Is hydrogen in niobium (besides Q-disease) responsible for performance limitations?

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1 Is hydrogen in niobium (besides Q-disease) responsible for performance limitations? Ganapati Rao Myneni Accelerator Division, Jefferson Lab & Materials Science and Engineering and Engineering Physics, University of Virginia TTC Meeting Milano, Italy Feb 28-March 3,

2 Q-disease, hydrogen & cavity performance Q-disease in the cavities is an example of a gross manifestation of hydrogen effect similar to gross air leak in a high vacuum system If we are looking to improve the cavity performance further we need to understand the effects of proton in niobium and further minimize the solid-solution of protons similar to eliminating smaller air leaks in UHV systems Hydrogen is difficult to measure quantitatively at the concentration levels that we have to in materials in general and greatly in Nb Like vacuum leak standards, we need to develop Nb-hydrogen standards 2

3 Hydrogen absorption with BCP and EP Very high equilibrium hydrogen activities (fugacity) have been estimated when Nb metal is in contact with water or BCP solution Hydrogen is readily absorbed into Nb when the protective oxide layer is removed Lower H fugacities are obtained due to an anodic polarization of Nb during EP and hence lower hydrogen absorption Fine grain Nb has high energy grain boundary morphologies and orientations that make hydrogen induced heterogenous nucleation of second phases or micro-voids with BCP Ingot niobium will have very few to none of the micro-voids R.E. Ricker, G. R. Myneni J. Res. Natl. Inst. Stds. Tech 115 (8), (2010) NIST/JLab 3

4 JLab Qo improvement studies 4

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6 High temperature annealing removes gross hydrogen NbH is very much in existence after anneals NCSU/JLab 6

7 Hydrogen Interactions N15 nuclear reaction analysis - UNY, Albany Internal friction data - NIST, Gaithersburg O-H Interaction Peak Hydrogen is most mobile at room temperature, interacts with defects, interstitials and, is influenced by residual stress concentration gradients and affects the magnetic properties 7

8 NRA Analysis (PNNL): H Depth Profiles in Nb 1.40E+021 L33 : No Heat Treatment H( 19 F, αγ) 16 O resonant reaction 3 L31 : After 800C 2hr and 120C 24 hr H Concentration (atoms/cm 3 ) 1.20E E E E E E % atomic 1.1% atomic Significant H below surface Profile 0.4µm deep with 9 MeV, can reach 1-2µm with 11MeV Depth (microns) Depth (µm) Plan to repeat at higher energy F. Stevie et al FLAVS-FSM Symposium, March 7,

9 Niobium hydrogen phase diagram 9

10 H/Nb intensity trend with temperature. Similar trend is seen in all the experiments conducted Prateek Maheswari, NCSU 2/23/11 10

11 Principle compounds of niobium John Wallace, Ganapati Myneni in review Nature 11

12 Atomic model of proton in niobium John Wallace, Ganapati Myneni in Review Nature 12

13 Ionization energies potential well depth John Wallace, Ganapati Myneni in review Nature 13

14 RF and optical measurement system Casting Analysis Corporation/JLab 14

15 Niobium-hydrogen measurement cells 15

16 RF reflection measurements Proton in SRF niobium, J. P. Wallace, SSTIN10 AIP CP 1352,

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18 Clean UHV furnace 18

19 Summary Cavity Qo and Hpk improved with heat treatments & baking followed by no chemical processing which would have introduced hydrogen PRSTAB 13, (2010) Visintin et al confirms that presence of hydrogen vacancy complexes and Their dissociation by baking could both explain rf losses observed at high fields (Q drop) and its cure PRSTAB 13, (2010) DOE NP funded Qo improvement program at JLab is making great progress in understanding proton in niobium; A new quantum mechanical model of a proton in Nb which allows Calculation of the activation energies for diffusion matching experimental data has been introduced. This model can be the basis to further study the effect of various concentrations of H to the superconducting & mechanical properties of Nb 19

20 Acknowledgements A. Hutton, G. Ciovati, P. Kneisel JLab F. Stevie, P. Maheswari, D. Griffis NCSU R. Ricker NIST J. Wallace Casting Analysis Corporation B. Lanford UNY, Albany 20