum pumps, ground vibrations
33
Cavity welding the general way There are
differences of welding processes in industry

• Degreasing and rinsing of parts
• Drying under clean condition
• Chemical etching at the welding area ( Equator)
• Careful and intensive rinsing with ultra pure
  water
• Dry under clean conditions
• Install parts to fixture under clean conditions
• Install parts into electron beam (eb) welding
  chamber
• ( no contamination on the weld area allowed)
• Install vacuum in the eb welding chamber lt 1E-5
  mbar
• Welding and cool down of Nb to Tlt 60 C before
  venting
• Leak check of weld

34
Experiences on cavity fabrication
Deep drawing 1. Reproducibility depends on
tool design and tool material ?
specification investigation in tooling 2.
Dependency on Nb supplier found 3. Different
shape from ingot to ingot found (Hardness / grain
size) ? Better quality control
specification ? reproducibility

• Measurements
• 1. Rf measurement of cups / dumb bells ? Time
  consuming
• Mechanical measurements of sub units ? Time
  consuming
• ( F part HOM tube / flanges /dumb-bell 3 D
  measurement complex
• ? combination of mechanical and rf
  measurement possible ?
• ( 3 D imaging of units)

• Fabrication
• Sequences need to be adopted to the company
  hardware
• Companies need to be trained an stay trained
• ? learning curve to stable production
• Control on subcontractors
• Dependency on major products of company ?
  training of personal

35
Cavity Preparation
Actually there are 3 general lines
36
The preparation process can be split up into 4
major steps
Preparation step A Removal of demage layer / post
purification / tuning
Preparation step B Final cleaning and assembly
for vertical test
Preparation step C Welding of connection to H
vessel / He vessel welding
Preparation step D Final cleaning and assembly
for module / horizontal test
37
Fabrication(1)example Ichiro cavity
38
Fabrication(2)
39
Fabrication(3)
40
Fabrication(4)
41
Fabrication(5)
42
Fabrication(6)
43
Fabrication(7)
44
Fabrication(8)
45
Fabrication(9)
46
Tuning G. Kreps et al, 9th workshop on RF
Superconductivity, Santa Fe(1999), paper WEP 031
Frequency measurement of half cell

• Computerized tuning machine at DESY
• Equalizing stored energy in each cell
• by squeezing or pulling
• Straightening of cavity

Frequency measurement of dumbbell
47
Field Flatness Tuning

• H.Padamsee et alRF 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.
48
TuningExample 5-cell TRASCO Cavity

• As manufactured

p/5-mode
2p/5-mode
3p/5-mode
4p/5-mode
Tuned
p-mode
49
Manufacturing TechnologySNS/Jlab
50
Manufacturing TechnologySNS/Jlab
51
Electron Beam Welding(Jlab)

• Dumbbells Stiffening Rings

52
Cavity Fabrication(Jlab)

• Endgroups Cavity

53
Manufacturing TechnologyJlab

• Electron Beam Welding

54
Alternative Fabrication Techniques

• Besides the standard cavity fabrication of
  producing
• niobium half cells and electron beam weld them
  into
• multi-cell cavities there exist alternative
  method
• Spinning of multi-cells
• Hydroforming of multi-cells
• Use of composite material NbCu
• Thin film coating of Cu cavities
• Combining two 9-cell structures into a
  superstructure

55
Fabrication

• Hydro forming (W.Singer,DESY) Spinning
  (V.Palmieri,INFN Legnaro)

56
Nb/Cu clad Material4
57
Nb/Cu clad Material5
58
Nb/Cu clad Material3
59
Nb/Cu clad Material2
60
Nb/Cu clad Material6

• Problems
• Possibility of leaky welds because of Cu
  contamination
• Nb/Cu cavities still quench,resulting in
  Q-degradations
• Cooldown needs to be very uniform because of
  thermo currents
• Cooldown of cryomodules would need modification
• Cracks sometimes appear in iris region during
  fabrication
• No industrialization efforts yet

61
Nb/Cu clad Material7
62
Thin Niobium Films(1)
63
Thin Niobium Films(2)
64
Thin Niobium Films(3)
65
Superstructure/Weakly Coupled StructuresJ.
Sekutowicz, DESYJ. Sekutowicz et al.,
Superconducting Superstructure for the TESLA
Collider A Concept, PR-ST AB,1999 J.
Sekutowicz et al, PAC2003, paper ROAA 003
66
How many cells for a structure?
67
Multi-cell Structures and Weakly Coupled
Structures

• Pros and cons for a multi-cell structure
• Cost of accelerators is lower (less
  auxiliaries LHe vessels, tuners, fundamental
• power couplers, control electronics)
• Higher real-estate gradient (better fill
  factor)
• Field flatness vs. N
• HOM trapping vs. N
• Power capability of fundamental power
  couplers vs. N
• Chemical treatment and final preparation
  become more complicated
• The worst performing cell limits whole
  multi-cell structure

