Materials Studies: Niobium

Pole figures for niobium texture measurements.

High purity niobium is preferred for present-day SRF cavities, due to its high transition temperature, high critical magnetic field, and high thermal conductivity.  The higher the thermal conductivity of the niobium, the more stable the cavity is against thermal breakdown (quench) due to small normal conducting spots on the superconducting surface.

Because the RF currents flow in a very thin layer near the inside surface of a cavity, the surface properties of niobium strongly affect the performance.  The mechanical properties of the niobium are also important, as niobium sheets must be formed by deep drawing or spinning in order to fabricate a finished cavity.  To make a complete cavity, parted are usually joined by electron-beam welding.  The welding step can affect the properties of the niobium.  Alternative forming and joining techniques may offer advantages, but may also affect the material properties in different ways.

Materials studies related to the use of niobium for superconducting cavities are being undertaken as a collaboration between NSCL and the MSU College of Engineering.  Areas of interest include heat transfer studies, surface texture and formability studies, characterisation of thermal, electrical, and mechanical properties, alternative forming methods, and alternative joining methods.

Related Papers

2007

A. Aizaz, N. T. Wright, T. L. Grimm, “Thermal Design Studies of Niobium SRF Cavities,” presented at the 13th International Workshop on RF Superconductivity, Beijing, China, October 2007.  PDF (SRF 2007 Web site)

D. Baars, T. R. Bieler, A. Zamiri, F. Pourboghrat, C. Compton, “Crystal Orientation Effects During Fabrication of Single or Multi-Crystal Nb SRF Cavities,” presented at the 13th International Workshop on RF Superconductivity, Beijing, China, October 2007.  PDF (SRF 2007 Web site)

D. Baars, T. R. Bieler, K. T. Hartwig, H. Jiang, C. Compton, T. L. Grimm, “Processing Strategies for Niobium Sheet Used in Advanced Superconducting Particle Accelerator Cavities,” Journal of the Minerals, Metals and Materials Society 59, p. 50-55 (June 2007).  Paper (Springer)

Chris Compton, Ahmad Aizaz, Derek Baars, Tom Bieler, John Bierwagen, Steve Bricker, Terry Grimm, Walter Hartung, Hairong Jiang, Matt Johnson, John Popielarski, Laura Saxton, Claire Antoine, Bob Wagner, Peter Kneisel, “Single Crystal and Large Grain Niobium Research at Michigan State University,” in Single Crystal - Large Grain Niobium Technology: Proceedings of the International Niobium Workshop: Araxá, Brazil, 2006, G. R. Myneni, T. Carneiro, and A. Hutton, Editors, AIP CP 927, American Institute of Physics, Melville, New York, 2007, p. 98-105.  Paper (AIP) PDF (preprint)

H. Jiang, D. Baars, A. Zamiri, C. Antoine, P. Bauer, T. R. Bieler, F. Pourboghrat, C. Compton, T. L. Grimm, “Mechanical Properties of High RRR Niobium with Different Texture,” IEEE Transactions on Applied Superconductivity 17, p. 1291-1294 (June 2007).  Paper (IEEE)

D. Baars, H. Jiang, T. Bieler, C. Compton, P. Bauer, T. Grimm, “Crystal Orientations Near Welds in High RRR Niobium with Very Large Grains,” IEEE Transactions on Applied Superconductivity 17, p. 1295-1298 (June 2007).  PDF (preprint) Paper (IEEE)

Ahmad Aizaz, Pierre Bauer, Terry L. Grimm, Neil T. Wright, Claire Z. Antoine, “Measurements of Thermal Conductivity and Kapitza Conductance of Niobium for SRF Cavities for Various Treatments,” IEEE Transactions on Applied Superconductivity 17, p. 1310-1313 (June 2007).  PDF (preprint) Paper (IEEE)

2006

A. Zamiri, F. Pourboghrat, H. Jiang, T. R. Bieler, F. Barlat, J. Brem, C. Compton, T. L. Grimm, “On Mechanical Properties of the Superconducting Niobium,” Materials Science and Engineering A 435-436, p. 658-665 (November 2006).  Paper (Elsevier)

H. Jiang, T. R. Bieler, C. Compton, T. L. Grimm, “Cold Rolling Texture Evolution in High Purity Niobium Using a Tapered Wedge Specimen,” Physica C 441, p. 118-121 (July 2006).  Paper (Elsevier) PDF (preprint)

H. Jiang, T. R. Bieler, C. Compton, T. L. Grimm, “Creep and Dimensional Stability of High Purity Niobium Electron-Beam Welds,” Physica C 441, p. 122-125 (July 2006).  Paper (Elsevier) PDF (preprint)

A. Aizaz, T. L. Grimm, “Thermal Limitations in Superconducting RF Cavities: Improved Heat Transfer at Niobium-Helium Interface,” in Advances in Cryogenic Engineering, Vol. 51, J. G. Weisend II et al., Editors, AIP CP 823, American Institute of Physics, Melville, New York, 2006, p. 1179-1186.  Paper (AIP) PDF (preprint)

2005

Terry L. Grimm, Ahmad Aizaz, Matt Johnson, Walter Hartung, Felix Marti, Dave Meidlinger, Mandi Meidlinger, John Popielarski, Richard C. York, “New Directions in Superconducting Radio Frequency Cavities for Accelerators,” IEEE Transactions on Applied Superconductivity 15, p. 2393-2396 (June 2005).  PDF (preprint) Paper (IEEE)

2003

H. Jiang, T. R. Bieler, C. Compton, T. L. Grimm, “Mechanical Properties, Microstructure, and Texture of Electron Beam Butt Welds in High Purity Niobium,” in Proceedings of the 2003 Particle Accelerator Conference, Joe Chew, Peter Lucas, & Sara Webber, Editors, IEEE Publishing, Piscataway, New Jersey, 2003, p. 1359-1361.  PDF (JACoW)

Related Report

Measured properties of High RRR Niobium

PDF format, 1.2MB

Abstract:  The National Superconducting Cyclotron Laboratory (NSCL) is initiating a superconducting radio frequency (SRF) cavity research and development program including the construction and testing of SRF cavities for the acceleration of charged particles.  The cavities are formed using high purity niobium sheet metal that has been properly processed and formed to eliminate impurities and to develop a fine, recrystallized grain structure.  In order to operate and hold the desired electrical fields needed for acceleration, the properties of the niobium material must have a high residual resistivity ratio (RRR) value.  RRR is the ratio between the resistivity of the material at room temperature (298°K) and the resistance at superconducting temperature (~ 4°K).  This RRR value directly depends on the impurity levels of the parent niobium ingot.  The niobium sheets are formed into the desired cavity shape using a die and a hydraulic press.  The fine, recrystallized grain structure allows the niobium sheet to be formed into the cavity shape without tearing.