  We describe a liquid-cryogen free cryostat with ultra-low vibration levels
which allows for continuous operation of a torsion balance at cryogenic
temperatures. The apparatus uses a commercially available two-stage pulse-tube
cooler and passive vibration isolation. The torsion balance exhibits torque
noise levels lower than room temperature thermal noise by a factor of about
four in the frequency range of 3-10mHz, limited by residual seismic motion and
by radiative heating of the pendulum body. In addition to lowering thermal
noise below room-temperature limits, the low-temperature environment enables
novel torsion balance experiments. Currently, the maximum duration of a
continuous measurement run is limited by accumulation of cryogenic surface
contamination on the optical elements inside the cryostat.
