Fiber Bragg gratings for strain sensing in high temperature superconducting magnet

Fiber Bragg grating (FBG) for measuring stress and strain in 77 K and high magnetic field environment for a high temperature superconducting (HTS) magnet has been studied. The sensing characteristics of FBG in the cryogenic environment were studied on the basis of a series of experiments. To study the strain sensing behavior of FBG at 77 K, the principle of the cantilever which used a aluminum plate clamped at one end and deployed as a cantilever was applied. The results demonstrated that the FBGs still possess good linear strain sensing property at liquid nitrogen temperature. The function of micro-strain and wavelength shift is determined as Delta lambda(B) = 1.23 mu epsilon(Z) at 77 K. Based on this equation, the hoop strain of a HTS magnet wounded by Bi2223 was measured. The hoop strain difference between the measured results by FBG and the calculated results by ANSYS is very small.