Update on SRF Activities at Argonne

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Update on SRF Activities at Argonne

• Mike Kelly, Peter Ostroumov, Mark Kedzie, Scott
  Gerbick (PHY)
• Tom Reid, Ryan Murphy (HEP)
• Thomas Proslier, Jeff Klug, Mike Pellin (MSD)
• June 7, 2010

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• ATLAS
• ILC
• National Security
• Atomic Layer Deposition
• SRF at the Advanced Photon Source (SC undulator
  and crab cavity)

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I. ATLAS Energy Upgrade Commissioned June
2009Exceeds previous state-of-the-art (at
TRIUMF) by 50
EP in Joint Facility
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I. ATLAS Efficiency and Intensity Upgrade Phase
I RFQ and new cryomodule

• New 60.625 MHz CW RFQ
• New cryomodule with 7 QWRs ?OPT0.077
• Total 9.86M ARRA funds
• Complete in March 2013

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I. ATLAS Energy and Intensity Upgrade
CryomoduleCommissioning in July 2012
(for scale)
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I. Pushing performance for low-beta SRF cavities
b0.077 f72.5 MHz Bp/Eacc 4.8
mT/MV/m Ep/Eacc3.25

• Obvious benefits for ATLAS
• Replace aging split-ring cryomodules
• Higher energies (30-40 beam energy increase with
  Phase I)
• Higher intensities
• Real possibilities for high-gradient low-beta for
  applications
• National security (non-destructive interrogation
  methods)
• Nuclear medicine (accelerators as solution to
  Mo99 crisis)
• Renewed interest for waste transmutation
• To push for better performance in the intensity
  upgrade
• VCX fast tuner g Piezoelectric transducer 4 kW
  coupler
• Better performance through the use of techniques
  learned in FNAL collaboration particularly
  horizontal electropolishing on completed jacketed
  niobium cavity

New center conductor die Courtesy AES, June 4,
2010
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II. Joint ANL/FNAL Cavity Processing Facility

• Full operations (chemisty/clean room) since Mar
  2009
• Two new EP operators trained
• Excellent single cell results, recent good 9-cell
  results
• Electropolishing system refinements
• Possible improvements still to be had in
  operating parameters
• Collaboration with JLab on KEK on EP optimization

Ultrasonic Cleaning
Electropolishing
High-pressure rinse
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II. Cavities Electropolished/Assembled at the
ANL/FNAL SCSPF in 2010
Date Cavity Name Cavity Type EP Type Target Removal (µm) Process Run Time (min)
1/27/2010 TB9RI026 9-Cell Bulk 130 390
1/28/2010 TB9ACC007 9-Cell Light 20 70
2/15/2010 TB9RI026 9-Cell Heavy 100 300
2/18/2010 TE1ACC003 1-Cell Light 40 120
2/22/2010 TE1CAT002 1-Cell Bulk 120 360
3/26/2010 TB9RI024 9-Cell Light 20 70
3/30/2010 TB9RI026 9-Cell Light 20 70
4/2/2010 TB9AES003 1-Cell Light 20 70
4/7/2010 TE1CAT001 1-Cell Light 20 70
4/8/2010 NR-6 1-Cell Light 20 70
4/16/2010 TE1CAT001 1-Cell Light 30 100
4/20/2010 NR-6 1-Cell Light 30 100
4/28/2010 TB9RI029 9-cell Light 20 110
5/11/2010 TB9RI024 9-cell Light 20 120
5/25/2010 TB9RI020 9-cell Heavy 120 450
6/3/2010 TB9RI024 9-cell Light 20 100
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II. Feedback from FNAL SRF Cavity Diagnostics
(KEK Camera) to ANL Cavity Processing

• Intra-grain structure is due to disruption of
  viscous layer from acid injection
• Cathode holes covered and orientation changed to
  upward to reduce/remove this effect

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II. New Low Voltage 9-cell cavity
electropolishing parameters
Cavity Temp.
Current
Voltage
Acid Temp.
Acid Temp.
Water Temp
Acid Flow
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II. In the 2nd Chemistry Room QWR
electropolishing based on existing mechanical and
electrical hardware
rotating carbon brush assembly
sliding Bosch rail
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II. Electropolishing for 650 MHz 5-cell cavity

• Scaled cavity geometry shown with the existing EP
  hardware
• Cavity with twice radial dimension of the 1.3 GHz
  9-cell fits into the existing system with modest
  modification (no cavity frame shown, may need to
  shim under blue stands)
• 55 gallon acid handling limit OK
• 2 ½ times surface area, EP supply OK, 50 larger
  chiller
• Cavity handling similar to 9-cell (crane in
  hi-bay, hoist in chemistry room)
• No major difficulties in adapting EP to this
  geometry

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III. SRF for National Security

• Accelerators for interrogation of special nuclear
  materials
• Based short high-intensity pulse of protons
• Secondary neutron production induces detectable
  g-rays
• Very high accelerator real estate gradients
  needed (both low and high-b)
• ANL-PHY funded to develop high real estate
  gradients for low-b
• Fabrication/processing/diagnostic technique to
  achieve ILC type surface fields (120 mT)
• Innovative design techniques to reduce surface
  fields/increase packing factor

Concept for a stackable half-wave cavity with
very low surface fields
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IV. Surface impedance Magnetic impurities the
residual resistance and more
Experimental evidence -Data courtesy JLab
(Ciovati) -Theory, Argonne Hot spots have higher
concentration of Magnetic impurities than cold
spots
Bake 120C
Bake 180C
3 parameters -e, a effect of Magnetic
impurities on the Nb superconductivity, give Rres
, ? and TC. Here e0.2 fixed. -Normal
conductivity s0 shift RST vertically, give the
mean free path L
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IV. Surface impedance Magnetic impurities the
residual resistance and more

• Summary of results
• More magnetic impurities after baking (consistent
  with Casalbuoni SQUID), Conc 200 ppm
• Longer mean free path thus cleaner after baking.
• Smaller gap but larger ?/kTc after baking.

• Unknowns and next experiments
• Where are the magnetic impurities coming from
  Oxides for sure but something else also?
• EPR (electron paramagnetic resonance) to probe
  mag. moments on EP samples.
• -Refine the model introduce inhomogeneity or
  surface layer.

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IV. Superconducting layer by ALD
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Thin films 10 nm
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Summary SRF at ANL

• Phase I ATLAS Intensity Upgrade funded work
  proceeding completion in 2013
• Cavity processing at the joint ANL/FNAL facility
• Good cavity throughput
• Tweaking chemistry and clean room techniques
  based on test results and discussions with
  JLab/KEK
• Interest and support for SRF for non-basic
  science applications
• Material Science
• Atomic layer deposition to produce new
  superconducting layers for cavities
• Magnetic impurities to explain SRF properties of
  niobium