Yixiang Hu

Simulation Analysis of Transmission-Line Impedance Transformers With the Gaussian, Exponential, and Linear Impedance Profiles for Pulsed-Power Accelerators

Based on the transmission-line code, a 1-D circuit model for the transmission-line impedance transformer with an arbitrary impedance profile is developed, and the simulation results are compared with those of the existing literatures. By using this model, the power efficiencies and pulse compression ratios of the transformers (with Gaussian, exponential, and linear impedance profiles) were quantified as functions of Ψ (the ratio of the output impedance to the input impedance of the transformers) and Γ (the ratio of the pulsewidth to the one-way transit time of the transformers). The simulation results indicate that the exponential transformers have the maximum power efficiencies and pulse compression ratios. However, in the limit h <; 0.05 (where h is the Gaussian parameter), the Gaussian transformers almost have the same power efficiencies and pulse compression ratios as the exponential ones. Finally, the performances of a radial transformer line in smoothing the arrival time variations in the forward-going power pulses were studied. The simulation results show that, for the cases considered, the rise time (0-1.0) of the output pulse is prolonged by about half of the maximum difference in the time at which the pulses are launched, and the reduction of the peak output power is less than 2% when the maximum difference is 30 ns.

Optimized Design of Azimuthal Transmission Lines for the Cell Driven by Two PFLs in Induction Voltage Adders

In this paper, a full-size 3-D electromagnetic model (without electrons) and an equivalent circuit model of a single cell in magnetically insulated induction voltage adders has been established. The simulation results of these two models agree well with each other. On the basis of these two models, azimuthal transmission lines for a cell driven by two pulse forming lines (PFLs) have been optimized. The optimization process aims at matching the impedance to the feed PFLs, ensuring uniform potential distribution along the insulator-stack, maximizing the symmetric current flow around the bore, and minimizing the waveform distortion of the injected pulse. A formula is presented to estimate the azimuthal impedance and an asymmetric coefficient is also defined to quantify the asymmetric extent of the feed pulses. The profiles of the total four candidate azimuthal lines have been simulated and analyzed. The simulation results indicate a relatively low feed asymmetry for all the four profiles. However, considering the waveform quality of the cell output voltage, the azimuthal line profiles with four points connected or wholly connected to the cathode plate are the most suitable for induction cells with two PFL feeding. And the corresponding coefficients

Circuit Model of Magnetically-Insulated Induction Voltage Adders Based on the Transmission Line Code

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Experimental Study on the Current Loss of MITL With Cathode Made of Different Stainless Steel

are 3.1% and 7.6%, respectively. It is concluded that, when optimizing azimuthal lines for cells with two PFL feeding, the principal consideration should be matching the impedance instead of symmetrizing the current flow.

Experimental and Simulation Studies of a 1-m-Long Magnetically Insulated Transmission Line With 2-cm Anode–Cathode Gap

Based on the transmission line code (TLCODE), a 1-D circuit model used for the analysis of magnetically-insulated induction voltage adders (MIVAs) was developed. Using cells improved from those of the JianGuang-I facility, a 10-stage MIVA was conceptually designed, and its equivalent TLCODE circuit model was described in detail with consideration of the magnetic insulation. To verify the effectiveness of this model, simulation results were compared with those of a PSPICE model (with no electron emission) under both synchronously triggering mode and ideal time-sequence triggering mode. The comparisons show that calculation results of these two models are accord with each other perfectly (within 0.1%). In addition, features of the calculation results were particularly analyzed and verified by the existent literatures. Considering the magnetic-insulation process, the inner stalk of the 10-stage MIVA was designed, and its output parameters were simulated with various electron emission thresholds (150, 200, and 250 kV/cm). Furthermore, qualitative analysis was done to present the models abilities of the magnetic-insulation treatment.

