Development of resonant cavity-based microwave filters for axion detection

Resumen

This PhD thesis addresses several investigations for the detection of axions and for the improvement of satellite communications using resonant cavities in waveguide technology. The axion is a hypothetical particle theorized that could explain the strong CP problem (Charge conjugation Parity symmetry) in quantum chromodynamics (QCD) and which, if it exists, could be a component of dark matter. In this line, the development of axion dark matter detectors, commonly called haloscopes, has been booming in the last 20 years. In this work, several methods have been developed for the improvement of these haloscopes using structures based on subcavities coupled by irises. On the other hand, it is well known that the electromagnetic spectrum in satellite communications is saturated due to the high demand for radio communication systems. In addition, the cost of putting a satellite into orbit grows exponentially with the weight on board, the reduction of which will be key in any space program. Thus, this PhD thesis deals with different waveguide bandpass filter designs for optimizing the weight, volume, and on-board footprint of future communication satellites. The frequency spectrum swept by the axion community in search of the coveted particle is increasing day by day, which means that there is a high level of competition to develop high-performance detectors. In addition, the extreme conditions to which a dark matter axion detector must be subjected in order to meet the detection conditions (cryogenic temperatures, high magnetostatic field, etc.) further complicate this task. Some of the parameters that govern the performance of a haloscope based on resonant cavities are its volume, quality factor and form factor. During the development of this work, several novel topologies have been designed, manufactured, and characterized for the creation of these detectors, optimizing the three above-mentioned parameters, achieving satisfactory results. This PhD thesis has been carried out within the framework of the RADES (Relic Axion Detector Exploratory System) axion group. Research work has been carried out to improve the quality factor in structures manufactured in the first stages of this experimental group through the application of various treatments, such as soldering. In addition, as the axion mass is unknown, it is important to scan in frequency to search for the axion over a range as large as possible, as mentioned above, for which tuning systems must be implemented to allow resonant frequency shift and other arrangements for adjusting the input / output coupling of the system (another key haloscope parameter). There are two types of frequency tuning, mechanical and electronic. For mechanical tuning systems, studies have been carried out on the behaviour of the fabricated prototypes when they are opened by a vertical cut, which will change their axion search frequency. On the other hand, for electronic tuning systems, various designs have been developed for the introduction of ferromagnetic and ferroelectric materials, which will change the operating frequency by changing the permeability and permittivity of the medium, respectively, by applying a change of voltage or temperature. A much more extensive study has been made for the use of ferroelectric tuning systems. Electronic systems avoid certain problems that occur in mechanical systems, such as motion failure at cryogenic temperatures or lack of scalability. For ferroelectric elements, a novel design as been achieved which has brought great value to the scientific community for the application of this type of material in any haloscope. Also, coupling systems have been developed between subcavities with ferroelectric films, avoiding the need to manufacture irises, which can cause problems in certain systems. For the input / output coupling adjustment systems, a preliminary prototype has been developed which has provided good experimental results. Other research works have also been carried out on the development of other haloscope enhancement techniques. One of them is the rejection of unwanted resonances near the axion mode by means of the combination of several coaxial ports with the phase-matching method, for which several simulations and fabrications have been carried out, obtaining positive results that make this method feasible. Other secondary studies have been the implementation of QuBit devices to reduce the system temperature (another key parameter for haloscope performance), the use of HTS (High Temperature Superconductor) elements to increase the quality factor, the haloscope design at frequencies in the UHF and W bands, and the electromagnetic analysis of axion-photon coupling in haloscopes using the BI-RME (Boundary Integral-Resonant Mode Expansion) 3D method. Finally, as a spin-off from the development of haloscopes, several studies have been carried out for the design, manufacture, characterization, and improvement of bandpass filters for satellite communications using the same technology (resonant cavities coupled by irises in waveguide). Several evanescent filters based on 3D printing or low-cost additive manufacturing and CNC (Computer Numerical Control) machining have been developed. A screw tuning system has been applied to these filters to improve the electrical filtering response. On the other hand, the design of a horizontally folded asymmetric filter for the implementation of transmission zeros, to increase the rejection capabilities of the filter, has been carried out. These filters could be of great value to the scientific community as they allow to advance in the state of the art of high-performance filters (low weight, volume, and footprint) for satellite communications.