Force at spark discharge in pin-to-plate system

We have investigated whether any force is generated by a spark discharge in a pin-to-plate system. Because it was difficult to measure the force directly over a short sparking period, three independent methods were employed to evaluate the magnitude of the force indirectly: (1) Axial vibration was observed for the pin electrode supported flexibly by a cantilever to the axial direction at the spark discharge that occurred periodically. The force was implicitly calculated in the case that the calculated vibration agreed with the measured. The result indicated that the force was almost 0 N during the spark period. The vibration was generated not by the force at the spark discharge but by alternative force of the Coulomb force at the period of no discharge and reaction force due to the ionic wind at the corona discharge. (2) A similar investigation was conducted whether the vibration magnitude depended on the spark current based on the assumption that the force at spark discharge depends on the spark current if any substantial force is generated at the spark discharge. We deduced that the force was not generated during the spark period and it was irrelevant to the spark current. (3) We made a hypothesis that axial vibration of the pin electrode could be observed if the spark discharge did not take place but the varying voltage was applied of which pattern was common with that with the spark discharge. To confirm the hypothesis an experiment was conducted with two parallel-connected pin-to-plate systems, the air gap of one system was slightly shorter than the other. The axial vibration was observed even in the system that the spark discharge did not take place and the vibration agreed also with the calculated. These three results suggested that no substantial force was generated at the spark period.