Accelerator Components Research Articles

Radiological characterization of large electromagnets in view of their elimination as very low-level wastes

The operation of particle accelerators at CERN requires the use of electromagnets, which are accelerator components used to guide and focus charged particles. In the framework of maintenance activities and machine upgrades or dismantling, a large number of magnets are removed from the accelerator complex and required characterization in view of their disposal as radioactive waste. The present document describes a new characterization methodology, which is applied to radioactive magnets with masses up to 25 tons and lengths up to 6 meters. The characterization of such large electromagnets is challenging due to their heterogeneous composition, variable radiological history, technical constraints related to handling, and the operational complexity of evaluating activity values with gamma spectroscopy . The innovative method proposed in this paper is based on the establishment of transfer functions which convert dose-rate to a radionuclide inventory. This method is validated by comparison with accurate gamma spectroscopy and benchmarking.

Stabilization of Gaze during Early Xenopus Development by Swimming-Related Utricular Signals.

Locomotor maturation requires concurrent gaze stabilization improvement for maintaining visual acuity [1, 2]. The capacity to stabilize gaze, in particular in small aquatic vertebrates where coordinated locomotor activity appears very early, is determined by assembly and functional maturation of inner ear structures and associated sensory-motor circuitries [3-7]. Whereas utriculo-ocular reflexes become functional immediately after hatching [8, 9], semicircular canal-dependent vestibulo-ocular reflexes (VORs) appear later [10]. Thus, small semicircular canals are unable to detect swimming-related head oscillations, despite the fact that corresponding acceleration components are well-suited to trigger an angular VOR [11]. This leaves the utricle as the sole vestibular origin for swimming-related compensatory eye movements [12, 13]. We report a remarkable ontogenetic plasticity of swimming-related head kinematics and vestibular end organ recruitment in Xenopus tadpoles with beneficial consequences for gaze-stabilization. Swimming of older larvae generates sinusoidal head undulations with small, similar curvature angles on the left and right side that optimally activate horizontal semicircular canals. Young larvae swimming causes left-right head undulations with narrow curvatures and strong, bilaterally dissimilar centripetal acceleration components well suited to activate utricular hair cells and to substitute the absent semicircular canal function at this stage. The capacity of utricular signals to supplant semicircular canal function was confirmed by recordings of eye movements and extraocular motoneurons during off-center rotations in control and semicircular canal-deficient tadpoles. Strong alternating curvature angles and thus linear acceleration profiles during swimming in young larvae therefore represents a technically elegant solution to compensate for the incapacity of small semicircular canals to detect angular acceleration components.

Effects of near-fault earthquakes on existing bridge performances

The vertical component of seismic acceleration, often overlooked in ordinary structures, plays a role of primary importance in the case of bridges and viaducts. In particular, it induces both the appearance of uncommon stress conditions on vertical structures, and in some cases, it is a really important factor for bearing device capacity of girders. In fact, seismic excitations may give rise to great relative displacement between deck and piers or abutment in bridges. Among many structural damages of bridges during past earthquakes, the unseating failure is one of the most severe and recurring damages of girder bridges. When relative displacements exceed a pre-assigned seating length, the unseating of span will then take place. Therefore, for seismic design of new bridges or for a check of existing bridge, to take into account the vertical component due to seismic acceleration is an important issue. This paper presents a numerical analyses about damage effects of near-fault seismic events on existing bridge performances. The near-fault earthquakes are characterised by own some fundamental characteristics, such as forward-directivity phenomena, relatively high acceleration amplitudes and elastic response spectra, which are very different with respect to the reference ones defined in the codes. With this background, the purpose of this paper is to highlight the role of this kind of analysis of understanding the response behavior of girder bridges subjected to near-fault earthquakes. Furthermore, a case study and parameter studies are performed to evaluate its effectiveness in preventing bridge spans from unseating failure and protecting the piers and the abutment of bridges from damage.

LES simulation of terrain slope effects on wind enhancement by a point source fire

Fire-driven flows associated with wind intervention can dangerously threaten buildings in bushfire-prone areas by increasing pressure load on the structures through fire-wind enhancement phenomenon. This phenomenon through which wind is enhanced by interacting with fire is exacerbated when the affected terrain is located in a positive slope area. This study employs LES simulations using FireFOAM platform to investigate the extent to which the wind enhanced by a point source of fire is affected by terrain slope. A module was appended to the FireFOAM solver to extract and output fire-induced forces and acceleration components for the analysis. The effects of terrain slope on wind velocity enhancement as well as the location at which local maximum wind enhancement occurs were studied. The LES results showed that with the increase of terrain upslope angle, wind enhancement along the centerline is significantly intensified, whereas local maximum wind enhancement that occurs at each side of the centerline is less affected. It was also shown that global maximum wind enhancement occurs immediately downstream of the fire source for all upslope angles. Moreover, similar to the local maximum wind enhancement, the rate of increase in global maximum wind enhancement reduces with the increase of terrain upslope angle.

