Power Supply of High-Voltage Power Supply for Electron Microscope to Superconducting Quantum Interference Device (SQUID)

1. Application Background and Technical Requirements
Electron microscopes (such as Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM)) are core equipment for material microstructure characterization, and their resolution is directly related to the stability of accelerating voltage. As an ultra-high-sensitivity magnetic detection device, the Superconducting Quantum Interference Device (SQUID) is often combined with electron microscopes to study the correlation between "microstructure and magnetic properties" of quantum materials. When the two work together, the power supply system must meet both the high-voltage stability of the electron microscope and the ultra-low noise requirement of the SQUID. If the accelerating voltage of the electron microscope fluctuates, it will cause the energy deviation of the electron beam and reduce the imaging resolution; if the SQUID is disturbed by power supply noise, it will directly affect the magnetic moment detection accuracy (the sensitivity up to 10^-15 T is extremely vulnerable to electromagnetic noise).
2. Key Technical Design of Power Supply System
1.Control of Core Indicators of Electron Microscope High-Voltage Power Supply
To meet the adjustable accelerating voltage requirement of 10-300kV for the electron microscope, the power supply must achieve a voltage stability of 0.01%/h and control the ripple voltage below 5μV. The "high-frequency inversion + multi-stage voltage doubling" topology is adopted, and the switching frequency is increased to 100kHz by using silicon carbide (SiC) power devices to reduce the output voltage ripple. At the same time, a PID closed-loop feedback based on a high-precision voltage sensor (error < 0.001%) is introduced to adjust the on-time of power devices in real time, offsetting the voltage deviation caused by power grid fluctuations and load changes.
1.Ultra-Low Noise Power Supply Scheme for SQUID
The SQUID works in a liquid helium low-temperature environment (4.2K) and requires a stable DC bias current at the nA level. The power supply system adopts the "linear voltage stabilization + multi-stage filtering" design: the front stage suppresses 50Hz power frequency interference through LC filtering, the middle stage uses a low-noise operational amplifier to form a linear voltage stabilizer, and the output voltage ripple is reduced to 2μV; the final stage adds a magnetic core filter inductor and a copper foil shielding layer to block high-frequency electromagnetic radiation (such as noise generated by the motor of the electron microscope vacuum system). In addition, the power supply, electron microscope, and SQUID adopt a single-point grounding design to avoid additional noise caused by ground loops.
3. Practical Application Effects
In the quantum dot material characterization experiment, the power supply system improved the imaging resolution of the electron microscope from 0.2nm to 0.15nm, meeting the needs of atomic-level microstructure observation; the detection sensitivity of the SQUID to the magnetic moment of quantum dots was increased by 20%, successfully capturing the magnetic moment reversal process of a single quantum dot. This scheme provides a stable and reliable power supply guarantee for the "electron microscope-SQUID" combined system, promoting the progress of multi-dimensional characteristic research of quantum materials.