Longitudinal Space Research Articles

Gluon generalized TMDs and Wigner distributions in boost invariant longitudinal space

We present the gluon generalized TMDs for non-zero skewness and Wigner distributions in the boost invariant longitudinal space. The boost-invariant longitudinal space is defined as σ=12b−Δ+ and is conjugate to the skewness variable ξ. We use the dressed quark model, where a high-energetic quark is dressed by a gluon. This two-particle system has the advantage of addressing both the gluon and the quark sectors. The different contributions in Wigner distributions coming from different polarization of gluon and the dressed quark system are investigated.

Conditional guided generative diffusion for particle accelerator beam diagnostics

Advanced accelerator-based light sources such as free electron lasers (FEL) accelerate highly relativistic electron beams to generate incredibly short (10s of femtoseconds) coherent flashes of light for dynamic imaging, whose brightness exceeds that of traditional synchrotron-based light sources by orders of magnitude. FEL operation requires precise control of the shape and energy of the extremely short electron bunches whose characteristics directly translate into the properties of the produced light. Control of short intense beams is difficult due to beam characteristics drifting with time and complex collective effects such as space charge and coherent synchrotron radiation. Detailed diagnostics of beam properties are therefore essential for precise beam control. Such measurements typically rely on a destructive approach based on a combination of a transverse deflecting resonant cavity followed by a dipole magnet in order to measure a beam’s 2D time vs energy longitudinal phase-space distribution. In this paper, we develop a non-invasive virtual diagnostic of an electron beam’s longitudinal phase space at megapixel resolution (1024 × 1024) based on a generative conditional diffusion model. We demonstrate the model’s generative ability on experimental data from the European X-ray FEL.

Operation of Rf Systems During Joint Booster and Nuclotron Sessions

The article discusses the results of commissioning of RF systems of the NICA injection complex and plans for their further development. The preparation of the injection complex for injection into the collider requires an increase in the beam intensity in the Nuclotron outlet by about two orders of magnitude. Obtaining the required intensity will be achieved by accumulating the beam on injection energy using electronic cooling and reducing acceleration losses. This will require optimization of all systems of the complex, including a significant reduction in losses associated with RF systems. The experience allows us to choose the optimal strategy for the further development of HF systems. The main directions are: (1) accumulation of the beam in the longitudinal phase space during injection into the Booster, (2) reduction of the growth of the longitudinal emittance during acceleration, (3) bypass of the beam clot-in-clot from the Booster to the Nuclotron without growth of the longitudinal emittance, and (4) minimizing losses during acceleration and beam bypasses. The latter requires matching the acceleration rate with the capabilities of existing HF systems.

Disentangling brain atrophy heterogeneity in Alzheimer's disease: A deep self-supervised approach with interpretable latent space

Alzheimer's disease (AD) is heterogeneous, but existing methods for capturing this heterogeneity through dimensionality reduction and unsupervised clustering have limitations when it comes to extracting intricate atrophy patterns. In this study, we propose a deep learning based self-supervised framework that characterizes complex atrophy features using latent space representation. It integrates feature engineering, classification, and clustering to synergistically disentangle heterogeneity in Alzheimer's disease. Through this representation learning, we trained a clustered latent space with distinct atrophy patterns and clinical characteristics in AD, and replicated the findings in prodromal Alzheimer's disease. Moreover, we discovered that these clusters are not solely attributed to subtypes but also reflect disease progression in the latent space, representing the core dimensions of heterogeneity, namely progression and subtypes. Furthermore, longitudinal latent space analysis revealed two distinct disease progression pathways: medial temporal and parietotemporal pathways. The proposed approach enables effective latent representations that can be integrated with individual-level cognitive profiles, thereby facilitating a comprehensive understanding of AD heterogeneity.

Making goals count: A theory-informed approach to on-shift learning goals.

