Development of a Multi-Axis B-dot Probe Array for COBRA Pulsed-Power Experiments

Measuring the magnetic field and current distribution in high-energy-density (HED) plasmas remains a significant challenge. While several non-perturbative spectroscopic and optical techniques have been developed, these also present their own unique difficulties. The most conceptually straightforward approach is to use miniature inductive loops commonly referred to as B-dot probes. To minimize perturbation to the plasma, experiments have historically used single loop probes that only measure one component of the magnetic field at one location. When placed inside of the plasma, these probes are generally destroyed in an experimental shot. Measuring the magnetic field components in multiple directions and at multiple points along a linear probe array allows for the calculation of the current density and increases understanding of where current is flowing in the plasma (not simply in the
$Z$
direction) and if there is turbulence. To create an easy-to-build, survivable probe array, a design was formulated consisting of multiple “chip” clusters in a linear configuration inside of an alumina tube. Each cluster contains three orthogonal inductor loops [1] to measure the full 3D field at each radial position. The probe array was constructed, calibrated, and fielded in gas puff z-pinch experiments on the COBRA generator at Cornell University.