Measurement of the voltage evolution on a load of X-pinch plasma system using the Pockels effect

A diagnostic system using the Pockels effect (linear electro-optic effect) has been developed to measure a voltage on a load of the SNU X-pinch device [Ryu et al., Rev. Sci. Instrum. 92, 053533 (2021)]. The sensor component of the diagnostic system comprises of a lithium niobate (LN) crystal and its mount. When the LN crystal is subjected to an external electric field, the refractive indices of the LN crystal change due to the Pockels effect, leading to a change in the polarization state of the propagating laser beam through the crystal. This concept allows the separation and shielding of electronic devices from the intense electric pulses generated by the X-pinch system. Furthermore, the compact size and high electric field tolerance of the LN crystal enable us to position the sensor in a close proximity to the load of the X-pinch, facilitating the measurement of voltage evolution on the load. In contrast to circuit-based voltage probes, our sensor possesses low inductance, allowing us to measure resistive-dominant voltage even in the presence of rapid current changes within the X-pinch system. In this paper, we outline the configuration of our voltage measurement system using the LN crystal within the X-pinch device and provide measurement results of the load voltage. Additionally, we explore the temporal evolution of the voltage in relation to the phase transition of the load.