Each of the two JET flywheels weighs 775 tons. Before a plasma shot, these nine meter wide steel wheels are set into a horizontal rotation to store hundreds of megawatts of power. An 8.8 megawatt electric motor – stronger than the motor of high speed trains like TGV or Eurostar – accelerates each wheel to 225 rounds per minute. At this spinning rate, the flywheel edge rotates at a speed of 380 km/h.
One plasma pulse at JET requires around 500 megawatts of power, the peak power surge can even exceed 1000 megawatts. If JET was to draw all this power directly from the grid, the lights in the surrounding cities would go black. Therefore more than half of it is stored on the flywheels and used to build up the magnetic field. On an average experimental day, the flywheels are set into rotation 22 times.