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ST407 - Investigation on the Dielectric Material Parameters and the Electric Conductivity of Syntactic Foam at the Liquid Nitrogen Temperature Range (Contest runner-up)

Investigation on the Dielectric Material Parameters and the Electric Conductivity of Syntactic Foam at the Liquid Nitrogen Temperature Range

Daniel Winkel, Ralf Puffer, and Armin Schnettler

Institute for High Voltage Technology
RWTH Aachen University, 52056 Aachen, Germany

 
Abstract — Liquid nitrogen (LN2) based insulation systems for superconducting components are state of the art. As the dielectric strength of LN2 based insulation systems can be significantly reduced if bubbles occur an alternative insulation system could be a solid insulation system using LN2 only for cooling but not as electrical insulation material. This paper discusses syntactic foam as a solid substitution of LN2 based insulation systems. Syntactic foam consists of a polymer matrix with embedded hollow microspheres (HMS) which have diameters of several 10 μm. Compared to the pure matrix material the HMS filled matrix features a lower density and a significantly reduced thermal contraction when being cooled to cryogenic temperatures. Several syntactic foams are investigated regarding their dielectric parameters (relative permittivity, loss factor) and electric conductivity at liquid nitrogen temperature (LNT). The results show that the investigated parameters of syntactic foam are almost constant in the temperature range of LNT. Furthermore, the loss factor and the relative permittivity at LNT are lower than at room temperature. These effects can be explained by the existence of a secondary glass transition of polymers. At cryogenic temperatures a decrease of the electric conductivity of syntactic foam is detected presumably due to the rise in required energy to lift valence electrons to the conduction band of the polymer at lower temperatures.
 
Keywords (Index Terms) — Cryogenic temperature, dielectric parameters, electrical conductivity, liquid nitrogen, syntactic foam.
 
IEEE/CSC & ESAS SUPERCONDUCTIVITY NEWS FORUM (global edition), January 2015.
Received August 14, 2014; Selected September 02, 2014. Reference ST407; Category 12.

ASC 2014 manuscript 2MPo1-04 published online in IEEE Trans. Appl. Supercond.
(IEEE XPLORE) DOI: 10.1109/TASC.2014.2376190 on November 26, 2014.