Modern deep learning relies nearly exclusively on dedicated electronic hardware accelerators. Photonic approaches, with low consumption and high operation speed, are increasingly considered for inference but, to date, remain mostly limited to relatively basic tasks. Simultaneously, the problem of training deep and complex neural networks, overwhelmingly performed through backpropagation, remains a significant limitation to the size and, consequently, the performance of current architectures and a major compute and energy bottleneck. Here, we experimentally implement a versatile and scalable training algorithm, called direct feedback alignment, on a hybrid electronic-photonic platform. An optical processing unit performs large-scale random matrix multiplications, which is the central operation of this algorithm. We perform optical training of modern deep learning architectures, including Transformers, with more than 1B parameters, and obtain good performances on language, vision, and diffusion-based generative tasks. We study the scaling of the training time and demonstrate a potential advantage of our hybrid opto-electronic approach for ultra-deep and wide neural networks, thus opening a promising route to sustain the exponential growth of modern artificial intelligence beyond traditional von Neumann approaches.

The proton-coupled electron transfer (PCET) process is central to sustainable electrochemical energy conversion (e.g., electrocatalytic nitrate reduction (NO3RR) to ammonia). Decoupling electron transfer (ET) and proton transfer (PT) could suppress the *H dimerization that happens in the Volmer-Tafel process, thereby enhancing activity and product selectivity. Herein, we demonstrate that π-conjugated cyanamide (NCN2-) groups featuring a flexible structure ([N═C═N]2- ⇔ [N≡C─N]2-) function as an electron accelerator and proton relay in NO3RR, leading to a decoupled ETPT process. The electron-withdrawing [N═C═N]2- induces the polarization of [Bi2O2] catalytic layers, with more σ holes and an enhanced surface electrostatic potential (VS(r)), which facilitates ET and forms high-valence NO3(1+δ)- (δ > 1) traps. Simultaneously, switchable [N≡C─N]2- serves as a proton relay that accelerates PT in the hydrogenation of NOx intermediates. This sequential ETPT is validated by various in situ experimental characterizations and molecular dynamic modeling. The ETPT-dominant NO3RR process achieves 95.3% Faradaic efficiency for NH3 and stably works for over 500 h at an industrial current density (500 mA cm-2) in a paired electro-refinery system. This work establishes sequential ETPT regulation as a general strategy for optimizing PCET-mediated sustainable energy conversion systems.

Magnetic Confinement Fusion aims to provide a virtually limitless, low-carbon energy source by harnessing nuclear fusion reactions of light nuclei under extreme temperature and pressure conditions, where matter exists as plasma. Magnetic Reconnection (MR) events are fast transient phenomena which directly impact plasma stability, energy losses, and overall efficiency of fusion devices, making their study relevant for the realization of commercial fusion energy. The world's largest Reversed-Field Pinch (RFP) fusion device is currently under development in Padova, Italy, and is called RFX-mod2. In this work, the development of a neutron/gamma diagnostic system for RFX-mod2 is presented. The diagnostic system aims primarily at obtaining experimental information on ion and electron acceleration to suprathermal energies driven by MR events. However, it could also be useful for other purposes, such as enabling neutron yield estimation and, in future RFX-mod2 tokamak discharges, the study of runaway electrons. The main results of neutron and gamma-ray measurements related to MR events, performed in the past at RFX-mod and the Madison Symmetric Torus (MST), are briefly summarized. Their main limitations are identified and the requirements for the new neutron/gamma diagnostic are outlined. The three-dimensional CAD (Computer Aided Design) model of the diagnostic system is presented, along with the need to develop a detector prototype to obtain experimental data at RFX-mod2 before assembling and commissioning the complete diagnostic system. An experimental characterization of the detector prototype is presented, including a neutron/gamma discrimination test.

