28 June 2015 to 2 July 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-

29 Jun 2015, 14:00
2h
Exhibit Hall (Arizona Ballroom) ()

Exhibit Hall (Arizona Ballroom)

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

Speaker

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

Description

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)

Co-authors

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