The concept of a variable-impedance, magnetically insulated transmission line (variable-impedance MITL) has been recently developed at the University of Rochester, LLE. [1] This approach allows us to significantly reduce the total inductance of the MITLs while preserving MITL power-flow performance. With newly developed algorithms, which combine Screamer circuit-simulations and MATLAB postprocessing procedures, we can quickly estimate the vacuum electron current flow inside MITL without running computationally expensive, particle-in-cell (PIC) simulations.

This paper focuses on the practical applications of the variable-impedance MITL for imploding loads at Z and for future, high-current drivers. Z today uses constant impedance MITLs. [2] Our simulations demonstrate that by replacing the 3.3-Ω, D-level MITL with a safe, variable-impedance MITL, we can increase the peak current up to 0.5 MA at Z. Furthermore, by implementing variable-impedance MITLs for all four, Z MITL levels, an additional up 1.2 MA of current can be gained. This increase in current happens with no increase in the level of vacuum electron flow immediately outside of the post-hole convolute (PHC). This is essentially free added current that can be made available at Z for all shots.

Regarding future, higher-current drivers, our simulations predict a significant decrease in the stack voltage and an increase in the load current compared to the constant-impedance MITL approach. These MITL innovations could lead to a reduction in overall pulsed-power risk and a substantial decrease in the cost of the proposed, future high-current facilities.

[1] R. B. Spielman & D. B. Reisman, Matter Radiat. Extremes 4, 027402 (2019).

[2] M. E. Savage, et al., in Proceedings of the 16th IEEE International Pulsed Power Conference, edited by E. Schamiloglu and F. Peterkin (IEEE, Piscataway, NJ, 2007), p. 979.

The Z facility at Sandia National Laboratories is home to the world’s largest pulsed power facility, supporting research in inertial confinement fusion (ICF) and high energy density (HED) physics for over 35 years. An ICF approach called MagLIF, in which cylindrical liners containing laser-heated and axially magnetized deuterium gas are imploded, has achieved >10¹³ DD-produced neutrons and magnetic trapping of charged fusion products. These results, along with scaling relationships and the high efficiencies achievable with pulsed power coupling to an inertial target, suggest that a larger-scale (~60 MA) driver could enable high-yield fusion in laboratory experiments.

The National Nuclear Security Administration (NNSA) is currently considering a Next-Generation Pulsed Power (NGPP) facility to replace the aging Z facility and extend the parameter space available to perform HED research. To achieve high-yield fusion on MagLIF targets and accomplish other HED research objectives, we anticipate NGPP would need to deliver 6 to 10 times the electrical power and energy of today’s Z Pulsed Power Facility.

In this talk, we will discuss conceptual architectures for a 60-MA NGPP, projected timelines, and anticipated technical and operational challenges associated with such a facility. We will present an overview of the capabilities and achievements of present and planned component and system testing facilities, which are used to advance the technology readiness level (TRL) of subsystems required to operate in new regimes on an NGPP facility. We will also highlight results from component development and improvement efforts necessary to enable the next generation of pulsed power research.

*Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.