Volume 1 of the FCC Feasibility Report presents an overview of the physics case, experimental programme, and detector concepts for the Future Circular Collider (FCC). This volume outlines how FCC would address some of the most profound open questions in particle physics, from precision studies of the Higgs and EW bosons and of the top quark, to the exploration of physics beyond the Standard Model. The report reviews the experimental opportunities offered by the staged implementation of FCC, beginning with an electron-positron collider (FCC-ee), operating at several centre-of-mass energies, followed by a hadron collider (FCC-hh). Benchmark examples are given of the expected physics performance, in terms of precision and sensitivity to new phenomena, of each collider stage. Detector requirements and conceptual designs for FCC-ee experiments are discussed, as are the specific demands that the physics programme imposes on the accelerator in the domains of the calibration of the collision energy, and the interface region between the accelerator and the detector. The report also highlights advances in detector, software and computing technologies, as well as the theoretical tools/reconstruction techniques that will enable the precision measurements and discovery potential of the FCC experimental programme. The content and structure of this report are guided by the scope and priorities defined in the mandate of the FCC Feasibility Study. It is therefore not intended to serve as an exhaustive review of the full physics potential of FCC. Several topics, already covered in earlier reports such as the FCC CDR, are not reiterated here or are addressed only briefly, in alignment with the study’s focus. This volume reflects the outcome of a global collaborative effort involving hundreds of scientists and institutions, aided by a dedicated community-building coordination, and provides a targeted assessment of the scientific opportunities and experimental foundations of the FCC programme.

We present the development, realization and setup of dielectric resonators, for the purpose of measuring the surface impedance at microwave frequencies of superconducting thin films. We focus on resonators designed to operate in dc magnetic fields, optimized for the measurements of the variation of the surface impedance with the applied field. Two resonators, operating at 8 and 48 GHz, are presented. We discuss different approaches to the measurement of the resonator parameters, with particular attention to the nonidealities of real setups in a cryogenic environment. Finally, we present some sample measurement of high-T _c and low-T _c superconducting films.

Dielectric loaded resonators, by virtue of their high sensitivity, are a de facto standard for the measurement of the microwave surface impedance Z of good conductors, including superconductors. However, new perspective applications of superconductors request measurements in increasingly extreme conditions: cryogenic and magnetic environments, often combined together. Careful evaluations of the dielectric resonator (DR) design are necessary to operate in these conditions. Moreover, the evaluation of the uncertainties and the issues related to an appropriate calibration become problematic. We present here a performance analysis of DRs designed for cryogenic temperature and high magnetic field operation and some sample experimental results on Z measurements on the most technologically interesting superconductors.

The hypothetical axion particle is an excellent cold dark matter candidate. Models predict an axion mass of tens of μeV (GHz frequency range). It is in principle possible to convert galactic axions into a monochromatic microwave signal or to detect them with an electron-spin flip. In both cases, to measure the resulting vanishing signal ( $P\approx10^{-23} W$ ) a high-Q cavity is needed, with $Q\sim10^6$ . Superconducting RF technology can satisfy the requirement of operation in moderate-to-high DC magnetic fields. In this contribution we present an experimental study of the behavior of superconducting cavities in the vortex state. This study has been realized using 14 GHz Cu-NbTi and $Cu-NbTiN_x$ film cavities. A new cavity geometry is presented. We measured the magnetic field dependence of the Q-factor and $\Delta f_{res}/f_{res}$ where $f_{res}$ is resonant frequency, in the range B=0-6 T at 4.2 K. Also Q versus temperature at fixed B in ZFC and FC setups has been considered. A comparison was made with Cu and Nb cylindrical bulk cavities. The data for Q(B) were analyzed in terms of the elastic and dissipative motion of flux lines, thus including flux flow and flux pinning. We discuss whether the field-induced quasiparticle contribution is relevant in our field and temperature range.

The high frequency vortex motion in Nb ₃ Sn was analyzed in this work up to 12 T. We used a dielectric loaded resonator tuned at 15 GHz to evaluate the surface impedance Z of a Nb ₃ Sn bulk sample (24.8 at.%Sn). From the field induced variation of Z , the high frequency vortex parameters (the pinning constant k _p , the depinning frequency ν _p and the flux flow resistivity ρ _ff ) were obtained over a large temperature and field range; their field and temperature dependencies were analyzed. Comparison with other superconducting materials shows that high frequency applications in strong magnetic fields are also feasible with Nb ₃ Sn. In the present work, we report the first measurements about the microwave response in Nb ₃ Sn in strong magnetic fields.