Accepted
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Abstract +
The Kapitza’s pendulum is inverted pendulum that is dynamically stabilized by a fast driving of its pivot point. Many applications of Kapitza stabilization in quantum systems have been proposed, such as optical molasses, the stability of optical resonators, preparation of molecular ions, the breaking of translation symmetry, the periodically driven sine-Gordon model, polariton Rabi oscillation, the stabilization of bright solitons in a Bose-Einstein condensate, and so on. In particular, Kapitza stabilization can be used to trap particles. The most notable example of such an application is the Paul trap.
Recently, the Kapitza trap is created by superimposing time-tuned focused laser beams to produce a periodic driven harmonic potential for ultracold atomic gases. This work opens up new possibilities to study Floquet systems of ultracold atomic gases. So we consider the periodic driven harmonic potential, and investigate the properties of soliton in ultracold atomic gases by numerical simulations. It is interesting found that, when the soliton is located at the center of the harmonic potential, a resonance phenomenon of soliton amplitude oscillation occurs under specific driven frequency. In addition, the oscillation amplitude increases with the increasing of the trapping frequency of the harmonic potential, and the resonance frequency increases with the increasing of the soliton initial amplitude.
The change of driven frequency and initial phase has a significant effect on soliton motion when the soliton is located at the edge of the harmonic potential. When the initial phase is zero, there is a characteristic driven frequency. For the case of the driven frequency is equal to the characteristic frequency, soliton motion exhibits periodic oscillations. For the case of the driven frequency is slightly lower than the characteristic frequency, the resonance of soliton oscillation can be found. While the driving frequency is slightly higher than the characteristic frequency, the anti-resonance of soliton oscillation can be found. In addition, it was found that the characteristic driven frequency increases linearly with the increasing of the trapping frequency of the harmonic potential. When the initial phase is not equal to zero, the irregular oscillation, quasi-periodic oscillation and periodic oscillation can be observed with increasing driven frequency. While the driven frequency is equal to a specific value, the resonance of soliton oscillation can also obtained. Furthermore, the fast driving has no effect on the motion trajectory of solitons. These results can provide help for the precise controlling of ultracold atomic gases.
Recently, the Kapitza trap is created by superimposing time-tuned focused laser beams to produce a periodic driven harmonic potential for ultracold atomic gases. This work opens up new possibilities to study Floquet systems of ultracold atomic gases. So we consider the periodic driven harmonic potential, and investigate the properties of soliton in ultracold atomic gases by numerical simulations. It is interesting found that, when the soliton is located at the center of the harmonic potential, a resonance phenomenon of soliton amplitude oscillation occurs under specific driven frequency. In addition, the oscillation amplitude increases with the increasing of the trapping frequency of the harmonic potential, and the resonance frequency increases with the increasing of the soliton initial amplitude.
The change of driven frequency and initial phase has a significant effect on soliton motion when the soliton is located at the edge of the harmonic potential. When the initial phase is zero, there is a characteristic driven frequency. For the case of the driven frequency is equal to the characteristic frequency, soliton motion exhibits periodic oscillations. For the case of the driven frequency is slightly lower than the characteristic frequency, the resonance of soliton oscillation can be found. While the driving frequency is slightly higher than the characteristic frequency, the anti-resonance of soliton oscillation can be found. In addition, it was found that the characteristic driven frequency increases linearly with the increasing of the trapping frequency of the harmonic potential. When the initial phase is not equal to zero, the irregular oscillation, quasi-periodic oscillation and periodic oscillation can be observed with increasing driven frequency. While the driven frequency is equal to a specific value, the resonance of soliton oscillation can also obtained. Furthermore, the fast driving has no effect on the motion trajectory of solitons. These results can provide help for the precise controlling of ultracold atomic gases.
, , Received Date: 2025-01-24
Abstract +
Fe-based amorphous alloys are widely used in electronic devices such as high-frequency transformers and choke cores due to their low coercivity, low loss, and high saturation magnetic induction intensity. However, these alloys have a relatively low crystallization temperature and are prone to oxidation, which limits their applications in high-temperature environments. The addition of copper and niobium elements can suppress the growth of crystal nuclei and improve thermal stability. However, the influences on the alloy's high-temperature oxidation resistance and structural evolution are still unclear. In this work, static air oxidation is used to investigate the microstructure evolution of Fe73.5Si13.5B9Cu1Nb3 amorphous alloy after high-temperature oxidation and its influence on magnetic properties. Besides, long-time oxidation, say, 3000 hours or longer at 500 ℃, is generally hard to perform in the laboratory. Thus, the Van’t Hoff’s rule is used to evaluate outcomes under the condition of the long-time and relatively low-temperature oxidation through using rapid high-temperature oxidation. Based on Van’t Hoff’s rule, the oxidation at 650°C for 5 min will show similar or more severe oxidation effects on the microstructure of Fe73.5Si13.5B9Cu1Nb3 alloy after oxidation at 500 ℃ for 2730 h. The microstructure evolution reveals that silicon and niobium in this alloy will quickly diffuse toward the sample surface during oxidation at 650 ℃, and these two elements will form a dense layer to impede oxygen diffusion. Meanwhile, an α-Fe(Si) phase mainly composed of iron elements will be generated in the alloy, with its grain size slowly increasing in the oxidation process. Thermodynamic analysis indicates that the segregation of silicon and niobium can preserve the thermodynamic stability of the alloy system during oxidation and suppress the formation of intermetallic compounds during crystallization. The magnetic hysteresis loop results show that the coercivity of Fe73.5Si13.5B9Cu1Nb3 alloy after 5-min oxidation at 650°C will stay at approximately 0.3 Oe, suggesting that the Fe73.5Si13.5B9Cu1Nb3 alloy may be a candidate for operating at 500 ℃ for more than 2700 h. Subsequently, its coercivity gradually increases to 61 Oe as the oxidation time rises to 0.5 h, while its saturation magnetic induction intensity remains unchanged (~140 emu/g).