68
RF Parameters
Field flatness factor
The above formulae estimate sensitivity of a
multi-cell field profile to frequency errors of
an individual cell for the accelerating mode
(p-mode)
69
Multi-cell Structures and Weakly Coupled
Structures Cavities
? Field flatness vs. N
Original Cornell N 5 High Gradient N 7 Low Loss N 7 TESLA N9 SNS ß0.61 N6 SNS ß0.81 N6 RIA ß0.47 N6 RHIC N5
year 1982 2001 2002 1992 2000 2000 2003 2003
aff 1489 2592 3288 4091 3883 2924 5040 850
Many years of experience with heat treatment,
chemical treatment, handling and assembly allows
one to preserve tuning of cavities, even for
those with bigger N and weaker kcc
For the TESLA cavities field flatness is better
than 95
70
Multi-cell Structures and Weakly Coupled
Structures Cavities
? HOM trapping vs. N
no e-m fields at HOM couplers positions,
which are always placed at end beam tubes
N 17
N 13
N 9
N 5
e-m fields at HOM couplers positions
Less cells in a structure helps always to reach
low Qs of HOMs.
71
Weakly Coupled Pairs
Motivation cont.
To keep the real estate gradient we should have
fewer interconnections between structures and in
addition they should be as short as technically
possible.
Example TDR TESLA500 9-cell structures are
connected by 283 mm interconnection
The effective gradient drops by 21.5 from 35
MV/m to 27.5 MV/m (even to a lower value due to
long interconnections between cryomodules)
Can we do it better ?
72
Cryogenic Load, RF-distribution system and Real
Estate Gradient

• RF-distribution system and Real Estate Gradient
  (contd)

Standard layout
SST layout saves thousands of these components
73
Weakly Coupled Structures
Motivation cont.
We save many of FPCs and thousands of components
in the RF distribution system.
Courtesy of V. Katalev
74
Multi-cell Structures and Weakly Coupled
Structures Cavities
Weakly coupled structures concept
(superstructure, SST)

• Two main limitations in N
• Field unflatness
• HOM trapping
• can be overcome in weakly coupled structures
  (JS, M. Ferrario, Ch. Tang, PRST-AB, 1999).

SST layout Two (or more) N-cell
structures are coupled by ?/2 long tube(s).
Each structure has its own
cold tuner and HOM dampers.
tuner
tuner
Energy flows via very weak coupling 10-4
one FPC/(2N) cells
75
Weakly Coupled Pairs
Advanced 3D modeling of HOM damping
F1.4293GHz Q1816.2
F1.4329GHz Q6159.0
Courtesy of Z. Li and K. Ko, ACD, SLAC
F1.5110GHz Q39689
F1.5112GHz Q121340
76
Cryogenic Load, RF-distribution system and Real
Estate Gradient

• RF-distribution system and Real Estate Gradient
  (contd)

Standard layout
SST layout saves thousands of these components
77
Cryogenic Load, RF-distribution system and Real
Estate Gradient

• RF-distribution system and Real Estate Gradient

FPC, Waveguides Directional Coupler, Loads,
Bends, Circulator, 3-stub Transformer
x20592
78
Weakly Coupled Pairs
Towards the weakly coupled pair 2x9-cell
This option is technically the closest to the
well known 9-cells at DESY a Cu models of the
2x9-cell was built RF-properties like FM-field
profile, HOM damping have been studied (Shu-xin
Zheng) We have well advanced set of technical
drawings and mechanical modeling
Recently ACD SLAC group started 3D modeling of
the RF-properties (HOM damping)
79
Weakly Coupled Pairs
The preparation of the experiment begun in
1999. In 2002, two 2x7-cells SSTs were
assembled in the cryomodule and installed next to
the injector in the TTF linac for the test.
Two 2x7-cell pairs in HF-lab for field profile
adjustment and HOM measurements
80

• Weakly coupled structures (SST)
• Significantly lower cost of the RF-system (40-50
  less components).
• 40-50 less Input Couplers, therefore
  cleaning/assembly/processing time and cost
  reduced
• Tunnel shorter by 5-6, because of shorter
  inter-cavity connection
• Less openings in cryostat (40-50), simplified
  assembly and design.
• Less time for assembly of cryostats in the
  linac.
• Less LLRF units.

Cons No much experience with beam (Proof of
Principle at TTF is the only test). More
difficult production and cleaning, unless we will
have sc-joint. 1.8-2 x higher power capability
of Input Couplers (fortunately it is
Ø4). Cold tuner on He vessel (like the blade
tuner), more experience needed.
81
Superconducting Seal and Big Grain Nb

• What should be then the next steps
• Simplification of the fabrication and
  preparation, to make them similar to the
  fabrication and preparation of the standard
  9-cell structures.
• Experiments with beam to gain very limited
  experience we have at present.

