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Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
Tajima - DC and RF Measurements of Thin Film MgB2
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Tajima - DC and RF Measurements of Thin Film MgB2

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DC and RF Measurements of MgB2 thin films (Tsuyoshi Tajima - 30')
Speaker: Tsuyoshi Tajima - Los Alamos National Laboratory | Duration: 30 min.
Abstract
In order to overcome the fundamental limit of an accelerating gradient of ~50 MV/m for Nb SRF cavities, thin film coating of MgB2 has been studied. Results of DC measurements using Magnetic Property Measurement System (MPMS) SQUID at LANL and of RF measurements using 11.4 GHz high-power pulsed Klystron with a TE013-mode copper cavity at SLAC will be presented. While DC measurements show very promising results, i.e., Bc1>200 mT at 4.5 K, two RF measurements have shown a quench field of ~25 mT at 3 K.

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  • 1. DC and RF Measurements of Thin Film MgB2 Tsuyoshi Tajima The 4th International Workshop on: Thin Films and New Ideas for Pushing the Limits of RF Superconductivity, Padua, Italy, 4-6 October 2010 LA-UR-10-06587 UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 1
  • 2. Major contributors  Sample preparations • Brian Moeckly (STI) and Toshiya Doi (Kagoshima Univ.)  DC measurements • Nestor Haberkorn and Leonardo Civale (LANL)  RF measurements • Jiquan Guo and Sami Tantawi (SLAC National Accelerator Laboratory) Other contributors are listed at the end of this presentation UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 2
  • 3. Outline  Introduction  DC measurements and results  RF measurements and results  Issues and concerns  Summary and future plans UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 3
  • 4. Outline  Introduction  DC measurements and results  RF measurements and results  Issues and concerns  Summary and future plans UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 4
  • 5. How can we increase the Eacc to >50 MV/m, a limit associated with the critical magnetic field of ~200 mT (2000 Oe)?  Some ideas include: • Improving the cell design to decrease Bpeak relative to Eacc. — This can improve the Eacc by ~10 %, but the shape might not be appropriate for surface treatment and it is mechanically weaker than the standard shape • Use traveling mode instead of using standing wave mode (~42% increase possible? FNAL is working on this.) • Coating some thin layers of another superconductor that has higher Hc1 and Tc than Nb (suggested by Alex Gurevich in 2005). This could increase achievable Eacc significantly UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 5
  • 6. The key idea of using a thin film superconductor is the fact that Bc1// increases when the thickness (d) is d< l (magnetic penetration depth)  The RF critical magnetic field HRF in  Use thin films with thickness d < lL a type-II superconductor is to enhance the lower critical field somewhere between Hc1 and Hc2  The higher the Hc1//, the better to prevent vortex penetration [Gurevich, APL 88 (2006) 012511] Predicted Hc1 as a function of film thickness 900 800 Assumptions: MgB2 Coherence length 5 nm 700 Penetration depth 140 nm Bc1 mT Hc, RF 600 500 400 300 200 60 80 100 120 140 Film Thickness nm UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 6
  • 7. An example: Coating 105 nm MgB2 layer could sustain 355 mT, corresponding to ~100 MV/m with Bpeak /Eacc ~ 3.6 mT/(MV/m) if Nb layer can sustain 170 mT Simple single-layer example Eacc ~ 100 MV/m  Assumptions Bc1(Nb) = 170 mT H0 = 355mT λL(MgB2) = 140 nm Hi = 170mT ξ(MgB2) = 5 nm  Hc1(MgB2) = 355 mT  d = 105 nm  The film thickness needs to be determined Nb so that the decayed field at the Nb surface MgB2 is below the RF critical field of Nb (~200 mT). Dielectric material d = 105 nm UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 7
  • 8. Outline  Introduction  DC measurements and results  RF measurements and results  Issues and concerns  Summary and future plans UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 8
