Abstract
A 3D fully electromagnetic (EM) model of the principal pulsed-power components of a high-current linear transformer driver (LTD) has been developed. LTD systems are a relatively new modular and compact pulsed-power technology based on high-energy density capacitors and low-inductance switches located within a linear-induction cavity. We model 1-MA, 100-kV, 100-ns rise-time LTD cavities [A. A. Kim et al., Phys. Rev. ST Accel. Beams 12, 050402 (2009)] which can be used to drive $z$-pinch and material dynamics experiments. The model simulates the generation and propagation of electromagnetic power from individual capacitors and triggered gas switches to a radially symmetric output line. Multiple cavities, combined to provide voltage addition, drive a water-filled coaxial transmission line. A 3D fully EM model of a single 1-MA 100-kV LTD cavity driving a simple resistive load is presented and compared to electrical measurements. A new model of the current loss through the ferromagnetic cores is developed for use both in circuit representations of an LTD cavity and in the 3D EM simulations. Good agreement between the measured core current, a simple circuit model, and the 3D simulation model is obtained. A 3D EM model of an idealized ten-cavity LTD accelerator is also developed. The model results demonstrate efficient voltage addition when driving a matched impedance load, in good agreement with an idealized circuit model.
Highlights
Linear transformer drivers (LTDs) are a rapidly developing area of pulsed-power technology that are capable of delivering high-power, high-current, 100–300 ns output pulses in a compact configuration [1,2,3,4,5,6]
The parallelplate radial transmission line is either directly connected to a load or feeds a coaxial transmission line that joins many similar LTD cavities in serial to form a type of induction voltage adder (IVA) [7]
We describe a new EM computational modeling capability that is being developed to analyze the generation and propagation of EM energy in single LTD cavities and through a ten-cavity accelerator (Mykonos) presently under construction at Sandia National Laboratories (SNL) [10,11]
Summary
Linear transformer drivers (LTDs) are a rapidly developing area of pulsed-power technology that are capable of delivering high-power, high-current, 100–300 ns output pulses in a compact configuration [1,2,3,4,5,6]. Has been extended significantly by Hughes et al [37] to include a hysteresis (B-H) loop model, multiple windings, and asymmetric material conductivity to set the value r in time This model was used successfully in the analysis of electrical breakdown characteristics inside the DARHT-II [38,39] accelerator cavities [37,40,41]. The inductance of the single-cavity simulation model was determined in a separate simulation that removed the switch conductivity channel, setting the core resistance to zero and driving a voltage pulse into cavity through the outlet path. The mutual inductance between the core-current path along the interior of the cavity and the main brick current path through the switch, capacitors, and connecting hardware was estimated at 3:4 Æ 0:1 nH Equations (5) with initial conditions (6) are solved numerically using an adaptive step size Runge-Kutta algorithm in MATHEMATICA [42]
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