Experimental Study and Electromagnetic Model of a 1-MV Induction Voltage Cavity

Magnetically insulated transmission lines (MITLs) are key components in present high-power generators. In our experiments, the current density flows in the cathode of the MITL are so high that current loss cannot be neglected. At an input current of 0.7-1.4 MA, an experimental study on current loss is performed with austenitic and martensitic stainless steel. An empirical relation between loss current density and input current density was found. For current density around 1 MA/cm, the results show that the loss current density is nearly a power function of the input current density, and the power indices for austenitic and martensite stainless steel are about 4.3 and 3.3, respectively.

Azimuthal Transmission Lines for Inductive Voltage Adders With Four PFLs Driving Simultaneously or Separately

Based on the “QiangGuang-I” facility, a 1-m-long magnetically insulated transmission line (MITL) with a 2-cm anode-cathode gap was designed and experimentally studied. The experimental results show that with the load resistance of 2.07 , current loss along the 1-m-long MITL is negligible, and nearly all of the current loss occurs in the transition from conical disk to coaxial geometry or the output port of the line. At the same time, a 1-D circuit model was developed for the analyses of the MITL on the basis of the transmission-line code. By using this model, the experimental MITL was simulated, and pivotal parameters were estimated. Comparisons indicate that the simulation results agree to 5% within those of the experiments.

Exponential Impedance-Transformer Stalks Used for Magnetically Insulated Induction Voltage Adders

Magnetically insulated induction voltage adders are pulsed-power accelerators widely used in various fields. Preliminary cavity experiments concerning the current uniformity have been done on a prototype induction cavity. The cavity is single-point fed by a 1.0-MV/200-kA/60-ns pulse of Chenguang accelerator. Three different configurations of azimuthal lines are tested. The results indicate that the azimuthal variations of feed currents for all these configurations are less than 40%. And under this extent of nonuniformity, the current distributions slightly affect the cavity output voltage. An electromagnetic (EM) model is proposed for this prototype cavity. The characteristics of cavity output responses and current uniformity are simulated and analyzed. The EM model could reproduce the major experimental results well.

Simulation analysis of transformer oil and glycerin as dielectric medium in inductive voltage adders

In this paper, an inductive cell driven by four pulse forming lines (PFLs), capable of operating at two modes to create a single pulse or four separate pulses, is proposed. A single hardware configuration of azimuthal lines must meet the different requirements of the two operating modes. The optimizations and tradeoffs of azimuthal lines for these two modes are presented. Four candidate azimuthal line configurations that are compatible with either mode are proposed. The cell output voltage and azimuthal uniformity of feed currents are simulated, respectively. The simulation results indicate that the cylinder azimuthal line with four equidistant tabs connected to the cathode palates is the most suitable configuration. As the input pulses are 1000 kV and 25-ns rise time, at the mode with four PFLs driving simultaneously, the cell would produce a pulse with a peak of 865 kV and a rise time of 46 ns into 1.5-Ω load. Meanwhile, it could create four separate pulses of 980 kV and 32-ns rise time into 5-Ω load with each PFL driving separately. In this case, the azimuthally asymmetric coefficient is calculated to be 25.6%. In addition, the voltage of undriven ports, i.e., the voltage applied across the separating switches, is estimated to be about 1150 kV.

Influence factors on the azimuthally uniform feed in single-point feed induction voltage adder

An exponential impedance-transformer stalk was proposed for magnetically insulated induction voltage adders (MIVAs). Based on a 10-cell TLCODE model, performances of stalks with linear, stepped, and exponential profiles were quantified and analyzed as a function of m (the ratio of the adder output impedance to the one that is driver matched, m ≥ 1). Simulation results show that when m ≥ 1.5, stalks with the exponential profile result to the highest adder output voltages with a reverse voltage ~7.5% of the dominative voltage, and the η (the ratio of the subtraction between adder peak voltages with exponential and stepped profiles to the one with stepped profile) increases as the m goes up (when m = 5, η is as much as 8%). Simulation results also indicate that with exponential impedance profile, the highest feeding voltage of the 10 cells is ~2 MV when 1 ≤ m ≤ 10, and it always occurs at one of the last five cells. Moreover, it is found that with the exponential profile, the reverse coefficient β (the maximum ratio of the reverse peak voltages to the nominal) is ~9.5%.