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In order to guide the design of effective shielding layer to reduce the risk of dielectric electrostatic discharge in high-power and high-voltage spacecraft under GEO environment, it is necessary to explore the influence of grounding method and the joint action of high working voltage and deposited charge on the deep dielectric charging characteristics. In this article, based on the FLUMIC3 model, the electron flux of GEO environment is calculated, and an assessment method for the dielectric electrostatic discharge risk is established by combining Geant4 and a finite element method. Then, this method is used to calculate and analyze the influence of the grounding method and operating voltage on the electric field distribution of the polyimide under different shielding thicknesses. The results show that increasing the shielding thickness and grounding area can effectively reduce the polyimide internal electric field, and the aluminum shielding safety threshold required under the worst conditions is 2.920 mm; the influence of the working voltage mainly depends on the application method and the voltage value. During the working voltage increase from 100 to 5000 V, assume the working voltage ( $V_{s}$ ) is applied to one side of the polyimide sample, when the other side is suspended, namely, not grounded (B, $V_{s}$ -S; C, S- $V_{s}$ ), the maximum electric field depends on the deposited charge and it does not change with the working voltage; when the other side of the sample is grounded (A, $V_{s}$ -G; D, G- $V_{s}$ ), the maximum electric field and its distribution are determined by the working voltage and the deposited charge. Within this voltage range, the safety threshold of the aluminum shielding layer needs to reach 4–5 mm. In summary, under high working voltage, the grounding area of the sample can be increased, and the appropriate working conditions can be selected to determine the optimal shielding thickness that can suppress dielectric electrostatic discharge.

The effects of super-Gaussian chirped laser pulse and inhomogeneity of plasma on space distribution and amplitude of wakefield are studied. The different super-Gaussian chirped laser pulse envelopes are used to strike the uniform and various inhomogeneous plasmas. The results show that compared with the unchirped laser pulse, the chirped laser pulse can enhance the wakefield generation, make the bubbles’ structure deformative seriously, reduce the numbers of bubbles in the same longitudinal distance, and enlarge the size of the wakefield bubbles. Besides, the stronger wakefield is generated in inhomogeneous plasma compared with a uniform one. Moreover, the characteristics of the wakefield can be controlled efficiently by the super-Gaussian pulse index. That is, the amplitude and spatial structure of the plasma wakefield can be modulated by the super-Gaussian chirped laser pulse and the inhomogeneity of the plasma.

The surface electric field (SEF) for the quasi-static negative corona discharge in atmospheric pressure air is investigated by the general fluid model which contains the continuity equations of electrons, positive ions, and negative ions coupled with Gauss' equation, considering the secondary electron emission. The SEF for the monopolar ion flow, which assumes that the whole interelectrode gap is filled with monopolar ions, is also investigated by the simplified model under the same boundary conditions at the anode. The results predict that the SEF remains constant at the onset value for both the negative corona plasma and the monopolar ion flow under a low corona current. With the increase of the corona current, the SEF is slightly strengthened for the negative corona plasma and significantly weakened for the monopolar ion flow in a wide range of conductor radii. The results for the monopolar ion flow are consistent with those deduced from the experimental data in the literature.

A nonlinear self-consistent simulation code is employed to investigate the behavior of the outer-slotted-coaxial waveguide gyrotron traveling-wave amplifier (gyro-TWA). The influences of the velocity pitch, frequency, and input power of the electron beam on efficiency, output power, and saturated gain are simulated and discussed in detail. It is predicted that this design with 95 GHz, TE/sub 3,1/ will yield a peak output power of 264.3 KW, a peak efficiency of 33.7%, and saturated gain of 44.2 dB.

A coaxial-waveguide gyrotron-traveling wave amplifier is proposed, which may be suitable for the operation in the spectrum of the short millimeter and submillimeter waves with good mode selectivity, high power, and ultrahigh gain. An example is presented in terms of the linear gyrokinetics and nonlinear simulations. Theoretical results show that tens of kilowatts with ultrahigh gain up to 67 dB might be achieved for the operation of the coaxial-waveguide mode TE/sub 28,16/ in the fundamental cyclotron harmonic at the frequency of 140 GHz. The power enhancement by a tapered magnetic field is discussed.