Accepted
, , Received Date: 2025-09-17
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, , Received Date: 2025-09-18
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Based on the generalized reduced R -matrix theory, this work performs a comprehensive analysis of all available experimental data for the 6He system by using the R -matrix analysis code (RAC). A complete set of evaluated nuclear data is obtained for major reaction channels induced by triton beams in an energy range of 10–2—20 MeV. The evaluated integral cross sections include T(t, 2n)4He, T(t, n)5He, and T(t, d)4H reactions, and the differential cross sections include T(t, 2n)4He, T(t, n)5He, T(t, d)4H, and T(t, t)T. The evaluation results show that they are in good agreement with experimental data and the evaluated data of ENDF/B-VIII.1. In particular, for the T(t, 2n)4He reaction, the evaluated cross sections are consistent with the existing experimental results over the full energy range, and a resonance dominated by the 2+ level is observed near 2.9 MeV. At 1.9 MeV, where experimental measurements of both integral cross sections and angular distributions are available, the evaluation accurately reproduces both observables. The combined constraint of integral and differential data significantly improves the stability of R-matrix parameters and the reliability of the evaluation. Based on the global analysis of the 6He system, this work also provides supplementary cross section data for the T(t, n)5He and T(t, d)4H reactions. The results contribute to the nuclear data foundation for fusion-related reactions and lay the groundwork for future joint evaluation with the mirror 6Be system.The datasets presented in this paper are openly available at https://www.doi.org/10.57760/sciencedb.j00213.00202 .
, , Received Date: 2025-09-18
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For terahertz systems where reflected signals carry effective information, such as terahertz time-domain reflection systems and full-duplex communication systems, existing nonreciprocal terahertz devices often treat reflected signals as interference and suppress them during isolation. This makes them incompatible with the requirements of such systems for isolating incident signals while directionally extracting and detecting reflected signals. To address this limitation, this study innovatively proposes a terahertz isolator based on a magneto-optical selection–multi-port architecture. The device converts linearly polarized light into a specific circular polarization state through orthogonal double gratings, and by combining the magneto-optical selectivity of InSb material, a nonreciprocal transmission path is constructed. Furthermore, the magneto-optical regulation mechanism innovatively combines branch waveguides with multiple ports and the characteristic of regulating terahertz transmission paths, while achieving isolation of incident/reflected signals and directionally extracting the reflected signals. The simulations of the influences of structural dimensions and external environmental conditions on the nonreciprocal characteristics of the device indicate that when the temperature is 250 K, the magnetic field is 0.3 T, and the structural parameters are set as follows: branch length of 170 μm, center-to-center spacings of adjacent branches of 125 μm, 125 μm, 120 μm, and 120 μm, InSb layer thickness of 5 μm, grating layer thickness of 50 μm, and substrate layer thickness of 20 μm, then the device achieves a high isolation of 63.12 dB at 0.73 THz. Additionally, at 0.78 THz, the bidirectional transmission efficiency reaches 36.31%, with a 3 dB bandwidth of 0.25 THz. This device has the advantages such as high isolation, low operating magnetic field strength, and integration of dual functions. It reduces interference from incident signals on reflected signals, simplifies subsequent processing steps such as noise reduction and localization of effective reflected signals, and improves the system's detection performance for weak signals. This provides essential support for expanding terahertz applications to more fields, including non-destructive testing and communication.
