Transverse Spread Research Articles

Design and experiment of an inverse magnetron injection gun for a Ka-band gyro-TWT with non-superconducting magnet

A triode inverse magnetron injection gun (IMIG) for a Ka-band gyrotron traveling wave tube (gyro-TWT) with non-superconducting magnet is proposed in this paper. Nowadays, the applications of gyro-TWT are intended to expand to moveable and fast-startup systems, so room-temperature magnet and system miniaturization are necessary. For a Ka-band gyro-TWT, to adapt to a room-temperature magnet with 20 mm bore radius, the IMIG form is adopted. Compared with conventional MIG, the gun maximum radius is reduced by 44%. On one hand, a curved emitter and cathode steps are utilized for better beam quality. On the other hand, isolation gaps and a cooling structure are designed to suppress stray electrons. A velocity ratio of 1.14 and a transverse velocity spread of 2.43% are obtained finally. The stray electrons are analyzed, and the IMIG tolerance is also evaluated. Finally, the cathode is fabricated, and its surface morphology is tested. It is then assembled into a gun shell, and the cathode temperatures are measured under both no cooling and cooling conditions. When the temperature of the emitter reaches 1050 °C, the heat powers are 84 and 115 W, respectively. The temperatures of the inner and outer electrodes are low enough to reduce the proportion of stray electrons.

An Experimental Study of the Morphological Evolution of Rills on Slopes under Rainfall Action

Accurately monitoring the morphology and spatiotemporal evolution characteristics of the entire process of slope erosion rill development is essential to circumvent the limitations inherent in traditional methods that rely on average flow velocity for hydrodynamic parameter calculations. This study employs an environmental chamber and a self-developed slope erosion test device to perform erosion tests on slopes with varying gradients and rainfall intensities. By integrating the structure-from-motion (SfM) method, fixed grid coordinate method, and continuous camera combined with the dye tracer technique, the morphological indexes and hydrodynamic parameters of the entire rill development process are precisely computed. The main conclusions are as follows: The entire process of slope rill development can be divided into three distinct stages. The initial stage is characterized by the appearance of tiny rills with mild erosion. The middle stage involves severe transverse spreading erosion and longitudinal undercutting, resulting in diverse rill morphologies. The final stage is marked by the stabilization of morphological characteristics. The peak slope soil loss is observed during the middle stage of rill development. The most effective parameters for characterizing slope soil loss from the beginning to the end are the Reynolds number and flow shear stress, the Froude number and flow shear stress, and the Froude number during different periods. Throughout the development of rills, the flow velocity initially decreases and then gradually increases until it stabilizes. The morphological indexes, including rill density, dissected degree, inclination, and complexity, generally show an increasing trend. However, in the middle stage, the rate of increase slows down, followed by a sharp rise at certain points. The optimal hydraulic parameters for evaluating rill density across different slope gradients, which were found to be the Darcy–Weisbach drag coefficient and real-time flow velocity, for assessing rill dissected degree, complexity, and inclination, were the Reynolds number and flow power. Under varying rainfall intensities, the most effective hydraulic and kinetic parameters for evaluating rill density, dissected degree, and inclination were flow shear stress and Reynolds number; for assessing rill complexity, the Reynolds number and flow power were used. The findings of this research enhance the accuracy of hydrodynamic parameter calculations in rill erosion tests, enable precise prediction of rill development trends on slopes, and offer innovative approaches for real-time dynamic monitoring of rill morphology and characteristics. These advancements are of significant importance for soil and water conservation and sustainability.

Manipulating a beam of barium fluoride molecules using an electrostatic hexapole

An electrostatic hexapole lens is used to manipulate the transverse properties of a beam of barium fluoride molecules from a cryogenic buffer gas source. The spatial distribution of the beam is measured by recording state-selective laser-induced fluorescence on an emccd camera, providing insight into the intensity and transverse position spread of the molecular beam. Although the high mass and unfavorable Stark shift of barium fluoride pose a considerable challenge, the number of molecules in the low-field seeking component of the N = 1 state that pass a 4 mm diameter aperture 712 mm behind the source is increased by a factor of 12. Furthermore, it is demonstrated that the molecular beam can be displaced by up to ±5 mm by moving the hexapole lens. Our measurements agree well with numerical trajectory simulations. We discuss how electrostatic lenses may be used to increase the sensitivity of beam experiments such as the search for the electric dipole moment of the electron.