Ad 1. RD Superconducting Seal
NbTi flange II
NbTi flange I
sc gasket (Nb?)
82
5. Superconducting Seal and Big Grain Nb
The first approach at DESY 2000/2001 for an
assembly of the 4x7-cell SST.
B at the gasket 30mT
Max Eacc 5 MV/m was demonstrated with that
gaskets
B in the interconnection region at 25 MV/m
83
5. Superconducting Seal and Big Grain Nb
Test in the vertical cryostat is filled up below
the end-cup Q-switch happens at 5 MV/m.
Gasket immersed in LHe Eacc 16 MV/m
Gasket above in LHe Eacc 5 MV/m
84
5. Superconducting Seal and Big Grain Nb
We need a second approach (RD program funded by
ILC, in progress)
Nb
NbTi
NbTi
2.3 GHz cavity for testing of sc gaskets
85
Estimation of Potential Cost Reduction

• Present coupler costs are 30000
• Goal is 10000
• Actual costs maybe in between 20000
• Coupler Processing estimated cost/coupler 3000

Table III. Potential savings
FPC price 30000 20000 10000
Savings 398106 292106 189106
86
Surface Preparation

87
Why Surface Treatment?

• Damage layer influences cavity Performance

88
What is the goal of the surface treatment?

• Get as close as possible to an ideal surface,
  achieve
• fundamental limits of the material very low
  Rres ,
• Hcrit 185 mT
• Remove the surface damage layer ( gt 100 mm)
• Defect-free surface
• Contamination-free to avoid FE
• Smooth for better cleaning, avoid field
  enhancements

89
Diagnostics

• Some conclusions about phenomena occurring inside
  a cavity can be
• Deducted from the rf signal response such as e.g.
  multipacting or
• quenches
• The application of diagnostic methods allows to
  gain understanding of localized phenomena on a
  cavity surface
• Each energy loss mechanism in a sc cavity will
  lead to a flux of heat into the helium bath
  surrounding the cavity
• This heat flux raises the temperature of the
  intermediate helium layer between outer cavity
  surface and the bulk helium bath
• Qo vs Eacc gives a global picture of the
  behaviour of a superconducting cavity
• With an array of thermometers sliding around the
  cavity surface a temperature map can be
  compiled
• Conclusions about the loss mechanisms inside the
  cavity can be drawn.

90
Cavity Surface(Cartoon)

• Based on many T-maps and subsequent inspection
  of the cavity surface different sources of
  localized losses have been identified
• Geometrical irregularities
• Accumulation of foreign material
• These defects because of their increased losses
  heat up their surroundings and eventually cause
  a thermal instability, if locally T gt TC
• T DT DTK TB lt TC

91
Temperature Mapping

• First application of temperature measurements on
  a cavity surface to locate the Quench was done
  by C. Lyneis ( Proc. 1972 Acc. Conf., p.98),
  using 100 Ohm, 1/8 Watt Allen Bradley Carbon
  resistors
• Later developments
• subcooled Helium increases sensitivity (H.Piel,
  M. Romjin, CERN EF/FRO 80-3(1980)
• increase in speed by use of a large
• number of resistors and high speed electronics,
  superfluid He J.Knobloch
• et al., Rev.Sci.Instr. 65(11), 3521 (1994)

92
Temperature Mapping, contd

• First rotating T-mapping system
• implemented at CERN, used in
• subcooled helium
• T signal 10 x larger than in
• saturated He, best conditions Tgt Tl
• p 1000 torr
• increase in heat transfer resistance from metal
  to He bath
• absence of nucleate boiling therefore no
  micro-convection due to bubbles
• surface temperature increases compared to
  saturated He
• T-sensors are thermally decoupled

93
T-Mapping (1)

• T-mapping system 600 Allen-Bradley C-resistors

94
(No Transcript)
95
Obstacles to Ideal Performance

• Even if the low field Q is high (residual
  resistance
• low), there is typically a field dependence of
  the Q-value

Medium field Q-slope
Low field Q-slope
Theoretical Dependence
High field Q-drop
96
Q vs Eacc , Q-drop

• For high RRR niobium often a degradation of the Q
  value is observed at gradients (magnetic surface
  fields) above 20 MV/m (gt90 mT)
• In situ baking of the cavities at 120C for long
  periods of time ( 48 hrs) improves the Q-values
• at lower power and in the Q-drop regime
• The improvement is often more pronounced for EP
  cavities, but is also observed for BCPd cavities
• The physics of the Q-drop is still not understood
• explanations range from field enhancements at
  grain boundaries to effects in the metal-oxide
  interface or weak links at grain boundaries
• It is clear that oxygen diffusion from the
  surface into the material plays a role the depth
  of the affected zone is several hundred nm

97
Q vs Eacc , Q-drop
Buffered Chemical Polished(111)
B.Visentin,SRF2003
electropolished
98
4
4
99
Procedures general remarks

• Enemies of good cavity performance are
• insufficient material removal, defects and
  contamination
• ( field emission)
• All procedures need to deal with these problems
  and the most difficult is control of
  contamination
• Many of these procedures take place in the
  controlled environment of a clean room
• Level of contamination is different in different
  labs and depends on facilities, design, auxiliary
  parts, hardware
• ( e.g. bolts, gaskets..) and people
• Optimum procedures have to be developed for each
  lab and project

100
Cleaning/Contamination
101
Clean Room
102
Contamination

• Sources
• Processing Chemicals (filtered!)
• High Purity Water ( gt18 MWcm, lt0.02 mm filter)
• Clean Room environment (entrance, class 10)
• Particulates on equipment,tooling,hardware,clothin
  g, gloves..
• Remedies
• Stringent control of processes and procedures
• In-line monitoring of particulate levels in air
  and liquids
• Scheduled maintenance
• Blow-off with filtered N2 , monitored by
  particle counter
• Use of appropriate hardware ( e.g. bolts..)
• Clever designs (e.g.gaskets, clamp rings,
  fixtures)
• Consistant use of best practices through whole
  assembly process

103
Cleanroom Technology

• Standard
• HVAC(Heating Ventilation Air Conditioning )-
  Systems
• Filtration technology of Air/gases and Liquids
• Processes under clean conditions,
• e.g.Vacuum-, Temperature- and Wet-Processes
• Personal Clothing and Behaviour in Clean room
• Clean room compatible equipment
• and tooling
• Arrangement of equipment to maintain laminar flow
• Cleaning and Service Processes
• of clean room and equipment (daily wiping,
  filter change, on-line monitoring of air
  quality..)

