Understanding effect of teflon room temperature phase transition on coax cable delay in order to improve the measurement of TE signals of deuterated polarized targets

A half-lambda-wavelength teflon cable is part of a tuned circuit for the measurement of polarization in nuclear polarized targets. In trying to improve this measurement, the author noticed a large change (0.1%) in electrical cable length as the teflon goes through a room-temperature chemical-molecular phase transition. He reports some test results on commercially available cables. Measurements indicate that the electrical length of the cable changes by 1000 ppm over a 13-19 degrees C change. The amplitude of the thermal equilibrium (TE) signal is equivalent to a change in the cable length of approximately 0.6 ppm. It was possible to keep the cable length stable to better than 0.1 ppm by understanding the phase transition effect. Hence, it could be expected that the TE measurement will be improved by an order of magnitude.<
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