We report the design and initial experimental results of an 800-GHz second harmonic gyrotron prototype, in which a 15-T pulsed magnet is applied. This gyrotron prototype is developed at the Wuhan National High Magnetic Field Center (WHMFC). An in-house software for analyzing and designing terahertz gyrotrons and an experimental research platform are developed. In addition, alignment adjustments, eddy current effects, and radiation tests are discussed. The initial experimental results show that the prototype gyrotron can irradiate ~40 W at fundamental harmonic 383.7-GHz (TE _1,4 ) waves at 14.14 T and a few milliwatts at second harmonic 0.8-THz (TE _8,5 ) waves at 14.86 T.

A triple-coil pulsed magnet aiming at 100 T (Tesla) was designed and tested at the Wuhan National High Magnetic Field Center. The magnet was powered by a 100 MJ pulse generator, a battery bank, and 25 kV capacitor banks in combination. The magnet failed at 83 T, while the whole structure remained intact. The failure process was analyzed by using the recorded waveforms of the voltage and the current, as well as disassembling and dismantling the failed magnet. It shows that the inner coil broke down first, and then the electrical breakdown occurred between the middle and outer coils. The possible reasons were also discussed. The buckling analysis results show that the inner and middle coils would buckle at 71 T and 83 T, respectively, which were consistent with the experimental results. The cross-ply reinforcement method is proposed to enhance the structural stability of high field magnets.

To accurately characterize the effect of the cavity surface roughness on the ohmic loss in gyrotron oscillators, this article proposes a method by using the gradient conductivity (GC) assessment model, in which a derived effective conductivity parameter is used to characterize the surface roughness. The results show that it has higher accuracy than the conventional methods such as the H-B formula, especially in the terahertz frequency band. This model also provides a reasonable explanation for the low-efficiency problem in terahertz gyrotrons, and it is beneficial to promote the design and analysis of gyrotrons.

The risk of damage in high-field pulse magnets is very high, with numerous and intricate factors contributing to potential failures. The buckling of separating layers due to the axial Lorentz force is a critical instability factor in pulsed magnets, yet it has received limited attention in previous studies. After discussing the buckling mechanism, this article utilizes the Donnell theory and a dynamic finite element analysis (FEA) model to thoroughly investigate this buckling phenomenon in pulsed magnets. This in-depth analysis takes into consideration the complex composite structure of the windings and meticulously assesses the influence of the Lorentz force. The simulation results are consistent with experimental data.

The double-stator superconducting brushless machine (DS-SCBM) combines high torque density and excellent static sealing characteristics, as well as advantages in reliability and cost-effectiveness. To ensure the long-term stability of the superconducting magnet and Dewar (SCMD) system, this study evaluates the pressure-bearing capacity and heat leakage from the support frame, selecting appropriate materials and dimensions. Furthermore, a model of the thermal and mechanical fields for the SCMD system is developed using finite element analysis which assesses the impact of various reinforcement structures on the mechanical and thermal properties of the superconducting (SC) magnet. Based on this analysis, the dimensions of the reinforcement structures, Dewars, and vacuum interlayer are optimized. Subsequently, efforts are made to manufacture the designed system and its performance is tested.