• For SRF Application
• Dedicated process equipment
• Ultrasonic cleaning
• BCP/EP etching, electropolishing
• HPR High Pressure rinsing
• Pumping system,leak check and venting equipment
• Tooling for handling and assembly, e.g. lift
  carts, assembly bench
• furnaces

104
Cleanroom
105
Surface Treatment Procedures

• Eddy CurrentScanning, Squid Scanning
• (successfully used at DESY on TTF cavities)
• Degreasing ( ultrasound soapwater, solvents)
• BCP ( HFHNO3 H3PO4 as 111, 112,114)
• (room temperature or below to avoid excessive
  hydrogen pick-up)
• Electropolishing (HF/H2SO4 Siemens-KEK-Recipes)
• Barrel Polishing
• High Pressure Ultrapure Water Rinsing (HPR)
• High Temperature Heat Treatment (600C to 1400C
  for Hydrogen degassing, Post Purification)
• In-situ baking ( typically 120C forgt 24 hrs)
• Alternative CleaningCO2 Snow, Megasonic, UV
  Ozon..

106
Scanning of Niobium Sheets

• Successfully developed at DESY to pre-screen Nb
• Sheets for defects eddy current, resolution
  100 mm
• squid, resolution lt 50 mm

(W.Singer, X.Singer)
107
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108
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109
Electropolishing, contd

• Activities

Lab What has been done/is being done? Reference
KEK/ Nomura Plating Developed EP based on Siemens Recipe Successfully applied to Tristan B-factory cavities Developed Hydrogen free EP HNO3 add K.Saito(1991) T.Higuchi,K.Saito (2003)
DESY/ TTF Implemented,commissioned and uses system for multi-cell EP CARE optimizing parameter (Saclay) industrializing/automating (INFN) CARE 2004-Meeting
Jlab Implemented and commissioned system in 2003/2004, starting to develop parameters
Cornell Vertical system for single cells R.Geng(2004)
110
EP- Systems

• KEK/Nomura Plating DESY JLab

Cornell
INFN
111
Buffered Chemical Polishing(BCP)
DESY
External BCP,Jlab
BCP Mixture of HF/HNO3/H3PO4 in ratios 111 or
112 _at_ 10-15C 2Nb 5NO3 Nb2O5
5NO2 Nb2O5 6HF H2 NbOF5 NbO2 F 0.5H2O
1.5H2 O soluble non
soluble NbO2 F 0.5H2O 4HF H2 NbF5 1.5 H2
O soluble
JLab
Exothermic reaction Removal rate 2 mm/min _at_ 10C
112
High Pressure Water Rinsing

• Universally used as last step in surface
  preparation
• Water ultrapure, resistivity gt 18 MWcm
• Pressure 100 bar ( 1200 psi)
• Nozzle configuration varying, SS or sapphire
• Scanning single or multiple sweeps,
• continuous rotation up/down
• Add. HPR after attachment of auxiliary components

113
High Pressure Rinse Systems
KEK-System
DESY-System
Jlab HPR Cabinet
114
High Pressure Rinsing
115
High Pressure RinsingResearchPaolo Michelato,
INFN
116
HPR activities at INFN Milan
Open Questions

• How to qualify an HPR systems?
• How to compare different systems?
• Pressure
• Throughput
• Linear Speed
• Distance
• Number of nozzles

Transportable system for measure parameters in
the HPR systems jet force, jet profile and water
jet effects
117
Possible strategy for HPR process study
Measurement of Force and profile
HPR effect on Nb
Correlations?
Cleaning
Niobium oxidation
HPR process optimization
? easy to be measured quantity
118
Water Jet force vs. pump pressure
Nozzle with sapphire orifice
Nozzles
Target
Target
Water jet
Shield
Load cell
Load cell
Pressure regulator
From Bernoullis law the expected force is 3.9 N
119
Jet profiling
If we approximate the jet radial dependence with
a Gaussian profile, from the information of the
behavior of the force vs. displacement on the
target borders, we can extimate the spot
dimension applying
F0 is the total force and s is the spot size. The
jet parameters are calculated fitting F(z) to the
experimental values.
120
Water jet interaction on a not perpendicularly
surface force measurement
Nozzle with sapphire orifice
Measured Force
Water jet
2q
30, 45, 60
Load cell
Load cell transversal load rejection Is good
about 95 . Residual is 5. (5g over 100g).
Calibration done in a separated set-up.
121
Very preliminary data
Distance nozzle - sensor TTF Equator
Data are calculated as the water will loose all
the energy in the impact and no energy was loss
during the flight from the nozzle
122
High Temperature Heat Treatment

