Calculation of hysteresis losses in hard superconductors carrying ac: isolated conductors and edges of thin sheets

Abstract

Two methods of calculating hysteresis losses in hard superconductors are described. The London model is assumed in which the critical current density is taken independent of magnetic field. Losses in isolated wires of different cross section are considered but it is found that losses for solid wires vary by at most a factor of 3 for different shaped wires of the same current-carrying capacity. The loss at saturation current is usually 0.4-0.6 I c z p~/ n. Losses at theedges of thin sheets are also calculated and a fourth-power dependence on current (for low current) is found. Three systems are examined: a slit parallel to the current in a wide sheet (L e-poj2g2r3F4/24), one pair of the edges of two wide strips set back-to-back and carrying antiparallel currents (Le 2 ponj2s2F4/6) and a long thin wall parallel to the current flow on a wide sheet (L c~p~. r r 3 j 2 a 2 F ' i / 3). Le is the loss per cycle per unit length, F is the current peak as a fraction of saturation current, g the width of the slit, s the spacing of strips, a the height of the asperity and j the critical current density per unit width. All in MKS units.

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