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

The study addresses how to create a practical ground-based low-gravity simulator with a much larger and more uniform functional volume than conventional magnetic levitation-based simulators (MLSs). Reduced gravity affects biological systems (e.g., cell growth and astronaut health), fluid dynamics (e.g., sloshing, drop oscillations, cavitation, boiling), and materials processing, necessitating systematic research. Existing microgravity platforms (drop towers, parabolic flights, sounding rockets) offer only short durations, while rotational simulators do not produce true low gravity and may introduce unwanted forces and flows. MLSs enable adjustable gravity and long operation but suffer from highly non-uniform force fields, yielding tiny usable volumes (typically a few µL) and often large power consumption when resistive magnets are used. The research question is whether a new MLS architecture can deliver an unprecedentedly large, isotropic low-force functional volume while remaining practical using superconducting technology, and whether it can emulate reduced gravities (e.g., Martian gravity) over large volumes.

Prior work has shown microgravity’s impacts on biology (e.g., gene expression, physiology, bone loss) and on physical processes like cryogenic propellant sloshing, drop oscillations, cavitation, and boiling heat transfer. Spaceflight provides ideal microgravity but is constrained by cost and payload limits. Ground-based platforms such as drop towers, parabolic flights, sounding rockets, and suborbital flights offer seconds to minutes of microgravity. Rotational systems (clinostats, rotating wall vessels, random positioning machines) provide time-averaged gravity vectors but can introduce centrifugal forces and flows and do not replicate true low gravity. Diamagnetic levitation of materials and organisms has been demonstrated, with no evidence of harmful cumulative field effects at high static fields. Conventional solenoid MLSs are limited by non-uniform force fields and high energy demands (e.g., megawatt-level power for resistive magnets). Some efforts have explored shaping magnetic sources or topology optimization to improve levitation stability, but large, uniform functional volumes have remained elusive. Advances in superconducting magnet technology (including uniform high fields >20 T and all-superconducting 32 T magnets) and the classic Maxwell gradient coil concept provide a path to generate both strong uniform fields and uniform gradients.

Theory: For a small sample of volume ΔV in a magnetic field B(r), the magnetic energy change is ΔEB = −χ B^2(r) ΔV / [2 μ0 (1 + χ)]. Including gravity, the specific potential energy is E(r) = −χ B^2(r)/[2 μ0 (1 + χ)] + ρ g z, producing a force density F = χ/(μ0 (1 + χ)) (∇B) B − ρ g ez. Levitation occurs where the magnetic field-gradient force balances gravity and E has a local minimum. Water at ambient conditions (χ = −9.1×10^−6, ρ = 1000 kg/m^3) is used as the reference sample. Baseline solenoid analysis: A finite solenoid (diameter D = 8 cm, height 3D/2) is modeled. The magnetic field B(r) for a solenoid with turn-current NI is computed via known Biot–Savart-based formulas for finite solenoids. From E(r), the trapping region (local minima of E) and the low-force region (net acceleration < 0.01 g) are identified; their overlap defines the functional volume V1%. Gradient-field MLS concept: To enlarge and isotropize the functional volume, a strong uniform base field B0 is superimposed with a weaker, approximately linearly varying field B1(r) with near-constant gradient, produced by a gradient-field Maxwell coil: two identical coaxial loops of diameter D, separated by 3D/2, with opposite current directions. This yields an approximately uniform total field with nearly constant gradient in the central region. Field calculations: B1(r) from the Maxwell coil is computed via the Biot–Savart law, decomposed into axial and radial components with axial symmetry. The total field is B(r) = B0 + B1(r). E(r), trap and low-force regions, and V1% are evaluated as above. Optimization: For a given B0, the loop current I is varied to maximize V1% (denoted Vopt). Then B0 is varied to find the overall maximum functional volume V and corresponding optimal I and B0. Size scaling: The above optimization is repeated for coil diameters D from 6 cm to 14 cm to assess scaling of V, I, and B0. Practical MLS design: A realizable configuration uses a 24 T superconducting magnet (120 mm bore) to generate B0 and four sets of gradient-field Maxwell coils built from REBCO superconducting pancake rings (each ring: 94 turns of 4 mm wide, 0.043 mm thick tape; cross-section ~4 mm × 4 mm). Pancake rings are arranged along the diagonal lines of a Maxwell coil with average diameter ~8 cm, providing B1 with minimal deviation from the ideal gradient coil. The main magnet is liquid-helium cooled; the compact REBCO coil set is conduction-cooled by a 4 K pulse-tube cryocooler within a shielded vacuum housing. A room-temperature center bore up to ~6 cm enables sample access. Operating current of ~290 A per REBCO tape yields total turn-current NI = 4 × 94 × 290 A ≈ 109 kA; REBCO critical currents of ~700 A at 30 T support safe operation. Simulations for the practical geometry repeat the optimization to evaluate V1%. Reduced gravity emulation: By lowering NI, the system can partially cancel Earth’s gravity to emulate Martian gravity gM = 0.38 g. The effective gravity uniformity regions (within 1% and 5% of gM) are computed, and the functional volume VM (within 5% of gM) is optimized versus NI and B0. Numerical implementation: Fields are computed in the r–z plane exploiting axial symmetry using MATLAB. Computational domains match those shown in figures, discretized with Δr = Δz = 10 µm, providing converged results. Water properties at ambient conditions are assumed, but methods are general to other materials.