• UHV Heat Treatment of Niobium used since the
• beginning of times nowadays
• Hydrogen degassing 600C for 10 hrs at Jlab
• 750 C for 3 hrs at KEK
• Annealing 800 C, several hrs
• Post- Purification 1200C to 1400C in
  presence of a solid state
  getter, e.g.Ti
• Improvement of RRR
• Loss of mechanical properties
• grain growth

123
High Temperature Heat Treatment

• Heat Treatment Furnace at Jlab up to 1250C

124
Post purification of Nb W.Singer, 2003
Thermal conductivity of samples from the niobium
sheets used in the TESLA cavities before and
after the 1400 ºC heat treatment (RRR 270 and
RRR 500 respectively)
Cavity post purification (solid state gettering)
The heat treatment also homogenize the Nb (
reduction of magnetic flux pinning centers shown
by magnetization measurement)
Eacc versus RRR of TTF cavities
125
KEK-Recipe
126
Centrifugal Barrel Polishing(CBP)(1)

• Barrel Polishing (tumbling) developed at KEK
  for smoothening of surfaces/welds
• plastic stones, water abrasive
• Process very slow, by adding motion, removal
  rate increased 10fold 44 mm in 8 hrs
• During the process, hydrogen is dissolved in the
  niobium(Q-disease) and needs to be removed by
  furnace treatment
• Hydrogen-free CBP accomplished by using
• a different (hydrogen-free) agentFC-77
• (C8F18,C8F16 O) T.Higuchi,K. Saito SRF 2003

127
Centrifugal Barrel Polishing(2)
T.Higuchi, K. Saito, SRF 2003
128
CO2 Snow Cleaning

• Developed at DESY (D.Reschke) as an alternative
  to
• HPR or in situ cleaning for modules
• A prototpye system has been fabricated and
  initial tests have been made on samples and on
  single cell cavities
• optimization of process necessary (cleaning
  effect avoidance of condensation, mass flow)
• A production system is under construction and
  will be completed some time in the autumn of 2005

129
Preliminary Tests

• - successful cleaning of Nb samples gt
  investigation of field emission properties
  reduction of particlescollaboration with G.
  Müller, University of Wuppertal, Germany see SRF
  Workshop 2001

Optical microscope images before (left) and after
(right) dry-ice cleaning of ansample
intentionally contaminated with Fe and Cu
particles (500x mag) L.Lilje, CARE Meeting Nov.
2004, DESY
130
Cavity Tests on Mono-cells

• - dedicated nozzle system for cavity cleaning
  developed L.Lilje, CARE Meeting Nov. 2004, DESY

131
First Results of Cavity Tests

• Q-values up to 4,0 1010 at 1.8 K gt no surface
  contamination
• gradients up to 33 MV/m gt field emission is
  limiting effect
• L.Lilje, CARE Meeting Nov. 2004, DESY

Q(E)-performance of two monocells before (black)
and after (red) dry-ice cleaning
132
Large Grain/Single Crystal Niobium

• CBMM Ninxia Wah Chang

Ingot D,800 ppm Ta
Heraeus
Ingot A, 800 ppm Ta
Ingot C, 1500 ppm Ta
Ingot B, 800 ppm Ta
133
Large Grain/Single Crystal Niobium

• Large grain Ingot D from CBMM

134
Single Crystal BCP

• Provides very smooth surfaces as measured by
  A.Wu, Jlab
• RMS 1274 nm fine grain bcp
• 27 nm single crystal bcp
• 251 nm fine grain ep

135
Surface Treatment BCP

• App. 100 micron removed with 112 BCP

136
Large Grain/Single Crystal Niobium

• Cavity

• Discs from Ingot

Epeak/Eacc 1.674 Hpeak/Eacc 4.286 mT/MV/m
137
Single Crystal Cavity
138
Single Crystal Cavity (2)
139
Large Grain/Single Crystal Niobium

• Potential Advantages
• Reduced costs
• Comparable performance
• Very smooth surfaces with BCP, no EP necessary
• Possibly elimination of in situ baking because
  of Q-drop onset at higher gradients
• Possibly very low residual resistances (high
  Qs), favoring lower operation temperature (B.
  Petersen), less cryo power and therefore lower
  operating costs
• Higher thermal stability because of phonon-peak
  in thermal conductivity
• Good or better mechanical performance than fine
  grain material (e.g. predictable spring back..)
• Less material QA (eddy current/squid scanning)

140
Fundamental Power CouplersI. Campisi, SNSW.-D.
Moeller, DESYWorkshop on High Power Couplers for
SC Accelerator, http//www.jlab.org/HPC2002
141
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142
Fundamental Power Couplers(1)

• A coupler is a transition region in a
  transmission line designed to provide the proper
  rate of energy transfer to a resonator
  characterized by Qext
• For sc cavities a power coupler
• Establishes the electromagnetic fields in the
  cavity
• Has to support high thermal gradients ( 300K to
  2K)
• Has to provide a vacuum barrier
• Has to prevent contamination
• Must not suppress cavity performance
• Requirements on couplers are becoming
  increasingly more demanding
• Higher gradients require more standing wave power
• Higher beam currents more traveling wave power
• Pulsed power transient conditions, transient
  gas loads

