分类： 物理学 >> 核物理学 提交时间： 2023-06-09 合作期刊: 《Nuclear Science and Techniques》
摘要： In the Chinese ADS front-end demo superconducting radiofrequency linac (CAFe) at the Institute of Modern Physics, a burst-noise signal-triggered cavity fault frequently appears during beam commissioning. These events are characterized by a rapid burst noise in the cavity pick-up, which may lead to an unexpected low-level radiofrequency (LLRF) response that eventually causes a cavity fault. To eliminate the undesirable reaction of the LLRF control loop, we propose a method that uses a burst-noise detection and processing algorithm integrated into the LLRF feedback controller. This algorithm can prevent undesired regulations in LLRF systems. Data analysis revealed that some burst-noise events did not exhibit measurable energy loss. In contrast, the other events were accompanied by a rapid loss of cavity stored energy and exhibited similarities to the “E-quench” phenomena reported in other laboratories. A particle-in-cell simulation indicated that the suspected E-quench phenomenon may be related to a plasma formation process inside the cavity. Fortunately, the LLRF algorithm is robust to the two different types of burst-noise events and can significantly mitigate the corresponding cavity faults in CAFe beam commissioning.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Although the spatial curvature has been measured with very high precision, it still suffers from the well known cosmic curvature tension. In this paper, we propose an improved method to determine the cosmic curvature, by using the simulated data of binary neutron star mergers observed by the second generation space-based DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO). By applying the Hubble parameter observations of cosmic chronometers to the DECIGO standard sirens, we explore different possibilities of making measurements of the cosmic curvature referring to a distant past: one is to reconstruct the Hubble parameters through the Gaussian process without the influence of hypothetical models, and the other is deriving constraints on $\Omega_K$ in the framework of non-flat $\Lambda$ cold dark matter model. It is shown that in the improved method DECIGO could provide a reliable and stringent constraint on the cosmic curvature ($\Omega_{K} = -0.007\pm0.016$), while we could only expect the zero cosmic curvature to be established at the precision of $\Delta \Omega_K=0.12$ in the second model-dependent method. Therefore, our results indicate that in the framework of methodology proposed in this paper, the increasing number of well-measured standard sirens in DECIGO could significantly reduce the bias of estimations for cosmic curvature. Such constraint is also comparable to the precision of Planck 2018 results with the newest cosmic microwave background (CMB) observations ($\Delta \Omega_{K} \approx 0.018$), based on the concordance $\Lambda$CDM model.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： A scheme for measurement of microwave (MW) electric field is proposed via multi-photon coherence in Rydberg atoms. It is based on the three-photon electromagnetically induced absorption (TPEIA) spectrum. In this process, the multi-photon produces a narrow absorption peak, which has a larger magnitude than the electromagnetically induced transparency (EIT) peak under the same conditions. The TPEIA peak is sensitive to MW fields, and can be used to measure MW electric field strength. It is interesting to find that the magnitude of TPEIA peaks shows a linear relationship with the MW field strength. The simulation results show that the minimum detectable strength of the MW fields is about 1/10 that based on an common EIT effect, and the probe sensitivity is improved by about 4 times. Furthermore, the MW sensing based on three-photon coherence shows a broad tunability, and the scheme may be useful for designing novel MW sensing devices.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this paper, we investigate the possibility of testing the weakly interacting massive particle (WIMP) dark matter (DM) models by applying the simplest phenomenological model which introduces an interaction term between dark energy (DE) and WIMP DM, i.e., $Q = 3\gamma_{DM} H\rho_{DM}$. In general, the coupling strength $\gamma_{DE}$ is close to $0$ as the interaction between DE and WIMP DM is very weak, thus the effect of $\gamma_ {DE}$ on the evolution of $Y$ associated with DM energy density can be safely neglected. Meanwhile, our numerical calculation also indicates that $x_f\approx20$ is associated with DM freeze-out temperature, which is the same as the vanishing interaction scenario. As for DM relic density, it will be magnified by $\frac{2-3\gamma_{DM}}{2}[{2\pi g_* m_{DM}^3}/{(45 s_0 x_f^3})]^{\gamma_{DM}}$ times, which provides a new way to test WIMP DM models. As an example, we analyze the case in which WIMP DM is a scalar DM. (SGL+SNe+Hz) and (CMB+BAO+SNe) cosmological observations will give $\gamma_{DM}=0.134^{+0.17}_{-0.069}$ and $\gamma_{DM}=-0.0008\pm0.0016$, respectively. After further considering the constraints from DM direct detection experiment, DM indirect detection experiment, and DM relic density, we find that the allowed parameter space of the scalar DM model will be completely excluded for the former cosmological observations, while it will increase for the latter ones. Those two cosmological observations lead to an almost paradoxical conclusion. Therefore, one could expect more stringent constraints on the WMIP DM models, with the accumulation of more accurate cosmological observations in the near future.