Supervisors often ask emergency medicine trainees for their learning goals at the start of a clinical shift, though they may do so without considering the reasons for this practice. Recognizing the underlying rationale for voicing on-shift learning goals and proactively considering solutions for some of the associated challenges can help learners and supervisors employ this practice to its full potential. Goal articulation is rooted in educational principles such as self-regulated learning, targeted performance feedback, and collaborative relationships between learner and supervisor. Despite the potential for on-shift learning goals to augment learning, there are numerous barriers that make it challenging for learners and supervisors alike to create or follow up on meaningful goals. Learner-related challenges include uncertainty about how to develop goals within an unpredictable clinical environment and creating goals too narrow or broad in scope. Supervisor-related challenges include difficulties integrating direct observation into the clinical workflow and a desire to avoid negative feedback. The learning environment also presents inherent challenges, such as lack of longitudinal supervisor-learner relationships, time constraints, space limitations, and incentives for learners to conceal their knowledge gaps. The authors discuss these challenges to effective on-shift learning goals and propose solutions that target the learner's approach, the supervisor's approach, and the learning environment itself.

Wakefield generation in hydrogen and lithium plasmas at FACET-II: Diagnostics and first beam-plasma interaction results

Plasma wakefield acceleration provides ultrahigh acceleration gradients of tens of GeV/m, providing a novel path toward efficient, compact, TeV-scale linear colliders, and high brightness free electron lasers. Critical to the success of these applications is demonstrating simultaneously high gradient acceleration, high energy transfer efficiency, and preservation of emittance, charge, and energy spread. Experiments at the FACET-II National User Facility at SLAC National Accelerator Laboratory aim to achieve all of these milestones in a single-stage plasma wakefield accelerator, providing a 10 GeV energy gain in a <1 m plasma with high energy transfer efficiency. Such a demonstration depends critically on diagnostics able to measure emittance with mm mrad accuracy, energy spectra to determine both percent level energy spread, and broadband energy gain and loss, incoming longitudinal phase space, and matching dynamics. This paper discusses the experimental setup at FACET-II, including the incoming beam parameters from the FACET-II linac, plasma sources, and diagnostics developed to meet this challenge. Initial progress on the generation of beam ionized wakes in meter-scale hydrogen gas is discussed as well as commissioning of the plasma sources and diagnostics. Published by the American Physical Society 2024

Reconstructing phase space of injection beam based on the measurement of accumulated beam: A novel tomography algorithm and its applications

The measurement of phase space has always been an important topic in the field of accelerator physics, playing an indispensable role in understanding the beam dynamics. The phase space distribution of the injected beam is crucial for optimizing the multiturn accumulation injection process in synchrotrons. However, directly and accurately measuring the phase space distribution is a challenging task. In this study, we propose an innovative tomographic algorithm based on the measurement data of the accumulated beam profile obtained from the wall current monitor (WCM) in a synchrotron, to reconstruct the longitudinal phase space of the injected beam. Simulations were conducted for various initial distribution scenarios, and the results showed that this algorithm can achieve a difference of about 4% in the rms momentum spread between the initial and reconstructed phase space distribution of the injected beam. This algorithm has been applied to the China Spallation Neutron Source and successfully measured the momentum spread of the injected beam. Machine studies considering the phase error of the injected beam showed a high consistency between the reconstructed beam profiles and the measurement results from the WCM on Rapid Cycling Synchrotron. The research results demonstrate that this algorithm can be an effective approach for measuring the momentum distribution of the injected beam in a synchrotron. Furthermore, this method also has the potential to be extended to reconstruct the transverse phase space of the injected beam. Published by the American Physical Society 2024

Longitudinal phase space diagnostics with a nonmovable corrugated passive wakefield streaker

Time-resolved diagnostics at free-electron laser (FEL) facilities, in particular electron beam longitudinal phase space (LPS) and FEL power profile measurements, provide information highly valuable for users, machine development studies, and beam setup. We investigate the slice energy resolution of passive streaker setups, in particular the effect of an energy chirp on the measured slice energy spread. Downstream of the hard x-ray SASE2 beamline at the European XFEL, these measurements are enabled by a single-plate nonmovable passive wakefield streaker, essentially a rectangular corrugated plate placed inside a vacuum chamber. We show measurements with a time resolution down to a few femtoseconds and an energy resolution down to a few MeVs. Published by the American Physical Society 2024

Digital smart internal fixation surgery for coronal process basal fracture with normal joint spaces or radius-shortening: Occult factor of radius-ulna load sharing

