Ramping Process Research Articles

Correction of dynamic magnetic field errors at the rapid cycling synchrotron of China Spallation Neutron Source

At a Rapid Cycling Synchrotron (RCS), dynamic magnetic field errors, such as magnetic field tracking errors and dynamic fringe field effects, can cause time-dependent tune shift during beam acceleration. If the tune shift is significant enough to pass through resonance lines, it can lead to emittance growth and beam losses. Correcting time-dependent tune shift during acceleration is crucial for a RCS. Modulating the exciting current and magnetic field of quadrupole magnets at a RCS, which are powered by resonant circuits, is challenging during the ramping process. Correcting time-dependent tune shift at a RCS poses a significant technical challenge. We have proposed a method for correcting time-dependent tune shift at the rapid cycling synchrotron of China Spallation Neutron Source (CSNS), based on waveform compensation at the quadrupole magnets. This approach involves modulating the magnetic field variation process by injecting time harmonic exciting current into the quadrupole magnets. This method has been validated during the CSNS beam commissioning and has been applied at the RCS of CSNS to correct various dynamic magnetic field errors.

Competitive integration of time and reward explains value-sensitive foraging decisions and frontal cortex ramping dynamics.

Patch foraging presents a ubiquitous decision-making process in which animals decide when to abandon a resource patch of diminishing value to pursue an alternative. We developed a virtual foraging task in which mouse behavior varied systematically with patch value. Mouse behavior could be explained by a model integrating time and rewards antagonistically, scaled by a latent patience state. The model accounted for deviations from predictions of optimal foraging theory. Neural recordings throughout frontal areas revealed encoding of decision variables from the integrator model, most robustly in frontal cortex. Regression modeling followed by unsupervised clustering identified a subset of ramping neurons. These neurons' firing rates ramped up gradually (up to tens of seconds), were inhibited by rewards, and were better described as a continuous ramp than a discrete stepping process. Together, these results identify integration via frontal cortex ramping dynamics as a candidate mechanism for solving patch foraging problems.

Dynamic fringe field effect of the rapid ramping quadrupole magnets at a Rapid Cycling Synchrotron

For a DC quadrupole magnet, the normalized magnetic field distribution along the beam trajectory is mainly determined by the mechanical structure of the magnet and remains almost independent of the exciting current. However, the magnetic field measurement results of the Rapid Cycling Synchrotron (RCS) at the China Spallation Neutron Source (CSNS) show that the normalized magnetic field distribution along the beam trajectory varies during the exciting current ramping process for rapid ramping magnets. Consequently, for rapid ramping quadrupole magnets, there are significant differences between the dynamic and static magnetic field gradient distribution. And the changes in the distribution of the magnetic field gradient can cause time dependent tune-shifts during the exciting current ramping process. For RCS, the tune is crucial, and the shifts of tune may lead to the beam approaching the resonance line, thereby causing beam loss. The impact of the fringe field effect of the rapid ramping quadrupole magnets on beam dynamics at CSNS-RCS was detailly studied. A new method for correcting the time-dependent tune shifts caused by the dynamic field distribution, based on waveform compensation at the quadrupole magnets, has also been proposed for the RCS of CSNS. Related simulation and experiment have been conducted, and the simulation results and experimental results are consistent with theoretical study results.

Development of high-level applications for High Energy Photon Source booster

The High Energy Photon Source (HEPS), is the first fourth-generation storage ring light source being built in the suburb of Beijing, China. The storage ring was designed with the emittance lower than 60 pm.rad with a circumference of 1.36 km and beam energy of 6 GeV. Its injector contains a 500 MeV S-band Linac and a 454 m booster which was designed as an accumulator at the extraction energy. In the energy ramping control design of HEPS booster, the ramping process was programed to be able to stop and stay at any energy between the injection energy and the extraction energy. This feature enables us to conduct energy-dependent machine studies and ramping curve optimization. The beam commissioning of HEPS Linac finished in June, 2023. And the beam commissioning of booster started in the end of July, 2023. In November 17, main target values proposed in the preliminary design report has been reached. The high-level applications (HLAs) are essential tools for beam commissioning. The development of HLAs, which are based on the framework named Python accelerator physics application set (Pyapas), started in the end of 2021. The HEPS physics team spent more than one year to develop and test the HLAs to meet the requirements of beam commissioning of the booster. Thanks to the modular design, the principle based on physical quantities, and the ability of running simulation models online from the Pyapas, the development efficiency and reliability of the HLAs have been greatly improved. In particular, the principle based on physical quantities allows us to control the beam more intuitively.

