NSF Nugget for FY06Improving the New Superconductor MgB2

Sept. 2006FRG on Two Gap Superconductivity

Wisconsin-Penn State- Arizona State-Puerto Rico-Mayaguez collaboration

DMR-0514592PI David Larbalestier, Eric Hellstrom and Paul Voyles

(UW), Zi-Kui Liu (Penn State), Nate Newman and John Rowell (Arizona State), and Oswald Uwakweh (U. Puerto

Rico Mayaguez)

Improving the New Superconductor MgB2

Work in groups of Eric Hellstrom and David Larbalestier (UW), in collaboration with Oswald Uwakweh, UPRM, DMR-0514592

Above: Scanning electron image of MgB2 grains. Grains in the enlarged portion are only ~30 nm is size

Right: Transmission electron image of an MgB2 grain showing beneficial lattice dislocations (TEM in Paul Voyles group).

The new superconductor MgB2 promises advances in magnet technology for MRI, fusion energy, and particle accelerators, and in aerospace applications. To achieve that promise, the electric current carrying capacity (Jc) in a magnetic field of MgB2 must be improved.

Jc can be increased by creating MgB2 with a smaller grain size, more crystal lattice defects, alloying with elements like carbon, and grains that are well connected to each other with no second phases blocking the flow of the supercurrent.

We have pioneered mechanical alloying of carbon into MgB2. This process has given us record high Jc under applied fields (8x104 A/cm2 at 8T 4.2K) for bulk MgB2. Our method simultaneously refines grains, generates intragranular defects, and alloys C into the MgB2.

We have also developed a method to purify the B powder used to make MgB2. Purified B results in MgB2 with cleaner grain boundaries, increasing the current carrying fraction of the sample by a factor of up to 2.

100 nm

high density of defects high density of defects inside an MgBinside an MgB22 grain grain

Education:One graduate (Ben Senkowicz), three undergraduates (Jason Mantei, Richard Mungall, Jonathan Hedstrom), one young sabbatical visiting scientist (Akiyoshi Matsumoto of NIMS Japan), worked on bulk MgB2 research supported by this NSF Award. Close collaboration with P. Voyles graduate student, Ye Zhu, is also occurring.

Camp Badger – Ben Senkowicz led Camp Badger demos and Mantei did ESTEAM demos (ESTEAM is a Saturday activity in fall semester where high school students with high SAT score who are interested in engineering are invited on campus to show them what is available in engineering.)

Societal Impact:The ability to transport electric current without dissipating electricity as heat is of paramount importance for electrical transport and electro-magnet technologies. This work could enable a new generation of magnets for MRI, fusion energy, and particle accelerators.

Support of the PREM at UPRM – we are collaborating with UPRM on alloying of MgB2 – UPRM needed a glove box to be able to mill MgB2 without contamination. Uwakweh’s student Richard Perez came to Madison to work in our glove box, packed up a spare and shipped it to UPRM where it is now installed. Our first joint paper on the effect of milling atmosphere has just appeared.

Improving the New Superconductor MgB2

Work in groups of Eric Hellstrom and David Larbalestier (UW), in collaboration with Oswald Uwakweh, UPRM, DMR-0514592