, , Received Date: 2025-01-07
Abstract +
The mechanism of controlling single-photon scattering in a hybrid system consisting of superconducting qubits coupled to aSu-Schrieffer-Heeger (SSH) topological photonic lattice is investigated under the influence of an artificial gauge field. This research is driven by the growing interest in the intersection between quantum optics and condensed matter physics, particularly in the field of topological quantum optics, where the robustness of photon transport against defects and impurities can be used for quantum information processing. To achieve this, a theoretical model, which incorporates the phase of the artificial gauge field into the coupling between superconducting qubits and the SSH photonic lattice, is developed in this work. The analytical expressions for the reflection and transmission amplitudes of single photons are derived by using the probability-amplitude method. The results show that the artificial gauge field can effectively control single photon scattering in both the upper energy band and the lower energy band of the SSH lattice, thereby enabling total transmission in the upper band and total reflection in the lower band. This band-dependent scattering behavior exhibits a high degree of symmetry with respect to the lattice momentum and energy bands. Importantly, the reflection coefficient can be made independent of the lattice coupling strength and dependent solely on the topological properties of the lattice. This finding suggests a robust method of detecting topological invariants in photonic lattices. Furthermore, our analysis is extended to various coupling configurations between superconducting qubits and the photonic lattice, highlighting the versatility of the artificial gauge field in manipulating photon transport. These findings not only provide new insights into the control of photon transport in topological photonic lattices, but also open the door to the development of novel quantum optical devices and robust quantum information processing platforms.
, , Received Date: 2025-01-05
Abstract +
NASICON-type Li1+xAlxTi2–x(PO4)3 (LATP), as a promising solid-state electrolyte for lithium-ion batteries, has received significant attention due to its simple preparation , low material cost, and good stability in water and air, but the formation of lithium dendrite greatly limits the applications. To elucidate the source of formation of lithium dendrite, in this study, the effects of Al content on the stability, electronic and Li+ mobility properties of the LATP surface with three Al doping concentrations (2AlTi, 4AlTi, 6AlTi) are investigated by combining first-principles calculations and molecular dynamics simulations. The LiTi2(PO4)3 (LTP) surface is also considered for comparison. The results indicate that the (012) surface terminated with Li atoms is the most stable facet. Further, the surface energy of LATP(012) decreases from 0.68 J/m2 to 0.43 J/m2 with the increase of Al content, suggesting that Al doping can effectively improve the stability of the LATP(012) surface. Electronic structure analysis reveals that the surface of LTP(012) retains the semiconductor properties consistent with the bulk phase, whereas the LATP(012) surface exhibits metallicity, which provides an electron pathway for forming the metallic Li . Consequently, the metallic characteristic of the LATP(012) surface is a reason for its lithium dendrite growth. For the Li+ transport properties, two different migration modes: vacancy migration and interstitial migration, are included. When Li+ migrates within the outermost surface, the migration barrier via vacancy is 1.67/1.69 eV for the LTP/LATP (012) surface, while the migration barrier via interstitial is 1.16 eV for LTP(012) and decreases from 1.31 to 0.87 eV with the increase of Al content for LATP(012). Obviously, within the outermost surface, Al doping can reduce the migration barrier of Li+. When Al doping concentration is 6AlTi, the migration barrier is lowest (0.87 eV). Nevertheless, the lowest migration barrier (0.87 eV) for Li+ on the LATP surface is significantly higher than its bulk minimum value of 0.34 eV. When Li+ migrates from the subsurface layer to the outermost surface, the migration barrier is 2.76 eV for LTP(012) and 2.05 eV, 3.20 eV, and 3.06 eV for LATP(012) with 2AlTi, 4AlTi, and 6AlTi content, respectively. All these migration barriers are greater than 2.00 eV, which prevents Li+ from migrating from the subsurface layer to the outermost surface for both LTP and LATP surfaces. Hence, the slow Li+ migration represents another important factor contributing to lithium dendrite growth on the LATP surface. Fortunately, increasing the Al doping concentration can reduce the migration barrier of Li+ and thus enhance its diffusion performance on the LATP surface. Molecular dynamics simulations further reveal that the diffusion behavior of Li+ on the LATP surface is influenced by a combination of factors, including Al content, Li+ occupancy, and ambient temperature. In particular, LATP(012)/6AlTi, LATP(012)/4AlTi, and LATP(012)/2AlTi possess their highest Li+ diffusion coefficients at 900 K, 1100 K, and 1300 K, respectively. Besides, Li+ near the Al doping site is easier to diffuse on the LATP(012) surface. Thus, our study indicates that by changing Al content, Li+ occupation positions, and the temperature, the Li+ diffusion performance of LATP(012) can be effectively modified, thereby suppressing the formation of lithium dendrites on the LATP(012) surface.
