Influence of mechanical losses in AC superconducting coils having composite materials reinforced with Dyneema and glass fibers

When a Dyneema fiber reinforced plastic (DFRP) is used as a superconducting coil´s bobbin, the decrease of the winding tension during cooling down is prevented. Therefore, it is expected that a mechanical loss generated in AC superconducting coils is reduced. The DFRP has the high Young´s modulus to the fiber direction, however the modulus to the perpendicular direction is lower than the modulus of the glass fiber reinforced plastic (GFRP), which is generally used as a structural material in superconducting coils. Therefore, a Dyneema and glass fiber reinforced plastic (DGFRP), which was compounded the Dyneema and the glass fibers, was fabricated for the purpose of the intensification of the DFRP, and total losses of the superconducting coils having some kinds of DGFRP bobbins were measured under AC operation. In loss measurements, the coil whose loss was the smallest was the coil having the strongest winding tension at cryogenic temperature, and the coil whose loss was the largest was the coil having the weakest tension. Moreover, comparing with the results of the loss measurement in the coils fabricated with the DFRP bobbin, the losses of the coils having the DGFRP bobbins were slightly large due to the mixture of the Dyneema and the glass fibers. This paper reports the effect of the reduction of the mechanical losses in the coils having the DGFRP bobbins and the comparison with the coils whose bobbins are the DFRP and the GFRP.