Bridge measurement of very low dielectric loss at low temperatures

The paper describes a Schering bridge, the associated apparatus and the techniques used for the determinaticm of very small values of loss tangent at power frequency, low electric stress and liquid helium temperatures. The loss tangents of several small samples of polyethylene and polytetrafluoroethylene have been measured to be less than 10¿5radians at 4.2 K. Liquid helium was used as the loss reference. It is proposed that this method is also suitable for measuring the dielectric loss of large samples.