Vol.32,

Harmonic cavities (HCs) are widely used in electron storage rings, mainly to increase the Touschek lifetime by lengthening bunches. HCs have become critical components of almost all fourth-generation synchrotron light sources. In addition to the benefits of increasing the Touschek lifetime, they also affect the collective beam instabilities in electron storage rings. However, the influence of HC settings on collective beam instabilities not well understood. HCs are typically designed to operate under so-called ideal lengthening conditions, which do not necessarily optimize the suppression of collective beam instabilities. We therefore extended earlier studies of collective beam instabilities to consider more general HC settings. We present preliminary studies and analyses of the influences of different HC settings on microwave and transverse mode-coupling instabilities.

540

The physical design for a novel low-energy compact-storage-ring-based extreme ultraviolet (EUV) light source was systemically studied. The design process considers the linear and nonlinear beam optics, including transverse matching and the optimization of the dynamic aperture, momentum aperture, and beam lifetime. With a total circumference of 36.7 m and a beam energy of 400 MeV, the storage ring can operate with an average beam current of up to 1 A. With the undulator as the radiator, this facility has the potential to emit EUV radiation at 13.5 nm with an average power exceeding 10 W within the bandwidth. In addition, the collective instabilities of the lattice at high beam current were analyzed; it was found that the typical instabilities which may occur in an electron storage ring can be reasonably controlled in our design. With the advantages of variable beam energy and current, this design exhibits great promise as a new candidate for various extreme ultraviolet (EUV) lithographical applications requiring tunable radiation power.

525

To further improve the performance of accelerators, the first cryogenic normal-conducting RF gun in China was designed and manufactured. As a new and attractive trend, this optimized cryogenic RF gun can generate a low-emittance beam with a short-driven laser pulse because of its promising high gradient on the cathode. In this paper, optimization of the RF design and beam dynamics, including suppression of the peak RF field and elimination of the multipole mode, is presented. In addition, the emittance growth caused by the alignment deviation and RF jitter is discussed. After the gun was manufactured, a cold test was conducted at both room temperature and cryogenic conditions. At room temperature, the field distribution was obtained by the bead pull method. Under cryogenic conditions, the RF properties, such as the coupling coefficient and quality factor, varied with temperature. The test results agreed with the design. In the cryogenic test, vibration measurements were performed. Without vibration isolation, a maximum vibration of 50 μ m was observed. These cold test results are the basis of the following high-power test.

473

The high-temperature reactor pebble-bed module (HTR-PM) is a modular high-temperature gas-cooled reactor (HTGR) demonstration power plant. Its first criticality experiment is scheduled for the latter half of 2021. Before performing the first criticality experiment, a prediction calculation was performed using PANGU code. This paper presents the calculation details for predicting the HTR-PM first criticality using PANGU, including the input model and parameters, numerical results, and uncertainty analysis. The accuracy of the PANGU code was demonstrated by comparing it with the high-fidelity Monte Carlo solution, using the same input configurations. It should be noted that k_eff can be significantly affected by uncertainties in nuclear data and certain input parameters, making the criticality calculation challenging. Finally, PANGU is used to predict the critical loading height of the HTR-PM first criticality under design conditions, which will be evaluated in the upcoming experiment later this year.

334

The molten salt leakage accident is an important issue in the nuclear safety analysis of molten salt reactors. While the molten salt leaks from the pipeline or storage tank, it will contact the insulation layer outside; hence, the processes of penetration and spreading play an important role in the development of leakage accidents. In this study, the penetration and diffusion of leaking molten salt (LMS) in an aluminum silicate fiber (ASF) thermal insulation layer were studied experimentally. A molten salt tank with an adjustable outlet was designed to simulate the leakage of molten salt, and the subsequent behavior in the thermal insulation layer was evaluated by measuring the penetration time and penetration mass of the LMS. The results show that, when the molten salt discharges from the outlet and reaches the thermal insulation layer, the LMS will penetrate and seep out from the ASF, and a higher flow rate of LMS requires less penetration time and leaked mass of LMS. As the temperature of the LMS and thickness of the ASF increased, the penetration time became longer and the leaked mass became greater at a lower LMS flow rate; when the LMS flow rate increased, the penetration time and leaked mass decreased rapidly and tended to flatten.

