A speedy switching device is an NPN avalanche transistor fitted with a coil between base and emitter. The transistor is initially switched off and about 300 volts exists across its collector-base junction. This voltage is high enough that a charge carrier in this region can create more carriers by impact ionisation, but the probability is too low to form a proper avalanche; instead a somewhat noisy leakage current flows. When the preceding stage switches, the emitter-base junction is pushed into forward bias and the collector-base junction enters full avalanche mode, so charge carriers injected into the collector-base region multiply in a chain reaction. Once the Marx generator has completely fired, voltages everywhere drop, each switch avalanche stops, its matched coil puts its base-emitter junction into reverse bias, and the low static field allows remaining charge carriers to drain out of its collector-base junction. Applications One application is so-called boxcar switching of a Pockels cell. Four Marx generators are used, each of the two electrodes of the Pockels cell being connected to a positive pulse generator and a negative pulse generator. Two generators of opposite polarity, one on each electrode, are first fired to charge the Pockels cell into one polarity. This will also partly charge the other two generators but not trigger them, because they have been only partly charged beforehand. Leakage through the Marx resistors needs to be compensated by a small bias current through the generator. At the trailing edge of the boxcar, the two other generators are fired to "reverse" the cell. Marx generators are used to provide high-voltage pulses for the testing of insulation of electrical apparatus such as large power transformers, or insulators used for supporting power transmission lines. Voltages applied may exceed two million volts for high-voltage apparatus. In food industry Marx generators are used for Pulsed Electric Fields processing to induce cutting improvement or drying acceleration for potato and other fruits and vegetables. See also ATLAS-I Cockcroft-Walton generator – a similar circuit which has the same "ladder" structure. CW generator produce rectified DC from an AC input. Vector inversion generator A transmission line device using a similar charge in parallel discharge in series approach Explosively pumped flux compression generator – A solution to the dual problem of creating high current pulses Ignition coil Induction coil Istra High Voltage Research Center Tesla coil References Further reading Bauer, G. (June 1, 1968) "A low-impedance high-voltage