Performance degradation of a water-filled coaxial Blumlein generator during its continuous operation

A water-filled Blumlein generator was operated at different repetition rates of up to 15 Hz, and its temporal performance was investigated. The Blumlein generator having an impedance of 10 /spl Omega/ provides a rectangular voltage pulse with an amplitude of 200 kV and a duration of 75 ns into a matched load. The resistance of the water in the line decreases quickly at >10 Hz during a continuous operation for an hour and results in a decrease in the output voltage of the Blumlein line. The generator works with a repetition rate of up to 6 Hz without serious degradation in the voltage, while the averaged power density dissipated in the water is approximately 40 mW/cm/sup 3/. The increase in the water temperature during operation is only a few degrees. This implies that the resistive heating of the water is not the dominant cause of the decrease in the water resistance. The tolerable repetition rate could be higher if we use a larger capacity water circulation system.