A theoretic model of upstream dielectric multipactor in TEM microwaves, taking both the rf electric field and rf magnetic field into account, is proposed. In this theory, the growth rate of the window multipactor is predicted. The multipactor is approximately independent of the rf frequency, and much more serious than Kishek's model (1998 Phys. Rev. Lett. 80 193) in the regions of weak dc electric fields and strong rf electric fields. Then, an electromagnetic Particle-In-Cell method is carried out to simulate the multipactor in TEM microwaves. Simulation results show a good agreement with the theoretical results. Furthermore, the lower boundary of multipactor is derived analytically, while there is no upper boundary any more. Finally, a gradually transition between Kishek's model and our model is found by examining microwaves of TE modes. It is found that the upper boundary reappears when the rf frequency of TE modes trends to the cutoff frequency of waveguide.

Particle-in-cell/Monte Carlo simulations of a low-pressure capacitively coupled radio-frequency discharge: Effect of adding H 2 to an Ar discharge J. Appl. Phys. 93, 5025 (2003); 10.1063/1.1563820Particle-in-cell/Monte Carlo simulation of a capacitively coupled radio frequency Ar / CF 4 discharge: Effect of gas composition J. Appl. Phys. 93, 2369 (2003); 10.1063/1.1542920Axisymmetrical particle-in-cell/Monte Carlo simulation of narrow gap planar magnetron plasmas. II. Radio frequency-driven discharge

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We present a fusion-oriented pulsed power module M-50, which is based on the linear transformer driver (LTD) and magnetically insulated inductive voltage adder (MIVA) technologies. The module M-50, which consists of 50 identical LTD cavities connected in series, is one of the 60 modules of a fusion-scale pulsed power facility. M-50 is a comprehensive test bed for LTD integration and engineering validation. Each cavity consists of 32 bricks and has an output capability of 90 kV=1.0 MA=120 ns to the matched load. The output power of the 50 cavities is added with a MIVA, whose operation impedance is approximately matched to both source and load. Therefore, it has a nominal output capability of 4.5 MV=1.0 MA=120 ns to 4.5 Ω resistive load. The module is divided into five groups, and each group has ten cavities in series. The inner stalk of the MIVA is divided into five main straight segments. Conical transitions are employed to connect adjacent straight segments. The output end of M-50 is shrunk and connected a ring-cathode diode, whose cathode and anode radii are identical to those of a 12-m-long transmission line in the fusion facility. In this paper, the general concept of the fusion accelerator, the physical design, engineering design and development progress of M-50 are described for the first time.

By using the electromagnetic Particle-In-Cell method, the multipactor of the dielectric window on the upstream side is observed directly even without presetting extra normal electric fields and compared to that on the downstream side. This paper shows: First, with the initial emission of electrons to provide extra normal electric fields, the secondary electron avalanche is much faster than that on the downstream side. Second, even without the initial emission of electron to provide extra normal electric fields, the secondary electron avalanche occurs on the upstream side, while it is nowhere to be found on the downstream side.