  • 9. Samples prepared with 2 methods have been measured so far Reactive co-evaporation at Co-evaporation with 2 E-beam guns Superconductor Technologies, Inc. at Kagoshima Univ., Japan (STI), Santa Barbara, CA, U.S.A At ~250 C At ~550 C B.H. Moeckly and W.S. Ruby, Supercond. Sci. Technol. 19 (2006) L21–L24 UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 9
  • 10. A Quantum Design Magnetic Property Measurement System (MPMS) SQUID is used to measure Tc and Hc1 In the Meissner State In a superconducting thin (total expulsion of magnetic flux): films: dm V  4 *  If H dH 1  D m: total magnetic moment then 1 – D ~ 0 H: magnetic field V: volume of the sample D: demagnetization factor H And if The Meissner slopes are different for each orientation because each one then 1 – D ~ 1 has a different demagnetization factor UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 10
  • 11. Magnetic field and magnetization alignment in thin films Hapl HII H V H II m   ; mII   V 4 1  D 4  VH mz   (cos2   11D sin 2  ) 4 If the film is exactly aligned with H (Q=0) the m H Meissner slope dm/dH gives the film volume. mII A calculated volume larger than the real one indicates misalignment. Alignment  0.1 or better is needed. UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 11
  • 12. An example of Hc1 measurements at different temperatures Meissner slope In this presentation, Hc1 is defined as the H where the data starts to deviate from the Meissner slope, indicating vortex entrance into the film. This may be an overestimate of Hc1 due to surface barriers, but it is the relevant field for cavities. Magnetization curves as a function of applied magnetic field at various temperatures for ~360 nm thick MgB2 film (Tc ~ 31.8 K) deposited on a Si substrate at Kagoshima Univ. , Japan. UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 12
  • 13. It has been found that the MgB2 thin films show Hc1 significantly higher than bulk Nb (~300 Oe) even d>l At 4.5 K, ~ 300 2000 MgB2 STI ~ 300 nm nm MgB2 MgB2 Kagoshima #1 ~360 nm showed Hc1 > MgB2 Kagoshima #2 ~400 nm 2000 Oe 1500 Nb rod Hc1 [Oe] 1000 500 0 0 5 10 15 20 25 30 35 40 T [K] UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 13
  • 14. Vortex entrance in MgB2 films from STI 0 H//surface (misalignment < 0.05) T=30K 2500 thickness  300nm -50 H*: clearly above m [emu] -100 vortex entrance 2000 -150 H* -200 1500 H [Oe] 0 500 1000 1500 2000 2500 H [Oe] 0.1 T=30K 1000 dm/dH [emu/Oe] Hderiv: kink in 0.0 H* derivative indicates 500 sudden entrance of Hderiv -0.1 large # of vortices. Hc2 Hderiv -0.2 0 0 500 1000 1500 H [Oe] 2000 2500 0 5 10 15 20 25 30 35 40 UNCLASSIFIED T [K] Operated by Los Alamos National Security, LLC for NNSA 14
  • 15. Comparison of Hder with two MgB2 films of different thickness: Vortex entrance in the thinner film occurs at a higher H STI films coated on sapphire These results are 2000 Thickness ~ 300nm significantly different from the curve obtained from 1500 two-fluid model. It seems that the thickness effect H [Oe] starts even d>l. 1000 We are writing a paper 500 on these results with Thickness ~ 500nm more detailed analysis. 0 0 5 10 15 20 25 30 35 40 T [K] UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 15
  • 16. Outline  Introduction  DC measurements and results  RF measurements and results  Issues and concerns  Summary and future plans UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 16
  • 17. RF measurements of 2-inch (~5 cm) diameter wafers (~1 mm thick) have been carried out at SLAC National Accelerator Laboratory using 11.4 GHz system Hemi-spherical TE013– Typical distribution of mode cavity with magnetic superconducting and normal- fields in parallel with the conducting regions after quench sample surface Radial H profile Temperature sensor Cold head Sample: <1.5 mm thick UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 17
  • 18. A summary of low-power tests of various samples: So far, only STI has been able to produce 2-inch samples, thus all the data herein are on STI samples. #4: MgB2(300nm)/Sapphire limited by the Q0 of copper dome 1/Rs, Lower surface resistance 400,000 #1: MgB2(100nm)/B(10nm)/Nb 350,000 #2: MgB2(1000nm)/Nb #3: MgB2(200nm)/B(200nm)/Nb 300,000 #4: MgB2(300nm)/Sapphire 250,000 Nb (single crystal RRR~300) Copper Q0 200,000 150,000 100,000 50,000 0 0 20 40 60 80 100 120 Operated by Los Alamos National Security, LLC for NNSA Sample temperature (K) UNCLASSIFIED Warning: some data are misleading since the effects of ambient magnetic field and cracks are also included. 18
