Electric propulsion systems are attractive for space missions because they have the advantage of higher specific impulse and payload capability compared with chemical engines. In an interplanetary mission, one often needs to simultaneously consider the spacecraft's trajectory and onboard system design, which increases the computational cost for design and optimization. This issue is further exacerbated by various combinations of gravity-assist maneuver (fly-bys) options (e.g., the fly-by sequence and the number of fly-bys). Large-scale coupled low-thrust trajectory and system optimization with variable fly-by options have not been well explored. This study will break this limit by proposing a new optimization framework considering low-thrust trajectory optimization with discrete fly-by options. The proposed optimization framework has two main layers: Dymos and dEGO. The Dymos layer uses NASA's OpenMDAO/Dymos framework for large-scale gradient-based low-thrust trajectory optimization with a given fly-by option. The Dymos layer will output the optimized objective function (e.g., time-of-flight or fuel burn) to the dEGO layer. The dEGO layer then uses discrete, efficient global optimization to update the fly-by option to send it back to the Dymos layer. This paper introduces the framework and showcases our preliminary results for low-thrust trajectory optimization with fly-bys using Dymos. We use the Earth-Venus-Mars case as a demonstration and optimize the fuel consumption by changing the thrust magnitude, direction, and dates for the departure, fly-by, and arrival. The proposed optimization framework has the potential to design more efficient spacecraft missions.

Non-evaporable getter is now widely employed in many accelerators to mitigate the resistive-wall effect of the Ti–Zr–V getter coated vacuum chambers in the next generation accelerators. Quaternary Ti–Zr–V–Cu getter films were deposited by direct current (DC) magnetron sputtering. The DC/high frequency impedance and activation kinetics were investigated by four-probes/waveguide methods and in situ synchrotron radiation photoelectron spectroscopy (SRPES). Compared to Ti–Zr–V films, Ti–Zr–V–Cu films showed better conductivity, which is beneficial to eliminate the resistive-wall effect. However, its initial activation temperature is above 200 °C, and it needs to be activated at a higher temperature to achieve the required pumping performance.

This paper presents an aerodynamic shape optimisation approach that utilises machine learning techniques to augment the turbulence model for the steady-state Reynolds-averaged Navier-Stokes (RANS) simulations-which are prone to inaccuracies for complex flows involving phenomena such as separation. We employ the field inversion and machine learning (FIML) approach which infers model discrepancies by solving a number of inverse problems (for different shapes and/or flow conditions) given some high-fidelity data, and uses machine learning (such as neural networks) to generalise the discrepancy fields for unseen cases. As a proof-of-concept we use direct numerical simulation (DNS) data for a set of parameterised periodic hills to augment the two-equations k - w SST model using FIML, then incorporating it in the CFD solver for aerodynamic shape optimisation where the cost function is the drag minimisation. To illustrate the inherent optimisation sensitivity to the choice of turbulence model, we also use theWilcox k - w model for comparison. Once the optimal shapes are achieved for the different turbulence models, we propose using the hybrid RANS-LES improved delayed detached eddy simulations (IDDES) to validate the flow predictions, which in turn is validated against the available DNS data. Results highlight the sensitivity of optimisation to the turbulence model in the presence of flow separation, and the FIML-augmented k - w SST model is able to achieve much higher drag reduction (20.8 - 25.3%) with fair agreement to the IDDES predictions (in terms of velocity and skin friction). The baseline SST model achieves a drag reduction of 4.5 - 6.5%, and the velocity and skin friction compares poorly to the IDDES results.

The Goubau line method has been recently proposed and used for the longitudinal beam coupling impedance measurement of vacuum components. To extend the application of this method, the measurement of transverse impedance using the Goubau line method is proposed in this work. The feasibility of measuring the transverse impedance using the Goubau line method has been tested using a pillbox cavity. Additionally, the frequency shift induced by the dielectric-coated wire in the Goubau line measurements has been investigated analytically. The contribution of the dielectric coating to the frequency shift has been studied. Finally, the Goubau line setup has been optimized and used to evaluate the longitudinal and transverse beam coupling impedance key vacuum components in the High Energy Photon Source.

The high-energy photon source (HEPS) is the first fourth-generation synchrotron light source facility in China. The HEPS injector consists of a linear accelerator (Linac) and a full energy booster. The booster captures the electron beam from the Linac and increases its energy to the value required for the storage ring. The full-energy beam could be injected to the storage ring directly or after “high-energy accumulation.” On November 17, 2023, the key booster parameters successfully reached their corresponding target values. These milestone results were achieved based on numerous contributions, including nearly a decade of physical design, years of equipment development and installation, and months of beam commissioning. As measured at the extraction energy of 6 GeV, the averaged beam current and emittance reached 8.57 mA with 5 bunches and 30.37 nm rad with a single-bunch charge of 5.58 nC, compared with the corresponding target values of 6.6 mA and 35 nm rad, respectively. This paper presents the physical design, equipment development, installation, and commissioning process of the HEPS booster.