BackgroundReasonable postoperative humeroradial and humeroulnar joint spaces maybe an important indicator in biomechanical stability of smart internal fixation surgery for coronoid process basal fractures (CPBF). The aim of this study is to compare elbow articular stresses and elbow-forearm stability under smart internal fixations for the CPBF between normal elbow joint spaces and radius-shortening, and to determine the occult factor of radius-ulna load sharing. MethodsCT images of 70 volunteers with intact elbow joints were retrospectively collected for accurate three-dimensional reconstruction to measure the longitudinal and transverse joint spaces. Two groups of ten finite element (FE) models were established prospectively between normal joint space and radius-shortening with 2.0 mm, including intact elbow joint and forearm, elbow-forearm with CPBF trauma, anterior or posterior double screws-cancellous bone fixation, mini-plate-cancellous bone fixation. Three sets of physiological loads (compression, valgus, varus) were used for FE intelligent calculation, FE model verification, and biomechanical and motion analysis. ResultsThe stress distribution between coronoid process and radial head, compression displacements and valgus angles of elbow-forearm in the three smart fixation models of the normal joint spaces were close to those of corresponding intact elbow model, but were significantly different from those of preoperative CPBF models and fixed radius-shortening models. The maximum stresses of three smart fixation instrument models of normal joint spaces were significantly smaller than those of the corresponding fixed radius-shortening models. ConclusionsOn the basis of the existing trauma of the elbow-forearm system in clinical practice, which is a dominant factor affecting radius-ulna load sharing, the elbow joint longitudinal space has been found to be the occult factor affecting radius-ulna load sharing. The stability and load sharing of radius and ulna after three kinds of smart fixations of the CPBF is not only related to the anatomical and biomechanical stability principles of smart internal fixations, but also closely related to postoperative elbow joint longitudinal space.

The dawn of personalized multi-omics: Detecting disease before you know it

Recent advancements in omics techniques have enabled deep profiling of an individual’s molecular makeup. The wealth of data produced offers insights into genetic predispositions, early disease markers, and personalized treatment strategies. However, the full potential of omics data emerges when combined into longitudinal and personal multi-omics space. Another interesting venue is the inclusion of continuous monitoring of physiological parameters through wearable technology. Wearable health devices, including smartwatches and biosensors, provide real-time data on heart rate, oxygen saturation, sleep patterns, activity levels, and much more. By integrating with omics data, wearables offer a comprehensive view of an individual’s health, allowing for early detection of deviations from normalcy. This convergence allows for the prediction and prevention of diseases at the individual level and provides a powerful monitoring tool in clinical and drug developmental settings. This review explores the fusion of omics and wearable technology, envisioning their synergy as a catalyst for a transformative shift in modern healthcare. Their merging enables predictive and personalized medicine. As these technologies continue to evolve, their translation into routine clinical practice holds the promise of a healthier future for all. Provided herein is a step-by-step vision for how longitudinal personalized multi-omics, combined with wearable devices, will guide proactive healthcare and transform drug discovery in translational medicine.

Improvements in longitudinal phase space tomography at PITZ

Methodical studies to improve the existing e-beam Longitudinal Phase Space (LPS) tomography were performed at the Photo Injector Test facility at DESY in Zeuthen. Proof-of-principle simulations were done to address some core concerns e.g. booster phase range, space charge effects and noisy artefacts in results. Phase advance analysis was done with the help of an analytical model that determined the booster phase range and step size. A slit was introduced before the booster to truncate the beam and reduce space charge forces. The reconstruction method adopted was image space reconstruction algorithm owing to its assurance of non-negative solution. An initial scientific presumption of LPS from low energy momentum measurements was established to reduce artefacts in the phase space. This paper will explain the proof-of-principle simulations highlighting the key aspects to obtain accurate results. Reconstructed LPS for different experimental cases will be presented to demonstrate the diagnostic capability.