  • 19. MgB2(300nm) showed a clear quench at 25 mT (250 Oe) at 3 K, which is significantly lower than the Hc1 measured by DC measurements (> 200 mT) 400,000 350,000 300,000 250,000 Q0 200,000 150,000 100,000 50,000 0 0 5 10 15 20 25 30 Bpeak (mT) UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 19
  • 20. Outline  Introduction  DC measurements and results  RF measurements and results  Issues and concerns  Summary and future plans UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 20
  • 21. Problem: BMgB2 or Al2O3MgB2 layers coated on bulk Nb at STI at 550 C caused inter-diffusion of Mg and O such as shown here. See more details at Roland Schulze’s talk. Auger depth profile Note the increase of O and Mg B Nb Actual Planned Mg MgB2 200 nm B 200 nm O Bulk Nb Mg UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA Slide21 21
  • 22. Clues to solve the inter-diffusion problem have been obtained  Recently, MgB2(200nm)/Alumina(300nm)/Nb showed a result comparable with MgB2(300nm)/Sapphire, i.e., Alumina coating can prevent the inter-diffusion with low RF losses. An optimization of necessary Alumina layer thickness needs to be done.  UHV baking of Nb substrates at 800 C for 4 hours have been tried and it seems to help reduce the oxygen diffusing from the bulk Nb and clean the surface according to the XPS surface analysis. See the detail at Roland Schulze’s talk. UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 22
  • 23. Outline  Introduction  DC measurements and results  RF measurements and results  Issues and concerns  Summary and future plans UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 23
  • 24. Summary and future plans  DC measurements have shown that Hc1 of MgB2 thin films is higher than bulk Nb even d>l. (>200 mT at 4.5 K)  RF measurements at 11.4 GHz, however, have shown that the Hc, RF is low (~25 mT at 3 K)  We need to identify the source of this discrepancy  We plan to do DC and RF measurements of Hc1 // with thinner and multi-layer films. Recently, three 2-inch samples of 4 layers of MgB2 (50nm)/Al2O3(10nm) have been prepared with the help from ANL for ALD Al2O3 (Thomas Proslier, Mike Pellin)  We will need to develop a technique to coat cavity inner surfaces. The good news is, now that we know Hc1 of even ~300 nm thick film could exceed bulk Nb performance, it might not be as difficult as we thought to realize the concept of increasing the sustainable magnetic field on the cavity surface. UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 24
  • 25. Thanks for your attention! Many thanks to the Defense Threat Reduction Agency (DTRA) for the funding and a number of people listed in the following slides. UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 25
  • 26. Acknowledgments  LANL • AOT-MDE: A. Canabal (now at U. Maine), G. Eremeev (now at JLab), et al. • MPA-STC: R. DePaula, A. Apodaca • MST-6: R. Schulze, A. Zocco, R. Edwards • MST-7: B. Day • MST-8: M. Hawley, P. Hosemann, V. Livescu • P-DO: P. Turchi • P-25: S. Greene, C. Morris UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 26
  • 27. Acknowledgments (cont.)  Other National Labs • SLAC — V. Dolgashev, D. Martin, C. Yoneda • JLab — G. Eremeev • ORNL — I. Campisi • ANL — T. Proslier, M. Pellin  Industry • Cabot Microelectronics Polishing Company (CBPC) — S. Lesiak UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 27
  • 28. Acknowledgments (cont.)  Collaborators in Japan • National Institute for Materials Science (NIMS) — Superconducting Materials Center: A. Matsumoto, H. Kumakura, M. Tachiki, — Advanced Electronic Materials Center: H. Abe — Nanotechnology Innovation Center: E. Watanabe • Kagoshima Univ. — T. Nishikawa, T. Nagamine, K. Yoshihara • KEK — H. Inoue UNCLASSIFIED Operated by Los Alamos National Security, LLC for NNSA 28

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