143
Fundamental Power Couplers(2)

• Most common types of coupling for high
• Power
• Waveguide Leapfrog(NC), SLAC CESR-B(SC),
  CornellCEBAF(SC),Jlab
• Coaxial Tristan, KEKB-factory,KEK SNS
  RIA,MSU LEP,CERNTESLA/ILCAPT,LANL
• Planar window
• Coaxial window

144
Fundamental Power Couplers(3)

• Power couplers for superconducting cavities are
  very complicated structures, which must perform
  at the limit of several technologies
• Brazing, welding, coating (copper), coating (TiN,
  anti-multipacting), vacuum (proper design and
  leak rate), rf power, cleaning,
  testing/conditioning (interlocks for arcing,
  electrons)
• In general, couplers are at least as delicate,
  vulnerable and as expensive as niobium cavities

145
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146
Fundamental Power Coupler
147
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148
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149
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150
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151
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152
Fundamental Power Coupler
153
Fundamental Power Coupler
154
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155
Higher Order Modes/HOM CouplersJ. Sekutowicz
156
3. RF Parameters

Cavities
The amount of energy lost by charge q to the
cavity is ?Uq kq2 for monopole
modes (max. on axis)
?Uq k-q2 for non
monopole modes (off axis) where k and k-(r) are
loss factors for the monopole and transverse
modes respectively.
The induced E-H field (wake) is a superposition
of cavity eigenmodes (monopoles and others)
having the En(r,f,z) field along the trajectory.
For individual mode n and point-like charge
Note please the linac convention of (R/Q)
definition.
Similar for other loss factors.
157
Beam-Cavity Interaction
HOM
Definition the wake potential W is the
potential seen by a test particle following the
unit charge losing the E-H energy to the
cavity.
The wake depends on
W (position of charge q, position of the test
charge, charge distribution q(z), shape of
cavity, s)
158
Beam-Cavity Interaction
HOM
Single passage
The energy lost by the bunch to a mode n totally
dissipates or/and radiates out of the cavity
before the next bunch enters the cavity (there is
no build up effect).
When does it happen?
tb
t
tn ltlt tb
where tn ?nQln is the decay time of mode n
Decay of the energy stored in mode n
159
Dangerous Modes
HOM

• Two kind of phenomena can limit performance of a
  machine due to the beam induced HOM power
• Beam Instabilities and/or dilution of
  emittance
• Additional cryogenic power and/or overheating
  of HOM couplers output lines

Beam instabilities and/or dilution of emittance
Transverse modes (dipoles) causing emittance
growth monopoles causing energy spread This is
mainly problem in linacs
TESLA or ILC, CEBAF, European XFEL, linacs
driving FELs.
Additional cryogenic power and/or overheating of
HOM couplers output lines
Monopoles having high impedance on axis are
excited by the beam and store energy which
must be coupled out of cavities, since it causes
additional cryogenic load, and induces energy
spread. This is mainly problem
in high beam current machines B-Factories,
Synchrotrons, Electron cooling.
160
Trapping of Modes within Cavities HOM
HOM couplers limit RF-performance of sc cavities
when they are placed on cells
no E-H fields at HOM couplers positions, which
are always placed at end beam tubes

• The HOM trapping mechanism is similar to the FM
  field profile unflatness mechanism
• weak coupling HOM cell-to-cell, kcc,HOM
• difference in HOM frequency of end-cell and
  inner-cell

That is why they hardly resonate together
f 2385 MHz
f 2415 MHz
161
Trapping of Modes within Cavities HOM
To untrapp HOMs we can 1) open both irises of
inner cells and end-cells (bigger kcc,HOM) and
keep shape of end cells similar
Example RHIC 5-cell cavity for the electron
cooling
Monopole mode kcc ,HOM 6.7
fHOM 1407 MHz
fHOM 1394 MHz
fHOM 1403 MHz
The method causes (R/Q) reduction of fundamental
mode, which in this application is less relevant.
162
Trapping of Modes within Cavities HOM
2) tailor end-cells to equalize HOM frequencies
of inner- and end-cells
Example TESLA 9-cell cavity, which has two
different end-cells (asymmetric cavity)
The lowest mode in the passband fHOM 2382 MHz
The highest mode in the passband fHOM 2458 MHz
The method works for very few modes but keeps the
(R/Q) value high of the fundamental mode.
163
Trapping of Modes within Cavities HOM

1. one can also split a long structure in weakly
   coupled subsections to have space for HOM
   couplers in mid of a structure.