Simulation of melt kinetics of in-situ molding of thermoplastic CF/PEEK composites

To reveal the interaction mechanism between the composites and the laser during the laser in-situ forming process of carbon fiber composites, the temperature change history and phase transition process on the surface of CF/PEEK composites under the action of flat-top beams with different moving directions were simulated by using COMSOL Multiphysics finite element simulation software. The results show that, due to the anisotropy of CF/PEEK composites, the transverse spread of the temperature field is always larger than the longitudinal spread, and when the moving angle is less than 45°, the surface temperature and the surface heat-affected zone of CF/PEEK composites increase with the increasing of the moving angle. The surface temperature and the area of heat affected zone are maximum when the angle of movement is 45°. As the angle of movement increases from 45° to 90°, the area and temperature of the heat-affected zone on the surface of the composite decreases with the increase in the angle of movement. The area of the melting zone is consistent with the distribution of the temperature field on the composite surface. The transverse broadening of the melting zone is always larger than the longitudinal broadening. The area of the melting zone is largest when the laser spot moves at an angle of 45°, and the area of the melting zone is smallest when the spot moves at an angle of 90°.

Towards Tests of an RFQ Cooler and Simulations

The cooling of secondary beams is important for accelerator-based nuclear physics. In the radiofrequency (RF) quadrupole cooler (RFQC), RF fields and ion-gas collisions may give a considerable increase or decrease of the beam transverse emittance and energy spread, depending on a delicate tuning of heating and cooling effects, dominated by the ion beam kinetic energy and the balance of collisions and confinement forces. An extra confinement may be added by a solenoid magnetic field, as in the RFQC prototype installed in the Eltrap machine. This provides a versatile test bench (distinct from a closed accelerator installation) for detailed studies of cooling dynamics and of several RFQC technical optimizations (for gas differential pumping and bias voltages). Modeling concepts and simulation results are summarized. The major RFQC parameters are reviewed, in particular for 133Cs+ collisions against He gas whose pressure pg ranges from 2 to 9 Pa in the reference case, with attention to the extraction, comparing triode/tetrode system, and to the bias voltages. Lower bias voltages request less pg , but provide less cooling of the energy spread.

Transverse difference of activation slip/twin system in wide AZ31 alloy plate during its rolling

The macroscopic finite element method (FEM) and the crystal plasticity finite element method (CPFEM) were combined to study the transverse difference of activation slip/twin system in wide AZ31 magnesium alloy plates during rolling. The macro-deformation and micro-texture evolution along the transverse direction of the plate during rolling were analyzed experimentally. The microscopic CPFEM was developed on the basis of the thermo-force coupling behavior during plate rolling obtained from macroscopic FEM. The CPFEM parameters were fitted by uniaxial compression experiments. This combination of two scale simulations accurately predicted the texture evolution during the rolling process and had been experimentally validated. Further examination of the deformation mechanism reveals that the transverse spread action of the plate is stronger at the edge region compared to center, and this transverse spread action has a more significant impact on the activation of the {10 1‾ 2} tension twin. The comparison of the activation and extension of pyramidal <a> slip in granular and plate-like grains reveals that plate-like grains are more prone to generate slip bands through the grain, leading to cracking of the grain along the slip activation band and further formation of sub-grains.