The Finite Fourier Series shape-based approach satisfies the equations of motion and thrust acceleration constraints on a problem at discrete points and returns a feasible trajectory for many trajectory design problems through a nonlinear programming problem. In this work, the three-body finite Fourier series method is extended to include necessary conditions for optimality such that not only are the trajectories returned by the method feasible, but they are also in the neighborhood of an optimal solution. Necessary conditions are derived for the earth-centered circular restricted three-body problem in polar coordinates, and a finite difference costate estimation technique is implemented to assert stationarity conditions in the solution of the nonlinear programming problem. Residual errors in the stationarity conditions are constrained to be small to satisfy optimality criteria as closely as possible. Numerical examples are presented for a low Earth orbit spiral out and two separate phasing problems in a Geostationary Earth orbit. The results demonstrate varying levels of reduction in cost with respect to baseline FFS solutions and show that this is a viable method to improve the cost of these shape-based trajectories.

Machine learning (ML) is a powerful tool for computational fluid dynamics (CFD) because it can use data to correct imperfect physical models (e.g., turbulence models) and improve the simulation accuracy for challenging flow conditions, e.g., separated flow. Among many ML approaches, field inversion ML has the advantages of model consistency and low data dependency and can train generalizable models with limited data. However, the field inversion has a high entry bar because it requires a CFD-solver-intrusive implementation of adjoint methods to compute gradients. Due to this limitation, all existing field inversion ML studies focused on improving steady-state flow predictions. This paper will break this limit by developing a time-accurate adjoint method to enable the field inversion of unsteady flow. We solve the unsteady incompressible flow using a segregated PIMPLE algorithm and then compute unsteady gradients using a new segregated adjoint method. We use the proposed PIMPLE-adjoint to demonstrate field inversion optimization for unsteady separated flow over a ramp, which is representative of many unsteady flows in aerospace engineering. We consider various options to formulate the objective function for unsteady field inversion using a laminar flow case. We find that the inverse flow field agrees well with the reference data if the objective function formulation includes all relevant unsteady flow physics. Then, we consider a turbulent case and multiply the production term of the Spalart-Allmaras (SA) turbulence model by a scalar field (beta). We run unsteady field inversion to optimize the SA model's beta field and make its predictions match the spatial-temporal distribution of reference data generated by the k-omega SST model. In addition, we evaluate the field inversion's capabilities to predict temporally unseen flow fields and predict flow variables not formulated in the objective function. The spatial-temporal distributions of inverse flow fields agree reasonably well with the reference data for all the above cases. The proposed method has the potential to train generalizable and accurate turbulence models for predicting challenging unsteady flow in aerospace engineering.

This paper proposes an aerostructural optimization benchmark for aircraft propellers working in a hover condition. This benchmark uses an untwisted and untapered blade with a NACA0012 sectional profile as the baseline design. The objective function is the propeller shaft power coefficient. The design variables include the propeller twist, shape, chord, span, and rotation speed. The constraints include the propeller thrust coefficient, mass, von Mises stress, and geometry (e.g., thickness and curvature). We propose three different optimization configurations with various combinations of design variables. The proposed propeller aerostructural optimization benchmark can be solved using various optimization algorithms and modeling fidelities. This paper showcases a high-fidelity gradient-based optimization approach. To be more specific, we use the finite-volume computational fluid dynamics and finite-element structural dynamics solvers to simulate the fluid and solid domains, respectively. We then use the discrete adjoint approach to compute the derivatives for gradient-based optimization with a large number of design variables. To consider fluid-structure interaction and coupled derivative computation, we utilize OpenMDAO/MPhys, an open-source framework that facilitates high-fidelity multidisciplinary design optimization. We compare the objective, constraints, and distributions of spanwise shape, twist, and thrust between the baseline and optimized designs. This study has the potential to build a common benchmark and promote collaboration in the propeller multidisciplinary design optimization community.

Purpose The physics design of the High Energy Photon Source (HEPS) was finished after many times of iteration. Hereby, the typical equilibrium electron beam parameters corresponding to the proposed two baseline operation modes in the baseline design of HEPS are presented. Methods To compute the equilibrium parameters of the electron beam, the lattice parameters, RF parameters, and the parameters of the insertion devices (IDs) were determined first. Furthermore, it is more precise to use the full-current electron beam parameters in the estimations of the performance of the synchrotron light. Therefore, not only the single-particle dynamics but also the current-dependent collective effects need to be considered in the computations of the full-current, equilibrium parameters of the electron beam. Both analytic computations and multi-particle tracking simulations were carried out. Results The full-current, equilibrium parameters of the electron beams in the HEPS storage ring are presented in this paper. Moreover, the main beam parameters in the injector (the booster and the LINAC), corresponding to the two baseline operation modes of the storage ring, are also presented. Conclusion The typical electron beam parameters corresponding to the two baseline operation modes are given in detail in this paper.