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Abstract +
Under the dual background of deep adjustment of global energy pattern and severe challenges of environmental issues, solid oxide fuel cell (SOFC) has become the focus of research on efficient and clean energy conversion technology by virtue of its many excellent characteristics. The electrochemical performance of SOFC is affected by various factors such as gas flow pattern (co-flow, counter-flow, cross-flow), flow rate (cathode and anode channel gases), and operating voltage, etc. Accurately analysing the variation of electrochemical indexes with each factor is the basis for proposing the design scheme of high efficiency reaction of the cell. Therefore, a three-dimensional multi-field coupling model of SOFC is established in this study, and the model parameters and boundary conditions covering electrochemistry, gas flow, substance diffusion, etc. are set to study the influence of the coupling between factors on the electrochemical performance of the cell. The results show that with the decrease of operating voltage, the electrochemical reaction rate of the cell increases significantly, the gas mole fraction gradient increases, and the inhomogeneity of the electrolyte current density distribution is enhanced. For low-voltage operating conditions, the cross-flow flow pattern shows better electrochemical performance advantages, and its power density profile takes the lead in different current density intervals. With the increase of the flow rate of the flow channel gas, the output power density curve of the cell shows an overall upward trend, and then the driving effect of the flow rate increase on the power density increase is gradually weakened due to the saturated cathodic reaction. This study reveals the influence of the coupling of flow pattern, flow rate and voltage on the electrochemical performance of SOFC, and provides guidance for the commercial application of SOFC.
Abstract +
The atomic nucleus is an extremely complex quantum many-body system composed of nucleons, and its shape is determined by the number of nucleons and their interactions. The study of atomic nuclear shapes is one of the most fascinating topics in nuclear physics, providing rich insights into the microscopic details of nuclear structure. Physicists have observed significant shape coexistence phenomena and stable triaxial deformation in isotopes of Zn, Ge, Se, and Kr. This paper aims to delve deeper into the impact of shape coexistence and triaxiality on the ground-state properties of atomic nuclei, as well as to verify new magic numbers.
We employed the density-dependent meson-exchange model within the framework of the Relativistic Hartree-Bogoliubov (RHB) theory to systematically study the ground-state properties of even-even Zn, Ge, Se, and Kr isotopes with neutron numbers N=32-42. The calculated potential energy surfaces clearly demonstrate the presence of shape coexistence and triaxial characteristics in these isotopes. By analyzing the ground-state energy, deformation parameters, two-neutron separation energies, neutron radii, proton radii, and charge radii of the atomic nuclei, we discuss the closure of nuclear shells. Our results reveal that at N=32, there is a notable abrupt change in the two-neutron separation energies of 62Zn and 64Ge. At N=34, a significant decrease in the two-neutron separation energies of 68Se and 70Kr is observed, accompanied by an abrupt change in their charge radii. Meanwhile, at N=40, clear signs of shell closure are observed. the maximum specific binding energy may correlate with the emergence of spherical nuclear structures. The shell closure not only enhances nucleon binding energy but also suppresses nuclear deformation through symmetry constraints. Our findings support N=40 as a new magic number, and some results also suggest that N=32 and N=34 could be new magic numbers. Notably, triaxial deformation plays a crucial role here. Furthermore, we explore the potential correlation between triaxiality and shape coexistence on the ground-state properties of atomic nuclei and analyze the physical mechanisms underlying these changes.
The discrepancies between current theoretical predictions and experimental data reflect limitations in modeling higher-order many-body correlations (e.g., three-nucleon forces) and highlight challenges in experimental measurements for extreme nuclear regions (including neutron-rich and near-proton-drip-line regions). Future studies could combine tensor force corrections, large-scale shell model calculations, and high-precision data from next-generation radioactive beam facilities (e.g., FRIB, HIAF) to clarify the interplay among nuclear force parameterization, proton-neutron balance, and emergent symmetries, thereby providing a more comprehensive theoretical framework for nuclear structure under extreme conditions.
We employed the density-dependent meson-exchange model within the framework of the Relativistic Hartree-Bogoliubov (RHB) theory to systematically study the ground-state properties of even-even Zn, Ge, Se, and Kr isotopes with neutron numbers N=32-42. The calculated potential energy surfaces clearly demonstrate the presence of shape coexistence and triaxial characteristics in these isotopes. By analyzing the ground-state energy, deformation parameters, two-neutron separation energies, neutron radii, proton radii, and charge radii of the atomic nuclei, we discuss the closure of nuclear shells. Our results reveal that at N=32, there is a notable abrupt change in the two-neutron separation energies of 62Zn and 64Ge. At N=34, a significant decrease in the two-neutron separation energies of 68Se and 70Kr is observed, accompanied by an abrupt change in their charge radii. Meanwhile, at N=40, clear signs of shell closure are observed. the maximum specific binding energy may correlate with the emergence of spherical nuclear structures. The shell closure not only enhances nucleon binding energy but also suppresses nuclear deformation through symmetry constraints. Our findings support N=40 as a new magic number, and some results also suggest that N=32 and N=34 could be new magic numbers. Notably, triaxial deformation plays a crucial role here. Furthermore, we explore the potential correlation between triaxiality and shape coexistence on the ground-state properties of atomic nuclei and analyze the physical mechanisms underlying these changes.
