We present a proposal to search for QCD axions with mass in the 200 µeV range, assuming that they make a dominant component of dark matter. Due to the axion-electron spin coupling, their effect is equivalent to the application of an oscillating rf field with frequency and amplitude fixed by the axion mass and coupling respectively. This equivalent magnetic field would produce spin flips in a magnetic sample placed inside a static magnetic field, which determines the resonant interaction at the Larmor frequency. Spin flips would subsequently emit radio frequency photons that can be detected by a suitable quantum counter in an ultra-cryogenic environment. This new detection technique is crucial to keep under control the thermal photon background which would otherwise produce a too large noise.

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.

Axions, originally proposed to solve the strong CP problem of quantum chromodynamics, emerge now as leading candidates of WISP dark matter. The rich phenomenology associated to the light and stable QCD axion can be described as an effective magnetic field that can be experimentally investigated. For the QUAX experiment, dark matter axions are searched by means of their resonant interactions with electronic spins in a magnetized sample. In principle, axion-induced magnetization changes can be detected by embedding a sample in an rf cavity in a static magnetic field. In this work we describe the operation of a prototype ferromagnetic haloscope, with a sensitivity limited by thermal fluctuations and receiver noise. With a preliminary dark matter search, we are able to set an upper limit on the coupling constant of DFSZ axions to electrons g aee < 4.9 × 10 −10 at 95% C.L. for a mass of 58 µeV (i. e. 14 GHz). This is the first experimental result with an apparatus exploiting the coupling between cosmological axions and electrons.

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The slowing down and capture by a plasma of externally injected 1+ ions, as a consequence of very frequent elastic Coulomb collisions, is the main mechanism involved in the charge breeding process based on electron cyclotron resonance ion sources. The Istituto Nazionale di Fisica Nucleare ion source group has been undertaking an intense activity on numerical simulations of the beam-plasma interaction, developing a code that has been proven to be very effective in reproducing several experimental results of charge breeding of light and heavy ions. This contribution will present the progress made in the development of the numerical code, focusing the attention on the latest simulations of charge breeding of Rb1+ ions employing a self-consistent plasma target model. The effect of the real plasmoid/halo structure on the capture process will be underlined, as well as the influence of different plasma excitation frequencies.