How quickly current and magnetic field build up in the coil when power is applied. This directly affects how sharp and strong the pulse edge is. A shorter time constant means faster rise and more responsive pulses. Tau = L/R where L is coil inductance (Henries) and R is total series resistance (Ohms). Current reaches 63% of its final value after 1 tau and 99% after 5 tau. The pulse width must exceed 5 tau for the coil to fully build current and deliver maximum peak Gauss.
Coil current does not switch on instantly; it builds up along this curve, set by the coil's L/R time constant. It reaches about 63% of full after one time constant, 95% after three, and 99% after five. If the pulse is at least about three time constants long, the current has essentially finished building, so the pulse is complete.