The discrepancies between current theoretical predictions and experimental data reflect limitations in modeling higher-order many-body correlations (e.g., three-nucleon forces) and highlight challenges in experimental measurements for extreme nuclear regions (including neutron-rich and near-proton-drip-line regions). Future studies could combine tensor force corrections, large-scale shell model calculations, and high-precision data from next-generation radioactive beam facilities (e.g., FRIB, HIAF) to clarify the interplay among nuclear force parameterization, proton-neutron balance, and emergent symmetries, thereby providing a more comprehensive theoretical framework for nuclear structure under extreme conditions.
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Abstract +
Objective The second-order auto-correlation technique based on Hanbury Brown-Twiss (HBT) can obtain the Fourier spectrum information of a target even in the conditions of incoherent source illumination and near-field detection, which has better advantages in the field of moving-target imaging, imaging in scattering media, and X-ray imaging. However, a mass of measurements is required and the imaging resolution is also restricted by the pixel scale of the detector for high-quality Fourier spectrum images for HBT. At present, many related data processing methods and reconstruction algorithms can reduce the number of measurements required for the acquisition of high-quality spectral information, but the time of image reconstruction required by such methods is usually long and cannot improve the system’s imaging resolution. In recent years, Fourier ptychography based on real-space image detection has proven that higher-resolution imaging can be obtained through spectral ptychography and frequency extension. In this paper, by combining the idea of Fourier ptychography with HBT, a processing method based on multi-point parallel correlation reconstruction and spectral ptychography is proposed, which attempts to obtain high-quality spectral information of the target and achieve super-resolution imaging at lower measurement times.
Methods The proof-of-principle schematic of super-resolution imaging method based on autocorrelation and spectral ptychography is shown in Fig. 1. The corresponding super-resolution reconstruction framework is displayed in Fig. 2, which mainly consists of three steps: multi-point parallel correlation reconstruction, spectral ptychography, and real-space image reconstruction based on phase-retrieval algorithm. Firstly, based on the physical mechanism described by Eq. (5), Fourier spectrum images of the target in different detection points are obtained through multi-point parallel correlation reconstruction. Secondly, according to the idea of spectrum ptychography, the frequency shifted spectrum obtained by multi-point parallel correlation reconstruction is aligned to form an extended spectrum. Finally, the target’s real-space image is reconstructed by phase-retrieval algorithm.
Results and Discussions The validity of the super-resolution imaging method based on auto-correlation and spectral ptychography is experimentally demonstrated by using the setup in Fig.1. When the number of measurements N=500, Fig. 4 gives the experimental results in different pixel scales of the detector. The results indicate that the imaging resolution increases with the pixel scale of the detector. However, when the number of measurements is small, both the Fourier spectrum and the real-space image obtained by single point detection are poor (Fig. 4 (c)). When the method of multi-point parallel correlation reconstruction and spectral ptychography is adopted, the signal-to-noise ratio of the reconstructed Fourier spectrum can be significantly improved and its spectral bandwidth can be expanded to twice that of the original spectrum in the same parameters (Fig. 4(c) and Fig. 4(f)). In addition, the experiments also show that for a 50×50 spectral image, high-quality super-resolution imaging can still be obtained even if the measurement times are 200 (namely the sampling rate is 8%) (Fig. 5).
Conclusions In summary, we propose a method based on multi-point parallel correlation reconstruction and spectral ptychography processing to improve the signal-to-noise ratio and spatial resolution of HBT system. Both theoretical and experimental results demonstrate that the proposed method can not only reduce the measurement number required for high-quality Fourier spectrum images of the target (with a sampling rate of 8%), but also achieve super-resolution imaging with two times ability capacity. This method provides important insights for super-resolution microscopy imaging and high-resolution imaging of moving target.
Methods The proof-of-principle schematic of super-resolution imaging method based on autocorrelation and spectral ptychography is shown in Fig. 1. The corresponding super-resolution reconstruction framework is displayed in Fig. 2, which mainly consists of three steps: multi-point parallel correlation reconstruction, spectral ptychography, and real-space image reconstruction based on phase-retrieval algorithm. Firstly, based on the physical mechanism described by Eq. (5), Fourier spectrum images of the target in different detection points are obtained through multi-point parallel correlation reconstruction. Secondly, according to the idea of spectrum ptychography, the frequency shifted spectrum obtained by multi-point parallel correlation reconstruction is aligned to form an extended spectrum. Finally, the target’s real-space image is reconstructed by phase-retrieval algorithm.
Results and Discussions The validity of the super-resolution imaging method based on auto-correlation and spectral ptychography is experimentally demonstrated by using the setup in Fig.1. When the number of measurements N=500, Fig. 4 gives the experimental results in different pixel scales of the detector. The results indicate that the imaging resolution increases with the pixel scale of the detector. However, when the number of measurements is small, both the Fourier spectrum and the real-space image obtained by single point detection are poor (Fig. 4 (c)). When the method of multi-point parallel correlation reconstruction and spectral ptychography is adopted, the signal-to-noise ratio of the reconstructed Fourier spectrum can be significantly improved and its spectral bandwidth can be expanded to twice that of the original spectrum in the same parameters (Fig. 4(c) and Fig. 4(f)). In addition, the experiments also show that for a 50×50 spectral image, high-quality super-resolution imaging can still be obtained even if the measurement times are 200 (namely the sampling rate is 8%) (Fig. 5).
