Axion helioscopes as solar magnetometers

TL;DR

This paper explores how next-generation axion helioscopes like IAXO could measure or constrain the Sun's magnetic field by analyzing solar axion flux, especially from longitudinal plasmons, with high energy resolution detectors.

Contribution

It introduces the potential of IAXO to use solar axion flux, including previously neglected components, as a probe of the solar magnetic field profile at various depths.

Findings

High energy resolution (<200 eV) enhances magnetic field measurement capabilities.

IAXO can access the inner 70% of the Sun's magnetic field with resolutions better than 10 eV.

The longitudinal plasmon flux exhibits a 2% geometric modulation useful for angular magnetic field measurements.

Abstract

Axion helioscopes search for solar axions and axion-like particles via inverse Primakoff conversion in strong laboratory magnets pointed at the Sun. Anticipating the detection of solar axions, we determine the potential for the planned next-generation helioscope, the International Axion Observatory (IAXO), to measure or constrain the solar magnetic field. To do this we consider a previously neglected component of the solar axion flux at sub-keV energies arising from the conversion of longitudinal plasmons. This flux is sensitively dependent to the magnetic field profile of the Sun, with lower energies corresponding to axions converting into photons at larger solar radii. If the detector technology eventually installed in IAXO has an energy resolution better than 200 eV, then solar axions could become an even more powerful messenger than neutrinos of the magnetic field in the core of the Sun. For energy resolutions better than 10 eV, IAXO could access the inner 70% of the Sun and begin to constrain the field at the tachocline: the boundary between the radiative and convective zones. The longitudinal plasmon flux from a toroidal magnetic field also has an additional 2% geometric modulation effect which could be used to measure the angular dependence of the magnetic field.