Abstract A nonlinear gyrokinetic simulation is applied to the magnetosphere‐ionosphere (M‐I) coupling system to investigate spontaneous growth of auroral structures and electron acceleration self‐consistently. Perturbations of electron density, potential and field‐aligned current in the auroral ionosphere develop through the feedback instability, resulting in nonlinear deformations of the auroral structures. The linear and nonlinear developments of the M‐I feedback coupling system are well captured by the gyrokinetic simulation. Simultaneously, a part of the electromagnetic field energy amplified through the M‐I coupling is transferred to electrons through wave‐particle interactions, providing field‐aligned acceleration by the parallel electric field. While the estimated electron acceleration does not quantitatively account for the Alfvénic aurora, further extensions of the present simulation will lead to a self‐consistent model which simultaneously explains enhancement of the broad‐band electromagnetic fluctuations and the electron acceleration.

Objective.Very high-energy electrons (VHEEs) offer deep penetration, low scattering, and the potential for ultra-high dose rate delivery, making them promising candidates for future radiotherapy. However, the collimation of VHEE beams to achieve sharp beam penumbra remains poorly characterized. This study experimentally and computationally investigates how collimator material, thickness, and beam characteristics affect penumbra and out-of-field dose for VHEEs and establishes an initial foundation for the design of clinically feasible VHEE collimators.Approach.Tungsten, lead, and brass 5 mm diameter collimators were evaluated using film dosimetry with a 200 MeV electron beam delivered at the CERN Linear Electron Accelerator for Research and validated through Monte Carlo (MC) simulations. Experimental measurements of penumbra and out-of-field dose were compared with simulations that systematically varied material (tungsten, lead, brass), thickness (20-80 mm), and beam energy (150-250 MeV). Additional sensitivity tests quantified the impact of beam instability on field shaping.Main results.For measurements in air, penumbrae increased linearly with distance from the collimator and was smallest for tungsten. Out-of-field dose decreased with increasing thickness, falling below 0.5% for a 40 mm thick tungsten collimator. Brass exhibited the highest out-of-field dose (up to 4.8%) and broadest penumbra. MC models reproduced experimental trends within 5% for penumbrae but underestimated out-of-field dose, particularly for brass. The simulations indicated that VHEE beam divergence, beam size and collimator misalignment strongly influence beam penumbra and out-of-field dose.Significance.The presented work demonstrates that collimator material and geometry play a critical role in defining VHEE beam quality. Tungsten provided optimal attenuation and sharpness compared to brass and lead. These results establish quantitative benchmarks for VHEE collimator design and emphasize the importance of beam stability.

It is widely believed that astrophysical shocks can accelerate particles to ultra-relativistic energy, via the well-established diffusive shock acceleration mechanism. However, this mechanism requires seed particles with kinetic energy sufficiently high, whose origin is still an enigma. Here we show observational confirmation of an efficient electron pre-acceleration mechanism at the Earth's bow shock. This mechanism relies on a special V-shaped magnetic field configuration in the upstream solar wind, which channels the shock-reflected electrons back and thus enables them to be reflected by the shock many times. This special field configuration arises when a solar-wind discontinuity-an ubiquitous and inherent structure in space plasmas-approaches and intersects the shock. The acceleration scenario is further confirmed by test-particle and numerical methods. The results demonstrate its ability to accelerate low-energy (approximately 17 eV) solar-wind electrons to >200kBTe. This study therefore provides important insights into the injection problem and generation of energetic particles in the universe.

With the increasing computational demands of artificial intelligence, photonic neural networks have emerged as a promising alternative to electronic accelerators, offering high speed, low latency, and energy efficiency. This paper presents a low-loss crossing waveguide-assisted silicon-based microdisk resonator (MDR) crossbar array integrated with phase change material (PCM) Ge2Sb2Se4Te1 (GSST) for optical neural network applications. The designed multimode interference (MMI) crossing waveguide features a compact footprint of 1 µm2 with a 70-degree offset, reducing the device area by a factor of 2.03 while maintaining low insertion loss (IL) and crosstalk (CT). By integrating GSST on the microdisks, we achieve nonvolatile and programmable weight control via crystallization degree modulation. A 3 × 3 MDR array is demonstrated to perform photonic matrix-vector multiplication with a computational efficiency of 1.2 × 1012 MAC/s/mm2. The scalability of the system has been further validated through image convolution tasks and fall detection tasks. This work provides a scalable and efficient architecture for on-chip photonic computing.

