5-Carb­oxy-2-isopropyl-1H-imidazol-3-ium-4-carboxyl­ate monohydrate

In the title compound, C8H10N2O4·H2O, the imidazole N atom is protonated and one of the carboxyl­ate groups is deprotoned, forming a zwitterion. An intra­molecular O—H⋯O hydrogen bond occurs. The crystal structure is stabilized by inter­molecular N—H⋯O and O—H⋯O hydrogen bonds. In addition, inter­molecular N—H⋯O and O—H⋯O hydrogen bonds link the mol­ecules into two-dimensional networks parallel to (10)

Theoretical study of a W-band-covering frequency tunable gyrotron

The gyrotron has already demonstrated the capability of generating high-power coherent electromagnetic (EM) radiation at high frequencies and finds application in fusion plasma heating and magnetic resonance spectroscopy. In this article, we propose a W-band gyrotron, which uses a so-called multimode switching scheme to realize ultrabroadband frequency tuning capability, nearly covering about 70% of the W-band (75-110 GHz) range. The tuning strategy used to suppress mode competition and stabilize gun parameters in such an open-cavity multimode switching gyrotron is presented. Theoretical study shows that the multimode switching gyrotron can generate a frequency tuning range much wider than a conventional step-tuning gyrotron or a single-mode tuning gyrotron. In addition, another technology that uses a slot-assisted circuit to select only axis-symmetrical TE operating modes is presented. Using such a circuit, a tuning range of about 25 GHz in the W-band is obtainable. The proposed multimode switching gyrotron is a promising ultrabroadband source for millimeter-wave and terahertz-wave applications

Smith-Purcell radiation from time grating

Smith-Purcell radiation (SPR) occurs when an electron skims above a spatial grating, but the fixed momentum compensation from the static grating imposes limitations on the emission wavelength. It has been discovered that a temporally periodic system can provide energy compensation to generate light emissions in free space. Here, we introduce temporal SPR (t-SPR) emerging from a time grating and propose a generalized t-SPR dispersion equation to predict the relationship between radiation frequency, direction, electron velocity, modulation period, and harmonic orders. Compared to conventional SPR, t-SPR can: 1) Provide a versatile platform for manipulating SPR emission through temporal modulation (e.g., period, amplitude, wave shape). 2) Exhibit strong robustness to the electron-grating separation, alleviating the constraints associated with extreme electron near-field excitation. 3) Introduce additional energy channels through temporal modulation, enhancing and amplifying emission.Comment: 6 pages, 3 figure

Bimodal vortex Smith-Purcell radiation

A vortex Smith-Purcell radiation (VSPR) with twin operation points, namely bimodal VSPR, is proposed based on a depth-modulated triple-slots helical grating. Due to the Brillouin-zone folding phenomenon, the dispersion of the helical grating is folded twice in the momentum space. Thus, two spoof surface plasmon (SSP) modes carrying orbital angular momentum can be directly diffracted into the vortex beam. When a ring-shaped e beam flies over the surface of the helical grating, the two SSP modes can be effectively excited owing to the momentum matching. Accordingly, a bimodal vortex Smith-Purcell radiation is achieved when the operating frequencies are in the radiation region, which is validated by the probed intensities and field distributions over the grating. The proposed bimodal vortex Smith-Purcell radiation may facilitate the generation and applications of vortex beams in microwave and terahertz band

Coherent terahertz Smith-Purcell radiation assisted by quasi-BIC

A free-electron-driven terahertz (THz) source based on coherent Smith-Purcell radiation (SPR) assisted by bound state in the continuum (BIC) is proposed in this paper. A reflection-type quasi-BIC with ultrahigh quality factor is formed by continuously tuning the structural parameter of the compound grating, which results from the wavevectors mismatch between the incident plane wave and the guided mode. When a sheet electron beam flies over the surface of the grating, the SPR will be enhanced at the resonant frequency of the quasi-BIC and become coherent accordingly. The forming process of the BIC through parameter tuning is analyzed, and the frequency spectrum of the coherent SPR wave demonstrates the enhancement effect of the quasi-BIC. The proposed quasi-BIC-assisted coherent THz SPR scheme may bring possibilities to the design and applications based on compact THz sources

Development of a 1-THz 4th-harmonic gyrotron

A design of a 1-THz 4th Harmonic Gyrotron is proposed in this paper. Fourth harmonic interaction is adopted to lower the strength of the external magnet. The magnet can be as low as 10T. Such a low-intensity magnetic field can be easily proposed by a superconduct magnet, which make the generation of continuous waves at 1 THz possible. Seeing that the mode competition is extremely fierce, a large orbit gun is employed as the driven source. An 80-kV, 0.7-A electron beam is injected into the interaction circuit to excite the fourth-harmonic electromagnetic waves. According to the cold dispersive diagram, the TE4, 8 mode of the cylindrical waveguide is selected as the operating mode to further suppress the mode competition induced by the fundamental modes, the 2nd harmonic modes and the 3rd harmonic modes. It could be inferred based on the multi-mode time-domain theory that an output power of 1.15 kW can be achieved. The scheme diagram for the hot test is proposed. The LOG is chosen as the electron gun. Particular structure is employed for improving the output efficiency in the interaction circuit

Design of an ultra-low spread magnetic cusp gun based on the compensation principle

In this paper, a design of a magnetic cusp gun with ultra-low velocity spread is proposed. Based on the Lagrange mechanics, the spread in the generalized angular momentum and the spread in guiding center radius can compensate each other for low velocity spread