Curvature, Hydrogen, Q

John Paul WallaceCasting Analysis Corp

Weyers Cave, VA

Ganapati Rao MyneniJefferson Lab

Newport News, VA21 September 2010

Acknowledgements

• R. Garwin & P. Kusch (EM), J. Steinberger & M. Gutzwiller (QM), J. Tien (Metallurgy) Columbia Univ.

• S. Tao (positron annihilation), New England Research Inst.

• R. Bates (hydrogen in steels), Westinghouse Research• E. Chang, E. Armacanqui, W. Gerberich and R. Oriani,

(hydrogen in the metals ) Univ. Minnesota• Andrew Hutton and Gigi Ciovati, (SRF technology) JLab• R. McDermott, (sputtered niobium and aluminum films)

Univ. of Wisconsin

Chemical Landscape for Nb

Tools

• Principal ToolsPrincipal Tools -> EM Theory and Non Relativistic Quantum Mechanics

• Experimental Tools in Order of First Application• Positron Annihilation 1974• X-ray Diffraction 1976• Reflection IR Spectroscopy 1978• Induction Spectroscopy 2008• Induction Permeability Measurements 2009

EM Boundary Value Reflection

Reflections Spectroscopy & Induction Cell

Major Problems With Resonant Tools

• Resonant Measurement of penetration depth in a material with a magnetic component is not a trivial exercise. The analysis is difficult and the number of variable do not allow the analysis to be inverted.

• Inverting Q cavity measurements to understand specific material properties requires luck. Too many variables and insufficient data to invert the date, extracting z(x,y,Q, ….) from Q(x,y,z,….) all of this first assumes the variables can be enumerated.

The Problem with Tools & Hydrogen

• High Diffusivity - measurement sampling times have to be sub microsecond or else the samples becomes macroscopic. (x SIMS, x TEM )

• Chemically active - compound formation in niobium ( x Thermal Desorption Spectroscopy, x Total Concentration Measurements by Thermal Purging )

• Significant Electro Migration Charge – DC biasing moves hydrogen, resulting in over or under estimating concentrations depending on the sign of the bias voltage. ( x SIMS, x TEM)

Curvature and Problems With Numerical Field Solvers

• The physical curvature of the cavity has a curvature dependent electromagnetic skin depth for the normal conduction electrons which may not have been notice in numerical modeling to increase the surface currents by ~ X ( 1+10^-4 ) in the high curvature regions.

• Closed form analysis is useful here where numerical modeling has a problem with non planar surfaces unless extreme efforts are made or the techniques of Non Standard Analysis are applied.

New Experimental work January to August 2010

• SRF Niobium containing trace hydrogen is a very complex soft magnetic material

• Sputter Niobium & Aluminum Thin Films are Principally Magnetic Materials at Room Temperature.

• Niobium and Aluminum Foils Exposed to Atmosphere have some transitions to very high electrical conductivity states just above 77K.

• SRF Niobium magnetic transitions are not associated with measurable bulk density changes.

SRF Niobium Induction Response to Heating and Cooling

Nb Foil Heating and Cooling Cycle

Simultaneous 635nm and 1.2 MHz Refelections for Transient Cooling

to 4 C.

New Theoretically work in September of 2010

• A rather simple QM model of dissolved hydrogen if solved first from the proton’s point view and then the electronic view point yields the activation energies for diffusion and isotope effects directly. A collection of these single proton states provides a basis to understand the complex magnetism in SRF Niobium.

• The resulting picture of diffusion is quite at odds with the current literature on classical diffusion and quantum tunneling. Diffusion is now the ionization proton from its potential well.

Spherical Flat Potential Well Energy Eigenvalues for Radius

of .0635 nm

Q Curve with Maximum

• Q has a maximum for drive levels above zero.

Indicating a gain that most probably reflects a reduction in temperature. Adiabatic spin disordering refrigeration mechanism operating on an ordered spin system driving disorder by moving embedded residual flux through the bulk resulting in incremental cooling.

• From our measurements on foils we have found some high conductivity responses at relatively high, -150 C, temperatures, it is not know how they will contribute to the composite Q as any local phase shifts can be viewed as a loss mechanism.

Useful Collateral Fall Out

• The representation of soft magnetic materials in EM theory is not correct unless Dirac’s arguments are extend to dealing with electronic spin in Maxwell’s equation directly.

• The current solutions underestimate the magnetic contribution and this is significant as it is a competing process in cavity resonance draining energy from the current flow in the cavity by shifting the phase locally and reducing the current.

Too Much Stuff

The current work has been complied into a book that will be available in draft form at the work shop on Friday and then included as an appendix to the Proceedings covering these topics and more to serve as a guide for doing experimental work and theoretical modeling.

Thank You