The process of direct laser acceleration of plasma electrons is considered in a strongly magnetized plasmoid with the magnetic field strength allowing for reaching the autoresonance without any special injection conditions. The plasmoid may be optically created by irradiation of specially designed targets with an auxiliary intense laser beam at the previous stage of interaction in a possible all-optical setup. Specifics of the acceleration in the strongly magnetized plasma solenoid, such as the magnetic field profile and its finite size, may be critical for the resonant processes where even a small deviation of the parameters destroys the matching conditions. The process of the autoresonant electron acceleration is analyzed for different configurations inherent in the possible realizations of the setup, and estimates for the efficiency of acceleration and resonance magnetic fields are proposed. Based on the provided analysis, it may be concluded that despite the modifications of the autoresonance conditions and the presence of collective effects, the generation of energetic electron bunches in a realistic setup may be both possible and effective.

In this letter, we present a physics-assisted design strategy for tapered suspended slot waveguides operating at 2 μm. The proposed methodology enables a precise control of the optical field, specifically tailored for laser-driven dielectric accelerating structures. By using calibration curves that link the silicon waveguide strips width to both the effective refractive index and the accelerating field amplitude, we ensure local phase synchronism along the propagation axis. The design was performed for an input energy of 79 keV, and validated by HFSS simulations as far as the optical field computation is concerned, and by ASTRA-code for the single-particle beam dynamics. The results show an output energy of 102 keV with the optimized structure, corresponding to 20% increase compared to the previous constant-field approach.

Abstract We study a self‐consistent configuration of the intense Electron‐Scale Current Sheets (ECSs) under the presence of strong guide field . The ECSs were observed within the tailward Bursty Bulk Flow in the extremely hot PS. The purpose of our paper is twofold. First, we would like to determine mechanisms supporting the quasi‐stationary ECS configuration, and, second, to investigate the possibility of additional electron acceleration by a strong ambipolar electric field, self‐consistently arising in the quasi‐stationary ECSs. We demonstrated that the intense ECSs ( nA/) have 1D planar configuration self‐consistently balanced by the central field‐aligned current and perpendicular currents in its southern and northern edges. The field‐aligned current is carried by the suprathermal high‐speed electron beam, while the perpendicular currents are supported by electron diamagnetic and drifts due to the presence of the strong ambipolar electric field ( mV/m). Electron anisotropy currents are negligible in this configuration. We found that the vertical pressure balance in the ECSs is mainly contributed not by the increase in guide magnetic field, but by the electron pressure enhancement. The strong ambipolar electric field related to the ECSs can accelerate field‐aligned electron beams providing the energy gain up to keV. This may lead to new ECSs formation in other PS locations contributing to the cascade generation of ECSs in the PS. Our study shed a new light on the mechanisms of the intense ECSs formation in hot collisionless plasma.

Abstract Heavy ion beam drivers, due to their high kinetic energy, offer the potential for transferring a large amount of energy to the witness beam. Limited by the relatively low velocity of heavy ion, the dephasing length is short leading to a low energy gain of the witness beam. The conventional method that linearly increasing the plasma density is ineffective because the mismatch between the RMS beam radius and plasma wavelength will make the wakefield degrade or even disappear. In this paper, we propose a method that periodically increases and decreases the plasma density to switch the witness beam between different accelerating phases, allowing it to shift between adjacent accelerating cavities. Using this method, electrons can be accelerated up to 1.34 GeV in a distance of 1.17 m, with an energy spread of 1.1 \%. This method helps maintain the structure of wakefield and increase the energy transfer efficiency. It provides a potential route for generating high energy, high intensity electron beams and offers a feasible path for future heavy ion driven plasma wakefield acceleration experiments.

