REBCO micro magnets, small enough to fit in the palm of your hand, have been developed by scientists to rival some of the strongest magnets in the world in terms of magnetic strength. Alexander Barnes and his colleagues at ETH Zurich have recently created a superconducting magnet that can match the strength of large magnets while having a diameter of only 3.1 millimeters.
Definition of REBCO Ceramic Material
REBCO (Rare Earth Barium Copper Oxide) is a high-temperature superconducting ceramic material with the chemical formula REBa₂Cu₃O₇₋ₓ (where RE represents rare earth elements such as Yttrium (Y), Gadolinium (Gd), etc.).
Characteristics of REBCO Ceramic Material
| Superconducting Properties: At liquid nitrogen temperatures (77K) and above, it exhibits zero electrical resistance and complete diamagnetism (Meissner effect), with a critical temperature (Tc) typically around 90K, significantly higher than conventional low-temperature superconductors, allowing it to operate under relatively easily achievable liquid nitrogen cooling conditions.
| Ceramic Characteristics: It belongs to the oxide ceramic family, characterized by brittleness, high hardness, and high melting points, but lacks the ductility and machinability of metals, making it impossible to fabricate wires or tapes directly through traditional metalworking methods.
| Layered Structure: The crystal structure is layered, with superconducting current primarily flowing in the copper-oxide (CuO₂) planes, exhibiting strong anisotropy, meaning the superconducting properties significantly differ in different directions.
Reasons for the High Magnetic Field Strength of REBCO Micro Magnets
| REBCO exhibits superconducting properties at liquid nitrogen temperatures (around -196°C) or lower, with zero resistance. When current flows through REBCO materials, it can transmit large currents without losses, providing the foundation for generating strong magnetic fields.
| REBCO is typically made into thin tapes that can be tightly wound into coils. By increasing the number of coil turns or using a multilayer stacked structure (such as “pancake” coils), current can be concentrated within a limited volume, enhancing magnetic field strength. Additionally, using an uninsulated winding technique to eliminate the insulation layer between coil turns allows for a more compact current path, further increasing current density and magnetic field strength.
Performance of REBCO Micro Magnets
Barnes’ team designed two or four flat pancake-shaped REBCO coils that can generate magnetic fields of 38 teslas and 42 teslas, respectively. In comparison, the magnetic field strength of a refrigerator magnet is typically less than 0.01 tesla. Currently, two magnets producing the world’s strongest steady-state magnetic fields reach up to approximately 45 teslas, but weigh several tons and require up to 30 megawatts of power. In contrast, magnets made from REBCO can be smaller than a palm and require less than 1 watt of power.
Potential Applications of REBCO Micro Magnets
| Magnetic Confinement Fusion: In nuclear fusion devices such as tokamaks, REBCO magnets can generate magnetic fields exceeding 10 teslas, critical for confining and stabilizing plasma at temperatures exceeding millions of degrees Celsius, making it a key technology for achieving controlled nuclear fusion. Compared to traditional low-temperature superconductors, REBCO can operate in the liquid nitrogen temperature range (77K), significantly reducing cooling costs while maintaining high current density at high field strengths, suitable for compact fusion reactor designs.
| Particle Accelerators: In particle accelerators, REBCO micro magnets are used to produce strong magnetic fields for guiding and controlling the trajectories of particle beams, improving acceleration efficiency and experimental precision. The high magnetic field strength and stability of REBCO micro magnets make them highly suitable for high-energy physics experiments, such as upgrades to the Large Hadron Collider (LHC) or new accelerator designs.
Challenges Facing REBCO Micro Magnets
Before REBCO micro magnets are widely applied, several challenges remain—such as the uniformity of the magnetic fields attained and how to manage and control the electromagnetic properties of these coils.
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Image Source: Gstatic & Microphotonics & Iopscience & Passive-components & Rs-online & Springernature & Symmetrymagazine
