Simultaneous emissions of X-rays and microwaves from long laboratory sparks and downward lightning leaders

Joan Montanya, Polytechnic University of Catalonia (UPC), Department of Electrical Engineering, Barcelona, Spain, Oscar A Van Der Velde, Polytechnic University of Catalonia, Electrical Engineering, Terrassa, Spain and Ferran Fabró Tapia, Politechnic University of Catalonia, Electrical Engineering, Terrassa, Spain