分类： 物理学 >> 核物理学 提交时间： 2024-05-23
wang ruoxu
Yuan He
shi longbo
Li chenxing
xue zongheng
jiang tiancai
xu xianbo
sun liepeng
zhang zhouli
摘要： 为验证RFQ腔体功率输入耦合器设计的合理性和减少腔体污染，设计了低损耗离线锻炼腔体，并进行了高功率试验。离线锻炼腔由两个耦合口和两个调谐器口组成。此外，耦合环的安装角度和调谐器的插入深度可以用来低腔体的功率损耗。对该离线锻炼腔体进行了电磁结构和多物理场模拟，结果表明该腔体的最小理论功率损耗为4.3%。当腔体频率变化为110kHz时，理论功率损耗增加到10%。因此，调谐器在调节过程中始终处于运动状态。多物理场模拟表明，腔体温度的升高对频率变化没有影响。当离线高功率锻炼平台建成后，测量了该系统的传输性能，功率损耗为6.3%，大于理论计算值。高功率离线锻炼采用了高效的自动扫福和驻波谐振锻炼方法。为了充分锻炼高功率输入耦合器，选择了13个驻波点。最大连续波功率大于20kW，优于预期目标。
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this paper, we investigate the possible deviations of the cosmic distance duality relation (CDDR) using the combination of the largest SNe Ia (Pantheon) and compact radio quasar (QSO) samples through two model-independent approaches. The deviation of CDDR is written as $D_L(z)/D_A(z)(1+z)^{-2}=\eta(z)$ and $\eta(z)=e^{\tau(z)/2}$, with the parameterizations of $F_1$ ($\tau(z) = 2\epsilon_1 z$) and $F_2$ ($\tau(z) = (1+z)^{2\epsilon_2}-1$). Furthermore, in order to compare the two resulting distances, two cosmological-model-independent methods, i.e., the nearby SNe Ia method and the GP method are employed to match the two distinct data at the same redshift. Our findings indicate that, compared with the results obtained in the literature, there is an improvement in precision when the latest SNe Ia and QSO samples are used. Specially, in the framework of nearby SNe Ia method, the CDDR would be constrained at the precision of $\Delta\epsilon_{1} = 0.013$ in Model $F_1$ and $\Delta\epsilon_{2}=0.018$ in Model $F_2$. Regarding the GP method, one observes that a larger data size would produce more stringent constraints on the CDDR parameters. Therefore, accompanied by further developments in cosmological observations and the analysis methods, our analysis provides an insight into the evidence for unaccounted opacity sources at an earlier stage of the universe, or at the very least the new physics involved.
分类： 物理学 >> 核物理学 提交时间： 2023-07-10
Jinying, Ma
Chengye, Xu
Andong, Wu
Guodong, Jiang
Yue, Tao
Zongheng, Xue
Longbo, Shi
Tiancai Jiang
Zhenglong, Zhu
Ziqin, Yang
Zheng, Gao
Liepeng, Sun
Guirong, Huang
Feng, Qiu
Yuan, He
摘要： The accurate measurement of parameters such as the cavity-loaded quality factor (QL) and half bandwidth (f0.5) is essential for monitoring the performance of superconducting radio-frequency (SRF) cavities. However, the conventional field decay method employed to calibrate these values requires the cavity to satisfy a zeroinput condition. This can be challenging when the source impedance is mismatched and produce nonzero forward signals (Vf ) that significantly affect the measurement accuracy. To address this limitation, we developed a modified version of the field decay method based on the cavity differential equation. The proposed approach enables the precise calibration of f0.5 even under mismatch conditions. We tested the proposed approach on the SRF cavities of the Chinese Accelerator Driven System Front-End Demo Superconducting Linac and compared the results with those obtained from a network analyzer. The two sets of results were consistent, indicating the usefulness of the proposed approach.
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