Superconducting RF, the history, challenges, and promise

1
Superconducting RF, the history, challenges, and
promise

• Hasan Padamsee
• Cornell University

2
Outline

• Survey on-going applications with highlights
• Evolution of gradients, outstanding issues, and
  quest for solutions
• High gradient applications
• CW operation (for medium gradient, CW
  applications)
• Future prospects near term and long term
• Is there a higher gradient (far) future beyond 50
  MV/m fundamental limit for niobium?

3
Four Decades of SRF Success Stories

• SRF Started as an exotic technology in the
  1960s
• Really took off in the 1980s

• Now become an enabling technology for many
  accelerators !

4
Major Impact on Broad Spectrum of Science

• High Energy Physics and Low Energy Nuclear
  Physics (1980 2000)
• TRISTAN, HERA, LEP-II ATLAS, StonyBrook...
• Penetrated Medium Energy Nuclear Physics (1987)
• CEBAF
• Storage Ring Light Sources (2000-2005)
• CHESS, CLS, TLS, DIAMOND, SLS..
• Linac Based Light Source (1990-2010)
• JLABFEL, TTF-I, FLASH
• Neutron Source - Proton Source (2005-2010)
• SNS
• Explosion of Future Applications ! (2010 and
  beyond)

5
World-Wide Collaboration Benefits SRF Technology
and Accelerator Applications

• SRF Workshops every 2 years
• Beijing, Cornell, Travemunde, Santa FeBerlin
  (2009)
• Next SRF Conference Fermilab/Argonne in 2011
• Generally preceded by several-day tutorials
• Most proceedings now on JACOW
• Tesla-Technology Collaboration (TTC) meetings
  every 6 months
• Delhi, Hamburg, KEK, Frascati, Orsay
• Next TTC meeting Fermilab, March 2010
• TTC focused on major technical issues
• E.g. Gradient yield RD, Industrialization,
  couplers, tuners
• Various Project Collaboration Meetings
• ILC, Project X, XFEL...
• Monthly

6
Present Applications HEP

• TRISTAN, HERA, LEP-II, CESR-C (total 3.5 GV) now
  decommissioned
• KEK-B Low Energy Ring (20 MV)
• Also used in Beijing Tau-charm Factory
• CESR-C now CESR-TA for ILC Damping ring RD

KEKB
7
KEK Crab Cavity Success

• 2 MV deflecting kick
• On May 6, 2009, KEKB broke the world luminosity
  record and achieved a luminosity of 1.96 x
  1034/cm2/sec using the crab cavities.

8
Present Applications Medium Energy NP

• CEBAF is a 5-pass 6 GeV CW recirculated linac
  based on SRF.
• originally 4 GeV design
  specification,
• Three experimental halls for nuclear physics
  research
• Nuclear structure, Gluonic excitation etc
• 421/4 original cryomodules assembled in-house.
• (Then) worlds largest 2K Cryo plant (5kW).
• Worlds Largest operating installed base of SRF.
• Soon to be upgraded to 12 GeV

9
CEBAF 12 GeV Upgrade

• Add 0.5 GV to both linacs to deliver 1.1GeV
  each.
• The total beam power will remain unchanged at one
  MW.
• Install 10 new 100 MV cryomodules with 7-cell
  cavities operating at 18 MV/m.
• CEBAF original 30 MV per cryomodule with cavities
  operating at 7.5 MV/m.
• Double cryoplant to 10 kW at about 2 K

10
Present Applications Low Energy NP

• ATLAS (Argonne)
• 68 cavities operating for three decades for
  heavy-ion, nuclear and atomic physics research,
• Logging gtgt 100,000 hours of beam-on-target
  operation.
• The split ring resonators have built up a track
  record in excess of 3 million unit-hours of
  operation with better than 99 availability.
• ATLAS upgraded in energy by 30 to 50 (depending
  on ion species)
• Single eight-cavity cryomodule containing seven
  quarter-wave and one half-wave cavity.

