Evaluation of SRF thin film properties using a properties using a - PowerPoint PPT Presentation

Evaluation of SRF thin film Evaluation of SRF thin film properties using a properties using a microstrip disk microstrip disk resonator resonator Daniel Bowring Daniel Bowring Motivation Disk resonator Preliminary Lawrence Berkeley National Laboratory results Future July 19, 2012 aspirations NbTiN postscript

Overview Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring Motivation small SRF Disk resonator Preliminary samples cavities results Future aspirations NbTiN postscript

Overview Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring small SRF Motivation Disk resonator samples cavities Preliminary results Future aspirations NbTiN postscript p resent work

Overview Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring 1 Motivation: Evaluating multilayer films Motivation 2 Disk resonator: operating principle, experimental design Disk resonator 3 Preliminary results Preliminary results 4 Future aspirations Future 5 Postscript: A note on NbTiN aspirations NbTiN postscript

We want a method to evaluate multilayer thin films. Evaluation of SRF thin film properties using a 1 5 microstrip disk 0.9 resonator 0 0.8 Normalized free energy G/G 0 −5 Daniel 0.7 Normalized field strength H/H 0 Bowring −10 0.6 −15 0.5 Motivation −20 0.4 −25 Disk resonator 0.3 symmetric currents 0.2 −30 no current Preliminary asymmetric currents (Nb,Ti)N alumina Nb 0.1 −35 results −60 −40 −20 0 20 40 60 Depth of vortex in thin film (nm) 0 0 100 200 300 400 500 600 Film depth (nm) Future aspirations Figure: This is why it works: Figure: Thin films screen the NbTiN asymmetric currents tilt the free postscript magnetic field from the bulk layer. energy profile of a flux vortex. � d / 2 φ 2 � 1 . 07 ξ cos π u d � 0 G / L = 4 πµ 0 λ 2 ln − φ 0 J ( z ) dz d u

Test this using NbTiN films. Evaluation of SRF thin film properties using a 6 microstrip disk resonator 5 Daniel Bowring 4 Log 10 Q 0 Motivation 3 Disk resonator 2 Preliminary results 1 Control resonator Future Thick film resonator aspirations Multilayer system 0 NbTiN 0 50 100 150 200 250 300 350 H (mT) postscript NbTiN has low H c 1 . This simplifies testing, leaves basic physics unchanged. We didn’t try to exceed 180 mT right away. Walk before you run.

What has been done? Evaluation of SRF thin film properties using a microstrip disk Theory resonator Daniel Modeling Bowring Design and fabrication Motivation Process development: reactive magnetron sputtering in Disk resonator JLab’s UHV system. Preliminary results Preliminary cryo/RF testing Future aspirations Material analysis NbTiN postscript Inconveniently-timed capital development at JLab → No clean multilayer films for testing. Yet.

Our experimental facility can evaluate multilayer thin films under cryogenic, RF conditions. Evaluation of SRF thin film properties Experimental design goals: using a microstrip disk resonator Reduce parameter space: evaluate multilayer physics using Daniel small, flat samples. Bowring Highest magnetic field must be on sample → sample is Motivation performance-limiting feature. Disk resonator Suppress multipacting, field emission as much as possible. Preliminary results Modular, easily-demountable samples → quick Future aspirations experimental turnaround. In the VTA, can get 2 NbTiN measurements per day if you push. postscript Small flat samples → easier & quicker post-facto surface analysis.

A microstrip disk resonator satisfies the above requirements. Pillbox-like TM 01 fields supported between a circular disk Evaluation of SRF thin film (which sets frequency) and a superconducting ground plane. properties using a microstrip disk resonator Daniel Bowring Motivation Disk resonator Preliminary 4 cm results Future aspirations NbTiN postscript f = 2 . 8 GHz, Q 0 ≈ 10 5 (very low U ). Capacitive coupling. Simulations via CST Microwave Studio.