Example 2x7-cell instead of 14-cell structure
(DESY)
High (R/Q) monopole mode trapped in the 14-cell
structure
2453 MHz, (R/Q) 230 ?
2451 MHz, (R/Q) 212 ?
E-H fields at HOM couplers positions, no trapping
164
HOM couplers and Beam Line Absorbers HOM
Waveguide HOM couplers
HOM ports
Design (1982) works at present in CEBAF both
linacs with Ibeam 80µAx4 _at_ Eacc 7 MV/m HOM
power is very low. It can be dissipated inside
cryomodule.
HOM loads
CEBAF/Cornell 1.5 GHz
Design proposed by G. Wu (JLab) 1500 MHz for 100
mA class ERLs LINAC2004
Design proposed by R. Rimmer (JLab) 750 MHz for
1A class ERLs PAC2005
165
HOM couplers and Beam Line Absorbers HOM
Waveguide HOM couplers, cont.
Design proposed by T. Shintake and continued by
K. Umemori (KEK) 1.3 GHz TESLA cavity, very good
damping. Proceedings ERL2005
Courtesy of KEK
166
14. HOM couplers and Beam Line Absorbers
HOM
Coaxial line HOM couplers
Design (1985/86), 48 work still in HERA e-ring cw
operation Ibeam 40 mA _at_ Eacc 2 MV/m TM011
monopole modes with highest (R/Q) damped in
4-cell cavity to Qext lt 900 !! Couplers are
assembled in the LHe vessel
HERA 0.5 GHz
3 couplers PHOM 100W
TESLA HOM coupler is a simplified version of HERA
HOM couplers for pulse operation with DF of a few
percent !!!!!
output
TESLA 1.3 GHz
FM rejection filter
2 HOM couplers ltPHOMgt few watts
Couplers are assembled outside the LHe vessel !!
167
HOM couplers and Beam Line Absorbers HOM
The TESLA like HOM couplers are nowadays
designed in frequency range 0.8-3.9 GHz
x1, z1
x2, z1
Cs
Ro
L1
Cf
L2
Co
168
HOM couplers and Beam Line Absorbers HOM
There is big progress in modeling (2D and 3D).
Example Modeling of HOM damping in TTF 9-cell
structures by ACD-SLAC (Nov, 2004) . Very good
agreement with the measured data !!!
E
B
Solid Omega3P Hollow Measured (TDR)
169
HOM couplers and Beam Line Absorbers HOM
Increasing Duty Factor, one needs to improve
cooling of HOM couplers.
SNS cavities Linac DF 6
(Courtesy of Oak Ridge Group I. Campisi, Sang-Ho
Kim)
With RF Tmax 7.4 K
No RF Tmax 6.4 K
170
HOM couplers and Beam Line Absorbers HOM
The main problem is heating of the output line.
Heat coming via. output cable from outside.
Nb antenna loses superconductivity, Nb, Cu
antennae will warm when the RF on
Heating by residual H field of the FM
Three solutions to that problem are currently
under investigation
171
HOM couplers and Beam Line Absorbers HOM
1. High heat conductivity feedthrough, ensuring
thermal stabilization of Nb antenna below the
critical temperature (9.2 K) at 20 MV/m for the
cw operation.
JLab RD for the 12-GeV CEBAF upgrade.
Al203 replaced with sapphire
2. New HOM coupler design with hidden output
antenna (JLab).
New HOM coupler.
Old HOM coupler.
172
HOM couplers and Beam Line Absorbers HOM
3. New HOM coupler design without output
capacitor (DESY).
The problem mentioned here looks very unimportant
but following projects need a solution to
it 12-GeV CEBAF upgrade, 4 GLS Daresbury, Elbe
Rossendorf, BESSY Berlin, CW upgrade of European
XFEL, ERL Cornell
173
HOM couplers and Beam Line Absorbers HOM
Beam Line Absorbers multi-cell cavities
BNL e-cooling for RHIC (four 704 MHz cavities 54
MeV
ERL-Cornell, 310 TESLA 1.3 GHz cavities with
modified end cells
TESLA 6 HOM couplers/cavity 2 Beam Line
Absorbers
174
He vessel/Tuners
175
Work Package 8Tuners1st Annual CARE
Meeting

• PRZEMYSLAW SEKALSKI
• DMCS, Technical University of Lodz, Poland

Hamburg, November 3rd, 2004
176
Why is a tuner needed? (1)
The cavities are pulsed at high field.
The field generates the radiation pressure, which
interacts with cavity walls.
The cavity changes its dimensions,
The master oscillator frequency is constant.
The change of the resonant frequency of the
cavity,
De-tuned cavity
177
Motivation
Why do we need a Lorentz force detuning system?
(2/2)
BEAM PULSE ON
178
Lorentz-Force Detuning

• From J. Delayen, Tutorial at SRF2005,
• http//www.lns.cornell.edu/public/SRF20
  05/

For TESLA/ILC Qext 107, Df 100 Hz
Coefficient k 1 Hz/(MV/m)2 Df 1225 Hz
179
Motivation (3/3)
How to maintain the constant phase and amplitude
during the RF pulse ?

• Additional RF power for field control could be
  used
• Passive detuning system (stiffness rings,
  stiffer cavity, fixture) could be used
• Active detuning system
• with piezoelectric and/or magnetostrictive
  device could be used

180
Current Tuner (1/2)
Designed and manufactured by CEA Sacley
181
Current Tuner (2/2)
Principle of operation
Important note The strength applied on the
cavity shall always be set in the state of
compression in order to avoid the neutral point
(equilibrium between pushing and pulling)
1. If the cavity elasticity response is much
lower than the piezo displacement speed then the
tuner will be in the neutral point.
2. The compression force applied to the piezo
element depends on the step motor position. To
guarantee 10 years lifetime of piezostacks the
preload force need to be set around 1.2 kN (?300N)
182
CEA Tuner (1/2)
Principle of operation
Super 3HC tuner
SOLEIL tuner
The tuner will never be in the neutral point.
183
2. TESLA Cavities and Auxiliaries as ILC Baseline
Design
Cold Tuners
Saclay Lever Tuner spec.

