[en] The operating characteristics and the nonstationary behavior of a 10-vane strapped magnetron oscillator was numerically analyzed using the three-dimensional particle-in-cell (PIC) code MAGIC3D. The saturated output power and the operating frequency were 1.07 kW and 2.470 GHz, respectively, agreeing well with the measured values of 1.04 kW and 2.465 GHz. The magnetron could be operated at a power conversion efficiency of 75 % for a beam voltage of 4.3 kV and an anode current of 0.33 A when an external axial magnetic field of 0.19 T was applied. A transition from the stationary state to the nonstationary state was observed when the cathode current was three times higher than the starting oscillation current.

[en] Highlights: • Complex dielectric constant of lipids in NaCl solutions is measured in 0.3–1.2 THz. • Fast water fraction inside multi-lamellar vesicles increased with NaCl concentrations. • Correlation between salt-induced change in water structure and lipid structure is observed. Salt-induced change in the structure of water molecules inside multi-lamellar vesicles is experimentally studied with terahertz time-domain spectroscopy. The complex dielectric constant of 1, 2-ditetradecanoyl-sn-glycero-3-phosphocholine model membranes dispersed in NaCl solution with different salt concentrations are measured. Structure of water molecules in the solution is characterized from the measured dielectric constant using Debye relaxation model. Combined with small-angle X-ray scattering observation, it is found that salt-induced change of water structure, especially fast water fraction, show strong correlation with the increase in nanometer-scale multi-lamellar repeat space. This suggests that water could be critical in nanometer-scale membrane-membrane communications.

[en] A method using a combination of a magneto-optical trap and a mass spectrometer, referred to as atom trap-mass spectrometry (ATMS), is employed for calcium-isotope analysis. A calcium magneto-optical trap with a Zeeman slower is used in the first isotope-selection stage of the ATMS. The trapped calcium isotope is ionized by using a frequency-doubled Nd:YAG laser, and the photoions are analyzed using a time-of-flight mass spectrometer. The isotope-selection characteristics of the combination method and further improvements in the method are discussed in this work.

[en] A simulation of coherent and super-radiant Smith-Purcell radiation is performed in the gigahertz regime using a three-dimensional particle-in-cell code. The simulation model supposes a rectangular grating to be driven by a single electron bunch and a train of periodic bunches, respectively. The true Smith-Purcell radiation is distinguished from the evanescent wave, which has an angle independent frequency lower than the minimum allowed Smith-Purcell frequency. We also find that the super-radiant radiations excited by periodic bunches are emitted at higher harmonics of the bunching frequency and at the corresponding Smith-Purcell angles

[en] A sidewall grating for the Smith-Purcell device is proposed to enhance the coupling of the optical mode with the electron beam and, consequently, relax the stringent requirements to the electron beam. With the help of three-dimensional particle-in-cell simulations, it has been shown that, comparing with the general grating, the usage of a sidewall grating improves the growth rate and dramatically shortens the time for the device to reach saturation. It is also found that the sidewall grating holds the potential to reduce the start current for the operation of a Smith-Purcell backward wave oscillator

[en] A novel backward wave oscillator (BWO) is presented by utilizing a slotted sine waveguide with a pencil electron beam to produce the high power terahertz wave. The high frequency characteristics including dispersion properties, interaction impedances, and transmission characteristics of the slotted sine waveguide are analyzed in detail. The high frequency system including the output coupler, slow wave structure (SWS), and reflector are designed properly. A 3-D particle-in-cell mode is applied to predict the device performance of the BWO based on the novel SWS. The investigation results demonstrate that this device can generate over 8.05 W output power in the frequency range of 363.4–383.8 GHz by using a 30 mA pencil electron beam and adjusting the beam voltage from 20 kV to 32 kV.

[en] A novel Ka-band folded waveguide (FW) amplifier for traveling wave tubes (TWT) is investigated. The dispersion curve and interaction impedance are obtained and compared to the normal FW circuit by numerical simulation. The interaction impedance is higher than a normal circuit through the whole band. We also study the beam-wave interaction in this novel circuit, and the nonlinear large-signal performance is analyzed by a 3-D particle-in-cell code MAGIC3D. A much higher continuous-wave (CW) output power with a considerably shorter circuit compared to a normal circuit is predicted by our simulation. Moreover, the novel FW even has a broader 3-dB bandwidth. It therefore will be useful in designing a miniature but high-power and broadband millimeter-wave TWT. (fundamental areas of phenomenology (including applications))

[en] The 60-GHz traveling-wave tube (TWT) prevails nowadays as the amplifier for the satellite communication and electronic countermeasures. The folded waveguide (FW) is a promising all-metal slow-wave structure (SWS) for the 60-GHz TWT with advantages of robust performance, fine heat dissipation, considerable power and bandwidth. A novel FW periodically loaded with rectangular grooves is analyzed for the purpose of gaining higher power and gain. The rf characteristics are investigated by numerical simulation, and the nonlinear large-signal performance of such a TWT is analyzed by a 3D particle-in-cell code MAGIC. Compared with normal circuits, relatively higher continuous-wave power (40–56 W) and similar bandwidth (5 GHz) are predicted by simulation. Meanwhile, the designed operation voltage is 10.5 kV, which keeps the low-voltage advantage of the popular helix TWT competitor. The novel FW will favor the design of a broadband and high-power 60-GHz TWT. (paper)

[en] The electromagnetic response of a metallic metamaterial to fast-moving electrons is studied by numerical simulations. The considered metamaterial is a one-dimensional array of slits perforated on a metallic film and is found to generate Cerenkov wakes when the electron beam travels near its surface. There is no energy threshold for the generation of such wakes, which would be promising to lower the operation energy of the electron beam in compact Cerenkov free-electron-lasers. Moreover, by analyzing the spectral dependence of the Cerenkov light, it is possible to map the dispersion relation of the guided modes supported by the metamaterial.

[en] An approach to the enhancement of terahertz (THz) Smith-Purcell (SP) radiation from an open rectangular grating driven by two electron beams is presented in this paper. In the present work, two electron beams with a velocity separation propagating over the grating are employed. With the help of a two-dimensional particle-in-cell simulation, some nonlinear processes from spontaneous emission to superradiant radiation are demonstrated. The simulation results show that the enhancements of SP radiation power, the shortened saturation time, and the lower threshold current can be obtained at an optimum voltage ratio due to the two-beam interaction