Development of in-situ inductive probes for pulsed-power-driven plasma experiments*

In situ measurements of magnetic fields using inductive (or b-dot) probes are important in high-energy-density plasmas in which the magnetic field can significantly alter the dynamics or transport within the plasma. In pulsed-power--driven experiments, these probes are subject to harsh plasma conditions, including photo-ionization by X-rays, large heat fluxes, and capacitively coupled plasma potentials. It is desirable to shield the probe from these effects, while also minimizing the probe size, to avoid perturbing the centimeter scale HED plasma. 

We constructed several designs of inductive probes, and tested them in the magnetized plasma outflows of an exploding wire array driven by the COBRA facility at Cornell. These probes include standard designs, based on small semi-rigid coax with a single loop, and pairs of counter wound loops made from thin magnet wire, where the two signals can be used for common mode rejection. We have experimented with various techniques for insulating, shielding and grounding the probes, and we present results to guide further probe development.