High-data-throughput and multimodal-acquisition experiments will prevail in next-generation synchrotron beamlines. Orchestrating dataflow pipelines connecting the data acquisition, processing, visualization and storage ends are becoming increasingly complex and essential for enhancing beamline performance. Mamba Data Worker (MDW) has been developed to address the data challenges for the forthcoming High Energy Photon Source (HEPS). It is an important component of the Mamba experimental control and data acquisition software ecosystem, which enables fast data acquisition and transmission, dynamic configuration of data processing pipelines, data multiplex in streaming, and customized data and metadata assembly. This paper presents the architecture and development plan of MDW, outlines the essential technologies involved, and illustrates its current application at the Beijing Synchrotron Radiation Facility (BSRF).

The fast-pulsed kicker of the collider ring of Circular Electron Positron Collider (CEPC) uses a ceramic vacuum chamber to reduce eddy currents and maintain the magnetic field waveform at the beam's track. But the image charges induced by beams will accumulate on the insulating ceramic to increase the beam impedance. Eddy current shielding and beam impedance are traded off by coating a discontinuous "pattern" of TiN (titanium nitride) film on the inner wall of the ceramic vacuum chamber. Several potentially effective coating patterns are proposed. The eddy current shielding effect and the beam impedance are analyzed by simulation software. The simulation results show that coating in a ladder-shaped pattern maintains the magnetic field waveform well and helps to reduce the impedance. Properties such as electrical conductivity and SEY (secondary electron yield) of the films are improved in coating experiments and the technical feasibility of coating in a racetrack-shaped ceramic vacuum chamber is verified. Finally, the impedance of a 1200 mm-long ceramic vacuum chamber coated with ladder-shaped pattern film and the effect on the kicker magnetic field are measured.

The 1.5-m-long superconducting undulator (SCU) must have its magnetic field measured in a vertical Dewar to verify the field quality before the SCU is integrated into a horizontal cryostat. The magnetic field measurement mechanism must ensure that the trajectory of the Hall probe scanning the magnetic field is in the center of the magnetic gap, that is, the trajectory of the beam passing through the SCU. The good field region of the SCU’s magnetic field and the position of the Hall probe are given by Opera and the magnetic field distribution formula. Precise machining technology assists the positioning of the Hall probe. Due to the existence of mechanical errors, there is no guarantee that the peak magnetic field is also uniformly distributed under a uniform gap. The adjustment of the gap helps the SCU magnetic field distribution to be improved. The adjustment amount of the gap is obtained by comparing the measured data with the theoretical value. After the SCU returns to room temperature, keep the electrical connection, and adjust the gap on-line. Both peak magnetic field uniformity and phase error of the adjusted magnetic field are improved. This greatly reduces the difficulty of SCU’s magnetic field correction and makes the subsequent SCU horizontal test meaningful.

Particle Image Velocimetry (PIV) is a widely used flow visualization technique for velocity measurement in experimental fluid mechanics. The classical PIV technique suffers from tremendous parameter tuning by hand. At the same time, the current state-of-the-art machine-learning-based PIV methods are intractable for very large displacement calculations and have difficulties in generalizing across different signal-to-noise ratios (SNR). Transformer is an attention-based method popular for capturing global correlation. In this study, based on the transformer, we proposed a new deep-learning-based PIV method called Global Motion Aggregation-PIV (GMA-PIV), capable of calculating large displacement and generalizing it to raw particle images with a lower SNR ratio. To our knowledge, this is the first practice utilizing a transformer-based deep neural network for particle image velocimetry.

Background Superconductive Nb films deposited on copper cavities has been widely studied, but simulation studies on the growth of Nb films have rarely been reported in the literature. Methods In this study, effects of Nb atom incidence energy, incidence angle and deposition temperature on Nb film growth were investigated by molecular dynamics simulations. Results It was found that for the growth of Nb films, a moderate increased the incidence energy of Nb atoms can attenuate the shadow effect, and both too high and too low incident energy are not conducive to the production of high quality Nb films, and the substrate temperature mainly affects the quality of the crystal structure of Nb films. Conclusion In a word, Nb atoms with higher incidence energy (i.e. 10 eV) deposited vertically on Cu substrates at 473.15 K are more favorable for the growth of Nb films with lower surface roughness, higher crystallinity and fewer defects, providing an important reference for the preparation of high quality superconductive Nb films on SRF cavities.