Analysis of warpage and reliability of very thin profile fine pitch ball grid array

With the evolution of advanced integrated circuit (IC) packaging technology, the use of experiments to identify package performance and life expectation will take a significant amount of time and cost to finish the job. To reduce the cost of research and testing, predictive analyses of reliability and performance using simulation tools have become a feasible approach for the IC assembly industry. Therefore, this study utilized Moldex3D molding simulation software to analyze very thin profile fine pitch ball grid array (VFBGA) packages and established a numerical analysis procedure from the molding and curing process, the post-mold cure (PMC) process, to a thermal cycling test (TCT) to predict the amount of package warpage during processing and reliability after TCT.The results showed that the warpage trends of both experiments and simulations during the same temperature ramping process were similar. In the thermal cycling analysis, potential failure locations were found to be at the copper pillars and redistribution layer (RDL), where the maximum Von Mises stress occurred at the lowest temperature (−65 °C). The fatigue life model, Coffin–Manson model, was used to calculate the potential fatigue life at the two locations, resulting in 1689 cycles (copper pillars) and 9706 cycles (RDL L1).

Beam dynamics in the booster synchrotron of Korea-4GSR project

In recent years, there have been several projects in the world to design and construct a diffraction-limited light source which pushes an emittance of electron beams in a storage ring close to an emittance of photon beams in the X-ray region to enhance brilliance by two orders of magnitude. In line with this trend, the Korea fourth-generation storage ring (Korea-4GSR) project was launched in 2021 to establish a new light source in the Republic of Korea with an ultra-low emittance of 50 pmrad at a beam energy of 4 GeV. For the Korea-4GSR project, a compact linear accelerator for generating 200 MeV and a booster synchrotron is chosen as an injector. The booster synchrotron ramps beam energy from 200 MeV to 4 GeV and the lattice is designed based on the FODO concept. It is crucial in the booster to achieve high beam quality for injection efficiency into a storage ring. Since the quality of the extracted beam relies on an energy ramping profile, the ramping process is important to be optimized. This paper represents the result of our studies on the effect of the energy ramping profile in the evolutionary physical process in a booster synchrotron.

Kinetically Stabilized Hafnia Ferroelectric of Al-Doped HfO$_{\text{2}}$ Film by Fast Ramping and Fast Cooling Process

Kinetically Stabilized Hafnia Ferroelectric of Al-Doped HfO$_{\text{2}}$ Film by Fast Ramping and Fast Cooling Process

Acceleration of solving drift-diffusion equations enabled by estimation of initial value at nonequilibrium

<abstract><p>In this study, a novel method enabled by estimation of initial value guess at nonequilibrium was proposed to accelerate drift-diffusion equations in semiconductor device simulation. The initial value guess was obtained by solving analytical model about electrical potential with the decoupling algorithm. By obtaining the initial value directly at the target bias voltage, the proposed method eliminated time-consuming bias ramping process in the classical method starting from the equilibrium state, thereby accelerating the whole process. The method has been applied to a junction barrier Schottky (JBS) diode for validation. Numerical results showed that the proposed method achieves convergence within 10 iterations at several reverse bias voltages, achieving significant reduction of iteration number compared to the classical method using the bias ramping process. It demonstrated that the proposed method holds high feasibility to facilitate the semiconductor device property prediction in relatively regular device structure in the case of low current. With further improvements, this method can also be applied to more complex devices.</p></abstract>

The Influence of Different Shear Directions on the Shear Resistance Characteristics of Rock Joints

The joint roughness coefficient JRC of rock joints is an important parameter for measuring the geometric morphology of rock joints. However, the parameter obtained from traditional calculation methods has certain limitations in reflecting the differences in shear strength of rock joints in different shear directions with the same orientation. Firstly, native joint surface test blocks were cast using three-dimensional reverse reconstruction technology. Subsequently, direct shear tests were conducted under different normal stress and shear direction conditions, followed by numerical simulations using the finite difference software Flac3d. The JRC coefficient calculation method proposed by Yuan was modified and extended by considering the percentage of climbing sections and the effective contact area during the ramping process. This study indicates that the numerical simulation results are in good agreement with the shear test results. The introduction of the shear climbing rate SCR and the curvature coefficient of profile CCP is used to reflect the geometric differences of the joint surfaces in different shear directions. These two parameters are nonlinearly fitted with the experimental results, leading to a calculation formula that characterizes the shear strength characteristics of the joint surfaces in different shear directions. This novel formula is an extension of the JRC–JCS model.

Dynamic fringe field effects of the rapid ramping quadrupole magnets at the Rapid Cycling Synchrotron of China Spallation Neutron Source

The dynamic fringe field of the quadruple magnets at the Rapid Cycling Synchrotron (RCS) of China Spallation Neutron Source (CSNS) was measured and studied using a small flip coil measurement system. For DC quadruple magnets, the normalized magnetic field distribution along the beam trajectory, which is determined by the mechanical structure of the magnet, is independent of the exciting current. However, the magnetic field measurement results at CSNS-RCS showed that the normalized magnetic field distribution along the beam trajectory varies during the exciting current ramping process for quadruple magnets. The variation of the normalized magnetic field distribution can induce a time-dependent tune during the ramping process. Therefore, in this paper, we analyzed and studied the dynamic fringe field effects of the rapid ramping quadrupole magnets at CSNS-RCS.