11
Present Applications Low Energy NP

• ALPI, Legnaro, Italy
• 64 QWR at 160 MHz delivering a total of 49 MV.
• At IUAC, DELHI, linac
• 27 QWRs, 3- 5 MV/m

12
RIB Facilities Nuclear AstrophysicsOperating
or Under Construction

• ISAC-II at TRIUMF in Canada, 20 QWR, 4 CM,6- 7
  MV/m
• SPIRAL-II at GANIL (Saclay, Orsay, France)
• 26 QWR, 6.5 MV/m
• MSU ReAccelerator, FRIB test-bed
• 3 CM with 15 QWR, 10 MV/m
• SARAF Israel, RIB
• and Medical Isotope
• 48 Half-Wave Resonators, 8 CM, 8 MV/m
• Near Future CERN- HIE-ISOLDE
• 30 resonators

SARAF Half-Wave
ISAC-II QWR
13
FRIB, Facility for Rare Isotope Beams at MSU

• FRIB will allow major advances in nuclear science
  and nuclear astro-physics
• 200 MeV/u, 400 kW driver linac
• 336 Resonators QWR and HWR

14
Light Sources Storage Rings

• CHESS (Cornell)
• Beam current 500 mA
• Power/coupler 160 KW
• Cornell Technology Transferred to ACCEL.
• Cornell systems used for storage rings around the
  world
• Taiwan Light Source
• Canadian Light Source
• DIAMOND light source
• Shangai Light Source
• NSLS-II at BNL (future)
• Pohang Light Source?

500 MHz
15
Taiwan and Diamond (UK)
16
JLAB - FEL

• Lased in the 1-6 mm wavelength range
• Average IR output power of 14 kW (Record !) at
  1.6 mm,
• Runs in the energy recovery mode with more than
  99.8 efficiency.
• More than 1.3 MW beam power was energy recovered
  with a beam of 9.1 mA at 150 MeV.
• Important milestone toward high beam power ERLs
  of the future.
• The accelerator has been configured with another
  recirculation for the UV upgrade.

FEL with ER
17
TESLA Test Facility (TTF) Now FLASH

• Six modules installed in FLASH at DESY provide 1
  GeV beam Lased at 6.5 nm
• With 48, 9-cell cavities operating between 20
  25 MV/m.
• Strong basis for XFEL which will also be a
  prototype for ILC

18
Best Module Performance Module in FLASH
19
FNAL 3.9 GHz Module Tested Successfully 20 MV/m,
October 09
20
SNS Linear Accelerator
Stuart Henderson ALCPG09

• TTF Progress in gradients and KEK progress in
  coupler power gt
• Worlds first high-energy superconducting linac
  for protons
• 81 independently-powered 805 MHz SC cavities, in
  23 cryomodules
• Space is reserved for additional cryomodules to
  give 1.3 GeV

21
Stuart Henderson ALCPG09
Individual and Collective Cavity Limits
Individual powering one cavity at a
time Collective powering all cavities in a CM at
the same time
CM19 removed
Large fundamental power through HOM coupler
Design gradient
Field probe and/or internal cable (control is
difficult at rep. rate gt30 Hz)
Average limiting gradient (collective)
Average limiting gradient (individual)
22
Evolution of SRF Technology Over 4 Decades

• Steady progress in Gradients due to
• Basic understanding of limiting phenomena
• Invention of effective cures
• Ignore all the failed (or not so successful) paths

23
Field Emission
Cures
RRR 250
Thermal breakdown
Multipacting
24
Niobium Purification
Interstitial O, N and C are the major impurities
limiting Nb RRR
25
Typical Progress in Thermal Conductivity (RRR)
(at Tokyo Denkai)
26
HPR and Clean Room Assembly
Fight Field Emission
27
TTF-I (2001) Field Emission Tamed, BCP, HPR Q-drop
25 - 30
30 - 35
35 - 40
20 - 25
15 - 20
10 - 15
CEBAF (1995)
28
Best 12 9-cells
EP and bake
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Lessons Learned

• Understanding ( science) drives performance
• Leads to effective solutions
• Multipacting solved spherical (elliptical)
  cavity geometry
• 5 8 MV/m
• Thermal breakdown solved high purity Nb
• 10 15 MV/m
• Field emission solved high pressure rinsing
• 15 25 MV/m
• Q-slope solved EP and bake
• 25 35 MV/m
• Thermometry has been the key to science

30
Thermometry Has Been the Key to Better
Understanding of SRF Cavity Performance
Limitations
The Miracles of Thermometry
31

• High Field Q-Slope

• Field Emission

• Movie Break !

• Quench

32
Quench Movie
Iris
Equator
Iris
33
Culprits Revealed by Thermometry/Dissection/SEM
EDX
Field Emitters
10 mm
20 mm
5 mm
Note Melted Region
Stainless Steel
C, O, Fe, Cr Ni
Quench Defects
100 mm
200 mm
50 micron Cu particle fell into cavity
500 mm
500 x 200 microns pit
34
Outstanding Performance Issues and How to Address
Them

• For the high gradient frontier (S0)
• Understand and fix the underlying causes of the
  high gradient yield problem for multi-cell 1.3
  GHz cavities (S0).
• Develop good procedures to maintain high
  performance in cryomodules (S1)
• For the high Q0 frontier important for CW
  applications
• What are the sources of loss that limit the
  ultimate Q0

