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

Detection of Quasi-periodic Oscillations in SGR 150228213

The detection of quasi-periodic oscillations (QPOs) in magnetar giant flares (GFs) has brought a new perspective to study the mechanism of magnetar bursts. Due to the scarcity of GFs, searching QPOs from magnetar short bursts is reasonable. Here we report the detection of a high frequency QPO at approximately 110 Hz and a wide QPO at approximately 60 Hz in a short magnetar burst SGR 150228213, with a confidence level of 3.35$\sigma$. This burst was initially attributed to 4U 0142+61 by $Fermi$/GBM on location, but we haven't detected such QPOs in other bursts from this magnetar. We also found that there was a repeating fast radio burst associated with SGR 150228213 on location. Finally, we discuss the possible origins of SGR 150228213

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

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

AtHMA4 drives natural variation in leaf Zn concentration of Arabidopsis thaliana

Zinc (Zn) is an essential element for plant growth and development, and Zn derived from crop plants in the diet is also important for human health. Here, we report that genetic variation in Heavy Metal-ATPase 4 (HMA4) controls natural variation in leaf Zn content. Investigation of the natural variation in leaf Zn content in a world-wide collection of 349 Arabidopsis thaliana wild collected accessions identified two accessions, Van-0 and Fab-2, which accumulate significantly lower Zn when compared with Col-0. Both quantitative trait loci (QTL) analysis and bulked segregant analysis (BSA) identified HMA4 as a strong candidate accounting for this variation in leaf Zn concentration. Genetic complementation experiments confirmed this hypothesis. Sequence analysis revealed that a 1-bp deletion in the third exon of HMA4 from Fab-2 is responsible for the lose of function of HMA4 driving the low Zn observed in Fab-2. Unlike in Fab-2 polymorphisms in the promoter region were found to be responsible for the weak function of HMA4 in Van-0. This is supported by both an expression analysis of HMA4 in Van-0 and through a series of T-DNA insertion mutants which generate truncated HMA4 promoters in the Col-0 background. In addition, we also observed that Fab-2, Van-0 and the hma4-2 null mutant in the Col-0 background show enhanced resistance to a combination of high Zn and high Cd in the growth medium, raising the possibility that variation at HMA4 may play a role in environmental adaptation

Manipulating spatial structure of high-order quantum coherence with entangled photons

High-order quantum coherence reveals the statistical correlation of quantum particles. Manipulation of quantum coherence of light in temporal domain enables to produce single-photon source, which has become one of the most important quantum resources. High-order quantum coherence in spatial domain plays a crucial role in a variety of applications, such as quantum imaging, holography and microscopy. However, the active control of high-order spatial quantum coherence remains a challenging task. Here we predict theoretically and demonstrate experimentally the first active manipulation of high-order spatial quantum coherence by mapping the entanglement of spatially structured photons. Our results not only enable to inject new strength into current applications, but also provide new possibilities towards more wide applications of high-order quantum coherence.Comment: 11 pages, 5 figure

Design of a 1-THz 4th-harmonic gyrotron driven by large-orbit beam

In this paper, the design of a 4th-harmonic gyrotron with 1-kW-level output power at 1 terahertz (THz) is presented. A unique advantage of this design is that, with a well-optimized magnetic-cusp large-orbit electron gun, the designed gyrotron can operate from 1st harmonic to 4th harmonic in multiple discrete bands by varying the operating voltage. By carefully balancing the competing modes, the gyrotron can be tuned to operate at six candidate modes, including TE1,2 for fundamental harmonic, TE2,3 and TE2,4 for 2nd harmonic, TE3,5 and TE3,6 for 3rd harmonic, and TE4,8 for 4th harmonic interactions. As the main operating mode, the TE4,8 can generate a peak output power of 1.68 kW, with an efficiency of about 2.1%, and a magnetically controlled frequency tuning range of about 1.8 GHz around 1 THz. The impact of the longitudinal nonuniformity of the cavity at high-harmonic interaction was also studied. It shows a radial tolerance of several micrometers will significantly elevate the start-oscillation current and deteriorate output performance. This design is towards the development of a synthesizing THz source with ultra-wideband tuning capability ranging from the sub-millimeter-wave to 1-THz bands