A study of the effect of salinity on pulsed arc discharge in water Seok-geun Lee, Sooseok Choi, Kyoung-Jae Chung and Y. S. Hwang Oct. 10-14, 2010 ICC Jeju, Jeju, Korea NUPLEX, Dept. of Nuclear, Seoul National University, 599, Gwanak-ro, Gwanak-gu, Seoul 151-742, Korea ssugny1@snu.ac.kr 3rd Euro-Asian Pulsed Power Conference 18th International Conference on High-Power Particle Beams LSG_NUPLEX-Oct. 2010

Outline Introduction Experimental setup Experimental results - pulsed arc discharge system - research motivation Experimental setup - pulsed arc discharge system with voltage, current probe Experimental results - relation of pressure peak and energy - voltage, current characteristic in sea water - voltage, current characteristic in experimental condition - pressure to conductivity Conclusion & future works

Pulsed arc discharge system High voltage electrode Pressure gauge 100 mm Before discharge At discharge Tungsten electrode Arc channel formation Electrode gap (5 mm) Anode f8 Cathode

Arc discharge in sea water to generate pressure wave Research motivation Arc discharge in sea water to generate pressure wave Pressure wave generation and propagation 1. Energy transfer from the capacitor to arc channel 2. Expansion plasma-water interface 3. Pressure wave generation and propagation What is effect on generating higher pressure wave in sea water

Research motivation Currents leak through the sea water Sea Water Chamber (Φ100 / L600, Tube) Charging Switch Discharging Switch High Voltage Power Supply ( ~ 20 kV) Capacitor ( ~ 0.5 ㎌) V I total I load I loss = I total – I load Max. loss current Currents leak through the sea water Power loss by leakage current Find out the relation of salinity, power transfer efficiency and pressure wave on pulsed arc discharge in water

Experimental setup Sea Water Chamber High Voltage electrode - Anode Ground electrode - Cathode Viewport Discharge Channel Camera Pressure Gauge Positively Charged High Voltage Capacitor Discharge Switch Rogowski Coil 2 (Load Current) Rogowski Coil 1 (Total Current) V Voltmeter (Load Voltage) 100 mm

Arc discharge in sea water Camera Setting Used camera & lens: Canon 50D, Pentax 200 mm Exposure time: 1 second Adjustment of radiation intensity: F8, F8 with ND400 Filter · At 16kV, arc channel does not develop · At 18kV, arc channel does not always develop - discharge irregular · At 20kV, arc channel develop at all times 16kV 18kV 20kV F8 Arc channel formation F8 with ND400 Filter

Determinant parameter to generation pressure wave Peak pressure wave is proportional to square voltage (P∝V2) Peak pressure wave is proportional to stored energy in capacitor (E=½CV2)

Experimental condition table : conductivity Goal conditions Conductivity (S/m) Resistivity (Ω∙m) Salinity (%) 0.0 S/m 0.00431 232 0.00 0.5 S/m 0.494 2.02 0.3 1.0 S/m 1.03 0.97 0.63 1.5 S/m 1.507 0.663 0.94 2.0 S/m 1.935 0.516 ~1① (Over Range) Sea water ~4.8 ~0.2 3.5 In one condition, experiments were performed 10 times. Charging voltage: 14kV (An arc channel is formed in pure water at 14kV.) ① conductivity measuring instrument(TOA, CM-14P) detection limit: 2.0 S/m, 1 % considered

Comparison of voltage, current characteristic in different condition Charging voltage : 14kV Pure water conductivity: 0.00431 S/m Sea water conductivity: ~4.8 S/m An arc channel is developed at 14kV in experiment condition. An arc channel is not developed at 14kV in sea water. A current is lower in pure water than in sea water. A resistivity is relatively higher in pure water than in sea water.

Tendency of discharge voltage to salinity Charging voltage : 14kV The discharge voltage is decreasing steeply with increasing conductivity. The current rising time is shorten with increasing conductivity. Current rising time

Tendency of discharge current to salinity Charging voltage : 14kV 0 S/m (0.00431 S/m) 2 S/m (1.935 S/m) Current leakage in 2 S/m Current leakage in 0 S/m Before current peak is shown, current difference (I total- I load) is higher in salinity water(2 S/m) than in pure water(0 S/m). It is considered that current leakage is high at high conductivity condition.

Plot of peak pressure to conductivity Charging voltage : 14kV ① A weak pressure wave is generated at high conductivity condition in the same stored energy(E=½CV2). The higher a conductivity is reached, the weaker a pressure wave is generated. The result shows that weak pressure wave is generated by energy loss caused current leakage. ① The strong pressure wave is generated enough to damage electrode cover in pure water. then, number of experiments is low

Conclusions Conclusion The strength of pressure wave is proportional to discharge energy stored energy in capacitor. The current leakage through the salty water is occurred out because of high conductivity. Energy loss through the salty water can make a strength of pressure wave weak. Future works necessary circuit analysis of arc discharge under water calculation of energy loss caused by current leakage