Optimal Design and Implementation of High-Stability and Long Flat-Top Magnetic Field System Based on Invasive Coil

High stability and long duration flat-top pulsed magnetic field (FTPMF) is crucial for scientific applications such as nuclear magnetic resonance and terahertz gyrotron. However, existing solutions face challenges in balancing high stability with extended flat-top durations, primarily due to magnetic field ripples and thermal limitations. This article proposes a magnetic field compensation circuit aimed at enhancing the stability and duration of FTPMF. This circuit features an invasive coil driven by a high-precision current control circuit, placed at the magnet’s center. The compensation circuit is isolated from the main power circuit, reducing voltage stress on devices and enhancing reliability. Additionally, the use of dual-pole compensation current mitigates heating in both the devices and coil, extending the flat-top duration. Furthermore, a hybrid PIR-PD control strategy is proposed. Its control loop provides higher gain at the magnetic field ripple frequency to achieve precise magnetic compensation and introduces a step reference during capacitor commutation to reduce overshoot. Finally, a high-precision magnetic field compensation system with$\boldsymbol{\pm}$300 A/$\boldsymbol{\pm}$0.58 T was developed, and experiments were conducted on the capacitor-magnet, achieving a flat-top magnetic field of 20 T/105 ms/187 ppm. The experiment results show that the proposed design increase the flat-top duration by 98.1% and stability by 54.5%.