An intraperiod arbitrary ramping-rate changing model in unit commitment

In traditional unit commitment models, the ramping process of coal-fired generators is often represented by either a static average ramping rate or a once-changing rate model. However, this approach fails to accurately capture the actual ramping process of the unit, resulting in scheduling biases, particularly in systems with renewable energy sources. To address this issue, we propose a dynamic piecewise linear ramping (DPWLR) model that allows arbitrary multi-changes of ramping rates within a single period. We shift our focus from slope changes to time changes. By using a series of location indicator variables that satisfy the type 2 special ordered set, we locate the forward and backward time change limits and then determine the up and down power output limits of the units at each hour. We tested the intraperiod multiple-changing DPWLR model, as part of the unit commitment model, on different systems, including a 3-unit system, a 10-unit system, the IEEE RTS-79, and a 100-unit system. Comparative analysis demonstrates the functionality and superior performance of our proposed model.

Analysis of Nonuniform Contact Resistivity Distribution on No-Insulation HTS Racetrack Coil

This paper presents a numerical analysis and experiment to investigate a contact resistivity distribution of a no-insulation (NI) high-temperature superconductor (HTS) racetrack coil. Since the racetrack coil consists of straight and curved sections with continuously varing curvatures, the local inhomogeneity of contact resistivity can occur. We adopt a partial element equivalent circuit (PEEC) method to investigate this inhomogeneity. A 50-turn NI HTS single pancake test coil is fabricated to figure out the discrepancy of contact resistivity, and the coil is charged up to 100 A in a liquid nitrogen bath. Voltage profiles between inserted voltage taps and the magnetic fields at the coil center are measured and compared with two simulation cases: 1) uniform contact resistivity; 2) nonuniform contact resistivity distribution. The results indicated that nonuniform distribution of contact resistivity may exist. Lastly, the current and Joule heat distribution during the ramping process is analyzed by the PEEC model.

Thermal mismatch engineering induced freestanding and ultrathin Ga2O3 membrane for vertical electronics

Inevitable thermal-expansion-coefficient mismatch at the interface of epitaxial-layer/foreign-substrate is generally considered as a weak side since considerable strain would be induced during the temperature ramping process. However, rather than the conventional strain minimizing strategy, engineering this thermal-induced strain, i.e., beyond the tolerance of the interfacial bond energy, may result in the exfoliation of the epitaxial layer from bulk substrate. In this work, Ga2O3 membrane, a promising and desirable material for deep ultraviolet (DUV) photonics and high-power electronics, could be exfoliated from a pre-deposited Si-doped Ga2O3/AlN template in a high-temperature environment, allowing the vertical device configuration and preferable thermal management regardless of the costly Ga2O3 substrates. The exfoliated Ga2O3 membrane, which is comparable to the commercial Ga2O3 substrates, is freestanding, centimeter-scale, but ultrathin. The exfoliated Ga2O3 membrane was applied to a vertical DUV photodetector, which demonstrated an on/off ratio of 4.20 × 104, responsivity of 170.3 A/W, and detectivity of 1.01 × 1013 Jones under 254 nm illumination at a bias of −5 V. The presented thermal mismatch engineering (TME) would allow researchers to look beyond the hetero-mismatch and unitize the interfacial strain for membrane exfoliation, e.g., freestanding Ga2O3 membrane for vertical electronics that avoid the ongoing high-cost native substrates.

Acceleration of semiconductor device simulation using compact charge model

In this work, we propose a method to get an initial guess for the semiconductor device simulation with a compact charge model. By using the obtained initial guess, we can perform the device simulation directly at the target bias condition without a time-consuming bias ramping process. In order to verify our method, rectangular Gate-All-Around (GAA) metal–oxide–semiconductor field-effect transistors (MOSFETs) having a long channel length are considered. Results clearly show that the device simulation can be accelerated through our method.

Contact Resistance Dependent Transient Loss of REBCO No-Insulation Magnet UsingT-AFormula During Ramping Process

The transient loss during the ramping process is an important evaluation metric for commercial large-scale magnet systems to meet refrigeration requirements; this loss is considerably influenced by contact resistivity. Due to the intrinsic bypass current of the no-insulation pancake, two parts of the transient loss were considered in this study: turn-to-turn loss generated by the radial direction current and the magnetization loss produced by the azimuthal direction current. A turn-distributed model was used to calculate the non-uniform current distribution, where the pancake coil is radially subdivided into each turn. The radial current was used to calculate the turn-to-turn loss. The turn azimuthal current was applied to the boundary condition of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T-A</i> formula to calculate the magnetization loss in a cylindrical coordinate system. The superconductor index value model was used for the simulations, where the critical current density is the conductor engineering current density estimated by a neural network fitting model. The contact resistance dependent turn-to-turn loss and magnetization loss were presented. This approach is expected to be used in magnet-level NMR/ MRI systems.

