June 28, 2015 to July 2, 2015
JW Marriott Starr Pass Resort
Etc/GMT-7 timezone

Mechanical problems for a Ni-alloy reinforced Bi-2223/Ag conductor -Towards a super-high field compact magnet-

Jun 29, 2015, 2:00 PM
Exhibit Hall (Arizona Ballroom)

Exhibit Hall (Arizona Ballroom)

Poster Presentation CEC-06 - Superconducting Magnet Systems C1PoK - Superconducting Magnets I


Mr Masato Nawa (Graduate School of Engineering, Chiba University)


Recently, tensile stress tolerance of a Bi-2223 conductor has been drastically improved. Conventional Bi-2223 conductors with copper-alloy reinforcements or stainless steel reinforcements show tensile stress tolerance of ~250 MPa. The stress tolerance has been improved to 400-500 MPa with Ni-alloy reinforcements in combination with a pre-compression of Bi-2223 filaments/Ag-matrix [1]. This type of high mechanical strength Bi-2223 conductors are promising for developments of super high field magnets as they tolerate high hoop stress, resulting from high current density and a high magnetic field beyond 23.5 T. However, it is probable that this type of composite conductor is easily damaged by a release of strain energy inside the conductor; note that the Bi-2223/Ag conductor has a compressive strain, while the reinforcement tensile strain. In fact, a notable fracture of a conductor after a thermal runaway was observed [2]. From the standpoint of coil protection, mechanism and a method to prevent this phenomenon are important. In this work, these are systematically investigated with a model experiment. A piece of a high-mechanical strength Bi-2223 conductor was heated on a hot plate. Temperature and strain along the conductor longitudinal direction on a surface of the conductor were measured with a thermocouple and a strain gauge, respectively. The strain gauge showed a drastic change in strain at a temperature of ~200 °C. After the experiment, the Bi-2223/Ag conductor shows a curve among the delaminated Ni-alloy reinforcements; i.e. the Bi-2223/Ag conductor was buckled. The result shows that strain energy was released by a melting of a solder which bonds the conductor and the reinforcements, resulting in a collapse of the composite conductor. The method to prevent the phenomenon will be investigated.

Primary author

Mr Masato Nawa (Graduate School of Engineering, Chiba University)


Dr Hideaki Maeda (Center for Life Science Technologies, RIKEN) Prof. hieki nakagome (Graduate School of Engineering, Chiba University) Dr yoshinori yanagisawa (Center for Life Science Technologies, RIKEN)

Presentation materials