Studies of helical conductor models for superconducting AC power transmission

In the BNL concept of a superconducting ac power transmission cable the conductors are made of Nb3Sn tapes wound helically on cylinders. Recently, it was decided to make each conductor in the form of a double layer winding in which the layers are of opposite helicity. This reduces undesirable consequences of axial flux generation. After reviewing the considerations which lead to the double helix conductor, experiments with short models (0.8 m long) are described. Results are given for ac loss and quench current measurements. Quench currents in excess of 3400 A/cm rms have been obtained. Ac losses are higher than those of short samples of the tapes used but are acceptable. Loss calculations for the double helix configuration are discussed.