Risetime Evolution in HEMP (High-Altitude Electromagnetic Pulse) E1Waveforms - Technology and Standards

There are many different definitions of the risetime of a transient waveform. In the context of HEMP standards, the 10-90% risetime of an idealized double exponential waveform has been defined and used for many decades. However, such a risetime definition is not strictly applicable to the transient voltage out of a pulse generator, since no practical switch can close in zero time. In this paper, we discuss various definitions and their applicability. More importantly, pulse power technology has evolved over 5 decades and the achievable risetimes have come down from 10’s of ns to 10’s of ps. As a corollary, the highest achievable voltage gradient has been going upwards of 10 V/s. In this paper, we review the definitions of risetime, and trace the evolution of technology and HEMP Standards, exclusively for the E1 environments. ---------------------This note is an adaptation of a paper published by the authors in IEEE Transactions on Electromagnetic Compatibility, Volume 55, Issue 3, June 2013, pp 484-491.