Conclusions In summary, we propose a method based on multi-point parallel correlation reconstruction and spectral ptychography processing to improve the signal-to-noise ratio and spatial resolution of HBT system. Both theoretical and experimental results demonstrate that the proposed method can not only reduce the measurement number required for high-quality Fourier spectrum images of the target (with a sampling rate of 8%), but also achieve super-resolution imaging with two times ability capacity. This method provides important insights for super-resolution microscopy imaging and high-resolution imaging of moving target.
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Abstract +
This research focuses on advanced noise suppression techniques for high-precision measurement systems, particularly addressing the limitations of classical noise reduction approaches. The noise level of laser sources is a crucial factor that directly impacts measurement sensitivity in applications such as gravitational wave detection and biomedical imaging. Classical feedback control techniques have been effective but often hit a bottleneck defined by the classical noise suppression limits. To overcome these challenges, this study proposes a novel method integrating quantum squeezed light with classical feedback control systems to achieve enhanced intensity noise reduction. By employing an amplitude-squeezed light field, a quantum-enhanced feedback control model is developed, theoretically examining the impact of both the feedback loop gain and the degree of squeezing on the noise suppression performance. The results show that the injection of squeezed light significantly reduces the intensity noise, approaching the shot noise limit (SNL), thereby improving the system's sensitivity beyond the classical noise reduction boundaries. Specifically, -10 dB squeezed state injection into the feedback system yielded an additional noise suppression of approximately 8.97 dB, surpassing what is achievable using classical feedback alone. This demonstrates the potential of the proposed approach for pushing measurement precision closer to the quantum noise limits without increasing the laser power.The analysis highlights the asymmetric noise suppression effects between the inner and outer feedback loops. While the outer loop benefits significantly from the squeezed light injection, achieving noise levels unattainable by classical feedback methods, the inner loop shows comparatively minor improvements. This asymmetry is attributed to the inherent characteristics of quantum squeezing and the limitations of the feedback loop design. Further investigation into the individual noise components reveals that the primary contributors to the intensity noise include input noise, photodetector noise, and beam splitter-induced vacuum fluctuations. The injection of squeezed light effectively mitigates these vacuum fluctuations, typically a major noise source in high-precision laser systems. Theoretical research results show that the use of squeezed light in feedback control systems can effectively enhance noise suppression equivalent to a tenfold increase in detected optical power, without the physical drawbacks of increasing laser power such as thermal noise. In conclusion, this study provides a theoretical validation of combining quantum squeezed states with classical feedback control to exceed classical noise suppression limits. The integration of a -10 dB squeezed state demonstrated significant noise reduction, showing that this hybrid approach could revolutionize noise management in precision measurement applications. The results pave the way for further exploration of quantum-enhanced control techniques in fields such as gravitational wave detection, quantum communication, and advanced optical sensing, offering a pathway to improved sensitivity and noise suppression without additional power requirements.
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The 1 K cryogenic system can provide a stable and necessary low-temperature environment for some fields such as quantum computing, condensed matter physics research, and cryogenic scientific instruments. Specifically, in the field of basic research, 1 K is an ideal condition for studying quantum phenomena in low-temperature physics (such as quantum Hall effect, topological phase transition, etc.); in the field of technical applications, 1 K is a necessary condition for some quantum devices (such as superconducting quantum interferometers, single-photon detectors, etc.) to achieve high-sensitivity operation; in the field of ultra-low temperature technology, 1 K is the pre-cooling stage of refrigeration technologies such as dilution refrigerators, and is the basis for further achieving mK temperature ranges and lower temperatures. At present, most domestic 1 K systems use GM cryocoolers for pre-cooling. The system has certain difficulties in achieving lower vibration control, lower electrical noise interference, lower pre-cooling temperature and higher liquefaction efficiency. The 1 K systems based on pulse tube cryocoolers pre-cooling have inherent advantages in solving these problems. This paper first developed a 4 K GM-type pulse tube cryocooler, using a domestic helium compressor and a developed rotary valve, and redesigned the cold-end heat exchanger and the room-temperature phase shifters, achieving a minimum cooling temperature of 2.14 K, and providing 1.5 W@4.2 K and 45 W@45 K cooling capacity simultaneously. Based on the self-developed pulse tube cryocooler as the pre-cooling stage, a 1 K cryogenic system was further constructed. By designing key components such as JT flow resistance, combined thermal switch, and anti-superflow structure, a minimum cooling temperature of 1.1 K was obtained, and a cooling capacity of 100 mW can be provided at 1.6 K. This study has laid an important foundation for the subsequent development of dilution refrigerators with larger cooling capacity.
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Complex multi-body interactions between ions and surrounding charged particles exist in hot and dense plasmas. It will screen the Coulomb potential between the nucleus and electrons, and significantly change the atomic structures and dynamic properties. This will further affect macroscopic plasma properties such as radiation opacity and the equation of state. Based on the atomic-state-dependent (ASD) screening model, we investigate the photoionization dynamic of Fe25+ ion in hot and dense plasmas. The photoionization cross section for all transition channels and total cross sections of n ≤ 2 states for Fe25+ are studied in detail, as well as the low-energy characteristics induced by plasma screening. Compared to the classical Debye Hückel model, the ASD model incorporated the degeneracy effects by inelastic collision processes, resulting in higher plasma density requirements for bound electrons to merge into the continuum. Near the threshold, the photoionization cross section obeys the Wigner threshold law after considering the screening effect. As the energy increases, the cross sections show low-energy characteristics such as shape resonance, Cooper minimum, low-energy enhancement, and Combet-Farnoux minimum, etc., which can significantly increase or decrease the cross section of the corresponding energy region. For example, the low-energy enhancement in the 2p→εs1/2 channel increases the cross section by several orders of magnitude, drastically changing the properties of the photoelectron spectrum. It is significant to study the low-energy characteristics for understanding the physical properties of the photoionization cross section. Fe is an important element in astrophysics. The cross section results in the middle and high energy region calculated by the ASD model in this paper can provide theoretical and data support for the investigation of hot and dense plasmas in Astrophysics and laboratory situations.
