A method for controlling the magnetic field near a superconducting boundary in the ARIADNE axion experiment

Abstract

The QCD axion is a particle postulated to exist since the 1970s to explain the strong-CP problem in particle physics. It could also account for all of the observed dark matter in the Universe. The axion resonant interaction detection experiment (ARIADNE) intends to detect the QCD axion by sensing the fictitious ‘magnetic field’ created by its coupling to spin. Short-range axion-mediated interactions can occur between a sample of laser-polarized 3He nuclear spins and an unpolarized source-mass sprocket. The experiment must be sensitive to magnetic fields below the 10−19 T level to achieve its design sensitivity, necessitating tight control of the experiment’s magnetic environment. We describe a method for controlling three aspects of that environment which would otherwise limit the experimental sensitivity. Firstly, a system of superconducting magnetic shielding is described to screen ordinary magnetic noise from the sample volume at the 108 level, which should be sufficient to reduce the contribution of Johnson noise in the sprocket-shaped source mass, expected to be at the 10−12 T / H z level, to below the threshold for signal detection. Secondly, a method for reducing magnetic field gradients within the sample up to 102 times is described, using a simple and cost-effective design geometry. Thirdly, a novel coil design is introduced which allows the generation of fields similar to those produced by Helmholtz coils in regions directly abutting superconducting boundaries. This method allows the nuclear Larmor frequency of the sample to be tuned to match the axion field modulation frequency set by the sprocket rotation. Finally, we experimentally investigate the magnetic shielding factor of sputtered thin-film superconducting niobium on quartz substrates for various geometries and film thicknesses relevant for the ARIADNE axion experiment using SQUID magnetometry. The methods may be generally useful for magnetic field control near superconducting boundaries in other experiments where similar considerations apply.

Optimization of Hight-Sensitivity SQUID Gradiometer for ARIADNE at CAPP

“…For the QCD axion, the scalar and pseudo-scalar coupling constants and are directly correlated to the axion mass. Since the axion couples to , which is proportional to the magnetic moment of the nucleus, the axion coupling can be treated as a ctitious transverse 'magnetic eld' through an interaction potential: [9].…”

Axion dark matter: How to see it?

“…The experimental scheme, shown in Fig. 6, involves an unpolarized sprocket mass as a monopole source, polarized 3 He nuclei for a dipole spin system, and an SQUID magnetometer to pick up the resonantly enhanced precession signal (110). The sensitive mass (frequency) range by this spin-dependent interaction is 0.1 to 10 meV (25 GHz to 2.5 THz), which is practically unreachable by the haloscope experiments.…”

Axion Dark Matter: How to see it?

“…The 3 He system is shielded by a superconducting shield, which is ineffective against the axion field. CAPP is in charge of the construction of the Nb-based shield and of the SQUID magnetometer in collaboration with KRISS scientists [92]. The experiment has been funded by NSF in the US and its first phase is expected to start data taking soon.…”