This time-lapsed rendering illustrates the formation of an umbrella-shaped plasma sheath (purple) being pushed down the length of a cylindrical electrode, eventually collapsing inward on itself to create a tremendously dense region (white). Simultaneously, an ion beam (green) is timed to pass through the device as the plasma collapses in on itself, which accelerates the beam particles. Image: Kwei Chu/LLNLAndrea Schmidt and her plasma research team received a big boost recently by procuring a $1-million award from the Defense Advanced Research Projects Agency (DARPA), a U.S. Dept. of Defense agency. The award will be used to fund their groundbreaking work in both modeling and experiments of a classic plasma configuration, the Z-pinch.

The Z-pinch is a plasma configuration that occurs when a pulsed high current arc discharges between two electrodes, causing a plasma column to implode under its own self-generated magnetic pressure. Over the years, researchers have had difficulty predicting and understanding its behavior.

DARPA is interested in using Z-pinches to make compact neutron sources. However, DARPA's applications require more neutrons than are produced by current dense plasma focus (DPF) experiments.

Modeling at the particle level
To increase the neutron yield on these devices, Schmidt's team in the Lawrence Livermore National Laboratory (LLNL)'s Engineering Directorate is using a model of the DPF Z-pinch to optimize the electrode design. Previous Z-pinch modeling took a fluid approach that averaged physical quantities over many particles, washing out beam formations and other important effects. Instead of using a fluid approach, the team developed the first fully kinetic model of a DPF plasma that enables physical quantities to be tracked at the particle level. This model predicts more accurate neutron yields, allowing it to be used as a design tool.

Schmidt and her team have performed new simulations that have reproduced experimentally observed ion beams and neutron yields, key features of these plasmas. They've also observed a type of instability that fundamentally drives the dynamics of these plasmas, in both the model and on their table-top DPF experiment at LLNL.

Team members will model various DPF electrode designs and optimize the design for high neutron yield. They also will conduct experiments in North Las Vegas using a National Security Technologies DPF that has 1 megajoule of stored energy, 250 times greater than the one they are currently using at LLNL.

The team's fully kinetic model was published in Physical Review Letters.

Source: Lawrence Livermore National Laboratory