366

The discrete ordinates (S_N) method requires numerous angular unknowns to achieve the desired accuracy for shielding calculations involving strong anisotropy. Our objective is to develop an angular adaptive algorithm in the S_N method to automatically optimize the angular distribution and minimize angular discretization errors with lower expenses. The proposed method enables linear discontinuous finite element quadrature sets over an icosahedron to vary their quadrature orders in a one-twentieth sphere so that fine resolutions can be applied to the angular domains that are important. An error estimation that operates in conjunction with the spherical harmonics method is developed to determine the locations where more refinement is required. The adaptive quadrature sets are applied to three duct problems, including the Kobayashi benchmarks and IRI-TUB research reactor, which emphasize the ability of this method to resolve neutron streaming through ducts with voids. The results indicate that the performance of the adaptive method is more efficient than that of uniform quadrature sets for duct transport problems. Our adaptive method offers an appropriate placement of angular unknowns to accurately integrate angular fluxes while reducing the computational costs in terms of unknowns and run times.

425

The point-contact high-purity germanium detector (HPGe) has the advantages of low background, low energy threshold, and high energy resolution, and can be applied in the detection of rare-event physics. However, the performance of HPGe must be further improved to achieve superior energy resolution, low noise, and long-term reliability. In this study, we combine computational simulations and experimental comparisons to deeply understand the passivation mechanism of Ge. The surface passivation effect is calculated and inferred from the band structure and density of interface states, and further confirmed by the minority carrier lifetime. The first-principles method based on the density functional theory was adopted to systematically study the lattice structure, band structure, and density of state (DOS) of four different systems: Ge-H, Ge-Ge-NH₂, Ge-OH, and Ge-SiO_x. The electronic characteristics of the Ge (100) unit cell with different passivation groups and Si/O atomic ratios were compared. This shows that H, N, and O atoms can effectively reduce the surface DOS of the Ge atoms. The passivation effect of the SiO_x group varied with increasing O atoms and Si/O atomic ratios. Experimentally, SiO and SiO₂ passivation films were fabricated by electron beam evaporation on a Ge substrate, and the valence state of Si and resistivity were measured to characterize the film. The minority carrier lifetime of Ge-SiO₂ is 21.3 μs, which is approximately quadruple that of Ge-SiO. The passivation effect and mechanism are discussed in terms of hopping conduction and surface defect density. This study builds a relationship between the passivation effect and different termination groups, and provides technical support for the potential passivation layer, which can be applied in Ge detectors with ultralow energy thresholds and especially in HPGe for rare-event physics detection experiments in the future.

436

Gamma-ray integrated detector (GRID) mission is a student project designed to use multiple gamma-ray detectors carried by nanosatellites (CubeSats), forming a full-time all-sky gamma-ray detection network that monitors the transient gamma-ray sky in the multi-messenger astronomy era. A compact CubeSat gamma-ray detector, including its hardware and firmware, was designed and implemented for the mission. The detector employs four Gd₂Al₂Ga₃O₁₂:Ce> (GAGG:Ce) scintillators coupled with four silicon photomultiplier (SiPM) arrays to achieve a high gamma-ray detection efficiency between 10 keV and 2 MeV with low power and small dimensions. The first detector designed by the undergraduate student team onboard a commercial CubeSat was launched into a Sun-synchronous orbit on October 29, 2018. The detector was in a normal observation state and accumulated data for approximately one month after on-orbit functional and performance tests, which were conducted in 2019.

614

Deuteron-driven spallation targets have garnered attention recently because they can provide high-energy neutrons to transmute long-lifetime fission products. In this study, the Geant4 toolkit was used to simulate the interaction between a deuteron beam at 500 MeV and a composite target composed of alternating lead-bismuth eutectic (LBE) and water. The water was used because it may be employed as a target coolant. The energy spectrum, neutron yield, average energy, and total energy of the emitted neutrons were calculated for different thicknesses and thickness ratios between the LBE and water. For a constant target thickness, the neutron yield increases with an increasing thickness ratio of LBE to H₂O, while the average energy of the emitted neutrons decreases with an increasing in the aforementioned thickness ratio. These two aspects support the use of a pure target, either LBE or water. However, with an increasing LBE to H₂O thickness ratio, the total energy of the emitted neutrons increases and then decreases. This resul t supports the addition of water into the LBE target. The angular distributions of the emitted neutrons show that the rear of the target is suitable for loading nuclear waste containing minor actinides and long-lifetime fission products.

332

The transmutation of long-lived fission products through spallation induced by light nuclides was investigated for the purpose of determining the feasibility of this approach for long-lived fission products, in both economic and environmental terms. The cross-section data were obtained from the TALYS Evaluated Nuclear Data Library (TENDL). A thick target model was used to study the consumption of the target isotopes in the transmutation process. The transmutation yield was calculated using the highest beam intensity available with the China initiative Accelerator Driven System. It was found that the light nuclide-induced spallation reaction can significantly reduce the radio toxicity of the investigated long-lived fission products. Using the transmutation target made of elemental LLFP and the proton beam with an intensity of 5 mA, the consumption of ⁹⁰Sr, ⁹³Zr, ¹⁰⁷Pd, or ¹³⁷Cs can reach approximately 500 g per year.

