3D Atom Probe Microscopy on Niobium for SRF Cavities

Fermi National Accelerator Laboratory (FNAL) is developing superconducting RF cavities for a future high-energy electron-positron linear collider as the next international, large-scale high energy physics discovery machine. Recently FNAL and the Northwestern University Center for Atom-Probe Tomography (NUCAPT), Evanston, Illinois, have joined forces to investigate the properties of the high purity niobium used for cavity fabrication. NUCAPT is among the world leaders in the field of threedimensional atom-probe tomography, particularly as result of the recent installation of a local-electrode atom-probe (LEAP) tomograph, manufactured by Imago Scientific Instruments (http://www.imago.com). Atomic-probe tomography consists of dissecting a specimen on an atom-byatom basis, employing pulsed field-evaporation, and determining the chemical identity of each fieldevaporated atom by time-of-flight mass spectrometry, with single atom identification capability, using a 2D position sensitive delay line detector, which yields the position of each atom in a specimen with sub-nanoscale resolution. Analysis rates of upwards of 72 million atoms hr have been achieved employing a LEAP tomograph at Northwestern. The collected data is used to reconstruct a specimen in three-dimensions, where the chemical identity of each atom is known. The collaboration between FNAL and NUCAPT will produce spectacular results with lasting impact and advance strongly the understanding of the surface chemistry in state-of-the-art high purity niobium for superconducting RF cavities.