Circuit models and three-dimensional electromagnetic simulations of a 1-MA linear transformer driver stage

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.

A Primer on Pulsed Power and Linear Transformer Drivers for High Energy Density Physics Applications

“…20. Full electromagnetic simulations have shown that indeed a forward going wave propagates through an impedance-matched module with very little back [116], [117].) reflection and very high efficiency (η ≈ 70%; see Fig.…”

“…reflection and very high efficiency (η ≈ 70%; see Fig. 21) [116], [117]. For detailed explanations on how impedance matching works in these systems, see Sec.…”

Commissioning and power flow studies of the 2.5-MeV Ursa Minor LTD

“…Circuit models range from lumped RLC circuits representing an entire cavity to detailed models which represent each component individually [2][3][4]. 3-D electromagnetic calculations have also been used to improve the modeling of inductance and stray capacitance in a LTD cavity [5]. Lumped element circuit models are sufficient for reproducing the peak power output and general pulse shape.…”

Impedance-matched Marx generators

“…A linear-transformer-driver (LTD) module is an induction voltage adder that is powered by circuits located within the cavities of the adder [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Since an LTD module can be designed to provide single-stage electrical-pulse compression and impedance matching, such modules are attractive candidates as prime-power sources for nextgeneration pulsed-power accelerators .…”

“…For each cavity, Fig. 3 models the cores as a resistive circuit element with resistance R cores located at the cavity output [7,13,[15][16][17][18][19][20].…”