Speaker
Description
Sandia’s Z Machine can deliver up to 27 MA in ~100 ns to drive high-energy density physics experiments. These parameters are achieved in part via use of four parallel Magnetically Insulated Transmission Lines (MITLs) that reduce overall system inductance. A Double Post-Hole Convolute (DPHC) acts as a current adder to combine the four parallel MITLs into a single transmission line. The DPHC is a complex three-dimensional structure that perturbs the azimuthally-symmetric topology of the insulating magnetic field. This perturbation to otherwise efficient vacuum power transport introduces current shunt paths that can reduce load current up to 5 MA, significantly impacting experiment performance.
We report on the first-ever direct measurements of negative particles contributing to current loss in the convolute during Z shots. Specialized DPHC anode posts use embedded faraday cups to provide time-resolved measurements of negatively charged particle fluence. Apertures spatially collimate charged species shunted across the vacuum gap. We employ filtering to discriminate negative ions and low-energy electrons from higher-energy electrons.
Data is presented from two aperture configurations. The DPHC’s 3D structure introduces null regions where magnetic insulation is lost between convolute electrodes. We present quantitative measurements that suggest these channels cannot support the entire shunt current. Another aperture provides insight about plasma dynamics prior to magnetic insulation in the region downstream of the DPHC, where simulation and spectroscopic measurements show vacuum gap closure velocities greatly exceeding conventional MITL theory.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
