Stable THz radiation in the multi-watt range, upwards of 2 watts and even up to 100 watts, is produced through the acceleration of electrons in bunches less than about 500 femtoseconds in length as measured at full width and half maximum, at relativistic speeds (>˜40 MeV) and at a high repetition rate (>˜5 MHz) followed by transverse acceleration thereof by a magnetic field to produce the desired THz emission as synchrotron radiation.