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The Gamma-ray Total Absorption Facility (GTAF), which is composed of 40 BaF2 detection units, is designed to measure the cross section data of neutron radiation capture reaction online, in order to comply the experimental nuclear data sheet. Since 2019, several formidable experiment results have been analyzed and published where we consumed that one of the most important sources of experimental background is initial α particles emitted from the BaF2 crystal, the core component of the detection unit in GTAF, itself.
The development of data analysis algorithms to eliminate the influence of alpha particles in experimental data has become a key aspect, considering the current industrial manufacturing process capabilities, impurities Ra, and its compound, cannot be completely removed from the BaF2. In this paper, to fulfill the need of data collect, online measurement and analysis of neutron radiation cross section, the data acquisition system of GTAF adopts the method of full waveform acquisition, resulting in a substantial amount of data recorded, transmitted, and stored during experiment, which also affects the uncertainty of the cross-section data. The amount of data stored in the online experiment is about 118 MB/s, resulting in a large dead time.
Based on the signal waveform characteristics of the BaF2 detection unit, to address the aforementioned issues, three methods, namely the ratio of fast to total component, pulse width, and time decay constant, are employed to identify and discriminate α particles and γ rays, with the quality factor FOM utilized as an evaluation value and several experiments using three radioactive sources (22Na, 137C, 60Co) used to verify.
Due to the slow components of BaF2 light decay time being about 620 ns, the waveform pulse should essentially return to baseline at approximately 1900 ns to 2000 ns, allowing for the complete waveform of the γ rays signal to be captured at that moment, which might provide the best energy resolution. Therefore, in the online experiment, the integration length for the energy spectrum is chosen to be 2000 ns in this paper.
The quality factors of fast total component ratio (fast component 5 ns, total component 200 ns) method are 1.19~1.41, pulse width (10% peak) method are 0.94~1.04, and time attenuation constant method are 0.93~1.07. Through the quantitative analysis of quality factor and the comparison of energy spectrum, it is determined that the fast total component ratio method has the best effect, which can effectively remove the background of α particles.
The next step is to upgrade the online experimental data acquisition system to reduce the amount of experimental data and the uncertainty of cross section data. The experiment data need to be recorded should be the crossing threshold time for each signal waveform (for the time-of-flight method) and the amplitude integration value of 5 ns after the threshold (for the fast component), of 200 ns after the threshold (for the total component) and of 2000 ns (for the energy), as well as the related detection unit number. These mentioned information should be sufficient to complete the online experimental data online processing, including processing the α particle background and (n,γ) reactions data. It is estimated that the data acquisition rate of the upgraded system will decrease from 118 MB/s to 24 MB/s, which can significantly reduce the dead time of the data acquisition system and thereby improve the accuracy of cross section data.
The development of data analysis algorithms to eliminate the influence of alpha particles in experimental data has become a key aspect, considering the current industrial manufacturing process capabilities, impurities Ra, and its compound, cannot be completely removed from the BaF2. In this paper, to fulfill the need of data collect, online measurement and analysis of neutron radiation cross section, the data acquisition system of GTAF adopts the method of full waveform acquisition, resulting in a substantial amount of data recorded, transmitted, and stored during experiment, which also affects the uncertainty of the cross-section data. The amount of data stored in the online experiment is about 118 MB/s, resulting in a large dead time.
Based on the signal waveform characteristics of the BaF2 detection unit, to address the aforementioned issues, three methods, namely the ratio of fast to total component, pulse width, and time decay constant, are employed to identify and discriminate α particles and γ rays, with the quality factor FOM utilized as an evaluation value and several experiments using three radioactive sources (22Na, 137C, 60Co) used to verify.
Due to the slow components of BaF2 light decay time being about 620 ns, the waveform pulse should essentially return to baseline at approximately 1900 ns to 2000 ns, allowing for the complete waveform of the γ rays signal to be captured at that moment, which might provide the best energy resolution. Therefore, in the online experiment, the integration length for the energy spectrum is chosen to be 2000 ns in this paper.
The quality factors of fast total component ratio (fast component 5 ns, total component 200 ns) method are 1.19~1.41, pulse width (10% peak) method are 0.94~1.04, and time attenuation constant method are 0.93~1.07. Through the quantitative analysis of quality factor and the comparison of energy spectrum, it is determined that the fast total component ratio method has the best effect, which can effectively remove the background of α particles.
The next step is to upgrade the online experimental data acquisition system to reduce the amount of experimental data and the uncertainty of cross section data. The experiment data need to be recorded should be the crossing threshold time for each signal waveform (for the time-of-flight method) and the amplitude integration value of 5 ns after the threshold (for the fast component), of 200 ns after the threshold (for the total component) and of 2000 ns (for the energy), as well as the related detection unit number. These mentioned information should be sufficient to complete the online experimental data online processing, including processing the α particle background and (n,γ) reactions data. It is estimated that the data acquisition rate of the upgraded system will decrease from 118 MB/s to 24 MB/s, which can significantly reduce the dead time of the data acquisition system and thereby improve the accuracy of cross section data.