, , Received Date: 2025-08-06
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GeSn alloy, as a novel silicon-based optoelectronic material, exhibits significant application potential in the field of infrared photonics due to its tunable bandgap properties and compatibility with silicon-based CMOS processes. Although the experimental performance of GeSn laser under low-temperature conditions has been preliminarily validated, the optimization and practical application of this device still face challenges such as insufficient understanding of material properties. This work addresses issues such as the unclear carrier dynamics mechanisms in GeSn alloy applications in infrared photonics. A theoretical model integrating band parameters, non-equilibrium carrier transport, and radiative recombination is proposed to systematically investigate the mechanism by which thermal excitation and phonon-assisted processes influence the direct-band spontaneous emission in GeSn alloys under variable temperature conditions. The results indicate that the carrier transfer process between the ΓCBM and LCBM energy bands of GeSn alloy exhibits significant composition dependence: for low-Sn-content GeSn alloy with Sn content below 10%, temperature-induced LCBM→ΓCBM electron transfer dominates, leading to an increase in direct band emission efficiency with temperature rising, whereas in high-Sn-content GeSn alloys with Sn content between 10% and 20%, the ΓCBM→LCBM electron escape process is more pronounced, resulting in a decrease in direct band emission efficiency with the increase of temperature. A modified Arrhenius model of the carrier dynamics competition further indicates that thermal excitation and phonon scattering synergistically regulate electron transfer between ΓCBM and LCBM. The analysis based on the modified Arrhenius model further indicates that both thermal excitation and phonon-assisted processes promote the injection and escape of electrons in the ΓCBM valley, acting as key factors in modulating the radiative recombination efficiency at the direct bandgap of GeSn alloy. The red shift of the peak position in the spontaneous emission spectrum of GeSn alloy is mainly due to the bandgap contraction effect; At the same time, phonon-assisted processes reduce the dispersion of carrier energy distribution, leading to a pronounced narrowing effect in the direct band emission spectrum. The quantitative findings further elucidate the mechanism by which thermal excitation and phonon-assisted processes influence the direct bandgap luminescence of GeSn alloy, providing theoretical guidance for the performance regulation of infrared optoelectronic devices.
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The deformation of metallic glasses is generally attributed to the rearrangements of local structures; however, the structural response mechanisms induced by different atomic bond types and cluster motifs during deformation remain unclear. To establish the correlation mechanism between atomic bonding characteristics and local structural evolution during metallic glass deformation, we employed pair distribution function (PDF) analysis of in-situ synchrotron high-energy X-ray total scattering to investigate the local structural evolution of metallic glasses with Pd77.5Cu6Si16.5metal-metalloid (M-Met) and Zr59(Cu0.55Fe0.45)33Al8 metalmetal (M-M) bonding during tensile deformation. Under elastic tensile strain, M-M systems exhibit reduced packing density in both short-range order (SRO) and medium-range order (MRO), and this process is dominated by the medium-range ordered structure, with the overall structure tending to disordering. By contrast, although the overall packing density of SRO and MRO in M-Met systems tends to decrease under strain, cooperative rearrangement of local bonds increases the SRO ordering and this ordering extends to the MRO regime. In the late stage of deformation, its structure gradually tends to disorder, and this response process is dominated by MRO structures. It is found that the bond type significantly affects the changes in interatomic correlation length and local order, thereby modulating microstructural heterogeneity and deformation behavior. These results provide new insight into the microstructural origins of deformation behavior in metallic glasses.
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Traditional GaN materials inevitably exhibit lattice mismatch and differing thermal expansion coefficients during epitaxial growth, which often leads to a sharp increase in dislocation density and interface defects. This results in severe current collapse, degraded high-frequency performance, and reliability degradation in GaN HEMT devices, representing one of the key bottlenecks facing GaN-based HEMT RF devices. Van der Waals epitaxial bonding between BN and GaN effectively suppresses dislocations and relieves material stress, playing a crucial role in enhancing the high-frequency performance and reliability of GaN HEMT devices. This paper fabricates AlGaN/GaN HEMT devices grown on BN buffer layers using van der Waals epitaxy. Test results indicate that compared to conventional devices without a BN buffer layer, not only has the on-resistance been reduced by 40% and the peak transconductance increased by 54%, but the maximum output current has also been boosted by 67%. Under strong negative gate voltage stress conditions, its performance significantly outperforms conventional devices, with a current collapse ratio of only 9.2%. During the pulse width reduction from 200 ms to 100 μs, only a minimal drift of approximately 0.09 V occurs. Under high-temperature conditions (125°C), the current collapse ratio is only 31%, with smaller reductions in transconductance and negative drift of Vth. The overall degradation is significantly lower than that of conventional AlGaN/GaN HEMT devices based on epitaxial systems, demonstrating excellent high-temperature dynamic stability. Additionally, RF performance improved, with fT increasing from 48 GHz to 90 GHz and fmax rising from 114 GHz to 133 GHz. This work fully demonstrates this interface optimization strategy simultaneously enhances carrier transport, suppresses trap effects, and improves RF performance, providing an effective pathway for realizing high-frequency, high-power, and highly reliable GaN HEMTs.
