Non-twisted stacks of coated conductors for DC magnets: analysis of inductance and AC losses

TL;DR

This paper analyzes the inductance and AC losses in non-twisted stacks of coated HTS conductors, showing they can be simpler, cost-effective, and have comparable losses to twisted designs, with implications for DC magnet applications.

Contribution

It provides a detailed analysis demonstrating that non-twisted stacks of HTS tapes can achieve similar performance to twisted stacks, simplifying design and reducing costs.

Findings

Twisting has negligible effect on inductance variations.

Replacing wide tapes with narrow stacks reduces AC losses.

Non-twisted stacks can be as effective as twisted ones for large cables.

Abstract

In the last 10-15 years, the most common strategy in the development of High Temperature Superconducting (HTS) cable for magnets has been to imitate Low Temperature Superconducting (LTS) cable designs. However, requirements for LTS materials are not valid for HTS materials, which are extremely stable. For example, non-twisted multifilamentary Bi-2223 tapes have been successfully used in several magnets. This paper review stability and analyse inductance and AC losses in non-twisted stack of HTS tapes. Numerical calculations show that twisting has negligible effect on inductance variations in a stack of tapes. Regarding AC losses, any magnet built with coated conductors have larger losses than LTS ones, because of the aspect ratio and large width of the tape. If a wide tape is replaced by a non-twisted stack of narrow tapes, losses and residual magnetisation could be reduced. In contrast with multifilamentary wires, twisting a stack of tapes reduces losses only marginally. Therefore, cables composed of non-twisted stack could be designed to have losses comparable to the one of twisted stack concepts. Few examples of large cables for fusion applications are discussed. Designs based on non-twisted stacks can be simpler, more robust and cost effective than twisted ones.