3D modelling of coupled electromagnetic-mechanical responses in REBCO coils involving tape inhomogeneity

Electromagnetic and mechanical properties are crucial components of high-temperature superconducting magnet in high-field applications. In this research, in order to predict the multi-field behaviors of REBCO coils during the ramping process, the coupled electromagnetic-mechanical model is constructed with consideration of the strain and magnetic field dependences of the critical current of coated conductors (CCs). The 3D modelling is used to characterize the longitudinal in-homogenous critical current of a CC, which also allows for handling the coil with local defects. To verify the reliability of the coupled model, a comparison of numerical simulations with experiments for a small REBCO coil is first performed with special attention on the hoop strain evolution during the magnetization process. On this basis, the coupled model is then utilized to study the influences of local critical current non-uniformity defined by a Gaussian statistical distribution. The numerical analysis shows that, the tape inhomogeneity has an obvious impaction on decreasing the critical current of REBCO coil. And in high-field scenario, the calculated critical current of coil is highly reduced when the mutual interaction between electromagnetic and mechanical fields is considered. Afterwards, a detailed comparative study is carried out in studying the screening current effects of REBCO coil with and without taking the tape inhomogeneity into account. Finally, the effects of cooling-down process, co-winding materials and local defects are investigated to understand their role in electromagnetic-mechanical response of high-field REBCO coils.

Study of Beam Transmission Efficiency in Injection and Ramping Process of the HEPS Booster

Study of Beam Transmission Efficiency in Injection and Ramping Process of the HEPS Booster

Design of High Energy Photon Source Booster beam size monitor

High Energy Photon Source (HEPS) Booster is designed to ramp up the energy of the beam from linac and inject high quality electron beam to the storage ring. To measure the transverse beam size, emittance and energy spread of HEPS Booster, we designed two beam diagnostic beamlines at visible-UV spectrum region. The source points are at two bending magnets with different chromatic dispersion, one has no dispersion while the other has large dispersion. By measuring the transverse beam sizes with synchrotron imaging system, beam emittance and energy spread can also be calculated. This paper introduces the extraction of visible-UV light, and the optical imaging system, the spatial resolution. It also introduces the design of beam spot changes measurement during beam ramping process.

Orthotropic Viscoelastic Properties of Chinese Fir Wood Saturated with Water in Frozen and Non-frozen States

Abstract In order to better understand the differences in orthotropic viscoelastic properties of Chinese fir (Cunninghamia lanceolata) in frozen and non-frozen states, the storage modulus (E′) and loss modulus (E″) of the longitudinal, radial, and tangential specimens were investigated under water-saturated conditions with temperatures ranging from −120°C (or 30°C) to 280°C. Results revealed that the order of magnitude in E′ for each orientation was consistent for temperatures below 0°C, while the anisotropy in E′ was reduced due to the enhancement effect of ice. Frequency-dependent γ-relaxation was observed at approximately −96°C for all orthotropic directions. A sharp discontinuity in E′ occurred at approximately 0°C for each specimen, together with the corresponding sharp peak in the E″ spectrum. Furthermore, the frozen free water had an effect on the orthotropic viscoelastic behavior in the water-saturated specimens within the range of −120°C to 280°C. Specimens with a frozen history leveled off at the initial temperature ramping phase for each orientation, while a frozen history reduced the decline in stiffness of the wood specimens. Similar to the variations in E′, the dramatic loss of water increased the complexity of the E″ values. The loss of free water also had a pronounced effect on the viscoelastic properties during the temperature ramping process. Thus, in the wood industry, it necessary to consider the variations in the orthotropic viscoelastic performance of specimens under water-saturated conditions during the water loss process.

Unit commitment considering the impact of deep cycling

Wind energy has been integrated into power systems with the hope that it can improve energy efficiency and decrease greenhouse gas emissions. However, several studies from around the world have implied that this integration has had an opposite effect, mainly because of the negative correlation between wind availability and load. Under this dynamic situation, coal power plants are forced to cycle, which is not within their designed mode of operation. To prevent this unwanted result, a unit commitment decision should include the fuel usage and emission rates during the ramp up/down process. This paper proposes a new unit commitment decision process to accommodate the economic and environmental costs associated with the ramping process. These costs are generally not convex, because there is a positive cost if a generator output changes significantly (regardless of direction). As a result, the problem might be nonconvex. A piece-wise linear cost curve is introduced to model the impact of ramping processes. With this curve, convex linear programming is formulated and the impact of governmental policy is discussed.