Mean transverse energy, surface chemical and physical characterization of CERN-made Cs-Te photocathodes

Cesium telluride photocathodes are known to offer high quantum efficiencies under UV illumination combined with good lifetimes compared to other semiconductor photocathodes, making them very popular electron sources for particle accelerator applications. The development of photocathode preparation, characterization, and related expertise at a single accelerator laboratory can be challenging, expensive, and time consuming. Recognizing this, we explored the use of a custom-designed ultrahigh vacuum suitcase for transportation of CERN-made (Switzerland) cesium telluride photocathodes to Daresbury Laboratory (UK) for characterization. We report the synthesis and characterization of a batch of four cesium telluride photocathodes corresponding to our second attempt of transport, following design and process improvements through lessons learned from our first attempt. The photocathode characterization involved, where possible, measurements of the surface elemental composition using x-ray photoelectron spectroscopy (XPS), surface roughness with an in-vacuum scanning tunneling microscope (STM), and quantum efficiency (QE) measurements. Transverse energy distribution curves were obtained over a wide range of illumination wavelengths using the transverse energy spread spectrometer (TESS) at room- and cryogenic temperatures, and the values for mean transverse energy (MTE) were extracted. The photocathodes exhibited distinct thicknesses ranging from ∼50 to ∼120 nm and significant MTE beyond the photoemission threshold which is attributed to the presence of CsxO and Cs phases, as confirmed by XPS analysis. The photocathode that exhibited no carbon or oxygen contamination was measured to have the highest QE of 2.9% at a wavelength of 265 nm at the end of the performance characterization process. The results presented herein offer an insight into the achievements possible through international collaborations by successfully utilizing long-distance transportation of photocathodes by land under ultrahigh vacuum conditions. Published by the American Physical Society 2024

Simulation and measurement of the interplay between electron cooling, impedance, intrabeam scattering, and space charge for coasting beams

The Low Energy Ion Ring (LEIR) at CERN is the first synchrotron in the Large Hadron Collider ions injector chain. The performance of LEIR is mainly determined by the number of charges extracted from the machine and transferred to the downstream chain of accelerators. Ions are delivered by the linear accelerator Linac 3. In the intensity accumulation phase, the machine operates with coasting beams: each injected beam is cooled, reducing its transverse dimensions and momentum spread, and brought into a stacking momentum position to allow subsequent injections. In this context, the evolution of the beam parameters for an injected beam under the effects of electron cooling, impedance, intrabeam scattering (IBS), and space charge is of interest in order to optimize the machine working point with respect to the accumulated intensity and to contribute to the understanding of the interplay of the different collective effects. This work describes the advancement in modeling coasting beam dynamics for LEIR accounting for the interplay of electron cooling, impedance, IBS, and space charge. Each effect is presented and progressively included to compute the simulated equilibrium longitudinal Schottky spectrum, which is found in good agreement with the measured one. Published by the American Physical Society 2024

Dynamic behavior of droplet impacting on a moving surface

The research specifically analyzes the characteristics of the impacting droplet and its behavior on the moving surface. The experimental results demonstrate that the droplet impact can be divided into two stages: spreading and stretching. The surface shear force is found to play a decisive role in the droplet's dynamic behaviors. Specifically, the surface shear force inhibits liquid fingers at the front edge of the liquid film during the spreading stage, but promotes the extension of liquid fingers at the trailing edge of the droplet during the stretching stage. The surface shear force has a significant influence on the longitudinal spreading factor of the droplet during the spreading stage. The transverse maximum spreading time decreases with the increase of shear weber number. The wake flow of the droplet is mainly divided into four types: wetting deposition, fracture separation, single finger, and multi-fingers. Additionally, the ratio of the horizontal maximum spreading factor to the longitudinal spreading factor in the same time is found to be positively correlated with the ratio of the two weber numbers. The research findings contribute to the fundamental understanding of droplet dynamics on moving surfaces and highlights the importance of considering surface shear force in understanding droplet dynamics and provides a basis for further research in this field.

Study of the influence of the mode of rotation of pipe in the cold rolling process on the microstructure, mechanical properties and accuracy

