A preliminary study of a torsion balance based on a spherical superconducting suspension

Abstract

We present details of the design and construction of a new superconducting, magnetically suspended torsion balance in which the levitation coil and the lift surface of the float lie on the surfaces of concentric spheres. We compare results from calculations of the variation of the inductance with the levitated height and transverse motion of the float with experimental measurements and show that the levitation system is stable. Angular motion of the torsion balance is detected using superconducting pick-up coils whose inductance is modulated by float rotation. The subsequent change in current flowing in the persistent circuit containing the coils is measured using a flux-gate magnetometer. The pick-up coils exert a restoring torque on the float which can be modified by adjusting the persistent current stored. Periods down to 60 s should be obtainable for a current of 2.5 A. Preliminary results of ring-down experiments in He gas at a pressure of 53Pa show that periods of angular oscillations of 24 s with quality factor, Q, of about 200 can be obtained. The moment of inertia of the float is 2 × 10-5 kg m2. The observed period of 24 s indicates that there is an additional restoring torque in the system which may be due to trapped flux. The observed value of Q is consistent with gas damping.

Experimental Searches for Dark Matter

“…A variant on the tuned cavity technique is to incorporate Rydberg atoms into the cavity where the | n 〉 to | n ′〉 transition is also resonant with the cavity [145]. In addition to the direct dark matter axion searches, there are a number of experiments looking for evidence of axion existence, such as axion telescopes pointed at the Sun [87] and torsion balance instruments looking for short-range weak force spin-coupling interactions of the type mediated by the axion [122, 98, 114, 134]. These have yet to achieve sufficient sensitivity.…”

Gas damping force noise on a macroscopic test body in an infinite gas reservoir

“…Gas damping of the motion of a macroscopic test body is a potentially sensitivity-limiting source of Brownian noise in variety of experiments that are sensitive to very small forces. Gas damping in the molecular flow regime is characterized by a viscous damping coefficient β tr = − dF dV in translation or β rot = − dN d φ in rotation, and has been found in numerous torsion pendulum experiments to be proportional to the residual gas pressure p [1,2,3]. The power spectrum of Brownian force noise associated with the molecular impacts is related to the damping coefficient via the fluctuation-dissipation theorem, which gives S F = 4k B T β tr .…”

Principle and performance of a superconducting angular accelerometer

“…Low temperature torsion balances have been developed to further reduce the Brownian noise contribution by lowering T and increasing Q. 10,11 The SAA utilizes relatively stiff pivots to allow flat response over a wide bandwidth, as well as operation in arbitrary orientation in the presence or absence of gravity. The high 0 is partly compensated by low T/( f ) and E SQ ( f ).…”

“…Though geometrically different, this design is similar in concept to that of Speake. 11 We are implementing this accelerometer design in a highly sensitive experiment searching for an interaction between intrinsic spin and mass, 19 as would be mediated by a particle like the axion.…”