The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 1 The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Laboratory-University Collaboration NHMFL-ASC, FSU Report ZH. Sung, A.A. Polyanskii, B. Starch, V, Griffin P. Lee, and David. Larbalestier Feb 16 th, 2011

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 2 Contents 1.Current investigations on deformed Nb coupons – MO imaging (Flux penetration), OIM-EBSD (Microstructure), SLCM (Roughness), Hall sensor* (H c1 ), VSM (Magnetic hysteresis loop) 2.Imaging processing of equator images by Optical inspection system at FNAL 3.Ongoing investigations on hot and cold spot from a single cavity * Using a Single micro-Hall sensor which has 50μm by 50 μm activation area on 0.4mm thick GaAs substrate, from Dr. Milan Polak

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 3 Nb coupons from FANL (Dr. Romanenko) Type Deformed % BCP Dimension (Dia./t) [mm] Weight [mg] Surface roughness [μm] Onset of flux 4.2K [mT] H c2 4.2K [mT] A094μm3.8 / B23158μm3.2 / C35141μm3.1 / D46126μm3.3 / ‡ Deformation and BCP treatments were accomplished at FNAL * Obtained from micro-Hall sensor measurements at 4.2K within surface perpendicular external fields. † Surface roughness examined by scanning laser confocal microscope (SCLM)

Microstructural variations along with deformation 00% 23% 35% 46% IPF OIM imageSubgrainIPF map Top bottom Top bottom Top

MO imaging - the observation of the flux penetration 00% 23% 35% 46% Top bottom Top bottom Top T=6K H=0, Remn after H=80 mT N z =0.6667, N enh =1/(1-N z )=3.001 N z =0.653, N enh =2.882 T=6K H=0, Remn after H=100 mT T=7K H=0, Remn after H=52 mT N z =0.649, N enh = T=6K H=0, Remn after H=56 mT T=6K H=0, Remn after H=96 mT N z =0.637, N enh =2.257 T=8K H=0, Remn after H=32 mT bottom Flux penetration is aligned to the deformed direction

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 6 Hall sensor – define the onset of the flux penetrations First kink = the onset of flux Penetrations. The vertex = H c2 (or may be H c3 ?) Field ramping up from 0mT to 500mT (External field // surface normal) H c (?) BCP 94 μm 158 μm 141 μm 126 μm

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 7 Bulk pinning variation along with deformation Undeformed (00%) sample shows the highest bulk pinning properties, but, surprisingly, highly (46%) deformed sample also show higher properties than others. It may be because of enhancement of pinning effects by dislocations on seriously cold worked area of the top layers. With an exception of 46% deformed sample, magnetic loops indicates that bulk pinning effects gradually decreases along with deformation. But at 7K this properties 4.2K5K7K

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 8 Summary - Studies on deformed Nb coupons 1.MO imaging shows that deformed structure induces non-uniformed premature flux penetration on the surface, which is almost aligned to the same direction of deformation. 2.From Hall sensor measurements, it is supposed that the onset of flux penetration can be controlled not by mechanical damage but by surface treatments. However, surface superconductivity may be influenced by mechanical deformations. 3.To verify this hypothesis, it is highly required to measure H c1 and H c3 values such as S. Casalbuoni’s work (2004) on BCP’ed, EP’ed, and Heat treated circular shape niobium samples. 4.Analytical microscopy (TEM/STEM) on top most layers of deformed sample is proposed to further understanding of the effect of surface structure on superconducting properties.

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 9 Imaging processing of equator images by Optical inspection system Basic Stitching of Single or Multi Row Which imaging programs are used: – Automatic: Panorama Studio 2 Pro – Manual: “MosaicJ” plugin ( for ImageJ ( – Manual: Photoshop (very manual) – “3D Reconstruction” plug-in for Image J (for surface 3D topology) Results:

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 10 Through-Focal for 3D Some promise but some way off quantitative. Did not work properly with any of the examples we’ve tried. It could be that the focal length:height difference is too great. – Would need a greater tilt between image pairs or smaller working distance.

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 11 PS2P animated image of e-beam welded equator by 2- row stitching What worked: stitched the top and bottom row together after splitting each PS2P generated alignment. Very laborious 2-row re-stitching: \\zdrive\ASC\Users\ZH Sung\SRF Nb cavity\FNL\FNL 13th\Image\TB9RI026_ \eq7a+b\Panorama\TB9RI02 6_eq7a-b_pano

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 12 Limitations to Panorama Studio 2 Pro Needs almost identical spacing of images – the end overlaps have to be manually aligned (we do it MosaicJ). Although PS2P can align multiple rows, the double “a” and “b” series will not align to each other – we think the top/bottom positions have to be the same We thought larger overlaps would help – but they did not. – You can do this (very) manually using MosaicJ MosaicJ Credits: P. Thévenaz, M. Unser, “ User-Friendly Semiautomated Assembly of Accurate Image Mosaics in Microscopy Microscopy Research and Technique,” vol. 70, no. 2, pp , February 2007 – This paper is available on-line at:

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 13 Ongoing investigation on Hot and Cold spot from a single cavity (from FNL: Dr. Romanenko) Location of thermo diode when Temp-mapping Inner surfaceOuter surface

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 14 Proposed series of multiple experiments 1.OIM-EBSD for surface microstructure. 2.Micro-Hall probe measurements to obtain the onset field of flux penetration and H c2 and H c3. 3.MO (magneto-optical) imaging to observe flux penetration 4.TEM/STEM analysis to observe atomic-scale surface structure 5.Send back to FNAL for further surface treatments like BCP and UHV baking, then return back to ASC for further measurements 6.This work plan is to understand the origin of surface superconductivity breakdown on SRF nb cavity by comparing properties of both regions. Over the course of this work, it is supposed that we can understand of the effects of several pits on hot or cold spot (we already found) on the degradation of SRF cavity performance.

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 15 Local field enhancement characterization using micro Hall sensor Micro Hall probe Hall probe sensor Fabricated by Dr. Milan Polak (2009) Al 2 O 3 BCP’ed Nb bi-crystal GB H Glass (t~126μm) Spec: ~ 2mm by 2mm Total thickness: ~0.4mm 0.4mm thick GaAs substrate 5μm thin InSb layer Activation area: 50μm by 50 μm Minimum distance between the sample surface and the Hall probe is ~0.2mm

The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University Z.H. Sung 16 Further efforts for the GB depairing critical current density BCP’ed Nb Bi-crystal (26° misoriented GB) B perp = H - η·M η = demagnetization factor M = magnetization Multi vortices rows Single vortex row 7° [001] tilted YBa 2 Cu 3 O 7-δ GB Micro-Hall Sensor Arrays GaAs/AlGaAs heterostructure Courtesy of Dr. Eli Zeldov ~ 420  m