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As a popular low-temperature plasma source, dielectric barrier discharge (DBD) has drawn significant attention due to its extensive application field including surface modification, material synthesis, sterilization, etc. DBD has presented different modes with varying experimental conditions. In order to address the formation mechanism of the different modes, a two-dimensional axis-symmetric fluid model is employed to simulate the characteristics of DBD in atmospheric pressure argon. Results indicate that DBD undergoes a scenario from a discretely-filamentary mode, a diffuse mode, a complementarily-filamentary mode, to a columnar mode with increasing voltage amplitude (Va) or discharge power (Pdis). Waveforms of applied voltage and discharge current indicate that for every discharge mode, the discharge current waveforms are always symmetrical for positive and negative discharge half-cycles. The discharge current exhibits single-pulse characteristics per half-cycle with low Va (or Pdis), and turns to double-pulse, triple-pulse, or multi-pulse characteristics per half-cycle with increasing Va (or Pdis). Spatial-temporal evolutions of electron density and electric field reveal that residual electrons play an important role in the discharge mode. Electric field (E) is mainly composed of its axial component, and its radial component only appears at the edge of the electrode in the diffuse mode. In the complementarily-filamentary mode, the locations of the strong-MDs and those of the weak-MDs alternate in the consecutive half-cycles. The strong-MD channels are stationary at fixed locations in the consecutive half-cycles for the columnar mode. In addition, the diameter of residual electrons in the columnar mode is larger than that in the filamentary mode. Moreover, the generation rate of Ar* increases, while the energy efficiency of the discharge shrinks with increasing Va (or Pdis). These results are of great significance for the deep understanding of discharge mode and the improving of DBD performance.
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Triboelectric nanogenerators (TENGs) have emerged as a transformative technology for self-powered sensing and harvesting ubiquitous ambient mechanical energy. However, a critical bottleneck hindering their long-term reliability is the inevitable material wear and performance degradation caused by sustained friction between contacting layers. This work presents a slotted rotor-based TENG (SRTENG) that fundamentally addresses this wear challenge through an intermittent contact mechanism. The core innovation lies in a unique structural comprising a rotating shaft with precisely machined axial slots and a rotor disk equipped with a spring-loaded pin. As the shaft rotates, the pin engages with the helical slots, converting the uniform rotary motion into a controlled, periodic vertical reciprocating motion of the entire rotor assembly. This mechanical transformation shifts the operational mode from continuous sliding contact to periodic contactseparation cycles between the rotor-mounted electrode and the stationary bottom triboelectric layer, drastically minimizing direct friction time. Systematic experimental characterization demonstrates the efficacy of this design. Quantitative analysis confirms a 90% reduction in contact friction duration per cycle compared to standard rotary TENGs. The SR-TENG consistently delivers a stable opencircuit voltage of 40 V at 200 rpm. More critically, the device exhibits outstanding durability. After a rigorous accelerated test spanning 288,000 continuous cycles, the SR-TENG retains over 95% of its initial electrical output. Microscopic inspection via scanning electron microscopy reveals that the delicate microstructures on the triboelectric layer surface remain intact with no observable abrasion, providing direct physical evidence of the wear-mitigation effect. Beyond energy harvesting, the SR-TENG functions as a self-powered rotational speed sensor. Its output signal frequency shows an excellent linear relationship with rotational speed, and the device boasts a rapid dynamic response time of less than 10 ms, enabling precise real-time monitoring. In conclusion, this study proposes a highly effective and mechanically elegant structural strategy to solve the wear problem in rotary TENGs. The SR-TENG design not only ensures exceptional long-term operational stability and performance retention but also demonstrates versatile functionality as a sensor. This work provides a viable pathway for developing durable self-powered systems, with significant application potential in industrial equipment condition monitoring, distributed IoT sensor networks, and smart infrastructure.
