The effect of different surface treatments on flux penetration and dissipation at 50 Hz in bulk niobium samples has been quantitatively investigated. It is shown that for a sufficiently smooth sample surface the onset of a.c. dissipation occurs when the peak applied magnetic field exceeds Hc1+ΔH, in striking contrast to earlier results. A comparison of experimental results with a generalized critical-state model yields good agreement.

Measurements of flux penetration and dissipation at 50 c/s have been made on niobium samples shaped to approach closely the case of slab geometry with a tangential applied field. When corrected for end effects the measured quantities are independent of sample thickness, which varies from 0·125 to 0·004 in. Comparison of the experimental results with the Bean-London model yields little quantitative agreement.

physica status solidi (b)Volume 23, Issue 2 p. K129-K132 Short Note Effect of Hcl on ac Losses in Niobium R. M. Easson, R. M. Easson Department of Electrical Engineering, The University, GlasgowSearch for more papers by this authorP. Hlawiczka, P. Hlawiczka Department of Electrical Engineering, The University, GlasgowSearch for more papers by this author R. M. Easson, R. M. Easson Department of Electrical Engineering, The University, GlasgowSearch for more papers by this authorP. Hlawiczka, P. Hlawiczka Department of Electrical Engineering, The University, GlasgowSearch for more papers by this author First published: 1967 https://doi.org/10.1002/pssb.19670230247Citations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat References 1 T. A. Buchhold, Cryogenics 3, 141 (1963). 2 R. M. Easson and P. Hlawiczka, Brit. J. Appl. Phys., to be published. 3 D. K. Finnemore, T. F. Stromberg, and C. A. Swenson, Phys. Rev. 149, 231 (1966). 4 C. P. Bean, Rev. Mod. Phys. 36, 31 (1964). 5 H. London, Phys. Letters 6, 162 (1963). Citing Literature Volume23, Issue21967Pages K129-K132 ReferencesRelatedInformation

Further experiments on ring shaped type II superconductors confirm the coexistence of critical a.c. currents and superimposed d.c. currents, with qualifications regarding sample geometry.

Experiments are described which demonstrate that the superconducting to normal transition in Type II superconductors is caused by a temperature rise above Tc due to a.c. losses, rather than by the peak a.c. currents rising to the thermodynamic critical value.

Thermal dissipation sets the maximum current in a.c. power transmission by a superconductor. Experiments show that the same maximum alternating current can be carried in the presence of a direct current, making possible combined a.c. and d.c. transmission.

A.c. losses measured on ring shaped samples of lead bismuth depend only on the surface current density, on the assumption of an exponential current distribution.