Thermal Expansion Coefficient Measurement of Stack Structure of REBCO Coated Conductors By Strain Gages At Cryogenic Temperatures

Abstract

Background

The structures of stack REBa₂Cu₃O_7-x (RE: rare earth elements) coated conductors (CCs), with epoxy impregnated, are commonly involved in superconducting cables and pancake magnet coils. Thermal stresses are inevitable in the stack structures because of the mismatch of coefficient of thermal expansion (CTE) between the CCs and epoxy at cryogenic temperatures.

Objective

It is essential to precisely measure the thermal deformation of the stack structure such that to determine the corresponding CTE. Here, a protocol for determine the CTE by strain gages was reported.

Methods

Copper was used as a standard reference material, and its cryogenic thermal expansion curve was determined by the digital image correlation method. This curve was then used to correct the thermal deformation curves of the testing samples, eliminating the heat output of the strain gage itself.

Results

Thermal deformation of an aluminum beam has been measured with a relative error of less than 5% compared to that from the National Institute of Standards and Technology of the United States. The maximum thermal deformation of the stack sample along the thickness direction was almost 4.5 times of those along other two orthogonal directions.

Conclusions

The approach presented was validated by the aluminum test, CTE for stack structure along the thickness direction was found to be larger than those along other two orthogonal directions.