Abstract +
Diamond holds significant application potential in microwave and deep-space observation windows due to its exceptionally low dielectric loss. This study aims to systematically investigate the key factors influencing the dielectric loss tangent (tanδ) of single-crystal diamond (SCD) and to establish correlations between its dielectric properties and material characteristics. To this end, dielectric property measurements were performed on SCD samples synthesized using microwave plasma chemical vapor deposition (MPCVD) systems under different growth conditions. A comprehensive material characterization was carried out using birefringence microscopy, Raman spectroscopy, photoluminescence (PL), and X-ray diffraction (XRD) to analyze crystal quality, defect distribution, and strain. The experimental results show that the measured tanδ of the SCD samples reached a minimum value of 4.94 × 10-5. Detailed analysis reveals that the dielectric loss in SCD is attributed to a combination of factors: the density and distribution of internal defects (e.g., vacancies and impurities), the presence of internal growth sectors and boundaries, and phonon polarization losses induced by lattice vibrations under an external electric field. It is conclusively identified that defect density is the predominant factor governing dielectric loss. Furthermore, the study demonstrates that as the test frequency increases, contributions from defect polarization and interfacial polarization at sector boundaries become more pronounced, leading to higher overall loss. Interestingly, it was found that certain periodic defect structures can partially suppress the phonon-polarization related loss mechanism, thereby contributing to a lower tanδ in some samples. In conclusion, this work elucidates the multi-faceted origins of dielectric loss in SCD and provides valuable insights and a methodological framework for guiding the synthesis and processing of diamond crystals with further enhanced dielectric properties for advanced microwave and terahertz applications.
Analysis of a Multi-user Quantum Teleportation Network Based on Continuous-Variable Entangled States
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Quantum teleportation enables the secure transfer of unknown quantum states between remote users and is a key technology in quantum information science. Networks based on continuous-variable entangled states can extend both the user capacity and the transmission distance of quantum teleportation. This paper analyzes quantum teleportation network schemes based on three types of continuous-variable entangled states (EPR entangled state, GHZ entangled state, and linear cluster entangled state). The results show that due to the correlation properties of different types of entangled states, different quantum teleportation networks have advantages in terms of fidelity, transmission distance, and quantum resource consumption of quantum teleportation. For low-error-rate applications such as quantum computing, EPR states provide the highest fidelity. When parallel teleportation of multiple states is required, networks based on EPR or cluster entangled states provide the necessary throughput performance. In scenarios where quantum resources are severely limited, the GHZ-based teleportation protocols minimize the number of entangled modes while preserving acceptable fidelity. For applications demanding controlled teleportation, both GHZ and cluster states supply the essential multi-party correlations. Notably, cluster states offer a practical trade-off between fidelity and resource overhead, rendering them attractive for certain implementations. This study provides a reference for the design of multi-user metropolitan quantum teleportation networks.
, , Received Date: 2025-11-09
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Based on the Gradient Boosting Decision Tree (GBDT) machine learning algorithm, this study develops a model for predicting the fusion reaction cross-section (CS) of $^{99-103}{\rm{Mo}}^*$, aiming to explore the optimal synthesis pathway for the medical isotope $^{99}{\rm{Mo}}$. The model inputs include characteristic quantities such as reaction energy, proton number, mass number, and binding energy, as well as relevant parameters calculated based on phenomenological theoretical models, with the output being the fusion reaction cross-section. It is found that the mean absolute error (MAE) between the machine learning-predicted CS and experimental values on the test set is 0.0615, which is superior to the 0.1103 predicted by the EBD2 model. On this basis, combined with the GEMINI++ program, the survival probabilities of the neutron decay channels for $^{99-103}{\rm{Mo}}^*$ were calculated to derive the evaporation residue cross-section of $^{99}{\rm{Mo}}$. It is found that the evaporation residue cross-section of the 2n de-excitation channel for $^{4}{\rm{He}}$ + $^{97}{\rm{Zr}}$ at a center-of-mass energy of 18.51 MeV is 1199.80 mb, making it the optimal pathway for synthesizing $^{99}{\rm{Mo}}$. This research validates the reliability of physics-informed machine learning methods in predicting fusion reaction cross-sections and provides a reference for optimizing reaction system selection and producing medical isotopes through fusion reactions in heavy-ion accelerators.