Other configurations are possible. Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring “Active” sample size set by frequency requirements. (1 cm Motivation radius → 6 GHz.) Disk resonator Rectangular ground plane not required. Can operate with Preliminary results circular samples (and minimal hardware changes). Future aspirations NbTiN postscript

Resonator assembly Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring Motivation Disk resonator Preliminary results Future aspirations NbTiN postscript Currently, minimum sample size is 4 cm diameter.

Dewar insert for operation in JLab’s VTA Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring Motivation Disk resonator Preliminary results Future aspirations NbTiN postscript

Preliminary results Evaluation of SRF thin film properties using a microstrip disk −15 resonator −20 Daniel 0.5π −25 Bowring Φ 0.75π 0.25π −30 |S 11 | π Motivation −35 S 11 -75 -50 -25 0 25 50 75 −40 Disk resonator 1.25π −45 1.75π Preliminary 1.5π −50 results −55 Future −60 aspirations 2.77 2.772 2.774 2.776 2.778 2.78 2.782 2.784 Frequency (GHz) Figure: Tuners permit critical NbTiN postscript coupling. Figure: f = 2 . 78 GHz, Q 0 ≈ 10 3 . Coupler upgrade, full system characterization must wait until TEDF is online.

Future aspirations Evaluation of SRF thin film properties using a microstrip disk Several people at this workshop have indicated a desire to resonator evaluate SRF properties of small samples. Daniel Bowring Upgrade couplers, amplifier. Motivation Add thermometry capabilities. Disk resonator This system is not only useful for multilayer films. Can Preliminary results also explore SRF films on various substrates; bulk Future properties from grain size, surface treatments; build aspirations large statistical database. NbTiN postscript T e − ∆ / kT + R 0 → at low temperatures, measure R s = A ω 2 R 0 directly.

In the future, use this system in Texas A&M’s cluster tool. Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring Motivation Disk resonator Preliminary results Future aspirations NbTiN postscript

A brief epilogue re: NbTiN Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring 300 DB−04 DB−05 DB−06 250 DB−07 T c = 13 . 2 ± 0 . 4 K Motivation DB−08 DB−09 Resistivity ( µΩ −cm) 200 Disk resonator RRR= 1 . 46 ± 0 . 58 Preliminary 150 (but this was during results 100 commissioning) Future aspirations 50 NbTiN 0 5 10 15 20 25 30 postscript Temperature (K)

What is NbTiN? Evaluation of SRF thin film properties using a microstrip disk resonator Typically, literature mentions T c with no further analysis. Daniel Bowring Everybody writes it in a different way: Motivation NbTiN Disk resonator (Nb,Ti)N Preliminary results δ -NbTiN Future Nb 1 − x Ti x N aspirations NbTiN Nb-Ti-N postscript

XRD comparisons to PDF Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring Motivation Disk resonator Preliminary results Future aspirations NbTiN postscript XRD measurements of JLab-made films with various P(N 2 ), compared with PDF. Powder Diffraction File, edited by S. Kabekkodu (International Centre for Diffraction Data, Newton Square, PA, USA, 2011).

XRD comparisons to PDF Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring Motivation Disk resonator Preliminary results Future aspirations NbTiN postscript Comparison of JLab-made film with other possible phases of the Nb-Ti-N system. Powder Diffraction File, edited by S. Kabekkodu (International Centre for Diffraction Data, Newton Square, PA, USA, 2011).

δ − (Nb,Ti)N Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring Substitutional solid solution. Motivation Disk resonator B1 structure similar to NbN. Preliminary Ti stabilizes the δ -phase. results Future aspirations NbTiN postscript

Acknowledgements Evaluation of SRF thin film properties using a microstrip disk resonator Daniel Bowring Motivation L. Phillips, J. Spradlin, A.-M. Valente-Feliciano, X. Zhao Disk resonator Preliminary results Future aspirations NbTiN postscript