Flux penetration and a.c. losses in superconducting niobium

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.