Precision Ultra-low Magnetic Field Measurement Device

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A high-performance walk-in sized magnetically shielded enclosure is being requested, to be used for precision measurements in fundamental physics and applications. Its main features are a magnetic background field of < 0.1 nT and a gradient of 0.1 nT/m in the central 1 m3. This is essential to access new experimental terrain in several disciplines. Commercial large-scale shielded enclosures are limited to approximately 1 nT residual fields and gradients of nT/m, comparable to the world’s largest shield at the Physikalisch-Technische Bundesanstalt. The chair for ‘Precision Measurements at Extreme Conditions’ at TU München gained significant experience over the last 13 years in the design of extremely shielded environments, triggered by the requirements for the search for the electric dipole moment of the neutron, an experiment in fundamental physics. For this, a field of < 0.1 nT and a gradient of < 0.1 nT/m over a m3 - sized volume was demonstrated in two installations only with passive shielding measures with < 1 fT noise. Key to the performance is (i) the optimization of the orientation of magnetic domains inside the wall material, a magnetizable alloy often called mumetal and (ii) measures for accurate and precise sensing. The shielded environment proposed here consists of an enclosure of nested shells of a highly permeable magnetizable material and a highly conducting shell, coils for generating magnetic fields and for magnetic equilibration; a pneumatic door with 1.15 m width and 2 m height for access for various experiments and people; a non-magnetic 5-axes robot, fluxgate- and atomic magnetometers for field and gradient characterization to ensure that the conditions can be characterized, optimized, and reproduced. The new facility serves measurements in different disciplines of research, to enable technology and knowledge transfer between fundamental physics and applications in physics, medicine and neuroscience. It is planned to share the facility for different research projects through a versatile concept. Planned activities are (i) precision spin clock measurements to probe the laws of nature at extreme precision (Electric Dipole Moment and Axion-like particle searches) and the development of novel experiments; (ii) development of quantum- and nano/micro-fabricated MEMS based (quantum) magnetometers; (iii) technology development for magnetic fetal heart imaging (fetal MCG) in combination with complementary diagnostic methods like ultrasound imaging and (iv) investigation of the brain’s magnetic signals (MEG) in connection to motion and movement of the body. All these activities share the need for extremely low magnetic field gradients and use similar techniques. We will use the new facility to continuously advance low magnetic field technology with dedicated staff personnel to ensure proper operation of the facility and to provide access for all envisaged applications.