Bremsstrahlung radiation as a source of coherent microwave power

Coherent microwave power in the 100-mw level is produced by the bremsstrahlung radiation of a prebunched 0.8 Mev beam. Two different schemes are analyzed and tested. The first consists of a prebunched beam impinging on a flat conducting surface; the second consists of a beam striking a flat dielectric surface. The power and radiation resistance in the frequency range between 30 and 40 kMc are measured and compared with theory. It is shown that the radiation resistance is independent of frequency as long as the bunch size is small compared to a wavelength and the structure is nondispersive. The power is in the form of periodic large bursts of energy; the duration of each burst is about 2 × 10^-12sec. The condition of coherence of electromagnetic radiation requires that the beam be pointwise tight in space. Hence a magnetic lens is used to focus the megavolt beam on the point of impact and thereby obtain power at the 42nd harmonic of the fundamental bunching frequency, i.e., at a wavelength equal to 2.56 mm. Based on the results obtained, the utility of bremsstrahlung radiation is discussed as a means of generating coherent power in the submillimeter region.