35
Residual Resistance Values for the SNS Medium
Beta Production CavitiesJlab data SNS MB 805
MHz G. Ciovati
High Q Frontier
More HPR
Max Q 6x1010
A lot of scatter, average 8 nO
36
Prospects for Improvement in Gradient Yield

• Progress takes time
• Everyone wants to follow a different path
  innovation, creativity
• Try better preparation techniques
• Examples later
• Find the quench producing defects in 9-cells with
  thermometry, inspect
• Slow method, several cold tests
• Test in several modes of 9-cell pass-band
• Indentify pair of culprit cells (or one center
  cell)
• Warm up, attach 1-cell or 2-cell thermometry to
  culprit cells
• Locate quench
• Repeat as necessary
• Fast Methods
• Locate multiple quench spots in one test with 2nd
  Sound in Superfluid He
• Apply 9-cell superfluid large-scale thermometry
• LANL system complete
• Use optical inspection tools
• KEK optical camera, Questar system
• Make a wax replica of defective area, carry out
  optical profilometry
• Example for one-cell

37
Field Emission Reduction By New Rinsing Methods

• Better cleaning after electropolishing
• Jlab Ultrasonic degreasing
• DESY Ethanol rinsing

Ethanol dissolved particle, but leaves an
imprint, Possible quench site? unknown
S particle deposited on sample during EP (Cornell
Basic RD)
38
Fast Method
Fixed thermometer locations
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Museum of Quench Sources (Pits and
Bumps)Identified by Thermometry and Optical
Examination
Bump found at Quench location on Niowave/Roark
1-cell cavity (Cornell) Deep scratch subsequently
found on Cavity Forming Die
26 mm
Pit found by KEK optical inspection with CCD
camera in AES 1cavity Quench at 18 MV/m
Bump found by KEK Optical Inspection with CCD
camera in AES 9-cell cavity with thermometry
(Jlab and FNAL) Quench at 18 MV/m
41
Wax Replica Method at FNAL
Optical Profilometry
42
9-cell Superfluid He Thermometry and Inspection
at LANL
43
9-cell defects for cavity AES003

• Pre-heating detected in all cases

Slide 43
44
The Ultimate Sacrifice !Temperature Map
Dissection

• General heating due to high field Q-slope
• Defect heating at pit before quench

45
Prospects for Higher Q0Map the Loss Distribution
for High Q Cavity
3 GHz, 1-cell Cavity - Wuppertal

• Apart from one defect,
• Dielectric and magnetic loss spots can be
  identified
• All other loss spots have residual resistance
• lt 1 nW
• Q0 3 x1011

Defect
Dielectric Losses
Magnetic losses
46
World Record Q0 (1.3 GHz Single Cell)
5 mGauss DC magnetic field
47
Future AdventuresSRF Based Projects

• A wide spectrum of ideas
• gt the large impact of success of existing
  srf-based facilities and srf technology advances
• Not likely that all projects will come to pass
• Classify descriptions according to science
• High Energy Physics
• Leptons (ee-, mm-, n), high intensity protons
• Nuclear physics
• Electrons, heavy ion
• Astrophysics (already covered FRIB)
• Rare isotopes
• Materials and biology
• Light source
• Storage ring, FEL, ERL
• Neutron source

48
Lepton Colliders beyond LHC
? By far the most likely!
E lt 1 TeV
CLIC
E gt 1 TeV
Multi TeV
Muon Collider
Welcome to Fermilab, Young-Kee Kim, October 19,
2009
48
49
ILC
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Progress for S1 at DESY-FLASH
52
Progress toward S2 at DESY- FLASH

• Beam current requirement (9mA)
• Successful 10 hr operation at 3 mA
• Short time at 6 mA
• Several hours of intermittent operation close to
  9 ma with short trains of 300 500 us
• Limited by beam loss
• Still need to show 31.5 MV/m operation with 9 mA
  beam

53
High Intensity Proton Accelerators for HEP

• Fermilab PX
• Neutrino beams, Rare decays, future source for
  neutrino factory, muon collider
• 2 MW beam power
• 2 GeV
• CERN SPL
• Higher luminosity for LHC
• Neutrino beams, future source for neutrino
  factory, muon collider
• Injector for EURISOL (Rare Isotope Facility)
• 5 GeV
• 2- 4 MW beam power

54
Project X Options

• 2 MW of beam power over the range 60 120 GeV
• Simultaneous with 2 MW beam power at 2 GeV
• Rare decay physics
• Compatibility with future upgrades to 8 GeV