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Abstract +
When the wall temperature of the thermal protection or insulation materials on the surface of an aircraft exceeds their tolerance limits under the heating of supersonic aerodynamic heat energy, degradation damage phenomena such as high-temperature thermochemical ablation and mechanical erosion will occur in the surface area. The ablation diffusion products (ablation particles) generated are ejected into the surrounding plasma flow field and suspended around the aircraft, forming a hypersonic plasma flow field with ablation diffusion substances. The presence of ablation diffusion substances can significantly affect the physical and electromagnetic characteristics of the original plasma flow field. To address this problem, this study establishes a coupled electromagnetic model of an ablative plasma flow field surrounding a blunt-nosed cone aircraft and analyzes the antenna radiation characteristics in the wake region of the ablative flow field. The research methodology consists of several key steps: Firstly, the plasma flow field around the blunt-nosed cone is simulated using ANSYS FLUENT, a computational fluid dynamics (CFD) software. This step provides the fundamental flow field parameters (e.g., electron density, temperature, and pressure distributions). Secondly, ablation particles, generated from thermal protection material degradation, are uniformly dispersed into the plasma flow. Then, the ablative plasma flow field is obtained. Thirdly, an X-band horn antenna is designed in ANSYS HFSS and loaded into the center of the wake region of the ablative plasma flow field. Based on above models, the ray-tracing method is employed to quantitatively evaluate the attenuation of antenna radiation as it propagates through the wake region. The numerical results demonstrate that the plasma flow field enveloping the aircraft induces significant attenuation of antenna radiation energy. More noteworthy is that the presence of ablation particles within the flow field substantially amplifies this energy dissipation effect. Both the ablation particle density and size distribution are identified as dominant factors controlling radiative energy loss, exhibiting proportional relationships with the incident field's attenuation. The study systematically proves the impact of ablation particle density and size on initial field energy attenuation. This research can provide a reference for addressing the electromagnetic wave propagation underlying the information transmission bottleneck of near-space hypersonic aircraft. It also offers a theoretical basis for further in-depth research on technologies such as target detection, identification, thermal protection/insulation materials, and system design of hypersonic aircraft.
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Abstract +
Divertor detachment is a critical technique for managing the thermal load on the divertor of the HL-3 tokamak, a key device in magnetic confinement fusion research. However, existing studies on detachment have largely overlooked the complex multi-species particle dynamics in the scrape-off layer (SOL) and divertor regions, particularly the interactions involving hydrogen isotopes (e.g., deuterium), externally injected impurities (e.g., neon), and intrinsic impurities (e.g., carbon). This study aims to address this gap by employing the newly developed multi-species particle transport code SD1D to investigate the effects of carbon impurities and neutral particles on two detachment scenarios in HL-3: plasma density ramp-up and neon injection into the divertor.
The SD1D code models the transport, collision, and radiation processes of various particles, including deuterium ions, atoms, and molecules, as well as carbon and neon impurities, along the magnetic field lines from the SOL upstream to the divertor target. The study focuses on understanding how carbon impurities and neutral particles influence the detachment mechanisms under different conditions.
The results reveal that carbon impurities generated in the divertor significantly enhance detachment in the density ramp-up scenario by increasing the density of deuterium atoms, molecules, and ions near the target plate, thereby boosting the total radiation power. This effect lowers the density threshold required for detachment and reduces the peak current on the target plate. However, carbon impurities have a minimal impact on detachment achieved through neon injection, as they do not significantly alter the density of deuterium species or the total radiation power in this scenario.
Furthermore, the study highlights the distinct roles of neutral particles in the two detachment mechanisms. In the density ramp-up scenario, the increased plasma density promotes the recycling process in the divertor, generating a substantial population of neutral particles. The energy and momentum losses resulting from plasma-neutral interactions are crucial for achieving detachment. In contrast, neon injection directly reduces the saturation current on the target plate, suppressing the recycling process and diminishing the importance of neutral particles.
In conclusion, this work demonstrates that carbon impurities play a significant role in facilitating detachment during plasma density ramp-up but have limited influence on detachment via neon injection. The findings underscore the importance of considering multi-species particle dynamics, including neutral particles and impurities, in understanding and optimizing divertor detachment strategies. Future work will involve validating the SD1D model against experimental data from HL-3 to further refine its predictive capabilities.
The SD1D code models the transport, collision, and radiation processes of various particles, including deuterium ions, atoms, and molecules, as well as carbon and neon impurities, along the magnetic field lines from the SOL upstream to the divertor target. The study focuses on understanding how carbon impurities and neutral particles influence the detachment mechanisms under different conditions.
The results reveal that carbon impurities generated in the divertor significantly enhance detachment in the density ramp-up scenario by increasing the density of deuterium atoms, molecules, and ions near the target plate, thereby boosting the total radiation power. This effect lowers the density threshold required for detachment and reduces the peak current on the target plate. However, carbon impurities have a minimal impact on detachment achieved through neon injection, as they do not significantly alter the density of deuterium species or the total radiation power in this scenario.
