Insulated Transmission Line System Research Articles

An Iterative Method to Determine the Vacuum Impedance of Magnetically Insulated Transmission Line System

In this article, the dimensionless ratio <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E/{\textit{cB}}$ </tex-math></inline-formula> at the starting point of constant-gap section of the magnetically insulated transmission line (MITL) at the time of peak MITL voltage was used as a figure of merit of a disk MITL. Taking a 15-MA driver as an example, the equivalent circuit model and the impedance iterative method are established by means of the TL-code circuit simulations. The vacuum impedance of the four-level outer-MITLs is determined. In particular, when the target ratio ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E/{\textit{cB}})_{i}$ </tex-math></inline-formula> is set to 0.25 (the ratio of flow current to anode current <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{f}/I_{a}$ </tex-math></inline-formula> is 3.12%), the impedance of the four-level MITLs is 1.70, 2.12, 2.88, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.16~\Omega $ </tex-math></inline-formula> . When ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E/{\textit{cB}})_{i}$ </tex-math></inline-formula> of the four-level MITLs is set to 0.15, 0.18, 0.20, and 0.22 (the ratio <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{f}/I_{a}$ </tex-math></inline-formula> is 1.23%), the impedances are 2.68, 2.89, 3.06, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.02~\Omega $ </tex-math></inline-formula> , respectively.

Circuit simulation of current loss in magnetically insulated transmission line system in 15- MA Z-pinch driver

In this paper, a transmission line circuit model of a magnetically insulated transmission line(MITL) system is developed for a 15-MA Z-pinch driver. The current loss characteristics of multi-level MITL and the ion emission due to the expansion of anode and cathode plasma in the post hole vacuum convolute(PHC) and inner-MITL region are analyzed. The spatiotemporal distribution of current loss of the outer-MITL and ion current of the PHC and inner-MITL of the 15 MA driver are obtained. The results show that the first electron emission happens at the end of constant-impedance MITL and the beginning of constant-gap MITL, and the end of constant-gap MITL firstly achieves fully magnetic insulation. Electron emission occurs at the start of load current and its duration is about 30 ns, which is short for a single pulse and has little effect on the rising edge nor peak value of the load current. The waveform of the electron flow varying with time resembles a saddle shape, whose amplitude first goes up, then comes down, and increases again. The electron flow current decreases from upstream to downstream in constant-gap MITL in space. The starting time of the loss current of the PHC is synchronized with the gap closing time. The loss current amplitude increases rapidly, reaching 4 MA at the peak load current time and 6.5 MA in the end. In the inner-MITL region, the main positive ion species are protons and oxygen 2+. At the beginning, the ion loss current of protons is larger than that of oxygen 2+, and then the protons are quickly magnetically insulated due to the small charge-to-mass ratio. The ion loss current of the inner-MITL region mainly increases after the peak load current time, and its peak value is 2.1 MA. Given the input conditions, the stack is going to deliver current of about 18 MA, the hold voltage is about 2.3 MV, and the peak load current is about 13.5 MA.

Investigation on Nonuniformity of Magnetic Field in Curved Coaxial Magnetically Insulated Transmission Line System

The curved coaxial magnetically insulated transmission line (MITL) generates nonuniform magnetic fields, causing substantial current loss and nonuniform current in the system. However, the nonuniform magnetic field can recover uniformity with a certain distance after the curved region. In this article, 3-D particle-in-cell simulations were carried out to investigate the mechanism of the recovery of nonuniform magnetic field in the region after the 90°-curved MITL and the factors influencing the distance needed for the recovery of the uniformity of magnetic field. The results indicate that a high-impedance load causes higher nonuniformity of the magnetic field in the MITL after the curved region than the situation with a low-impedance load. The profile of nonuniformity of the magnetic field in the MITL after the curved region transforms from an exponentially decreasing shape to a “W” shape when the MITL operates from a load-limited case to a self-limited case. The distance for the recovery of the nonuniform magnetic field after the 90°-curved MITL is about 2–3 times the radius of the anode, and has no independence with the radii of curvature and cathode. This work fascinates the improvement of magnetic field uniformity in the curved MITL system.

A Circuit Particle-in-Cell Coupled Simulation of a Magnetically Insulated Transmission Line System

We have developed a circuit particle-in-cell (PIC) coupled model for simulating a pulsed power system, based on a circuit algorithm of a pulsed power supply and a PIC simulation for a magnetically insulated transmission line (MITL) system. The coupled algorithm comprises an external circuit algorithm based on BERTHA and a coupled algorithm for the PIC and circuit interface based on the Mur absorbing boundary condition. In this paper, a simple coaxial MITL with a single linear transformer driver (LTD) was simulated to validate the coupled model compared with PSPICE and BERTHA simulations. The numerical results show that the circuit–PIC coupled model achieved almost the same outputs on the load. The coupled model was then applied to an MITL system driven by ten LTD cavities. The simulation results and experimental results were in agreement, which confirms that the circuit–PIC coupled model could provide a reference for the structural design of experimental apparatuses.

Dynamic Model for the Z Accelerator Vacuum Section Based on Transmission Line Code

The transmission-line-circuit model of the Z accelerator, developed originally by W. A. STYGAR, P. A. CORCORAN, et al, is revised. The revised model uses different calculations for the electron loss and flow impedance in the magnetically insulated transmission line system of the Z accelerator before and after magnetic insulation is established. By including electron pressure and zero electric field at the cathode, a closed set of equations is obtained at each time step, and dynamic shunt resistance (used to represent any electron loss to the anode) and flow impedance are solved, which have been incorporated into the transmission line code for simulations of the vacuum section in the Z accelerator. Finally, the results are discussed in comparison with earlier findings to show the effectiveness and limitations of the model.

Dynamic modeling of magnetically insulated transmission line systems

Negative conductors in vacuum transmission lines used in multiterrawatt applications emit electrons freely. These lines are efficient only because the self-magnetic field of the power flow forces the electrons to flow parallel to the electrodes. Excepting numerical simulations, dynamic modeling of systems of these transmission lines has generally either ignored electron flow, or has included only those electrons that cross immediately to the anode at the front of the forward wave. In this paper we describe an analytic model that includes flowing electrons and the effects of these flows on line voltage and on the reduction of magnetic flux. Axial electron currents are modeled using simple, measurable, and calculable parameters. Transverse electron currents are modeled using general patterns found empirically from simulation data. These currents are in turn related by an expanded set of Telegrapher equations. An example of the use of the model is compared to two-dimensional, time-dependent particle-in-cell simulations.

Metallic particle movement, corona, and breakdown in compressed gas insulated transmission line systems

A simplified computational algorithm has been developed to study the behavior of metallic particles in gas insulated transmission line (GITL) systems. The model provides an estimate of the effectiveness of particle trapping for a particular trap design at a given commissioning voltage. Results of measured breakdown probabilities of particle contaminated SF/sub 6/ show fair agreement with calculated values. A computational model was developed to calculate the corona inception voltage due to conducting particle motion in GITL systems. The computed results for various parameters were in fair agreement with the measured values. A corona pulse pattern is computed and plotted using the same algorithm. Oscillographic records of the transient corona show that particle discharge is larger for long particles, and its magnitude increases with voltage level. Corona patterns obtained in the laboratory indicate that conducting particles can be detected in GITL systems and that the particle size can be determined through partial discharge measurements with AC voltage at different gas pressures. >