The Continuing Role of SRF for AARD: Issues, Challenges and Benefits

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The Continuing Role of SRF for AARD Issues,
Challenges and Benefits
Hasan Padamsee Cornell University

• SRF performance has been rising every decade
• SRF installations for HEP (and other
  applications) have been rising steadily
• With strong support, SRF can continue to make
  major impact on future HEP accelerators
• ILC, TeV upgrade, Superbeams for Neutrinos,
  Neutrino Factory, Muon Collider, Multi-TeV
  colliders

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Steady Increase of Installed SRF Voltage in
Accelerators With Time
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Total Installation gt 1000 m Total Voltage gt 6 GV
KEK-B
SNS
SNS/Jlab
CEBAF
CESR
HERA
LEP-II
CESR
TRISTAN
Stanford
Cornell
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Steady Increase of SRF Gradients1980 20065
MV/m -gt 40 MV/m
Along the way
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1995 Gradients 26 - 27 MV/m reached in Three
5-cell structures
Cornell DESY Fermilab Collaboration
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Increase of SRF Gradients9-cells, 1995
2006-gt 40 MV/m
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SRF for ILC (0.5 TeV)
SRF technology in US needs serious catching up
! Need to engage ALL available resources in US
35 - 40 MV/m DESY-KEK 6 best cavities, Vertical
Tests
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Goals of Near Term RD for ILC
See talks by Holmes, Kephart, Kneisel

• Demonstrate reproducibility of performance
• Perfect EP, HPR, clean room techniques in US
• Long term performance characterization of full
  scale structures in cryomodules
• Assemble and operate one complete RF unit with
  all ILC building blocks
• US labs engaged
• Fermilab, Jlab, Cornell, Argonne
• (SMTF collaboration)

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Beyond 35 MV/m for TeV ILC

• Important work started
• BUT much more needed!
• Better shapes
• Better niobium
• Better understanding of SRF physics of niobium

See Talk by Kneisel
See Talk by Gurevich
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New Shapes Breakthrough50 MV/m in Single Cells
!Lower Surface Magnetic Field Lower Losses
Need Multi-cells Next
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Better NiobiumStarted at Jlab
- Reduction of grain boundary density improves
performance - Lower cost through ingot stage
material
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SRF for  Muon Colliders at Multi-TeV energies

• Biggest challenge is muon cooling
• being addressed elsewhere
• Muon collider is a cascade of SRF Recirculating
  Linear Accelerators (many turns each)
• Starting with linac at low frequency (e.g 200
  MHz) at 10 15 MV/m, followed by low frequency
  RLAs
• TeV scale energies after with several 30 MV/m
  gradient RLAs
• Total about 5 km of ILC-like linac

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Need High Quality Nb Coatings For Low Frequency
Applications

• For 200 MHz, cost of Nb is a major factor gt
  Develop Nb/Cu
• CERN/Cornell collaboration reached 10 MV/m
• Improved coatings needed for 15 MV/m
• Ionize Nb atoms using various methods
• Bias magnetron sputtering (Cornell/ACCEL)
• Electron cyclotron resonance in a Nb plasma
  (Cornell/Jlab)
• Vacuum Arc (Cornell/INFN-Rome)

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SRF for the Neutrino Sector

• Neutrino factory (Muons accelerated to 20 GeV via
  5-turn RLA, need about 4 GeV)
• Could serve as demonstrator for the muon
  collider
• Neutrino factory may or may not be needed
  depending on super-beams, as for example
• 8 GeV Proton Driver
• Main part of Proton Driver is SRF, ILC-like linac
  
• Could also be test linac for ILC (if needed)

Neutrino Beams
See Talk by Foster
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SRF for Colliders Beyond 1 TeVBoth gradients gt
50 MV/m Q 1011 can contribute

• Higher gradients
• Need New materials, e.g. Nb3Sn
• Simple theory
• RF critical magnetic field Superheating
  critical field
• Nb 2200 Oe (57 MV/m) Best achieved 2000 Oe
• Nb3Sn 4000 Oe (105 MV/m) Best achieved 1100
  OeWhy?
• Fundamental research needed on the RF critical
  field of highly Type II superconductors
• Theoretical studies
• Experimental work to determine Hcrit
• Coupled with fabrication of best materials
• Present funding level for this effort is nearly
  zero !

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Pulsed Measurements of RF Critical Field Nb
Nb3Sn
4000 Oe 105 MV/m in new shape cavities
T. Hays Cornell Campisi SLAC
Hc1- Nb3Sn
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Simple Theory of RF Critical Magnetic Field
Plane Nucleation Model For flux lines
Other Models Are these right??
Best Nb
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Increased Gradients Must Go Hand-in-hand With
Increased Q, to Keep Operating Costs in Line
For e.g. 80 MV/m will need Q 1011
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Best Nb Q gt 1011 at 25 MV/m, 1.6 K
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Best Nb3Sn Q at 2 K ! (But at low fields)
G. Mueller and P. Kneisel
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Conclusions

• Basic RD on SRF has steadily pushed gradients
• With many benefits to HEP, and non-HEP along the
  way (See Talk by Swapan C.)
• We must solidify our gains in the 35 40 MV/m
  range to realize ILC
• With other potential benefits to HEP ( Neutrino
  Factory, Proton Driver, Muon Collider)
• And non-HEP (Light sources, Neutron sources)
• Support needed to stay on the road to 100 MV/m
  and Q 1011 to realize multi-TeV energy.
• Continued evolution of the Livingston Curve?

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A Look into the Past and FutureInstalled SRF
Voltage
ILC
XFEL
SNS
LEP
CEBAF