# Presentation: 709347

## UW-Madison – FNAL: A Nb for SCRF Materials Collaboration

- Peter J. Lee, David C. Larbalestier, Alex V. Gurevich, Alexander Squitieri, Bill Starch, Anatolii Polyanskii

## Vision

- A Collaboration That Exploits the Complementary Facilities and Expertise at FNAL and the UW-Madison Applied Superconductivity Center to provide new insights into the properties of Nb for SCRF Cavities.

## FNAL—UW-Madison Collaboration

- Primary thrust:
- Better understanding of the effect of grain boundaries on the RF surface resistance using existing tools available at the Applied Superconductivity Center and FNAL
**Magneto-optics (Anatolii Polyanskii’s Talk)**
- Surface analysis – XPS and SAM
- Microscopy (some shown here)
- Transport measurements.
- Specific Heat and magnetization (at UW and FNAL)
*Theory (Alexander Gurevich’s Talk) – main DOE-HEP grant funded*

## Initial Scoping Studies

- Reported at ASC’04, LINAC04 and "Pushing the Limits of RF Superconductivity" workshop:
- “SRF Cavity and Materials R&D at Fermilab,” N. Khabiboulline, P. Bauer, L. Bellantoni, T. Berenc, C. Boffo, R. Carcagno, C. Chapman, H. Edwards, L. Elementi, M. Foley, E. Hahn, D. Hicks, D. Mitchell, A. Rowe, N. Solyak, I. Terechkine, A. Gurevich, M. Jewell, D. C. Larbalestier, P. Lee, A. Polyanskii, A. Squitieri, Paper MOP82 at LINAC 2004, held August 16-20, 2004 in Lübeck, Germany, published in LINAC 2004 - Proceedings. Download 0.3 MB PDF file: _[http://bel.gsi.de/linac2004/PAPERS/MOP82.pdf](http://bel.gsi.de/linac2004/PAPERS/MOP82.pdf)_
- “An Investigation of the Properties of BCP Niobium for Superconducting RF Cavities,” Pierre Bauer, Leo Bellantoni, Cristian Boffo, Helen Edwards, Matt Jewell, David Larbalestier, Peter J. Lee, Anatolii Polyanskii, Alex Squitieri, presented at the "Pushing the Limits of RF Superconductivity" workshop, held at Argonne National Laboratory, September 22-24, 2004. Argonne National Laboratory Report ANL-05/10, Ed. Kwang-Je Kim and Catherin Eyberger, pp 84-93, March 2005. report available at no cost from _[http://osti.gov/bridge](http://osti.gov/bridge)__. This individual report (1.2 MB) may be downloaded from: http://homepages.cae.wisc.edu/~plee/pubs/PLeePBauer_SRFLimits_RFNbMatStudy.pdf_

## HIGH PURITY NB SAMPLES

**	****Weld-sample (“BCP1”)**
**	****BCP100,HT8005hr,BCP20**

**	****Regular sample (50m) (“BCP2”)**
**	****BCP80,HT8005hr,BCP20**

**	****Large Grain sample (“Texas”)**
**	****(BCP2 + 1250C24hr+50mBCP)**

- 5 mm

## MAGNETIZATION:  AS RECEIVED AND AFTER BCP (100mm) & HT (800C/5hr)

**	****C. Boffo - FNAL**** **

**	****Result consistent with recent data for BCP & HT samples (RRR300) from Casalbuoni:**

**	****B****c,therm****(4.2K)=142 mT (–> 147 here)**
**	****B****c2****(4.2K)=267 mT  (-> 290 here)**

**MAGNETIZATION:  AS RECEIVED AND AFTER BCP (100mm) & HT (800C/5hr)**

## Topography: Differences in Topography Revealed

- Flatbed Scanner Images of Weld Region Sample Showing Grain Boundary Grooving

##  .  .  And Quantification Methods Explored

## Alternative Profilometry II:

- STEREO module of “AnalySIS” image analysis

- Edge Artifact

- Demo analysis performed by Andrew Cahill
- Soft Imaging System Corp.12596 W. Bayaud Ave.Suite 300Lakewood, CO 80228web: _[www.soft-imaging.com](http://www.soft-imaging.com/)__email:  aca@soft-imaging.com_

## Original Stereo Anaglyph used for analysis

## “AnalysSIS” analysis

## Grain Boundary Groove in Weld Region (Weld)

- 3D Movie

## Scanning Laser Confocal Microscope 

## AFM of BCP: Kläui and Lilje 2001

- As shown in dissertation of Lutz Lilje

## Weld vs.. BCP2 at same Magnification

**BCP2**

**Weld**

## BCP2 x 250

## Weld vs.. BCP2 x 1K

**BCP2**

**Weld**

## Magneto Optical Imaging Used to Show Spatial Variations in Superconducting Properties:

- #9-10  H=572 Oe,  27 Apr

- Flux has leaked to center, even as major flux fronts are only partially penetrated