The depth of field (DoF) is an important parameter in transmission electron microscopy (TEM) when considering inhomogeneous samples, tomographic schemes, or in-situ experiments. A large DoF enhances the robustness of the experiment against tight alignment demands and drift issues. The phase-contrast transfer in TEM is reviewed and updated with special regard to the correct derivation and quantification of the DoF for relevant single-transfer-band imaging like with Scherzer or Lentzen conditions. Consequences towards the optimisation of the imaging conditions are discussed. Additionally, the defocus-dependent information limit is treated as a different type of DoF. One result of this work is to prefer the original Scherzer defocus over the Scherzer defocus taught today if a large DoF matters in non-aberration-corrected instruments. In aberration-corrected instruments, the Lentzen conditions are well suited for a maximum DoF if one adapts the desired maximum spatial frequency accordingly, and higher-order spherical-aberration correction might help at lower electron acceleration voltages.

Aiming at the urgent demand for high-average-power, high-stability and low-energy-consumption electron irradiation accelerators in the industrial field, a 10 MeV 40 kW S-band (2856 MHz) constant-gradient backward-travelling-wave (BTW) linear accelerator (linac) was developed in this study. The BTW accelerating structure combines the advantages of travelling-wave (TW) and standing-wave (SW) structures, adopting magnetic coupling between cells and nosecone cavity design to achieve high shunt impedance, low power reflection and short filling time. A constant-gradient tapered design was introduced, which effectively improved the beam acceleration efficiency and power capacity. A comprehensive multi-physics simulation was carried out to optimize the thermal management of the structure, and the coupling disk was redesigned to solve the problem of heat dissipation. The prototype was fabricated by high-precision machining and vacuum brazing, and the low-power cold test was completed by the bead-pull method, which realized the accurate tuning of the electric field distribution and phase advance. High-power testing validates electron acceleration to 10 MeV with a peak pulse current of more than 300 mA, average current of 3.8 mA, and average output power of 40 kW. This BTW linac addresses key gaps in industrial and medical irradiation, offering a high-performance, reliable solution. This paper elaborates on RF design, multiphysics simulations, fabrication, tuning, high-power testing, and summarizes key findings.

Abstract Unlike Earth, where whistler‐mode chorus is generally observed outside the plasmasphere and hiss is predominantly confined within it, Jupiter's magnetosphere frequently hosts both wave modes simultaneously. Using Juno observations, we present a global survey of whistler‐mode waves at Jupiter, demonstrating that both chorus and hiss are prevalent over 6 < M < 13, with chorus confined to lower latitudes and hiss extending to higher latitudes. Based on the observed wave and plasma characteristics, we apply physics‐based global diffusion modeling to assess the separate and combined effects of chorus and hiss waves on energetic electron dynamics. The simulations show that, near regions of peak wave activity, chorus waves lead to net electron losses below ∼1 MeV while producing acceleration at higher energies. Hiss waves primarily drive electron losses, but in combination with chorus waves, they can also enable electron acceleration above ∼1 MeV at specific pitch angles.

Laser wakefield acceleration is promising for compact electron acceleration by offering an ultra-high electric field. However, producing stable, high-quality electron beams remains challenging, particularly in the shock-injection regime where most of the instabilities arise during the injection stage. This indicates a strong sensitivity of beam quality to the shock front structure and its position relative to the laser focal position. A Schlieren imaging system is developed with ∼1μm spatial resolution to directly visualize the shock structure and quantify its position stability. By reducing the fluctuation of the shock position from 9.9 to 4.3 μm, the electron beam pointing stability has been improved by an order of magnitude.