Improvement of the longitudinal phase space tomography at the J-PARC synchrotrons

The longitudinal phase space tomography, which reconstructs the phase space distribution from the one-dimensional bunch profiles, is used in various accelerators to measure longitudinal beam parameters. At the J-PARC, an implementation of the phase space tomography based on the Convolution Back Projection method (CBP) has been used to measure the momentum spread of the injected beam. The method assumes that the beam distribution rotates without significant deformation during the synchrotron oscillation. Because of the nonlinearity of synchrotron motion with sinusoidal RF voltage, the method can be used only in limited situations such as small amplitude synchrotron oscillation. Algebraic Reconstruction Techniques (ART) in conjunction with particle tracking, which is implemented in the CERN’s tomography code, allows accurate reconstructions even for nonlinear large amplitude synchrotron oscillations. We present the overview of the application of the CERN’s tomography code to the J-PARC synchrotrons. The results of benchmarking are also reported.

Tensor Coupled Learning of Incomplete Longitudinal Features and Labels for Clinical Score Regression.

Longitudinal data with incomplete entries pose a significant challenge for clinical score regression over multiple time points. Although many methods primarily estimate longitudinal scores with complete baseline features (i.e., features collected at the initial time point), such snapshot features may overlook beneficial latent longitudinal traits for generalization. Alternatively, certain completion approaches (e.g., tensor decomposition technology) have been proposed to impute incomplete longitudinal data before score estimation, most of which, however, are transductive and cannot utilize label semantics. This work presents a tensor coupled learning (TCL) paradigm of incomplete longitudinal features and labels for clinical score regression. The TCL enjoys three advantages: 1) It drives semantic-aware factor matrices and collaboratively deals with incomplete longitudinal entries (of features and labels), during which a dynamic regularizer is designed for adaptive attribute selection. 2) It establishes a closed loop connecting baseline features and the coupled factor matrices, which enables inductive inference of longitudinal scores relying on only baseline features. 3) It reinforces the information encoding of baseline data by preserving the local manifold of longitudinal feature space and detecting the temporal alteration across multiple time points. Extensive experiments demonstrate the remarkable performance improvement of our method on clinical score regression with incomplete longitudinal data.

Compact design of the 166.6 MHz superconducting cavity and its beamline elements for HEPS

The High Energy Photon Source (HEPS) is a 6 GeV diffraction-limited synchrotron light source under construction in Beijing. It will use five 166.6 MHz superconducting radio frequency (rf) cavities to accelerate the 200 mA electron beam in the storage ring. In the current lattice design, each straight section is 6 meters long to accommodate two 166.6 MHz cavities. The cavity adopts β=1 quarter-wave geometry, and the damping of the higher order modes is realized by using an enlarged cavity beam pipe to 505 mm and a ferrite absorber installed on the beam pipe. The low rf frequency, as well as the large beam aperture, added great challenges to the design of the 166.6 MHz cavity module to fit into a strictly limited longitudinal space. In addition, heat load optimization for the transition from room temperature to the cryogenic temperature, smooth tapering from the 505 mm beam aperture to the small diameter of the gate valves for impedance control, proper collimation of the synchrotron light to prevent thermal damage of delicate components, are also demanding requirements for a compact design. Accessibilities are also preserved for tuners and vacuum components to enable online maintenance. Finally, rf field leakage in the vacuum seal groove of the cavity is carefully examined to prevent overheating on the superconducting flange, which, in the worst scenario, may cause a thermal runaway, thus limiting the achievable accelerating gradient of the cavity. This paper presents the first compact design of the 166.6 MHz srf section for HEPS.

Tailoring of the longitudinal phase space for improved Free-Electron Laser performance

Free-electron lasers are capable of producing high-quality radiation in a wide wavelength range and at very high power and brilliance. To reach improved performance especially regarding coherence, bandwidth and wavelength stability, different seeding techniques are often required. However, a successful implementation of seeding typically demands a very high-quality electron beam, in terms of energy distribution and emittance. Techniques like Echo-Enabled Harmonic Generation (EEHG) and High-Brightness SASE (HB-SASE) require, or are significantly enhanced, by a flat distribution of particles in the longitudinal phase space. In this paper we describe how the initially chirped longitudinal phase space in the proposed Soft X-ray Laser (SXL) at the MAX IV laboratory can be tailored by first overcompressing and then de-chirping the electron pulse. We also show that it is possible to retain the properties of the electron bunch and how such an enhanced distribution can drive HB-SASE “seeding”, resulting in a significantly reduced bandwidth and a better wavelength stability.