Goal. Obtaining experimental results on the influence of the turning mode during cold rolling on the microstructure, mechanical properties and accuracy of the geometry of the pipes to improve their quality. Method. Experiments were carried out on equipment used in production and having appropriate inspections. We used a grinding machine, a device for electrolytic etching, a MIM 7 microscope, and a press for stretching samples. The accuracy of the geometric dimensions was determined using tube micrometers. Rolling route 25×2.5 mm → 16×1.5 mm. Steel 08Х18Н10Т. The results. Two rotation modes were performed: mode 1 – feed 2, 3, 4, 5 mm in front of the straight one, and the rotation before the reverse movement of the cage; mode 2 – feed 2, 3, 4, 5 mm in front of the straight, and turn in front of the straight and reverse movement of the cage.For mode 2, in comparison with mode 1, the grain size near the inner surface of the pipes is visually smaller than near the outer surface.The strength limit, yield strength and relative elongation for modes 1 and 2 were found to be close in value.With regard to the accuracy of the geometry of the pipes, it was determined that in mode 2 compared to mode 1: – the transverse thickness of the pipes decreases by 1.4–1.6 times; – the ovality of the pipes is reduced by 1–2 times (feeds from 2 to 5 mm); – the spread of the diameter along the length of the pipe decreased almost twice. Scientific novelty. For the first time, new experimental industrial data on the influence of the rotation mode on the microstructure were obtained. It is shown that the grain size near the inner surface of the pipes is smaller than near the outer surface.For the first time, obtained experimental industrial data on the effect of the tube rotation mode on the values of strength limit, yield strength and ultimate elongation showed that the rotation mode did not affect their change.Additional experimental dependences on the influence of the pipe rotation mode on the transverse variation, ovality and spread of the outer diameter of the pipes during cold rolling of the pipes were obtained - the reduction of the transverse variation was 1.4–1.6 times, ovality 1–2 times, and the diameter variation was almost 2 times. Practical significance. The obtained results are needed in the development of technologies for the production of pipes with increased quality requirements (microstructure, heterogeneity, ovality, diameter dispersion).

Spatiotemporal Acoustic Vortex Beams with Transverse Orbital Angular Momentum.

Recently, the discovery of optical spatiotemporal (ST) vortex beams with transverse orbital angular momentum (OAM) has attracted increasing attention and is expected to extend the research scope and open new opportunities for practical applications of OAM states. The ST vortex beams are also applicable to other physical fields that involve wave phenomena, and here we develop the ST vortex concept in the field of acoustics and report the generation of Bessel-type ST acoustic vortex beams. The ST vortex beams are fully characterized using the scalar approach for the pressure field and the vector approach for the velocity field. We further investigate the transverse spreading effect and construct ST vortex beams with an ellipse-shaped spectrum to reduce the spreading effect. We also experimentally demonstrated the orthogonality relations between ST vortex beams with different charges. Our study successfully demonstrates the versatility of the acoustic system for exploring and discovering spatiotemporally structured waves, inspiring further investigation of exotic wave physics.

Design and Preliminary Experiment of Room-Temperature Bitter Magnet for Compact Gyrotron

Magnetic field system is one of the most crucial components for gyrotron operation. A compact gyrotron with a custom-designed magnet would be a promising continuous radiation source for millimeter-wave power applications. In this article, a design and preliminary experiment of a room-temperature Bitter magnet for developing compact gyrotron are presented. To lengthen the magnetic field homogeneity region without dramatically improving power consumption, a special design that every Bitter segment with different outer radii is adopted. Both in simulation and experimental measurement, the length of the homogeneity region is 120 mm, and homogeneity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{B}$</tex-math> </inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{B}$</tex-math> </inline-formula> is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 0.9% is obtained. A 5 kV magnetron injection gun (MIG) was designed based on the experimental measurement of this Bitter magnet, in which a velocity ratio of 1.3 and transverse velocity spread of 12% were obtained at current 0.5 A in simulation.

The longitudinal energy spread of ion beams extracted from an electron cyclotron resonance ion source

