Research on the Performance Analysis andPrecise Measurement of High-Performance Magnetic Shielding.

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Experimental demonstrations in ultra-low magnetic field research has reached spectacular levels recently. With fields below 0.3 nT and gradients below 0.1 nT/m, with fT stability of hundreds of seconds, these developments will enable a variety of new research opportunities and are crucial to achieve the next level of precision in various fields of research, including fundamental and applied physics, geophysics, bio-medical, security and space applications. Walk-in magnetically shielded rooms (MSRs), like the user facility BMSR-2 at the Physikalisch-Technische Bundesanstalt (PTB), already show the feasibility of large- scale high quality environments. A decade later, the experimental facility at the Technische Universitat München (TUM) already set a new standard for shielding performance. With a continued improvement in modeling of the underlying physics, very recently an even further improved experiment of Harbin Institute of Technology (HIT) and TUM could demonstrate even further progress, pointing out the need for a structured and trans-national joint activity of these currently institutions to achieve the ultimate performance of magnetic shields with proper theoretical and numerical understanding, together with the development of suitable probing methods to be able to actually perform measurements at this level routinely. In this project, the methods to predict and measure shielding factor will be improved: a quantitative calculation method will be established to simulate the equilibration process of shields and also the static fields drift inside shields due to magnetization by external and internal fields. Phenomena like spontaneous magnetization jumps of the very weak field inside shields will be analyzed considering spurious effects like temperature changes and vibrations. Also, noise originating from magnetic shielding itself will be investigated. With improved understandings of the very weak field inside the shields, it will then be possible to enhance homogeneity and stability of applied fields inside shields, based on optimized coils design considering all possible coupling effects. Moreover, the measured signals will be disentangled from the damped external disturbances, the influences from shields, the target field from coils, and the interactions from various magnetometers. The theoretical analysis will be and demonstrated with experiments in magnetic shields in TUM and HIT. The findings also serve to characterize and optimize the performance of the new large and strong magnetic shielding facility constructed at HIT to set a new benchmark in the field, supporting the next level of fundamental physics experiments and other research at low fields.