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

I. ATLASII. ILCIII. National SecurityIV. Atomic Layer DepositionV. SRF at the Advanced Photon Source (SC undulator and crab

cavity)

I. ATLAS Energy Upgrade: Commissioned June 2009Exceeds previous state-of-the-art (at TRIUMF) by ~50%

EP in Joint Facility

CARIBU

MHB RFQ New cryomodule Energy upgrade cryomodule

Tandem

CARIBU

MHB RFQ New cryomodule Energy upgrade cryomodule

Tandem

I. ATLAS Efficiency and Intensity Upgrade Phase I: RFQ and new cryomodule New 60.625 MHz CW RFQ

New cryomodule with 7 QWRs OPT=0.077 Total $9.86M ARRA funds Complete in March 2013

I. ATLAS Energy and Intensity Upgrade: CryomoduleCommissioning in July 2012

(for scale)

I. Pushing performance for low-beta SRF cavities

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…1. VCX fast tuner Piezoelectric transducer + 4 kW coupler2. Better performance through the use of techniques learned in FNAL collaboration;

particularly horizontal electropolishing on completed jacketed niobium cavity

30 cm

=0.077f=72.5 MHzBp/Eacc= 4.8 mT/MV/mEp/Eacc=3.25

New center conductor dieCourtesy AES, June 4, 2010

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

II. Joint ANL/FNAL Cavity Processing Facility

Electropolishing

High-pressurerinse

Ultrasonic Cleaning

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

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

II. New Low Voltage 9-cell cavity electropolishing parameters

Cavity Temp.

Current

Voltage

Acid Temp.

Acid Temp.

Water Temp

Acid Flow

II. In the 2nd Chemistry Room: QWR electropolishing based on existing mechanical and electrical hardware

sliding Bosch rail

rotating carbon brush assembly

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

III. SRF for National Security

Accelerators for interrogation of special nuclear materials Based short high-intensity pulse of protons Secondary neutron production induces detectable -rays Very high accelerator real estate gradients needed (both low and high-

ANL-PHY funded to develop high real estate gradients for low-– 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

Bake 120C Bake 180C3 parameters: -ε, α : effect of Magnetic impurities on the Nb superconductivity, give Rres , Δ and TC. Here ε=0.2 fixed.

-Normal conductivity σ0: shift RS[T] vertically, give the mean free path L

Experimental evidence:-Data courtesy JLab (Ciovati)-Theory, Argonne

Hot spots have higher concentration of Magnetic impurities than cold spots

IV. Surface impedance & Magnetic impurities: the residual resistance and more

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 Δ/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.

IV. Superconducting layer by ALD

Thin films: 10 nm

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