Six-dimensional light-front Wigner distribution of the pion

We study the recently defined six-dimensional light-front Wigner distributions for the pion case. By using the light-cone spectator model, we calculate the Wigner distributions of the unpolarized, longitudinal-polarized, and transversely-polarized quark in the pion. We present the numerical results of six-dimensional light-front Wigner distributions by fixing certain coordinates. The Wigner distributions exhibit a diffraction pattern in the longitudinal position space, in similar to the single slit diffraction in optics. We also present the numerical results of the three-dimensional distributions in the subspace of longitudinal position and transverse position or transverse momentum coordinates. The six-dimensional light-front Wigner distributions not only contain the most complete information of parton distributions in the hadron, but also provide new physical quantities for future measurements.

One-dimensional longitudinal space charge calculation based on integrated green function approach

For fast longitudinal electron beam dynamics study or optimization in an x-ray free electron laser (FEL) linear accelerator, the one-dimensional longitudinal space charge (1D LSC) impedance, assuming a round cylinder beam with uniform transverse distribution is extensively used in both analytical analysis and numerical simulation. In this paper, instead of employing the impedance model in the frequency domain, we directly calculate the longitudinal electric field by convolving the longitudinal beam density with the slice green function, i.e., the longitudinal electric field generated by a slice beam. For high-energy electron beam, the slice green function rapidly diminishes to zero within a distance significantly smaller than the bunch length. In order to resolve the sharp variation, we report on a fast and high-precision method by applying the integrated green function (IGF) approach to compute the 1D LSC field numerically with few grid points, therefore, providing us with an alternative approach to the impedance model.

Establishment of a two-axis commercial vehicle 6DOF prediction model for nonlinear MPC controller

Most of the commercial vehicle dynamics models used by nonlinear MPC controllers are 3-DOF models, which do not reflect the motion constraints of sprung and unsprung masses, the coupling relationship between translational and rotational motion, and the coupling characteristics of lateral and longitudinal tire forces, so it is difficult to meet the model prediction requirements under extreme working conditions. Therefore, according to the dynamics theory, this paper firstly establishes a 14DOF model which can reflect the movement characteristics of the sprung mass in the lateral, longitudinal, and vertical space, the suspension characteristics and the movement characteristics of the wheels on both sides. Then, in order to reduce the computational burden of the model prediction and make it applicable to the nonlinear MPC controller, the 14DOF model is simplified to the 6DOF model. Finally, the established 6DOF model and the classical 3DOF commercial vehicle model were compared and evaluated based on the error in prediction horizon and performance in trajectory tracking. The results show that the model that, in extreme working conditions, the new 6DOF model has obvious accuracy advantages compared with the classical 3DOF model in the prediction horizon, and can achieve convergence to the reference states faster, so as to obtain a solution efficiency similar to or even higher than 3DOF.

Generation and optimization of electron bunch trains from nonlinear longitudinal space charge oscillation

Generation and optimization of electron bunch trains from nonlinear longitudinal space charge oscillation

Linearization of an Electron Beam’s Longitudinal Phase Space Using a Hollow-Channel Plasma

The removal of undesired beam nonlinear energy chirp (time-energy correlation) or linearization of the beam longitudinal phase space (LPS) is crucial for high-brightness linac-based scientific applications, such as x-ray free-electron lasers. In this paper, we propose that a low-density hollow channel plasma can be used as a near-ideal passive linearizer to significantly linearize the beam LPS and, at the same time, preserve the beam emittance. Physically, the passage of the beam through the hollow plasma channel excites a strong quasicosinoidal longitudinal wakefield that acts to mitigate the beam nonlinear energy chirp by superimposing a reverse chirp on the beam. The theoretical analyses and large-scale three-dimensional start-to-end simulations confirm that the beam longitudinal phase space can be almost completely linearized without noticeable beam emittance growth. Application of such a near-ideal linearizer may significantly improve the performance of numerous accelerator-based applications.