The limits to long pulse durations are the number of transferred electrons to the anode, sputter caused by ion bombardment at the cathode, and the temperature gradients of the glass. Pulses that are too long can vaporize large amounts of metal from the cathode, while overheating the glass will cause it to crack lengthwise. For continuous operation the cooling is the limit. Discharge durations for common flashtubes range from 0.1 microsecond to tens of milliseconds, and can have repetition rates of hundreds of hertz. Flash duration can be carefully controlled with the use of an inductor.