高空核电磁脉冲（HEMP）能够干扰或毁伤数百公里范围的电力电子系统。目前，HEMP环境研究多聚焦于早期E1，中期E2由于持续时间长、辐射源项成分复杂，数值模拟难度大，相关研究鲜有报道。论文针对早中期HEMP环境，研究辐射源项、电流源项和电磁场物理模型与计算方法，建立适用于E1和E2环境一体化数值模拟的方法和程序，实现了具有典型特征的E2环境模拟，系统研究了早中期HEMP环境特征，可为电力电子系统的电磁脉冲防护和毁伤效应评估提供可靠的环境参数。论文主要工作和成果如下：1. 基于早中期HEMP产生机理分析，采用γ射线单次散射解析模型和粒子输运蒙特卡罗（MC）方法，建立早中期HEMP的γ辐射源项计算方法，分析获得了典型高空核爆炸在HEMP源区的γ成分及方向、能谱和时间谱特征。针对γ和中子在大空间、长时间输运时MC方法模拟计算效率低、精度差问题，提出点通量角分布统计方法，并结合源偏倚、几何与时间分裂等MC减方差技术，实现散射γ和中子次级γ的能量-角度-时间联合谱的高精度高效模拟。2. 基于E2辐射源项具有复杂能谱和角分布，且离子电导率占主导的特征，建立适用于E1和E2一体化模拟的电流源项计算模型和方法，获得了具有γ能谱和角分布特征的康普顿电流，以及考虑离子电导率的传导电流。通过对能量和角度的分群处理，并结合康普顿散射和地磁场模型，实现了不同能群和不同角度反冲电子对电流贡献及康普顿电流密度时空分布的计算；同时通过修正电化学参数和加入离子电导率模型，考虑非平衡效应的影响和离子电导率的贡献。3. 在实现基于高频近似的一维求解基础上，基于E2场特征，建立了适用于早中期HEMP模拟的二维电磁场计算模型和方法，解决了一维模拟无法考虑视距方向以外电流源和电磁场影响的不足。推导了旋转椭球-双曲正交坐标系下的二维麦克斯韦方程组，引入推迟时间变换解决大空间模拟计算效率低的问题，使百公里级的大空间电磁场求解能够取较大的空间步长，且空间步长不受时间步长的限制。采用隐式差分求解方程组的方法，解决推迟时间变换带来的数值不稳定性问题。4. 基于辐射源项、电流源项及电磁场物理模型与计算方法，建立早中期HEMP环境的一体化数值模拟方法，模拟得到E2的典型特征及规律。编程计算研究了不同高空核爆炸条件下早中期HEMP环境，分析了直达、散射和中子次级γ射线对HEMP的影响，提取了E2环境的特征量，给出了其典型波形、频谱和场强分布特征，得到了HEMP特征量随爆高和爆炸威力的变化规律。

High-altitude electromagnetic pulses (HEMP) can disturb or damage electronic and power systems in a large region whose width can be thousands of kilometers. At present, most researches on HEMP simulation focus on the early-time E1, while few researches on the intermediate-time E2 are reported due to the difficulty in numerical simulation caused by its long duration and complex radiation source components. In this dissertation, based on the physical models and calculation methods of radiation source, current source, and electromagnetic field, the method and program of integrated numerical simulation of E1 and E2 are developed. The simulation results have typical characteristics of E2, and the characteristics of HEMP environment are systematically analyzed. The reliable environmental parameters are provided for researches on HEMP interactions with electronic and power systems. The main contributions of the dissertation are as follows:1. Based on the analysis of generation mechanism of E1 and E2, an analytical model of single-scattering γ and the Monte Carlo (MC) method of particle transport are used to establish the calculation method of radiation sources of E1 and E2, and the composition, direction, energy spectrum and time spectrum of γ in the HEMP source region by high altitude nuclear explosions are obtained and analyzed. In order to improve the efficiency and accuracy of the MC simulation of large-space and long-time transport, a statistical method of angular distribution of point flux is proposed, and the variance reduction methods, such as source bias, geometry and time splitting, are used. The energy-angle-time joint spectrum of scattered γ and neutron-secondary γ is simulated with high precision and high efficiency.2. Based on the complex energy spectrum and angular distribution of E2 radiation source and dominance of ion conductivity in E2 conductivity, the calculation method of current sources for E1 and E2 integrated simulation is presented. The obtained Compton current can reflect the characteristics of γ energy spectrum and angular distribution, and the conduction current can reflect the influence of ion conductivity. By grouping electrons according to energy and angle, combined with Compton scattering theory and geomagnetic field model, the contributions of the recoil electrons in different energy groups and angle groups to current are considered, and the spatial-temporal distribution of Compton current density is obtained. By modifying the ionization equilibrium equation and adding the ion conductivity model, the influence of ion conductivity and non-equilibrium effect is presented.3. Besides the 1D method based on high frequency approximation, according to the characteristics of E2 field, a 2D calculation method of electromagnetic field suitable for E1 and E2 simulations is established, solving the problem that the 1D method can not reflect the influence of the current source and electromagnetic field outside the line of sight. The 2D Maxwell equations are derived in the prolate spheroidal coordinate system, and the retarded time is introduced to improve the efficiency in large-space HEMP simulation for the reasons that the spatial discretization can be larger and the time step size is not limited by the space step size in retarded-time simulation. The implicit difference method is used to solve the problem of numerical instability caused by retarded time transformation.4. Based on the physical models and calculation methods of the radiation source, current source, and electromagnetic field, the integrated numerical simulation method of E1 and E2 environment is developed, and the typical characteristics and laws of E2 are obtained by simulation. The influences of direct γ, scattered γ and neutron-secondary γ on HEMP are analyzed. The characteristic quantities of E2 environment are extracted, and typical waveforms, spectrums and field strength distributions are given. The variation laws of HEMP characteristic quantities with explosion height and explosion yield are obtained.