HE ACTIVATED LOADING DEVICE FOR LOW-TEMPERATURE UNIAXIAL AND ANVIL CELL PRESSURE EXPERIMENTS

We report on a compact loading cell for the continuous variation of un iaxial forces up to a few tons in low temperature investigations. The cell is based on a He activated bellow and a mechanical force amplific ation system. Due to its modular design, it may be used in studies of the effect of uniaxial pressure on solids or the in situ variation of hydrostatic pressure in an anvil cell. High pressure He is supplied by a fine capillary, so that bellow, force amplifier, and experiment may be cooled uniformly to mK temperatures even at high magnetic fields. The pressure in the bellow is controlled by a simple proportional-inte gral regulator at room temperature. Characteristic features of a piezo electric sensor, used to measure the load at low temperature, are pres ented in detail. With the method described here, we observe long-term stability to better than +/-0.2 N in sweeps over a wide range of tempe ratures and fields. The performance of the loading device is illustrat ed by means of measurements into the superconducting state of URu2Si2. (C) 1997 American Institute of Physics.