• gt2 MW of beam power over the range 60 120 GeV
• Simultaneous with gt150 kW of beam power at 8 GeV

HIPA Workshop - S. Holmes
Page 54
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CERN Comes Back to SRF !
High Power SPL (HP-SPL)

• Start with Low Power SPL, 4 GeV, 20 mA
• Replacement of klystron power supplies, upgraded
  infrastructure (cooling electricity, etc.)
• Addition of 5 high b cryomodules to accelerate
  up to 5 GeV (p production for n Factory))
• Beam power 2 4 MW

SC-linac (160 MeV 5 GeV) with ejection at
intermediate energy
110 m 0.73 GeV
0 m 0.16 GeV
291 m 2.5 GeV
500 m 5 GeV
SPL description
Medium b cryomodule
High b cryomodules
Debunchers
High b cryomodules
To PS2 and Accumulator
From Linac4
Ejection
to EURISOL
Length 500 m
57
Neutrino Factory Muon Collider

• Proton Driver needs 4 MW
• Neutrino Factory needs about 4 GV acceleration,
  multiple passes
• Muon Collider needs 200 GeV acceleration
• Depending on number of passes in RLA
• Five passes?

58
European Spallation Source (ESS)Sweden

• 5 MW upgradable to 7.5 MW, 2.5 GeV
• 15 MV/m, coupler power 1.2 MW (dual couplers)
• Pulsed 2 ms, 20 Hz
• High reliability and low beam losses
• Synergies with EURISOL, SPL, eRHIC

59
Future Light Sources

• Probe matter at finer length and time resolution,
  
• Increased precision and detail
• Temporal evolution of electrons, spins, atoms,
  and chemical reactions down to the femtosecond
  time scale
• Spectroscopic and structural imaging of nanoscale
  objects or inhomogenities with nanometer
  resolution and ultimate spectral resolution
• High peak and average brightness
• photon flux in small phase space area
• Short pulses (lt ps)
• High spatial and temporal coherence (uncertainty
  limited)
• High energy resolution (uncertainty limited)
• Cover only a few of the many ideas under
  exploration

60
XFEL (20 GeV) Under Construction
FLASH
XFEL
The biggest SRF application to date 20 GeV
61
Energy Recovery Linacs vs. Storage Rings

• Storage rings are approaching limits of
  performance
• Low emittance for higher brightness requires
  bigger wigglers for damping
• Bunch length hard to get below a few picoseconds
• SRF Linacs can preserve very low emittances of
  todays and tomorrows electron sources,
• if potential gun performance realized in CW
• Emittance scales like 1/E
• Can run CW, both for high average power/rep rate
  and for multiple users
• Challenges
• 100 mA injector, HOM damping (for BBU and
  losses), halos, ions at very high average current

62
Cornell ERL Injector and ERL_at_CESR ConceptBased
on TESLA Technology BUT CW and Medium Gradient
ERL Injector Now Under Commissioning
Planning
Future 5 GeV ERL
63
Cornell ERL Injector Cavity Assembly
Injector Cavity Fabricated at Cornell

• ERL cavity with He vessel and INFN blade tuner
• Two TTF-III improved couplers for 50 kW CW power
• Beam line HOM absorbers

64
String Assembly in Clean Room
5 Cavity ERL Injector Cryomodule Assembled at
Cornell All Parts (except cavities) fabricated in
Industry
65
Finished ERL Injector Cryomodule

• Gradients to 15 MV/m reached with beam 8 mA CW
• Couplers tested to gt 50 KW CW
• But Q values 2 3 X109 (dust contamination?)
• Disassemble CM and HPR recover Q to 2 x 1010

66
KEK and Arc-En-Ciel (France)

• KEK Compact ERL

67
LBNL FEL Concept

• Soft X-ray FELs

68
FEL
69
ERLs also for NP
BNL ERL RHIC
For Prototype ERL at BNL
JLAB ELIC
70
Summary Total Voltage Installed (Near Future)

• 600 Cavities
• QWR
• HWR
• SSR
• TSR
• For
• SPIRAL-II
• MSU-ReA
• MSU-FRIB
• CERN HIE-Isolde
• ESS
• PX

XFEL
FLASH
SNS
MVolt
LEP-II
Jlab
Jlab-Upgrade
Year
71
Prospects for Continued Voltage Growth
(Optimistic)!
PX, SPL
ILC
v-facctory
XFEL
ESS, ERL, e-RHIC
72
Is there a higher gradient future gt 2025 beyond
Niobiums 50 MV/m fundamental limit ?
Nb3Sn Hc1
73
Nb3Sn An Uphill Climb for the Next Generation
ofSRF Enthusiasts

• Now ?!