The High Energy Photon Source (HEPS) is a greenfield 4th-generation light source. Its storage ring energy is 6 GeV and its ring cir-cumference is 1,360 m. One year after the HEPS complex buildings were constructed (Figure 1 ), we report here considerable progress, despite the COVID pandemic’s impact on supply chain and on-site personnel leading to unanticipated delays.

Superconducting undulators (SCUs) for advanced light sources are being developed rapidly to emit light with higher brightness and flux. The SCU consists of two superconducting magnets with a small gap, each with alternating poles. The SCU is invisible when operating in a Dewar or cryostat, so measuring the magnetic field in the narrow magnetic gap is a challenge in the development of the SCU. This paper presents a measurement system in vertical status for scanning the magnetic field of the SCU along the z-axis. The SCU is immersed vertically in 4.2 K liquid helium in a Dewar and the scanning is powered by a servo motor at room temperature. The measurement system overcomes the temperature difference of 300 K to drive the Hall probes to scan the magnetic field in the narrow magnetic gap of the SCU. In order to make the scanning area of the Hall probes coincide with the trajectory of the electron beam, a lot of detailed work on mechanical aspects has been done, such as controlling the positional accuracy of the Hall probes as they move, high precision machining and limiting the direction of movement. Unlike the currently reported magnetic field scans in the vertical status which are only available for SCU mock-ups of few periods, this system supports magnetic field measurements for SCUs up to 1.5 m long. The measurement system was validated on a 20-period SCU prototype, and after modification, the magnetic field of a liquid helium-cooled 30.5-period SCU was scanned. When the excitation current of the SCU with a magnetic gap of 7 mm is 450 A, the system measured a field distribution with a peak magnetic field of 1 T. The measurement system completed a full stroke trial run of 1750 mm before the 1.5 m SCU was machined. The results of magnetic field measurement from scanning in vertical status can be used as a reference for local shimming and correction of the magnetic poles of the SCU. This work establishes the SCU's ability to operate in cryostat horizontally.

Background In High Energy Photon Source (HEPS) the beam vacuum pipes employ TiZrVHf non-evaporable getter (NEG) coatings in order to meet the operation requirements. In many occasions it is inevitable to bring the sectors to atmosphere in order to open detectors, insert or change faulty parts. Consequently, NEG coatings will be saturated and followed with activation to restore the vacuum. Such an intervention would require heating up the whole sector to hundreds of degree and last from 2 to 4 weeks. Purpose Therefore, a Neon venting system is developed in HEPS in order to perform fast interventions without losing much of the performance of the activated NEG coating. Methods Preliminary experiments has been carried out to test the venting with Neon of different purity by comparing pumping speed lost and vacuum recovery before and after Neon venting. Results Results show that Neon with ultrahigh purity (purified by NEG cartridge purifier) could preserve full pumping performance of the NEG coated pipes. Neon with 6 N purity could preserve half pumping performance of the NEG coated pipes, but vacuum could be fully restored in only 2 days. Neon with 5 N purity could saturate the NEG coated pipes, leading to full pumping performance lost. Therefore, Neon with 6 N purity or above is promising in applications of efficient operations in HEPS.

The activation process of Zr, ZrVHf and TiZrV non-evaporative getter (NEG) thin films, prepared by direct current magnetron sputtering, is investigated by in situ synchrotron radiation photoemission spectroscopy. The activation temperatures of Zr and ZrVHf films are found to be 300 °C and 200 °C, respectively, and the activation temperature of TiZrV film is 120 °C—the lowest activation temperature reported on TiZrV. As the heating temperature increases, the transformation of metal-C bond follows the orders of V–C, Ti–C, Zr–C, Hf–C. It is found that the order of reduction difficulty of the same element oxides, that is, Zr oxide and V oxide in different films follows Zr film > ZrVHf film > TiZrV film. The order of difficulty in the reduction of oxides in the same alloy NEG films follows HfO2 > ZrO2 > TiO2 > V2O5. We propose that the above phenomena can be explained by interstitial diffusion, grain boundary diffusion of residual gas atoms and grain boundary precipitation of V and Ti in the solid solution of the NEG films.

The pumping performance of getter materials has becoming one of the hotspots in accelerator field. The recovery of pumping performance after air venting, also called aging effect, is important for applications in accelerators. In this work, we investigated the aging effect of Ti–V–Zr–Hf- and Ti–V–Zr-coated copper tubular chambers, and the effect of initial air exposure time on the aging properties. The samples presented hierarchically micro/nano-structures and showed a featured aging curve, giving about 9 effective pumping cycles. The pumping performance is inversely correlated with air exposure time suggesting that the getter coated chambers should be properly preserved before applied as a “pump”.