, , Received Date: 2025-09-23
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Borohydrides ($\mathrm{XBH_4}$, $\mathrm{X=Li,\; Na,\; K}$) exhibit an “elemental synergy” effect, characterized by the high neutron absorption cross-section of boron and the excellent moderation capability of hydrogen, making them promising candidates for neutron shielding materials. However, the current lack of experimental and evaluated thermal scattering data for borohydrides in international nuclear data libraries hinders the accurate assessment of their shielding and moderation performance.In this study, material properties including lattice parameters, electronic structures, and phonon densities of states were calculated based on first-principles density functional theory. Subsequently, the corresponding $S(\alpha, \beta)$ data and thermal neutron scattering cross-sections were developed. The simulated lattice parameters show good agreement with experimental data. By comparing the electronic structures and phonon densities of states of $\mathrm{XBH_4}$, the coherent elastic, incoherent elastic, and inelastic scattering cross-sections for the cations X, B, and H were obtained. The results indicate that the thermal neutron cross-sections of the constituent nuclides in $\mathrm{XBH_4}$ exhibit significant differences depending on the cation X.To evaluate the impact of thermal scattering data on neutron shielding effects, a simplified fusion source model was employed using the OpenMC code to compare the leaked neutron energy spectra under different physical models. The results demonstrate that the Free Gas Model (FGM) provides an inaccurate description of neutron moderation due to its neglect of lattice binding effects. Furthermore, owing to the large incoherent scattering cross-section of hydrogen, the coherent elastic scattering cross-sections of the various nuclides have a negligible impact on the neutron energy spectrum. This research fills the gap in thermal neutron cross-section data for borohydrides and establishes a foundation for further investigations into their application as neutron shielding materials. These findings partially fill the gap in thermal neutron cross-section data for borohydrides and lay a foundation for their future application as neutron shielding materials.The datasets presented in this paper, including the ScienceDB, are openly available at https://www.doi.org/10.57760/sciencedb.j00213.00219 .
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This study investigates the dynamic evolution of edge-localized modes (ELMs) in the China Fusion Engineering Test Reactor (CFETR) under the influence of a biased divertor target plate system using integrated numerical simulations. By combining magnetic field line tracing with the three-dimensional equilibrium code HINT and the nonlinear MHD instability code MIPS, the feasibility of employing a biasing system as an ELM control technique for CFETR is systematically evaluated. The results demonstrate that, for an optimal bias configuration, a bias-driven scrape-off layer (SOL) current of 1000 A can significantly alter the pedestal pressure distribution and reduce the saturated kinetic energy of ELM-related instabilities by approximately 70%.
ELM control in H-mode operation is essential for future tokamak reactors such as CFETR, as uncontrolled Type-I ELMs can impose intolerable transient heat loads on plasma-facing components. Although resonant magnetic perturbations (RMPs) are among the most effective ELM control techniques, their implementation in reactor environments is challenged by limited installation space and severe neutron irradiation. In parallel, the biased divertor approach provides a more reactor-compatible alternative by generating helical currents in the SOL without the need for in-vessel coils. In this work, a coupled HINT – MIPS modeling framework is employed to assess the impact of bias-driven SOL currents on three-dimensional MHD equilibrium and edge instabilities in CFETR.
The simulations are based on a 13 MA hybrid H-mode equilibrium. A filament current model combined with magnetic field line tracing is used to calculate the spatial distribution of bias-driven SOL currents along magnetic field lines, as illustrated in Fig. 1(a). The resulting three-dimensional magnetic perturbations are then obtained using the Biot – Savart law. Several representative bias configurations are examined, including“+ + + + + + ++”, “++ ++ ++ --”,“++ -- ++ --”,“+- +- +- +-”, and“-+ -+ -+ -+”. Analysis of the resonant magnetic spectra and magnetic topology reveals that the configuration with all electrodes biased positively exhibits the strongest resonant component at toroidal mode number n=4 maximizing the edge Chirikov parameter (Fig. 1(b)). This configuration is therefore identified as optimal for further investigation.
Using the HINT code, three-dimensional nonlinear resistive equilibria are calculated for different SOL current amplitudes. The bias-driven magnetic perturbations lead to the formation of magnetic islands at rational surfaces and stochastic magnetic fields near the plasma edge, resulting in significant modifications of the pressure profile. The magnitude of pressure redistribution increases with SOL current amplitude as shown in Fig. 2. These equilibrium changes directly affect the pedestal pressure gradient and thus the stability of edge MHD modes.