• 460 kHz tuning range
• 4 nm resolution 1.2 Hz (sufficient if lt5Hz)
• 1kHz fast compensation by piezo

Courtesy P. Bosland
Piezos
Stepping motor and gear box
184
TESLA Cavities and Auxiliaries as ILC Baseline
Design
Cold Tuners
Blade Tuner spec.

• 1 mm fine tuning (on cavity) ? ?F on all piezo
  (sum) 3.5 kN
• 1 kHz fast tuning ? 3 µm cavity displacement
  ? 4 µm piezo displacement
• 4 µm piezo displacement ? ? F on all piezo
  11.0 N
• 1 Hz resolution (sufficient if lt5Hz)

Stiffeners bars could be used in working cond. as
safety devices.
Courtesy A. Bossoti.
Piezo
Ti ring welded on the tank
Leverage arm
185
Blade tuner structural modelINFN

• Each component is modeled as a spring with proper
  stiffness

The tuner installed on a 9 cell cavity before
the test in the horizontal cryostat
Goal Integrate the structural model with the
cavity e.m. model to allow the design of the
fast tuning system
186
He-vessel/Tuner

• Present baseline design for ILC/X-FEL uses Ti
  He- vessel around cells, endgroups are cooled by
  conduction
• Mechanical (coarse tuner) is either of Saclay
  design (lever system) or the Blade tuner of INFN
  design.
• Incorporated in either design is a fine tuner of
  piezo stacks or a magneto-strictive design
• Much effort is presently going into the
  qualification and characterization of appropriate
  piezo and magneto-strictive material
• More information in e.g.
• M. Fouaidy, Status of IPN Orsay activities
  RD on Fast Active Cold Tuning System for SRF
  cavities https//ilcsupport.desy.de/cdsagenda/fu
  llAgenda.php?idaa062
• P. Sekalski, ibid

187
Assembly of Cavity Strings
188
String Assembly(1)

• 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

189
Assembly(3)
190
String Assembly(4)
The inter-cavity connection is done in class 10
cleanrooms
191
Assembly Vacuum Hardware(1)

• The cavity strings have to be vacuum tight to a
  leak rate of lt 1 x10-10 torr l/sec
• The sealing gaskets and hardware have to be
  reliable and particulate-free
• The clamping hardware should minimize the space
  needed for connecting the beamlines

192
Assembly Vacuum Hardware(2)

• AlMg-Gasket
• Radial Wedge Clamp

• Present choice for TESLA cavities
• diamond-shaped AlMg3 gaskets NbTi flanges
  bolts
• Alternative
• radial wedge clamp, successfully used for CEBAF
  upgrade cavities

193
Modules

• SNS Medium Beta Cavity String three 6-cell
• 805 MHz cavities

Pump-out assembly
194
String Assembly

• Jlab Upgrade String of eight 7-cell cavities in
  class 100
• Clean room on assembly bench

195
Cavity Testing Vertical(1)

• Cavities are typically qualified in vertical
• dewar tests. Measurements can include
• T-dependence of surface resistance between 4.2k
  and 2K
• Q0 vs Eacc at 2K and/or other temperatures in p
  mode
• Q0 vs Eacc at 2K and/or other temperatures in
  passband modes
• Radiation level vs Eacc / radiation spectra
• Pressure sensitivityf vs He-bath pressure
• Lorentz force detuning f vs Eacc
• Temperature maps

196
Cavity Testing Vertical(2)

• Vertical tests typically use phase-lock loop rf
• Systems

197
Cavity Testing Vertical(3)
198
Cavity testing Vertical(4)
199
Cavity Testing Vertical(5)
Insertion of Cavity into Dewar
Vertical Test Area at Jlab
200

• Results from Cavity Tests

201
Alternatives LL and RE Cell ShapesK.Saito et
al, KEK
202
Jlab/CBMM Technology

• Nb Discs

• LL cavity 2.3GHz

Epeak/Eacc 2.072 Hpeak/Eacc 3.56 mT/MV/m
203
DESY Nine-Cells Results and Perspectives for the
Next Modules

• Lutz Lilje
• DESY -MPY-
• Lutz.Lilje_at_desy.de

TTC Meeting Frascati, Dec. 2005
204
Principle Potential of EP Bake Process
205
Principle Potential of 800C EP Bake Process
206
Eacc vs. time
207
Eacc vs. time
208
Comparison 3rd and 4th Cavity Production First
Test after Full procedure (Eacc, max for Qgt1010)
209
Conclusion

• The ILC is a very ambitious project with
  performance goals for the cavities, which touch
  the limit of the technology
• Proof of principle has been established, but
  there is still a long way to go for achieving the
  design goals in a construction environment
• If the ILC becomes a project, it might be a
• life time job for some of you, how are
• interested in this technology