From the 1960s through the 1970s, methods have been developed to extract electrical energy directly from a hot gas (a plasma) in motion within a channel fitted with electromagnets (producing a transverse magnetic field), and electrodes (connected to load resistors). Charge carriers (free electrons and ions) incoming with the flow are then separated by the Lorentz force and an electric potential difference can be retrieved from pairs of connected electrodes. Shock tubes used as pulsed MHD generators were for example able to produce several megawatts of electricity in channels the size of a beverage can.