• Conventional 8 cm diameter solenoid MLS: A trapping region appears above a threshold NI ≈ 520 kA. V1% remains only a few µL at lower NI and reaches a peak near NI = 607.5 kA, but the functional volume is highly anisotropic and impractical despite the enhancement; required turn-currents are extremely large.
• Proposed gradient-field MLS (ideal Maxwell coil in uniform B0): For D = 8 cm, B0 = 24 T, and I ≈ 112.6 kA (turn-current per loop), the functional volume V1% = 4004 µL with a much more isotropic shape. Optimizing over I for each B0 gives Vopt; varying B0 shows an optimum around B0 ≈ 24.7 T with overall maximum functional volume V ≈ 4050 µL.
• Size scaling: Increasing D from 6 cm to 14 cm increases V from ~1500 µL to >21,000 µL (over 14×). The optimal loop current I and base field B0 scale approximately linearly with D by factors of ~4 and ~1.3, respectively.
• Practical REBCO-based MLS: Using four sets of REBCO pancake coils (each ring 94 turns; 290 A per tape; total NI ≈ 109 kA) in a 24 T, 120 mm bore superconducting magnet, simulations show Vopt ≈ 3450 µL at B0 = 24 T with NI ≈ 108.37 kA. Performance is close to the ideal Maxwell coil case, indicating minimal degradation from practical coil geometry.
• Martian gravity emulation: With B0 = 24 T and NI = 66.55 kA, the region where effective gravity is within 5% of gM has VM ≈ 22.5 × 10^3 µL. The peak VM increases rapidly with B0 and then saturates for B0 ≳ 24 T, so higher B0 yields only marginal gains.

The work addresses the central limitation of MLSs—non-uniform force fields that restrict usable functional volume—by superimposing a strong, highly uniform superconducting base field with a Maxwell coil’s uniform gradient. This combination yields a nearly constant magnetic force balancing gravity over an unprecedentedly large, isotropic volume, enabling more representative low-gravity conditions for larger samples and extended experiments. Compared to conventional solenoid MLSs, the proposed design expands V1% by roughly three orders of magnitude and significantly improves isotropy, mitigating internal stress gradients in samples. The use of superconducting technology reduces power consumption and supports stable long-duration operation, overcoming energy and thermal issues associated with resistive magnets. The practical REBCO implementation demonstrates that required currents and fields are achievable with existing materials and magnet systems, and that performance remains robust despite geometric deviations from the ideal coil. Furthermore, by tuning current and field, the same platform can emulate partial gravities (e.g., Mars), achieving tens of milliliters of uniform reduced-gravity volume suitable for small organisms or plants. These results directly support the research goal of creating a versatile, scalable, and energy-efficient ground-based low-gravity simulator for broad scientific applications.

An innovative MLS architecture combining a uniform superconducting base field with a gradient-field Maxwell coil achieves an unprecedented, isotropic 0.01 g functional volume of up to ~4 mL for an 8 cm coil, far exceeding conventional solenoid MLSs. The approach scales favorably with coil size, reaching >21 mL for a 14 cm diameter, and can be realized using REBCO superconducting coils in existing high-field magnets with minimal energy consumption. The same system can emulate Martian gravity with functional volumes exceeding 22 mL. This design offers a practical path to long-duration, adjustable low-gravity experiments for biological, fluidic, and materials research. Future work could include experimental validation of the practical coil system, extension to larger bore and higher-field magnets to further increase volume, assessment with different sample materials and configurations, and integration of in situ diagnostics and environmental controls for comprehensive low-gravity studies.

The study is based on numerical analyses without experimental validation of the full MLS system. The optimal performance requires access to high, uniform superconducting magnetic fields (~24–25 T) and specialized cryogenic infrastructure, which may limit accessibility and increase system complexity and cost. Achieving the specified currents and coil geometries necessitates precision REBCO coil fabrication and cryogenic operation. Reported functional volumes and uniformity depend on assumed material properties (water at ambient conditions) and idealized alignment; practical tolerances, vibrations, and heterogeneous samples could reduce performance. The room-temperature bore size (~6 cm) constrains maximum sample dimensions in the demonstrated practical configuration.