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Applied Superconductivity, IEEE Transactions on

Issue 3 • Date Sept. 1997

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Displaying Results 1 - 6 of 6
  • Operation of hybrid current limiter based on high-Tc superconducting thin film

    Publication Year: 1997 , Page(s): 3783 - 3790
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (191 KB)  

    A high-Tc superconducting (HTSC) thin film with an inductive shunt was investigated as the model of a hybrid current limiter based on the superconducting-normal state transition. In addition to features previously observed in operation of other current limiters, sharp peaks of rather high frequency were found to appear on the background of a basic low-frequency voltage signal. This is attributed to self-oscillations of temperature and current in the superconductor. The influence of the frequency and magnitude of the circuit current on the character of self-oscillations was experimentally investigated. Qualitative analysis of the conditions for appearance of the self-oscillations under dc and ac conditions was carried out. View full abstract»

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  • Development of a MAGLEV superconducting magnet for the Yamanashi test line in Japan: vibration characteristics and analysis for design

    Publication Year: 1997 , Page(s): 3791 - 3796
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (130 KB)  

    A high-performance and high-reliability magnetically levitated (MAGLEV) superconducting magnet (SCM) was developed. Its heat generation per unit time by the electromagnetic forces due to the spatially fifth ripple magnetic fields from levitation coils is under 2 W at the frequency range in which vehicles are levitated. The vibration mode of inner vessels that makes the largest contribution to heat generation in SCMs is clarified, the torsion mode. A modeling method to analyze SCM vibration, which considers the effect of the bogie frames of a vehicle, is examined, and heat generation in SCMs is calculated from the vibration of the inner vessel. Using the numerical analysis method, new SCMs combined with new bogie frames for the Yamanashi Test Line are designed. Good performance in vibration and heat generation of these SCMs is predicted by numerical analysis. View full abstract»

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  • From Bean's model to the H-M characteristic of a superconductor: some numerical experiments

    Publication Year: 1997 , Page(s): 3797 - 3801
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (213 KB)  

    We present a series of two-dimensional simulations in transverse field as validation of a simple finite difference method for the computation of fields inside superconductors described by an extended Bean model. View full abstract»

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  • Thermal budget calculations, design aspects, and device performance of high-Tc air-bridged microbolometers

    Publication Year: 1997 , Page(s): 3802 - 3807
    Cited by:  Papers (1)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (191 KB)  

    The thermal properties of an air-bridged microbolometer have been evaluated on the basis of a finite element calculation scheme for the first time. The numerical results show that the performance of the device's sensitively depends on geometry and layout. The degree of thermal coupling and interaction with the heat sink affects the thermal time constant and frequency range of operation. For identical geometries, experimental and modeled data are in good agreement. The length of the air-bridge is defining the effective thermal time constant but has little effect on the thermal responsivity. An unusually high responsivity has been calculated for configurations where the thermal coupling to the heat sink has been minimized. This design leads to an increase of responsivity of a factor of 200 and would establish superior operation of the device even at ambient temperature. View full abstract»

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  • Linewidth measurements and phase locking of Josephson oscillators using RSFQ circuits

    Publication Year: 1997 , Page(s): 3808 - 3811
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (89 KB)  

    We present a technique for linewidth measurement and phase-locking of Josephson oscillators using digital rapid single-flux-quantum (RSFQ) circuits. The oscillator consists of a resistively shunted 6 /spl mu/m/spl times/6 /spl mu/m Nb/AlO/sub x//Nb Josephson tunnel junction that is integrated with RSFQ input and output circuits. A cascade of RSFQ T flip-flops is used to directly monitor the output of the Josephson oscillator. Spectral characteristics have been measured directly for oscillator frequencies ranging from 10-50 GHz. The linewidth can be reduced by over 100 times by phase-locking the oscillator to an RSFQ pulse train generated by an external sinusoidal signal. These Josephson oscillators can be used as on-chip stable high frequency clocks for RSFQ circuits. View full abstract»

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  • Role of interdomain and interplatelet boundaries on magnetic flux penetration in melt grown YBCO

    Publication Year: 1997 , Page(s): 3812 - 3815
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (91 KB)  

    The microstructure of a melt processed YBCO sample reveals the presence of random domains with aligned platelets separated by microcracks inside the domains. The lower critical field (H/sub c1/) and critical current density (J/sub c/) of these boundaries will be less than that of the grains, and their role in determining the bulk properties cannot be neglected. We have employed a sensitive lock-in flat-band detection technique and recorded the low field ac M-H loops at 33 Hz and 77 K and derived the flux profiles. The results show an enhancement in H/sub c1/ due to melt processing. Inclusion of Y/sub 2/BaCuO/sub 5/, and Ag enhances the H/sub c1/ further. The flux profiles show distinct slope changes at certain fields which reflect different coupling strengths of weaklinks that become operative for flux entry at different applied fields. While the low field flux profiles are found to reflect the effect of residual weaklinks (like liquid phase and micropores) and domain boundaries, those at higher fields might reflect the effect of platelet boundaries. View full abstract»

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IEEE Transactions on Applied Superconductivity contains articles on the applications of superconductivity and other relevant technology.

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Editor-in-Chief
Britton L. T. Plourde
Syracuse University
bplourde@syr.edu
http://www.phy.syr.edu/~bplourde