After establishing the initial 3D equilibrium, the MIPS code is used to simulate MHD instabilities. This code solves the full set of MHD equations in cylindrical coordinates. Fig.3(a) shows the time evolution of MHD instability kinetic energy, comparing cases with and without the n=4 SOL helical current.
Subsequently, the MIPS code is applied to simulate the evolution of edge instabilities based on the reconstructed three-dimensional equilibria. As the SOL current increases from 0 to 1000 A, the linear growth rate and saturated kinetic energy of ELM-related instabilities decrease markedly, with the most pronounced stabilization occurring between 0 and 600 A (Fig. 3(a)). Further increases in SOL current yield diminishing returns, suggesting a combined effect of nonlinear pedestal modification and the intrinsic nonlinear dependence of ballooning-type instabilities on pedestal structure. Pressure perturbation analyses (Fig. 3(b,c)) confirm that the dominant modes are ballooning-like and that their amplitudes are strongly suppressed at higher SOL current levels.
These results clearly demonstrate the potential of biased divertor systems for effective ELM control in CFETR. The generation of SOL helical currents provides a promising and reactorrelevant pathway for mitigating edge instabilities and reducing transient heat loads in H-mode operation. Future work will extend this study using the MARS-F code to incorporate detailed resistive plasma response effects.
ELM control in H-mode operation is essential for future tokamak reactors such as CFETR, as uncontrolled Type-I ELMs can impose intolerable transient heat loads on plasma-facing components. Although resonant magnetic perturbations (RMPs) are among the most effective ELM control techniques, their implementation in reactor environments is challenged by limited installation space and severe neutron irradiation. In parallel, the biased divertor approach provides a more reactor-compatible alternative by generating helical currents in the SOL without the need for in-vessel coils. In this work, a coupled HINT – MIPS modeling framework is employed to assess the impact of bias-driven SOL currents on three-dimensional MHD equilibrium and edge instabilities in CFETR.
The simulations are based on a 13 MA hybrid H-mode equilibrium. A filament current model combined with magnetic field line tracing is used to calculate the spatial distribution of bias-driven SOL currents along magnetic field lines, as illustrated in Fig. 1(a). The resulting three-dimensional magnetic perturbations are then obtained using the Biot – Savart law. Several representative bias configurations are examined, including“+ + + + + + ++”, “++ ++ ++ --”,“++ -- ++ --”,“+- +- +- +-”, and“-+ -+ -+ -+”. Analysis of the resonant magnetic spectra and magnetic topology reveals that the configuration with all electrodes biased positively exhibits the strongest resonant component at toroidal mode number n=4 maximizing the edge Chirikov parameter (Fig. 1(b)). This configuration is therefore identified as optimal for further investigation.
Using the HINT code, three-dimensional nonlinear resistive equilibria are calculated for different SOL current amplitudes. The bias-driven magnetic perturbations lead to the formation of magnetic islands at rational surfaces and stochastic magnetic fields near the plasma edge, resulting in significant modifications of the pressure profile. The magnitude of pressure redistribution increases with SOL current amplitude as shown in Fig. 2. These equilibrium changes directly affect the pedestal pressure gradient and thus the stability of edge MHD modes.
After establishing the initial 3D equilibrium, the MIPS code is used to simulate MHD instabilities. This code solves the full set of MHD equations in cylindrical coordinates. Fig.3(a) shows the time evolution of MHD instability kinetic energy, comparing cases with and without the n=4 SOL helical current.
Subsequently, the MIPS code is applied to simulate the evolution of edge instabilities based on the reconstructed three-dimensional equilibria. As the SOL current increases from 0 to 1000 A, the linear growth rate and saturated kinetic energy of ELM-related instabilities decrease markedly, with the most pronounced stabilization occurring between 0 and 600 A (Fig. 3(a)). Further increases in SOL current yield diminishing returns, suggesting a combined effect of nonlinear pedestal modification and the intrinsic nonlinear dependence of ballooning-type instabilities on pedestal structure. Pressure perturbation analyses (Fig. 3(b,c)) confirm that the dominant modes are ballooning-like and that their amplitudes are strongly suppressed at higher SOL current levels.
