This article presents an experiment in which the gap distance was varied between 46 and 84 cm. Series of 15 voltage impulses were applied for each distance and different peak voltages with a rise time of 600 ns. The results of a total of 20 series of impulse voltages show that emissions depend on the electric field derivative within the gap
March, V. [et al.]. X-rays from laboratory sparks in air: the relationship between runaway electrons and the electric field. A: International Conference on Lightning Protection. "ICLP-2013". Viena: 2012.