Electron density measurement in low-density plasma of electrical wire explosion using a Shack-Hartmann wavefront sensor.

Measuring the electron density of low-density plasma has long been a challenge, as traditional diagnostic techniques often lack sufficient sensitivity or spatial resolution. To address this, this paper presents an electron density diagnostic method for corona plasma generated by electrical wire explosion, based on a Shack-Hartmann wavefront sensor. The diagnostic system integrates an 8 ns, 532 nm nanosecond pulsed laser, a 400 mm focal length lens array, and a high-resolution charge-coupled device camera. By integrating the proposed neural network methods with micro-lens optical simulations, we achieved sub-pixel-level centroid localization of the focal spot, reducing shift errors by 21% compared to conventional convolutional neural network methods and achieving sub-pixel accuracy with an error of only 0.25 pixels. The theoretical sensitivity of the system reaches 2 × 1015 cm-2. In experiments using a silver-wire load under pre-pulse conditions, this diagnostic technique demonstrated strong agreement with laser interferometry results in high density regions. In low-density regions, the electron density measured at 4.4 mm from the wire axis reached a minimum of 2.2 × 1016 cm-2, offering a broader spatial range for plasma electron density diagnostics compared to laser interferometry. This method effectively captured the electron density distribution of the corona plasma formed under pre-pulse conditions. Future work will focus on further optimizing the experimental system to reduce sources of error and extending the application of this technique to large-scale pulsed power facilities for diagnosing the formation and parameter distribution of low-density electrode plasmas.