We present a study of factors affecting the energy spread of ion beams extracted from a Charge Breeder Electron Cyclotron Resonance Ion Source (CB-ECRIS). The comprehensive simulations, supported by experiments with a Retarding Field Analyser (RFA), reveal that the longitudinal and transverse energy spread of the extracted beams are strongly affected by the electrostatic focusing effects, namely the extraction geometry and plasma beam boundary, to the extent that the electrostatic effects dominate over the magnetic field induced rotation of the beam or the effect of plasma potential and ion temperature. The dominance of the electrostatic focusing effect over the magnetic field induced rotation complicates parametric studies of the transverse emittance as a function of the magnetic field strength, and comparison of emittance values obtained with different ion sources having different extraction designs. Our results demonstrate that the full ion beam energy spread, relevant for the downstream accelerator, can be measured with the RFA only when all ions are collected. On the contrary, studying the effect of plasma properties (plasma potential and ion temperature) on the longitudinal energy spread requires heavy collimation of the beam accepting only ions near the symmetry axis of the beam for which the electrostatic and magnetic effects are suppressed. As the extraction system of the CB-ECRIS is similar to a conventional ECRIS, the conclusions of the study can be generalised to apply for all high charge state ECR ion sources. Finally, we present the results of systematic plasma potential measurements of the Phoenix-type CB-ECRIS at LPSC, varying the source potential, the microwave power and the axial magnetic field srength. It was observed that the plasma potential increases with the extraction magnetic field and the microwave power.

Characterization of a Continuous Beam Cold Atom Ramsey Interferometer

The use of atom interferometers in inertial systems holds the promise of improvement of several orders of magnitude in sensitivity over sensors using current technology such as micro-electro-mechanical (MEMS) devices or ring laser gyroscopes (RLGs). This paper describes the construction and characterization of an atomic interferometry system for eventual use in a dual-atom-beam accelerometer/gyroscope sensor. In contrast with current state-of-the-art atomic sensors which use pulsed cold atom sources and pulsed laser beams, the investigated apparatus relies purely on continuous atomic and laser beams. These differences can result in a sensor with reduced complexity, a smaller physical footprint, and reduced power consumption. However, these differences also introduce challenges resulting from laser and atomic beam divergences and from velocity averaging due to both longitudinal and transverse velocity spreads. In this work, we characterize our rubidium-based atom beam system and show that Ramsey-style interference can still be observed. The implications for future research are also outlined and discussed.

A carbon minibeam irradiation facility concept

In minibeam therapy, the sparing of deep-seated normal tissue is limited by transverse beam spread caused by small-angle scattering. Contrary to proton minibeams, helium or carbon minibeams experience less deflection, which potentially reduces side effects. To verify this potential, an irradiation facility for preclinical and clinical studies is needed. This manuscript presents a concept for a carbon minibeam irradiation facility based on a LINAC design for conventional carbon therapy. A quadrupole triplet focuses the LINAC beam to submillimeter minibeams. A scanning and a dosimetry unit are provided to move the minibeam over the target and monitor the applied dose. The beamline was optimized by TRAVEL simulations. The interaction between beam and these components and the resulting beam parameters at the focal plane is evaluated by TOPAS simulations. A transverse beamwidth of < 100 μm (sigma) and a peak-to-valley (energy) dose ratio of > 1000 results for carbon energies of 100 MeV/u and 430 MeV/u (∼ 3 cm and 30 cm range in water) whereby the average beam current is ∼ 30 nA. Therefore, the presented irradiation facility exceeds the requirements for hadron minibeam therapy.

Design Consideration of Cavity and MIG of a 170/230-GHz Dual-Frequency Megawatt-Class Gyrotron for CFETR

In this article, a dual-frequency, megawatt-class (MW-class) gyrotron for Chinese Fusion Engineering Testing Reactor (CFETR) is analyzed, which can operate individually at frequencies of 170 and 230 GHz with the operating modes of TE+33,12 and TE+44,16, respectively. A triode-magnetic injection gun (MIG) is investigated for this dual-frequency gyrotron. With the help of the time-dependent, multimode, self-consistent code, the startup scenarios are investigated with considering the realistic electron beams. The results show that the gyrotron can steadily operate at the operating modes with MW-class under the transverse velocity spreads from 3% to 7% together with the beamwidth from 3 to 5 times Larmor radii. When considering the velocity spreads of 7% and the electron radial thickness of 4 times Larmor radii, the output power of TE+33,12 mode can reach 875 kW with a beam voltage of 70 kV and a current of 48 A, and the output power of TE+44,16 mode can reach 805 kW with a beam voltage of 65 kV and a current of 45 A.

