Abstract
In the framework of the luminosity upgrade of the LHC, high-field magnets are under development. Magnetic flux densities of up to 13 T require the use of Nb3Sn superconducting coils. Quench protection becomes challenging due to the high stored energy density and the low stabilizer fraction. The thermal conductivity and diffusivity of the combination of insulating layers and Nb3Sn based cables are an important thermodynamic input parameter for quench protection systems and superfluid helium cooling studies. A two-stage cryocooler based test stand is used to measure the thermal conductance of the coil sample in two different heat flow directions with respect to the coil package geometry. Variable base temperatures of the experimental platform at the cryocooler allow for a steady-state heat flux method up to 100 K. The heat is applied at wedges style copper interfaces of the Rutherford cables. The respective temperature difference represents the absolute value of thermal conductance of the sample arrangement. We report about the measurement methodology applied to this kind of non-uniform sample composition and the evaluation of the used resin composite materials.
Highlights
The thermal conductivity and the thermal conductance Λ were determined from the proportionality between applied heat flux and recorded temperature difference Δ : Δ and Λ
The specimens are cut from the magnet coil and have variable cross section in the heat flux direction, Λ describes the thermal conductance of the defined coil specimen
Thermal conductivity values are calculated by using average data for cross section (smallest value is used in case of coil (B)) and the length of the impregnated coil
Summary
A coil sample with an overall length of 40 mm was provided to carry out the thermal conductivity tests [1]. The samples are probing the thermal conduction along the azimuthal direction along the Rutherford cable stack with the impregnation layers in between or across the two layers of the coil in radial direction, figure 1. Thermal conductivity values are calculated by using average data for cross section (smallest value is used in case of coil (B)) and the length of the impregnated coil.
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