549

The neutron capture cross section of ¹⁹⁷Au was measured using the time-of-flight (TOF) technique at the Back-n facility of the China Spallation Neutron Source (CSNS) in the 1 eV to 100 keV range. Prompt γ-rays originating from neutron-induced capture events were detected by four C₆D₆ liquid scintillator detectors. Pulse height weighting technology (PHWT) was used to analyze the data. The results are in good agreement with ENDF/B-VIII.0, CENDL-3.1, and other evaluated libraries in the resonance region, and in agreement with both n_TOF and GELINA experimental data in the 5-100 keV range. Finally, the resonance peaks in the energy range from 1 eV to 1 keV were fitted by the SAMMY R-matrix code.

905

The first experimental investigation of the tungsten behavior in ELMy H-mode plasmas with co-/counter neutral beam injection (NBI) and unfavorable/favorable B_t was performed on EAST. Tungsten was found to accumulate easily in ELMy H-mode plasma with co-NBI heating and unfavorable B_t. Thus, in this case the tungsten concentration can exceed 10⁻⁴, resulting in degradation of the plasma confinement and periodic H-L transitions. To reduce the tungsten concentration in steady-state type-I ELMy H-mode operation, counter-NBI is applied to modify the density and temperature and brake the plasma toroidal rotation. The applied counter-NBI decreases the PHZ+E_r inward pinch velocity and reverses the direction of neoclassical inward convection, thus decreasing the tungsten concentration from ~7 × 10⁻⁵ to ~2 × 10⁻⁵ in type-I ELMy H-mode plasma with favorable B_t. A comparison of the effects of different B_t directions on the tungsten behavior also shows that favorable B_t is beneficial for reducing the tungsten concentration in the core plasma. These results imply that counter-NBI with favorable B_t can effectively prevent tungsten accumulation and expand the operating window for exploring steady-state type-I ELMy H-mode operation of EAST.

426

A series of liner-like Z-pinch loads with a novel configuration, have been investigated experimentally for the first time on Qiangguang-I facility in China. The metallic layer is sputtered on the inner surface of the cylindrical SiO₂ substrate tube. In the preliminary experiment, the electric current flowed through the metallic load during the prepulse. However, the currents also flowed through the outer surface of the SiO₂ substrate during the main pulse. After the dielectric length had been increased in the formal experiment, most of the current flowed through the metallic load, until radial radiation peak was measured by radiation monitor. As the line mass of metallic load increases, the peak time of radial radiation also increases. Axial ultraviolet frames indicate that the radiations are nearly azimuthally uniform at first, but the uniformity becomes worse after radial radiation peak. The clearly separated boundary between metal plasmas and the substrate, has not been observed in the experiment. Experimental results are discussed and compared with simulation using the one-dimension radiation hydrodynamics code MULTI-IFE.

647

The visualization and data mining of tumor multidimensional information may play a major role in the analysis of the growth, metastasis, and microenvironmental changes of tumors while challenging traditional imaging and data processing techniques. In this study, a general trans-scale and multi-modality measurement method was developed for the quantitative diagnosis of hepatocellular carcinoma (HCC) using a combination of propagation-based phase-contrast computed tomography (PPCT), scanning transmission soft X-ray microscopy (STXM), and Fourier transform infrared micro-spectroscopy (FTIR). Our experimental results reveal the trans-scale micro-morphological HCC pathology and facilitate quantitative data analysis and comprehensive assessment. These results include some visualization features of PPCT-based tissue microenvironments, STXM-based cellular fine structures, and FTIR-based bio-macromolecular spectral characteristics during HCC tumor differentiation and proliferation. The proposed method provides multidimensional feature data support for constructing a high-accuracy machine learning algorithm based on a gray-level histogram, gray-gradient co-occurrence matrix, gray-level co-occurrence matrix, and back-propagation neural network model. Multi-dimensional information analysis and diagnosis revealed the morphological pathways of HCC pathological evolution and we explored the relationships between HCC-related feature changes in inflammatory microenvironments, cellular metabolism, and the stretching vibration peaks of biomolecules of lipids, proteins, and nucleic acids. Therefore, the proposed methodology has strong potential for the visualization of complex tumors and assessing the risks of tumor differentiation and metastasis.

495