Photocathode performance characterisation of ultra-thin MgO films on polycrystalline copper

The performance expected from the next generation of electron accelerators is driving research into photocathode technology as this fundamentally limits the achievable beam quality. The performance characteristics of a photocathode are most notably: normalised emittance, brightness and energy spread. Ultra–thin oxide films on metal substrates have been shown to lower the work function (WF) of the surface, enhancing commonly utilised metal photocathodes, potentially improving lifetime and performance characteristics.We present the characterisation of two MgO/Cu photocathodes grown at Daresbury. The surface properties such as: surface roughness, elemental composition and WF, have been studied using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The photoemissive properties have been characterised with quantum efficiency (QE) measurements at 266 nm. Additionally, we measure the Transverse Energy Distribution Curves (TEDC) for these photocathodes under illumination at various wavelengths using ASTeC’s Transverse Energy Spread Spectrometer (TESS) and extract the Mean Transverse Energy (MTE).

The measurement of photocathode transverse energy distribution curves (TEDCs) using the transverse energy spread spectrometer (TESS) experimental system.

The minimum achievable particle beam emittance in an electron accelerator depends strongly on the intrinsic emittance of the photocathode electron source. This is measurable as the mean longitudinal and transverse energy spreads in the photoemitted electron beam (MLE and MTE respectively); consequently, MLE and MTE are notable figures of merit for photocathodes used as electron sources in particle accelerators. The overall energy spread is defined by the sum of the MTE and the MLE, and the minimization of MTE is crucial to reduce emittance and thus generate a high-brightness electron beam. Reducing the electron beam emittance in an accelerator that drives a Free-Electron Laser (FEL) delivers a significant reduction in the saturation length for an x-ray FEL, thus reducing the machine's construction footprint and operating costs while increasing the x-ray beam brightness. The ability to measure the transverse energy distribution curve of photoelectrons emitted from a photocathode is a key enabler in photocathode research and development that has prompted the Accelerator Science and Technology Centre (ASTeC) at the STFC Daresbury Laboratory to develop the Transverse Energy Spread Spectrometer to make these crucial measurements. We present details of the design for the upgraded TESS instrument with measured data for copper (100), (110), and (111) single-crystal photocathodes illuminated at UV wavelengths around 266nm.

Turbulent dispersion of breath by the wind

The pioneering work of Taylor on the turbulent dispersion of aerosols is one century old and provides an interesting way to introduce both diffusive processes and turbulence at an undergraduate level. Low mass particles transported by a turbulent flow exhibit a Brownian-like motion over time scales larger than the velocity correlation time. Aerosols and gases are, therefore, subjected to an effective turbulent diffusion at large length scales. However, the case of a source of pollutant much smaller than the integral scale is not completely understood. Here, we present experimental results obtained by undergraduate students in the context of the COVID-19 pandemic. The dispersion of a fog of oil droplets by a turbulent flow is studied in a wind tunnel designed for pedagogical purposes. It shows a ballistic-like regime at short distance, followed by Taylor's diffusive-like regime, suggesting that scale-free diffusion by the turbulent cascade process is bypassed. Measurements show that the dispersion of CO2 emitted when breathing in a natural, indoor air flow is not isotropic but rather along the flow axis. The transverse spread is ballistic-like, leading to the concentration decaying as the inverse-squared distance to the mouth. The experiment helps students understand the role of fluctuations in diffusive processes and in turbulence. A Langevin equation governing aerosol dispersion based on a single correlation time allows us to model the airborne transmission risk of pathogens, indoors and outdoors. The results obtained in this study have been used to provide public health policy recommendations to prevent transmission in shopping malls.

Design of Magnetron Injection Gun and Solenoid for G-Band Gyro-TWT Based on Collaborative Optimization Method

In this article, a collaborative design method for gyrotron magnetron injection gun (MIG) and solenoid is proposed for the first time. On this basis, the shape of the electrodes and solenoid sizes is optimized by the means of global optimization techniques. Simplified theory and numerical methods of MIG have been developed, and the results agree well with the PIC simulation. By using the new method, the calculation time is reduced and the numerical stability has been greatly improved compared with that directly solving the Lorentz equation. As an example, a helical electron beam with a velocity pitch ratio of 1.20 and a transverse velocity spread of 1.65% is obtained for G-band gyro-TWT.