Speaker
Description
We present experimental data from the VULCAN laser facility that demonstrates how gigahertz EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes positioned outside of the target chamber, in front and behind the target interaction point. We obtained scalings with laser energy, pulse duration, defocus and pre-pulse delay. We also show that target stalk geometry, material, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. Plastic supports with spiral geometries reduced the measured EMP by over an order of magnitude compared with cylindrical supports made from Al and by a factor of ~7 compared with plastic cylinders. Furthermore, by switching from metal foils (3×8mm, 100μm thick Cu) to wire targets (⌀=25-100μm) it is possible to reduce the EMP energy by a factor of ~10. A combination of electromagnetic wave and 3D particle-in-cell simulations suggest that the efficacy of the modified supports can’t be attributed to a change in their induction or classical resistance. We are therefore looking to study the effect of photoionization and charge implantation on return currents in future work.
