10 research outputs found
The QUAX proposal: a search of galactic axion with magnetic materials
Aim of the QUAX (QUaerere AXion) proposal is to exploit the interaction of
cosmological axions with the spin of electrons in a magnetized sample. Their
effect is equivalent to the application of an oscillating rf field with
frequency and amplitude which are fixed by axion mass and coupling constant,
respectively. The rf receiver module of the QUAX detector consists of
magnetized samples with the Larmor resonance frequency tuned to the axion mass
by a polarizing static magnetic field. The interaction of electrons with the
axion-equivalent rf field produces oscillations in the total magnetization of
the samples. To amplify such a tiny field, a pump field at the same frequency
is applied in a direction orthogonal to the polarizing field. The induced
oscillatory magnetization along the polarizing field is measured by a SQUID
amplifier operated at its quantum noise level.Comment: 5 pages, Contribution for the proceedings of the TAUP2015,
International Conference on Topics in Astroparticle and Underground Physics,
7-11 September 2015, Torino, Ital
Design of Electrostatic Feedback for an Experiment to Measure <italic>G</italic>
The torsion pendulum at the heart of the apparatus to measure the gravitational constant, at the Bureau International des Poids et Mesures (BIPM) is used to measure the gravitational torque between source and test-mass assemblies with two methods. In the Cavendish method, the pendulum moves freely. In the electrostatic-servo method, the pendulum is maintained at a constant angle by applying an electrostatic torque equal and opposite to any gravitational torque on the pendulum. The electrostatic torque is generated by a servo. This article describes the design and implementation of this servo at the National Institute of Standards and Technology. We use a digital servo loop with a Kalman filter to achieve measurement performance comparable to the one in an open loop. We show that it is possible to achieve small measurement uncertainty with an experiment that uses three electrodes for feedback control