In order to develop a better understanding of current losses in the magnetically insulated region of high-power pulsed power machines, it is crucial to be able to conduct experiments at scale in smaller facilities. Here, we present a novel experiment that has been tested on the MAGPIE driver at Imperial College. The targets are inexpensive and easy to customize for experiments ranging from power flow to warm dense matter. Simulations in COMSOL indicated electric fields of up to 600 MV/m and magnetic fields of up to 300 T could be produced on MAGPIE. In initial testing, Electric fields exceeding 100 MV/m and magnetic fields exceeding 50 T were generated, and both magnetically insulated transmission and plasma-shorted transmission were demonstrated.

High-voltage laser-triggered switches (HV-LTSs) are used in pulsed-power applications where low jitter and precise timing are required. The switches allow operation in the megaampere, megavolt regime while maintaining low insertion losses. Currently, there is a lack of detailed plasma measurements in these switches, yet such measurements are needed to elucidate the detailed physics, which include a range of processes such as laser breakdown, streamer formation and growth, current flow, plasma evolution, and cooling. Detailed spatially- and temporally resolved measurements of plasma properties within the switches could contribute to validating and advancing numeric models of these systems. This contribution presents laser Thomson scattering measurements of the electron number density and temperature evolution in a HV-LTS. The switch was operated at 6 kV with current flow for a duration of 145 ns and a peak current density of 0.2 MA/cm2 into a matched load. The Thomson scattering diagnostic system uses a 532 nm probe from an Nd:YAG laser allowing a temporal resolution of ∼10 ns. We find that during the switch current pulse, the plasma electron temperature rose from a starting value of 8.1 ± 1.6 eV (due to cooling of the earlier trigger laser plasma) to a peak value of 26 ± 5 eV with an associated increase in the electron density from 8.6 ± 1.7 × 1017 to 3.1 ± 0.6 × 1018 cm−3.

Mega-Volt class High-Voltage Laser-Triggered Switches (HV-LTSs) are often simulated using the Martin/Braginskii model with sufficient accuracy to be largely predictive. However, recently developed switches operating with low inductance for nanosecond regime current pulses yield inconsistencies where the model both underpredicts rise times and overpredicts switch run time. The suspected reason for these inconsistencies lies in the model’s assumptions, specifically, that the plasma conductivity is both spatially and temporally uniform. This study investigates HV-LTS plasma channel conductivity during the rising edge of the current pulse through both derivative (V-Dot) electrical probes and electron temperature measurements via laser Thomson scattering. A HV-LTS testbed utilizing an aqueous (variable impedance) resistive load was designed to produce experimental conditions similar to those found in larger pulsed power applications. This paper describes the design of the load and experimental results under a variety of load conditions and operating voltages of order 5 - 6 kV. Our results indicate the electron temperature increases during the rising edge of the current pulse suggesting that the plasma conductivity is temporally dependent. Further, electrical measurements show an increase in plasma conductivity during the rising edge of the current pulse. Evidence from both optical and electrical measurements calls into question the assumption of a temporally constant plasma conductivity in our experimental setup. Finally, we show that Spitzer’s resistivity used by the Martin/Braginskii model does not accurately predict the measured plasma channel resistance.

This report describes the high-level accomplishments from the Plasma Science and Engineering Grand Challenge LDRD at Sandia National Laboratories. The Laboratory has a need to demonstrate predictive capabilities to model plasma phenomena in order to rapidly accelerate engineering development in several mission areas. The purpose of this Grand Challenge LDRD was to advance the fundamental models, methods, and algorithms along with supporting electrode science foundation to enable a revolutionary shift towards predictive plasma engineering design principles. This project integrated the SNL knowledge base in computer science, plasma physics, materials science, applied mathematics, and relevant application engineering to establish new cross-laboratory collaborations on these topics. As an initial exemplar, this project focused efforts on improving multi-scale modeling capabilities that are utilized to predict the electrical power delivery on large-scale pulsed power accelerators. Specifically, this LDRD was structured into three primary research thrusts that, when integrated, enable complex simulations of these devices: (1) the exploration of multi-scale models describing the desorption of contaminants from pulsed power electrodes, (2) the development of improved algorithms and code technologies to treat the multi-physics phenomena required to predict device performance, and (3) the creation of a rigorous verification and validation infrastructure to evaluate the codes and models across a range of challenge problems. These components were integrated into initial demonstrations of the largest simulations of multi-level vacuum power flow completed to-date, executed on the leading HPC computing machines available in the NNSA complex today. These preliminary studies indicate relevant pulsed power engineering design simulations can now be completed in (of order) several days, a significant improvement over pre-LDRD levels of performance.

Stockpile stewardship requires accurate and predictive models relying on the generation of extreme environments which is both incredibly difficult and profoundly necessary. Next generation pulsed power facilities (NGPPF), where these environments are created, may require a paradigm shift in equipment engineering/manufacture to fulfill this need. Therefore, this research aims to investigate the limitations, capabilities and efficacy of leveraging advancements in the field of additive manufacturing (AM) in order to produce novel power flow components for NGPPFs. This work focused on commercial 3D metal AM equipment producing several prototypes addressing prescient needs/shortcomings, and a technique wherein a lightweight polymer core is metalized. Ultimately, commercial 3D metal AM is considered a viable path forward but would require a sizeable investment and does not currently support the scale and complexity necessary for NGPPFs. Moreover, initial results from our composite technique are promising and is considered a realizable path forward given further investigation.

Open-path cavity ring-down spectroscopy provides a potential means for sensitive detection of trace gas species in compact, lightweight packages. This contribution presents studies of attainable sensitivity along with details of methane and ammonia sensors.