Abstract IGBT includes both merits concerning hidden MOSFET and hidden BJT. The insulated Gate performs like an MOSFET taking control of the whole IGBT just like the role of an igniter or a starter. The scenario does impose an idea that IDS in MOSFET stimulates BJT which is composed of many diodes and equivalently deserves to be placed in the exponential argument of characteristic curve of diodes. However, thermal radiations coming from acceleration and deceleration of electrons or holes do take “kink” effects and block carriers from moving. The heat arises from moving carriers, causes vibrations of lattices, and then resistively reduces the mobility of carriers. Indeed, the final formula, combining MOSFET-BJT-like formula and the kink effects, intimately fits IGBT electrical characteristic curves, and thus serves as a promising algorithm.


Efficient clinical workflow for intraoperative electron radiation therapy with a mobile electron accelerator.

High-harmonic generation (HHG) is a vital phenomenon in the field of attosecond science. Under the influence of a strong laser field, tunnel ionization, acceleration, and recombination of electrons can collectively produce extreme-ultraviolet and soft x-ray radiation. By tailoring the driving laser field, it is possible to manipulate the underlying electron dynamics and thereby the harmonic emission. In this work, we investigate how a temporally engineered two-color laser field can be used to modulate the yield of the high-order harmonics. Our two-color laser field consists of a femtosecond laser pulse (1030 nm) and its second harmonic (515 nm). By varying both the relative phase and the intensity of the two-color laser fields in a controlled way, we demonstrate that the harmonic generation shows strong sensitivity to these parameters. This modulation arises from the selective influence on tunnel ionization and the associated tunneled electron trajectories by the asymmetric laser field. Our semiclassical simulation captures these trajectory modifications and shows good qualitative agreement with our experimental observations.

Abstract Liu et al. (2020, https://doi.org/10.3847/2041‐8213/ab64d0 , ApJ, 935, 39) conducted observational study with Magnetospheric Multiscale (MMS) data to characterize bow shock events, analyzing shock parameters, electron flux/energy spectra (double‐power‐law with break energy), PADs, and energy‐dependent drift dynamics to confirm shock‐drift acceleration (SDA) dominance. This paper presents simulations of solar wind suprathermal electron acceleration at Earth's bow shock, compared with in situ observations from the MMS mission on 4 November 2015. The event involves a quasi‐perpendicular shock crossing below the subsolar point. Using test‐particle simulations, we derive pitch‐angle distributions (PADs) across 12 energy channels (0.295–25.924 keV), demonstrating robust consistency between modeled and observed electron fluxes—validating our model for bow shock particle acceleration studies. Key findings include: (a) Downstream‐to‐upstream flux ratios peak near pitch angle, indicating SDA dominance. (b) Omnidirectional energy spectra exhibit a double‐power‐law with a break at 40 keV; spectral indices of 2.8 (below) and 5.4 (above) align with observations. (c) SDA analysis (drift velocity, length, and time) confirms the mechanism's prevalence. These results demonstrate the physical consistency of our model and the observational findings of Liu et al.

In this study, we explore a novel approach to accelerating electrons by utilizing Bessel beam generated from an axicon lens alongside an externally applied wiggler magnetic field. Bessel beams are unique in their ability to maintain a non-diffracting profile over long distances, making them ideal for the efficient acceleration of electrons. The axicon lens converts a conventional Gaussian beam into a Bessel beam, creating a central bright spot surrounded by concentric rings, which enhances the stability of the interaction. Among the various orders of Bessel beam, the zeroth-order beam is especially advantageous due to its lower divergence and stronger focusing capabilities, leading to more efficient electron acceleration compared to higher-order beams. By utilizing the characteristics of zeroth-order Bessel beam and the oscillating effects of the wiggler magnetic field, we investigate the energy gain and trajectory modulation of electrons in this system. Our findings demonstrate that the presence of the wiggler field significantly enhances the focusing power of Bessel beam, resulting in enhanced acceleration rates compared to a fundamental Gaussian beam under identical conditions.