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Objective: To assess the possible influence of third-order shim coils on the behavior of the gradient field and in gradient-magnet interactions at 7 T and above., Materials and Methods: Gradient impulse response function measurements were performed at 5 sites spanning field strengths from 7 to 11.7 T, all of them sharing the same exact whole-body gradient coil design. Mechanical fixation and boundary conditions of the gradient coil were altered in several ways at one site to study the impact of mechanical coupling with the magnet on the field perturbations. Vibrations, power deposition in the He bath, and field dynamics were characterized at 11.7 T with the third-order shim coils connected and disconnected inside the Faraday cage., Results: For the same whole-body gradient coil design, all measurements differed greatly based on the third-order shim coil configuration (connected or not). Vibrations and gradient transfer function peaks could be affected by a factor of 2 or more, depending on the resonances. Disconnecting the third-order shim coils at 11.7 T also suppressed almost completely power deposition peaks at some frequencies., Discussion: Third-order shim coil configurations can have major impact in gradient-magnet interactions with consequences on potential hardware damage, magnet heating, and image quality going beyond EPI acquisitions., (© 2024. The Author(s).)

• Design of a prototype for a CICC magnet quench studies. • Cable-In-Conduit with copper profile filled with stagnant superfluid helium. • Numerical quench propagation studies in superfluid helium. • Phenomenological study of Thermal-Hydraulic-Quench-Back. • Impact of the friction forces in the quench propagation behavior. In the dark matter Axion research context, the MADMAX project acts as a figurehead in the physics research field. The goal of the project is to discover axion as dark matter. For this, it is necessary to design and manufacture a dipole, composed of 18 coils, that generates a Figure of Merit of 100 T2m 2. The MADMAX coils have several specific features though, as the use of Cable-In-Conduit-Conductor (CICC) with a copper profile that serves as thermal stabilizer and the use of stagnant superfluid helium inside the CICC conduit. With a 28 mm2 helium cross-section and a conductor of several hundred meters before reaching the helium bath, the quench dynamics appear then as a challenge of the design phase. To experimentally investigate the quench propagation in the MADMAX coils, we designed a MADMAX-like solenoidal prototype based on numerical simulations made with THEA® called MACQU (MAdmax Coil for Quench Understanding). This numerical study allowed analysing the physics behind the quench phenomenon and define the relevant current range for the experimental quench studies. Nevertheless, as THEA® has never been used for a CICC filled with superfluid helium, the results will have to be benchmarked by the quench testing campaign on MACQU. The different calculations made with THEA® show that the quench propagation is divided into two different phases: after the initiation, the propagation is at a constant speed of around 5 m/s, followed by an acceleration phase where the propagation speed reaches 40 m/s, at 17 kA. Among the different possible phenomena, we have found that the friction forces term, as defined in the THEA code, are responsible for this two-phase propagation because they initiate the pre-heating of the magnet before the quench, reducing then the local temperature margin. [ABSTRACT FROM AUTHOR]