Abstract

Pulsed plasma discharges are of interest for their capability to produce pulsed high energy radiation and particle beams. One of them is the dense plasma focus, a device that has renewed interest for physics research and possible industrial applications. In this work, the evaluation of UHF antennas is carried out as an alternative remote diagnostic of this device. The measurements were taken from a low energy dense plasma focus device PF-400J operating at 26 kV of charging voltage and using hydrogen at a pressure of 9.5 mbar. The device operation was simultaneously measured with an inductive sensor, an inductive sensor loop, and an antenna. Two antennas were used for evaluating which one of them could be used as a complementary diagnostic of the device operation: a monopole and a Vivaldi antenna. Both antennas were tuned in the UHF range and were previously designed for measuring partial discharge phenomena. The characterization of the device operation with the antennas was carried out comparing the time domain signals of the antennas and the inductive sensor, whose signals features had been known beforehand. Then, for quantifying both types of measurements, signal parameters of the inductive sensor and the antennas were correlated. Peak value and signal energy were determined from the antennas signal and they were correlated with the dip value feature of the inductive sensor which is an important indicator of the plasma dynamic of the discharge. The results indicate that antennas can be used for the detection of abrupt changes in the circuit current of the device. In particular, the plasma maximum compression, known as pinch, could be inferred from the antenna signal as a transient that started when the dip feature was detected with an inductive measurement. The correlation between antenna signals parameter and the dip value of the inductive sensor showed high data dispersion, although an increasing trend of the antennas signal parameter with dip values was found. This work, as an initial experimental survey, concluded that UHF measurement techniques can be applied to the remote diagnostic of pulsed plasma discharges. The understanding of the emitting mechanism of the device and proper design of UHF sensors will be considered in future work.