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Extended interaction oscillators (EIOs) are high-frequency vacuum-electronic sources, capable to generate millimeter-wave to terahertz (THz) radiations. They are considered to be potential sources of high-power submillimeter wavelengths. Different slow-wave structures and beam geometries are used for EIOs. This paper presents a quantitative figure of merit, the critical unloaded oscillating frequency (fcr) for any specific geometry of EIO. This figure is calculated and tested for 2π standing-wave modes (a common mode for EIOs) of two different slow-wave structures (SWSs), one double-ridge SWS driven by a sheet electron beam and one ring-loaded waveguide driven by a cylindrical beam. The calculated fcrs are compared with particle-in-cell (PIC) results, showing an acceptable agreement. The derived fcr is calculated three to four orders of magnitude faster than the PIC solver. Generality of the method, its clear physical interpretation and computational rapidity, makes it a convenient approach to evaluate the high-frequency behavior of any specified EIO geometry This allows to investigate the changes in geometry to attain higher frequencies at THz spectrum. [ABSTRACT FROM AUTHOR]

Extended interaction oscillators (EIOs) are millimeter-wave to terahertz vacuum electronic sources, based on the Smith-Purcell (Cerenkov) interaction between an electron beam of low to moderate voltage and a resonant slow-wave structure. They have been analyzed using the power-balance and Particle in cell (PIC) methods. In this paper, based on power-balance method, a load-line concept is introduced to investigate the EIOs. By this approach, the analysis of EIOs is much faster than the PIC method, and a wider quantitative and qualitative insight into the interaction process is obtained compared with the common power-balance method. To achieve the optimum RF power from an EIO, a region on the defined “beam-line” curve is assigned. A “frequency-shift line” curve is also derived to obtain the electronic tuning of the oscillator. In addition, the correct steady state in the multivalued solution conditions can be selected, which is not evident in the power-balance approach. A 94-GHz sheet-beam EIO is analyzed and optimized in this way, and the results are compared with those of a PIC solver. [ABSTRACT FROM PUBLISHER]

At lower frequency regime, altering the surface structure modifies the characteristics of propagating effective surface plasmons (ESPs), particularly their interaction with light. Movement of an electron beam in the proximity of the surface of a structured metallic grating excite these ESPs, which due to existence of a velocity phase match, they are able to emit terahertz (THz) waves known as Smith–Purcell (SP) radiation. By introducing a femtosecond perturbation (a single electron bunch), the important characteristics of a desired grating are revealed. Through our 3-D investigations, we find the incoherent THz radiation frequency span, and moreover we confirm that the frequency of the ESP is always less than the minimum SP frequency. Additionally, we find that the maximum of signal amplitude is distributed around 90°, only if the grating width is comparable to the longest SP wavelength. Also we learned that by increasing the grating length, the magnitude and spectral resolution of the radiation increases too. In order to study the coherent (superradiant) radiation, we use a train of electron bunches with variable bunch-to-bunch distances, and we calculate the radiation angle of the coherent SP signal. Simulations on the generation of SP radiation at THz frequencies are performed with the help of the 3-D particle-in-cell (PIC) finite integral (FI) method, in which the results agree very well with previously reported 2-D simulations. [ABSTRACT FROM PUBLISHER]

Over the past year, a collaborative effort between Advanced Energy Systems and Commissariat à l’Energie Atomique/Centre d’Etudes Scientifiques et Techniques d’Aquitaine has achieved the first lasing of a cylindrical Smith–Purcell free-electron laser (CSPFEL). These proof-of-principle experiments employed an 80-keV 45-A 200-ns full-width at half-maximum thin annular electron beam propagating just above a cylindrical grating. The interaction of the beam with the evanescent grating mode resulted in strong beam bunching and generation of high-power millimeter-wave radiation. First lasing of the CSPFEL was achieved with a grating period of 2 cm (5-GHz fundamental). Further experiments were performed with a 6-mm period grating (15-GHz fundamental) yielding 10 kW at the second harmonic, 30 GHz. This paper discusses only the second experiment. Comparison of the experimental results with particle-in-cell (PIC) simulations shows good agreement. An experiment at 100 GHz is in progress. The basic properties of Smith–Purcell radiation and the evanescent grating mode will be presented first. Then the experimental configuration and results will be discussed. The next section will cover the PIC simulations and comparison with the experiment. The final section will summarize the results and discuss the future directions for this research. The long-term goal is the development of compact terahertz devices with sufficient power to address applications that are impractical or impossible with the existing sources. [ABSTRACT FROM PUBLISHER]

The capabilities of two types of terahertz sources based on stimulated Smith--Purcell radiation of electrons in open cavities are discussed. A series of developed pulsed orotrons provides coherent radiation with an output power of 1-0.1 W in the frequency range of 90-410 GHz, with high frequency stability and broad-band electromechanical frequency tuning. A promising alternative source with smaller currents than that in orotrons is a frequency multiplier based on excitation of a surface wave of a periodic structure and Smith-Purcell radiation of arising electron bunches inside the orotron cavity. In contrast to a number of works where only an open grating is used, exploiting a cavity enables a stimulated radiation process with a much higher power. The developed theory demonstrates the possibility of single-mode generation in such multipliers with wide electron beams. [ABSTRACT FROM AUTHOR]

Presents a study which examined the frequency multiplication in the Smith-Purcell laser as a way to obtain a powerful millimeter/submillimeter radiation from a high-current moderately relativistic rectilinear electron beam. Triple resonance in Smith-Purcell oscillator; Simulations; Conclusion.

Presents a two-stage scenario for the generation of coherent Smith-Purcell radiation over a metallic grating by a relativistic electron beam. Mode structure and dispersion relation of slow waves supported by a metallic grating structure; Excitation of a slow wave by a relativistic electron beam; Schematic diagram of electron beam propagation over a metallic grating.