- Inhomogeneous flux penetration after ZFC to 7 K, then 57 mT, well above *H*c1 ~ 48 mT

## Sequential flux maps in increasing H and t, then decrease H to zero

- MOVIE

- Hc1 (7K) ~ 48mT (1.6 demagnetization factor ~30 mT)
- Hc2 ~120 mT

## MO image shows partial grain structure after magnetizing above Hc2

- Approximate 2D Current Streamlines

-  6K remanent MO image after 120 mT

- MO image shows partial grain structure after magnetizing above Hc2

- Trapped Flux Image
- Contrast: Perturbations in the current stream lines

## Current streamlines over GB map

**Current streamlines over GB map**

- Some GBs partially obstruct
- Others benign

- Green 3-20
- Red 20-50
- Black >50

## Flux profile of remanent image after magnetizing to 120 mT  

- H=0 (FC in H=1200 Oe)

- Flux profile of remanent image after magnetizing to 120 mT

- Reverse Gradient

- Current is changing direction due to barrier to current flow at grain boundary

## Now alter mechanically alter surface

**Now alter mechanically alter surface**

**Light Microscope: EDF 3D reconstruction**

**Remanent Field after 120 mT at 7K**

- Mech. Polish

## 1⁄2 Polish: FESEM anaglyph vs. MO

## 1⁄2 Polish: FESEM reconstruction

**1⁄2 Polish: FESEM reconstruction**

## Complete Mech. Smoothed Surface

**Remanent Field after 120 mT at 7K**

- Surviving contrast weakened

## Mechanically Smoothed Surface removed by Etch

**Remanent Field after 120 mT at 7K**

- Sharp GB contrast returns

## Large grain sample - some GBs appear after etching

- Large grains produced by 1250 °C, 24hr, 10-7 T  HT at JLAB

- FESEM Orientation imaging (Sang Il Kim)

- RRR dropped from ~400 to 260

## Inverse Pole Figure indicates some texture

- Blue

- Reddish

## Light Microscope Depth Reconstruction

- 120 μm range at 10 μm focus intervals
- ImageJ with Extended Depth of Field plugin by Daniel Sage @ epfl.ch

*B. Forster, D. Van De Ville, J. Berent, D. Sage, M. Unser, "Extended Depth-of-Focus for Multi-Channel Microscopy Images: A Complex Wavelet Approach," Proceedings of the Second 2004 IEEE International Symposium on Biomedical Imaging: From Nano to Macro (ISBI'04), Arlington VA, USA, April 15-18, 2004, pp. 660-663.*

## FESEM Image: Height Reconstruction from tilt pair

## BCP2 5 K

## Summary of Scoping Studies

- Magneto-Optical Imaging shows that non-uniform flux penetration can occur along some grain boundaries
- Is this topological or chemical or both?
- Considerable variation in surface topology observed
- Local inhomogeneity: Orientation of facet surfaces
- Grain size variation across weld region
- Grooved grain boundaries in weld region and grain-growth heat treatment.
- Software tools enable quantification of surface topology over large areas.

## Systematic Study Through-Processing

- Systematic Study Begun with both Weld and Regular Sheet Samples
- Samples Taken at Each Step of Process
- MO and Topology Characterized at Each Step
- Cold-worked as a result of machining (no EDM)
- ~2.8 mm thick, RRR~450

## 3rd Generation FNAL: Machined Samples

## Magnetization: Weld Region Shows Much Less

## Scanning Laser Confocal: Extended Depth of Field 

**End of Seam on Side of Weld Region Sample**

## Initial Results: MO

- MO imaging is already providing new insights into the effect of processing on local superconducting properties.
- Tolya’s Talk

## JLab – Large Grain Material

- Very Large Grain Material from CBMM
- The RRR value is app. 280.
- JLab have now built 2 cavities from the center large grain of the ingot and both cavities performed well
- One close to the theoretical critical field( at least what is believed to be this field): 185 mT and the other one went up to an accelerating gradient of 45 MV/m, close to the "world record". – Peter Kneisel

## Slice Overview

**Large Bi-Crystal Regions**

##  Jc/RRR single GB Sample From JLAB

- Sputtered Contact Method Successful

- 3 cm

- I-

- V2

- V1

- V3

- I+

- 1 μM Au
- Sputtered
- Contact strips

- Intragrain
- ~3 mm

- Intergrain
- ~5 mm

- B

## Etch+Au Sputter ~1 μm Step

**Etch+Au Sputter ~1 μm Step**

## Variations in Topology Still Evident in Large Grain Material

**Step Height at Grain Boundary:**
**Tri-Crystal JLAB#4**

## Grain Boundary in as-received Bi-Xtal

## New and Exciting Results to Follow

**New and Exciting Results to Follow**

**MO Revealing More About Local Superconducting Behavior and the Impact on Processing**
**Large Grain JLab material showing great potential and may still have room for improvement.**