Furthermore, the study highlights the distinct roles of neutral particles in the two detachment mechanisms. In the density ramp-up scenario, the increased plasma density promotes the recycling process in the divertor, generating a substantial population of neutral particles. The energy and momentum losses resulting from plasma-neutral interactions are crucial for achieving detachment. In contrast, neon injection directly reduces the saturation current on the target plate, suppressing the recycling process and diminishing the importance of neutral particles.
In conclusion, this work demonstrates that carbon impurities play a significant role in facilitating detachment during plasma density ramp-up but have limited influence on detachment via neon injection. The findings underscore the importance of considering multi-species particle dynamics, including neutral particles and impurities, in understanding and optimizing divertor detachment strategies. Future work will involve validating the SD1D model against experimental data from HL-3 to further refine its predictive capabilities.
Abstract +
H2 molecule and their isotopes represent one of the modern clean energy sources. It is imperative to understand their thermodynamic properties to comprehend their behavior under various conditions and facilitate their deeper applications. This paper utilizes the extended improved multiparameter exponential-type potential (EIMPET) combined with the quantum statistical ensemble theory to investigate and analyze the thermodynamic properties of H2 and HD molecules.
Firstly, reliable energy level data for molecules were obtained using the EIMPET potential. Subsequently, the one-dimensional Schrödinger equation was solved with the LEVEL program to determine the rovibrational energy levels of the molecules. Finally, the quantum statistical ensemble theory was integrated to determine the partition functions, molar heat capacity, molar entropy, molar enthalpy, and reduced molar Gibbs free energy of H2 and HD over the temperature range of 100-6000 K. The calculation results indicate that compared with IHH potential and IMPET potential, the EIMPET potential is closer to RKR data. A comparison of the calculated thermodynamic properties of the molecules revealed that the EIMPET potential-based method results agree well with the NIST database. Specifically, for H2, the root mean square errors (RMS) for Cm(T), Sm(T), Gr(T), and ΔHr(T) were were 0.6894 J•K-1•mol-1, 0.3824 J•K-1•mol-1, 0.1754 J•K-1•mol-1, and 0.9586 kJ•mol-1, respectively, while for HD, the RMS values were 0.3431 J•K-1•mol-1, 0.1443 J•K-1•mol-1, 0.0495 J•K-1•mol-1, and 0.4863 kJ•mol-1, respectively, all of these results are superior to that obtained using IMPET potential, and overall superior to IHH potential. These findings demonstrate the advantages of the EIMPET potential in calculating the thermodynamic properties of diatomic gas molecules and its practical applications, providing a foundation for subsequent research on the thermodynamic properties of triatomic molecules.
Firstly, reliable energy level data for molecules were obtained using the EIMPET potential. Subsequently, the one-dimensional Schrödinger equation was solved with the LEVEL program to determine the rovibrational energy levels of the molecules. Finally, the quantum statistical ensemble theory was integrated to determine the partition functions, molar heat capacity, molar entropy, molar enthalpy, and reduced molar Gibbs free energy of H2 and HD over the temperature range of 100-6000 K. The calculation results indicate that compared with IHH potential and IMPET potential, the EIMPET potential is closer to RKR data. A comparison of the calculated thermodynamic properties of the molecules revealed that the EIMPET potential-based method results agree well with the NIST database. Specifically, for H2, the root mean square errors (RMS) for Cm(T), Sm(T), Gr(T), and ΔHr(T) were were 0.6894 J•K-1•mol-1, 0.3824 J•K-1•mol-1, 0.1754 J•K-1•mol-1, and 0.9586 kJ•mol-1, respectively, while for HD, the RMS values were 0.3431 J•K-1•mol-1, 0.1443 J•K-1•mol-1, 0.0495 J•K-1•mol-1, and 0.4863 kJ•mol-1, respectively, all of these results are superior to that obtained using IMPET potential, and overall superior to IHH potential. These findings demonstrate the advantages of the EIMPET potential in calculating the thermodynamic properties of diatomic gas molecules and its practical applications, providing a foundation for subsequent research on the thermodynamic properties of triatomic molecules.
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Abstract +
The Compton camera for γ-ray imaging has the advantages of light weight, high detection efficiency and wide imaging energy range. However, it is difficult for the detection system to distinguish the Compton scattering event and scattering photon absorption event, which results in erroneous image reconstruction. In this paper, a simulation model of Compton camera based on a three-dimensional position-sensitive CdZnTe detector is constructed using GEANT4 program. The detection of characteristic γ-ray from a far-field 137Cs point-like source is simulated. The location of the interaction and energy deposition in the detector are recorded by means of event-by-event. The Compton scattering angle of effective Compton scattering events and imaging of the radioactive source are reconstructed using the simple back-projection algorithm which is a suitable image reconstruction algorithm for real-time imaging scenes. The effect of event sequence reconstruction on the imaging resolution and its improvement are investigated. The results show that the impact of incorrect sequence events on imaging is mainly in the region within 30° from the source position, resulting in a decrease in the density of the image point distribution at the source position. Incorrect reconstructed image points are generated near the source position and form a ring at 26°. The percentage of correctly sequenced events increase to 82% using Compton edge test and simple comparison method based on the deposited energy for sequencing events. The density of the image point distribution at the source location is improved by 47%, and the incorrect reconstruction of the image point distribution near the source location is greatly suppressed, resulting in an improved imaging resolution. The results provide support for the design of Compton camera and the optimization of image reconstruction.
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