The amount of energy converted to heat in the coil during a single pulse, expressed in millijoules (mJ). Heat per pulse increases sharply with higher current. Doubling the current produces four times the heat because the relationship is exponential. At low pulse rates, individual pulses can be relatively warm without causing problems. At high pulse rates, even modest heat per pulse accumulates into a significant continuous thermal load. This metric, combined with pulse frequency, determines the total heat the device must manage during a session.
Every pulse turns a little energy into heat in the coil, the heat per pulse. At a low pulse rate that heat has time to shed, but at a high rate it stacks up and the coil temperature climbs, step by step, toward the device safe limit. When it reaches that limit the device throttles, stepping the drive current, pulse width, or repetition rate down to hold the temperature, so measured output later in a session can read lower than at the start.
