A few years ago a new theory for producing coherent Smith-Purcell (SP) radiation from an initially continuous beam was proposed. This experiment confirms that two-dimensional theory. The beam was typically 10 cm wide, a few mm thick, with a peak current of 200 A and beam energy of 85 keV. The 10 cm-wide grating had twenty 2-cm periods, and radiation was produced at the fundamental frequency near 4.5 GHz. Second and third harmonics were observed at the expected angles. Beam bunching was measured using a B-dot probe placed at the end of a groove. Generally good agreement between this experiment and the 2D theory is found

Coherent Smith-Purcell radiation is a promising source of coherent emission in the THz domain. Although it has been observed in several experiments, some physical quantities related to the bunching of an initially continuous beam had not yet been studied experimentally. Among them, the gain as function of beam current, together with the value of the start current, needed to be addressed. We report here their measurements in a microwave experiment using a sheet beam. A start current of about 20  A/m was found. Two-dimensional simulations with a very thin beam agree well with our results.

High-power-microwave (HPM) emission has been observed in S-band with a compact magnetically insulated line oscillator (MILO). The device is driven by a low-impedance Marx generator which was designed and built at Commissariat à l'Energie Atomique, Centre d'Etudes Scientifiques et Techniques d'Aquitaine for HPM experiments. Measurements with fast and sensitive I-dot probes, installed inside the slow-wave structure (SWS), have given the evidence of the MILO oscillation. The main frequency at 2.40 GHz is confirmed by measuring the emitted radiation by using both an in-vacuum antenna and a horn placed in the far-field region. The frequency response of the MILO SWS is compared to a 3-D simulation performed with MAGIC, an electromagnetic particle-in-cell code. In the first configuration, a microwave output power of 1 GW has been obtained, which is in good agreement with the simulations. Then, an optimization of the cathode geometry has led to an increase of the pulse duration and to a better stability of the emission frequency. Finally, based on the fair agreement between the experimental results and the corresponding simulations, a novel design is presented, which should give a higher emitted power at 2.34 GHz.

No abstract

No abstract

An experiment at microwave frequencies confirms the recent prediction that a Smith-Purcell [S. J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953)] free-electron laser equipped with sidewalls can emit radiation at the frequency of the surface wave. The power output is considerably greater than for the previously observed emission at the second harmonic, in agreement with three-dimensional simulations. The dependence of frequency on beam energy and emission angle is in good agreement with three-dimensional theory and simulations. Provided that a reduction in scale can be achieved, a path is open to coherent Smith-Purcell radiation at terahertz frequency.

This paper presents the design, fabrication, and characterization of a compact wideband antenna for high-power microwave applications. The antennas proposed are array of high-power wideband patches with high compactness and less than λ/10 thick. The concept developed can be fed by highvoltage signals (up to 60 kV) in repetitive operation. Two designs are produced at central frequencies of 350 MHz and 1 GHz. Their relative bandwidth is larger than 40% at 350 MHz and 25% at 1 GHz for S11 < −10 dB, respectively. The arrays studied produce a gain of more than 14 dB.Index Terms-Broad-band antennas, high-power microwave (HPM) antennas, patch antennas.

No abstract