These results clearly demonstrate the potential of biased divertor systems for effective ELM control in CFETR. The generation of SOL helical currents provides a promising and reactorrelevant pathway for mitigating edge instabilities and reducing transient heat loads in H-mode operation. Future work will extend this study using the MARS-F code to incorporate detailed resistive plasma response effects.
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Abstract +
Two-dimensional topological materials are ideal candidates for low-dissipation electronic devices due to their non-dissipative edge states. As a typical two-dimensional system, graphene is theoretically predicted to exhibit the quantum spin Hall effect under the spin-orbit coupling interaction. However, the band gap in graphene is only in the order of micro-electron volt, which seriously restricts its practical applications. In this work, based on the first-principles calculations, we investigate the electronic structures and topological properties of strained Zr2C12, which is formed by substitutional doping graphene with the group ⅣB 4d transition metal Zr. The phonon spectrum calculation confirms that the freestanding Zr2C12 exhibits excellent dynamic stability. When the spin-orbit coupling is excluded, the bands cross linearly at the K point near the Fermi level, indicating the Dirac semimetal phase of freestanding Zr2C12. The Fermi velocity of the Dirac point is 0.677 × 106 m/s, which is approximately two-thirds of that in graphene (~ 1.00 × 106 m/s). When the spin-orbit coupling is considered, the Dirac point opens a gap of 4.09 meV, which is three orders of magnitude higher than that of undoped graphene. The parity analysis reveals that the Z2 topological invariant of the freestanding Zr2C12 is 1, indicating the system transits into a two-dimensional topological insulator. We also study the properties of Zr2C12 under strain regulation. The calculation results show that the system remains dynamically stable over a wide strain range of -5% to 6%. When the spin-orbit coupling is absent, the conduction band energy at the Γ point continuously rises with increasing strain, and the system maintains the Dirac semimetal phase. After including the spin-orbit coupling, the system remains the nontrivial topological insulator phase over a wide strain range of -5% to 6%, showing robust topological properties. The band gap at the Dirac point first decreases and then increases with increasing strain. When applying -1.6% compression strain, this band gap decreases to the minimum value of 0.059 meV. When the strain further increases to 6%, this gap increases to the maximum value of 8.41 meV. The edge states calculations of Zr2C12 under 6% expansion strain show that the gapless edge states connect the conduction bands and the valence bands, which further verify the non-trivial topological properties of this system under strain regulation. This study expands the research on transition-metal-doped graphene systems, providing a good material platform for further study of low-dissipation electronic devices and quantum computing and communication.
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Majorana fermions, particles that are their own antiparticles, have attracted significant attention in condensed matter physics due to their exotic properties and potential applications in fault-tolerant topological quantum computing. While nanowire-superconductor hybrid systems and topological insulator-superconductor heterostructures, are considered the most promising platforms for realizing Majorana fermions, recent experimental progress has been overshadowed by controversies, including the retraction of several high-profile papers claiming their observation. These controversies fundamentally originate from experimental data being selectively presented to conform to oversimplified theoretical models. Conventional phenomenological approaches, which model Majorana fermions through simplified effective Hamiltonians, neglect crucial experimental complexities such as quasiparticle excitations in superconductors and the effects of strong proximity tunneling and high magnetic fields. Consequently, they fail to predict the correct parameter regimes for Majorana fermion emergence in realistic devices, leading to false-positive signals in experiments. To overcome these challenges, we develop a comprehensive "dressed Majorana" theory that treats both the electrons in nanowire and superconducting quasiparticle excitations on equal footing. Our results reveal stringent conditions necessary for realization of Majorana fermions: precise alignment of chemical potentials (within ~1 meV in a 1 eV tuning range) and careful control of tunneling strength and magnetic field strengths. These findings explain the persistent absence of definitive signatures in experiments and provide quantitative guidelines for future studies. Notably, for alternative platforms like quantum dot-based "poor mans Majorana" syst ems, our analysis shows that the obtained Majorana wavefunctions are localized at both ends of the superconductor, demonstrating the superconducting components essential role in these configurations. In summary, our work not only clarifies the current controversies surrounding detection of Majorana fermions but also establishes a robust theoretical foundation guiding future experimental efforts toward unambiguous Majorana fermion observation.
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