From PBS's Tesla: Master of Lightning:
    Applications

    If, as happened in practice, Tesla made an antenna of the high-voltage end of his secondary, it became a powerful radio transmitter. In fact, in the early decades of radio, most practicable radios utilized Tesla coils in their transmission antennas. Tesla himself used larger or smaller versions of his invention to investigate fluorescence, x-rays, radio, wireless power, biological effects, and even the electromagnetic nature of the earth and its atmosphere.

    Today, high-voltage labs often operate such devices, and amateur enthusiasts around the world build smaller ones to create arcing, streaming electrical displays—it is not difficult to reach a quarter million volts. (One of the very first particle accelerator designs, by Rolf Wideroe in 1928, generated its high voltage in a Tesla coil.) The coil has become a commonplace in electronics, used to supply high voltage to the front of television picture tubes, in a form known as the flyback transformer.
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Bitt Faulk