A magnetic levitation based low-gravity simulator with an unprecedented large functional volume

Reduced gravity significantly impacts biological systems, fluid dynamics, and material growth. Weightlessness can hinder cell growth, cause cellular stress and bone loss in astronauts, and affect fluid dynamics in spacecraft. In material science, reduced gravity offers potential for tissue and crystal growth and materials processing. Spaceflight experiments provide ideal microgravity but are limited by high cost, small payload size, and constraints on experimental design. Ground-based simulators offer alternatives. Free-fall simulators like drop towers, parabolic aircraft, and sounding rockets provide near-zero gravity but only for short durations. Rotational facilities such as clinostats and rotating wall vessels produce a time-averaged small gravity vector but not a genuine low-gravity environment. Magnetic levitation-based simulators (MLS) use magnetic field-gradient levitation of diamagnetic materials, offering advantages including low cost, adjustable gravity, and practically unlimited operation time. However, a major drawback is the highly non-uniform force field, limiting the functional volume (V1%, where acceleration <1% of Earth's gravity) to a few microliters. This paper introduces a novel MLS design to overcome this limitation.

The paper reviews existing low-gravity simulation methods, highlighting their limitations. Free-fall methods provide short durations, while rotational methods don't produce true microgravity. Previous MLS designs are discussed, noting their small functional volume due to non-uniform force fields. The authors cite studies demonstrating magnetic levitation of various diamagnetic materials, including living organisms, emphasizing the safety and advantages of MLS. Existing research on improving MLS functional volume is mentioned, but a lack of significant progress is highlighted. The high energy consumption of conventional resistive solenoid MLSs is also discussed as a concern.

The paper begins by explaining the fundamentals of magnetic levitation using a solenoid magnet. The mechanism involves balancing the field-gradient force with the gravitational force. Equations for potential energy and force per unit volume are presented, and the analysis focuses on water as a sample material due to its widespread use in low-gravity research and its presence in living cells. A solenoid with specific dimensions (diameter D = 8 cm, height 3D/2) is modeled to calculate the potential energy and force fields. The functional volume V1% is defined as the overlapping region where the net force results in acceleration <0.01g. The analysis shows that V1% is small and anisotropic for conventional solenoid MLSs, even at high currents. To achieve a larger and more uniform field-gradient force, the authors propose a new MLS design that superimposes a strong uniform field (B0) produced by a superconducting magnet with a weaker field (B1) generated by a gradient-field Maxwell coil. The B1 field is calculated using the Biot-Savart law. The optimization analysis involves varying the coil current and the base field strength to maximize V1%. The analysis shows a peak V1% of over 4000 µL can be achieved with an 8 cm diameter coil and considers larger coil diameters, showing a significant increase in V1% with increasing coil size. The paper then discusses a practical implementation of the design using REBCO superconducting tapes. The design incorporates four sets of gradient-field Maxwell coils made of REBCO pancake rings, housed within a 24-T superconducting magnet. Calculations are repeated for this practical design, showing a peak V1% of ~3450 µL, demonstrating the feasibility of the proposed design. Finally, the authors demonstrate the capability of the MLS to simulate Martian gravity by reducing the current. The analysis shows a large functional volume (VM) where gravity varies within a few percent of gm.

The key finding is the design and analysis of a novel magnetic levitation-based low-gravity simulator (MLS) that significantly increases the functional volume compared to conventional designs. A conventional solenoid MLS typically has a functional volume (V1%) of only a few microliters. The new design, which uses a superconducting magnet in conjunction with a gradient-field Maxwell coil, achieves a V1% exceeding 4000 µL (for near-zero gravity simulation). Optimization analysis revealed an optimum base field strength and coil current to maximize the functional volume. The study further demonstrated that increasing the coil diameter increases the functional volume dramatically. Using a practical design with REBCO superconducting tapes, the authors showed that a similar functional volume could be achieved in a real-world setup. Simulations showed the ability to emulate Martian gravity with a functional volume exceeding 20,000 µL. This represents a substantial improvement in the functional volume of MLS, making it suitable for experiments involving larger samples. The use of superconducting materials minimizes energy consumption, ensuring long-term operation.

The results demonstrate the successful design of a magnetic levitation-based low-gravity simulator with a significantly larger functional volume than previously possible. This addresses the limitation of conventional MLS designs, making them more practical for a broader range of experiments. The isotropic nature of the functional volume is a significant advantage, allowing for more flexible experimental setups. The use of readily available superconducting materials like REBCO makes the design feasible for implementation. The ability to simulate Martian gravity is particularly valuable for research related to future space exploration. The achieved functional volume is large enough to accommodate small animals or plants, opening up possibilities for biological studies under simulated low-gravity conditions. The findings significantly advance the capabilities of ground-based low-gravity simulation, providing a valuable tool for various scientific disciplines.

This research presents a novel magnetic levitation-based low-gravity simulator with an unprecedentedly large and isotropic functional volume, exceeding previous designs by several orders of magnitude. The use of superconducting magnets ensures low energy consumption and stable long-term operation. The ability to accurately simulate both near-zero and reduced gravity (like that on Mars) opens new avenues for diverse low-gravity research, including studies on biological systems and fluid dynamics. Future research could explore further optimizations of the coil design, investigate the effects of different sample materials, and explore applications in various scientific fields.

The simulations presented in the paper rely on theoretical models and numerical calculations. Although the authors demonstrated the feasibility of building a real-world device using currently available technology, there may be practical challenges and unforeseen issues during the actual construction and operation of such a device. The analysis focused primarily on water as a sample, and further study could extend the findings to other materials with varying magnetic susceptibilities and densities. Additionally, the simulation assumes ideal conditions; small deviations from these conditions may affect the functional volume.