RFID aided SINS integrated navigation system for lane applications

To improve the lane vehicle position accuracy, RFID technology is applied to correct the position of the SINS irregularly with label positioning. The acceleration data of the vehicle in three directions is measured by the accelerometers of the inertial measurement unit, the attitude matrix is updated in real time using the angular velocity of the gyroscope output space, the acceleration component is transformed into the geographic coordinate system, and the acceleration of the inertial measurement unit. The data is subjected to an integral operation process to obtain a spatial displacement value of the vehicle. The real-time updating algorithm of the attitude matrix and the processing of the inertial measurement unit signal are presented. The quaternion-based algorithm is used to solve the attitude matrix as well as updating the coordinate system of the inertial navigation attitude matrix in real time. The Hilbert-Huang transform is used to filter the acceleration signal to solve the integrator saturation problem caused by the low-frequency component of the acceleration signal. The EMD algorithm based on the continuous root mean square error is applied in rejecting the low-frequency components in the signal. The simulation experiments show that the system can be reliable and high precision.

Optimal control of propellant consumption during insertion of rocket into a circle orbit of the Earth

The problem of launching a rocket into the Earth's orbit has already been solved using the regularization method in previous studies. But the regularization method remains relevant for application to solving integral equations of the first kind, which determine the components of speed and acceleration. The problem of optimal control of propellant consumption during the insertion of a rocket into a circle orbit of the Earth is solved using regularized solutions of integral equations of the first kind which are solutions of corresponding Euler equations on discrete-time net. The influence of the regularization parameter and some additional parameters on precision of discredited problem is investigated. Calculations are carried out for existing chemical rocket engine and promising plasmic one. Considered algorithm is summed up easily to problem of suborbital flights by setting desired coordinate system and modifying motion equations. Conclusions were drawn about the required speed for the lowest fuel consumption, as well as about the problem for a single-stage rocket. Thus, the development of a plasma rocket engine with an exhaust velocity is more than ten times higher than that of a chemical one.

A Hardware-efficient Weight Sampling Circuit for Bayesian Neural Networks

The main problems of deep learning are requiring a large amount of data for learning, and prediction with excessive confidence. A Bayesian neural network (BNN), in which a Bayesian approach is incorporated into a neural network (NN), has drawn attention as a method for solving these problems. In a BNN, the probability distribution is assumed for the weight, in contrast to a conventional NN, in which the weight is point estimated. This makes it possible to obtain the prediction as a distribution and to evaluate how uncertain the prediction is. However, a BNN has more computational complexity and a greater number of parameters than an NN. To obtain an inference result as a distribution, a BNN uses weight sampling to generate the respective weight values, and thus, a BNN accelerator requires weight sampling hardware based on a random number generator in addition to the standard components of a deep learning neural network accelerator. Therefore, the throughput of weight sampling must be sufficiently high at a low hardware resource cost. We propose a resource-efficient weight sampling method using inversion transform sampling and a lookup-table (LUT)-based function approximation for hardware implementation of a BNN. Inversion transform sampling simplifies the mechanism of generating a Gaussian random number from a uniform random number provided by a common random number generator, such as a linear feedback shift register. Employing an LUT-based low-bit precision function approximation enables inversion transform sampling to be implemented at a low hardware cost. The evaluation results indicate that this approach effectively reduces the occupied hardware resources while maintaining accuracy and prediction variance equivalent to that with a non-approximated sampling method.

Inequalities Applied to Kinematic Quantities

SummaryIt is known that velocity averaged over time is less than or equal to velocity averaged over distance. This inequality is illustrated with some routine applied mathematics problems involving simple harmonic motion and free fall motion. Generalizations to motion along space curves are explored, and inequalities involving spatial and temporal averages of other kinematic/dynamic quantities are derived from Chebyshev’s sum inequality. These quantities include kinetic energy, tangential and normal components of acceleration, work, and impulse.

Charged particle activation facility in NPI CAS and in future GANIL/SPIRAL2-NFS

The proton, deuteron and alpha induced reactions are of a great interest for the assessment of induced radioactivity of accelerator components, targets and beam stoppers as well as isotope production for medicine and also to nuclear astrophysics. We present a new irradiation chamber for activation measurements, that forms a prolongation of long-term experimental activities using stacked-foil activation technique in NPI CAS, Řež. The chamber is based on an airlock system and is coupled to a pneumatic transfer system delivered by KIT Karlsruhe. This system is installed in GANIL/SPIRAL2-NFS and will be used for proton, deuteron and alpha particle activation measurements with long- and short-lived isotopes.

Calculation of Neutron Energy Distribution from the Components of Proton Therapy Accelerator Using MCNPX

The passive scattering system nozzle of the proton therapy accelerator was simulated to evaluate the neutrons generated by each component in each nozzle by energy. The Monte Carlo N-Particle code was used to implement spread out Bragg peak with proton energy 220 MeV, reach 20 cm, and 6 cm length used in the treatment environment. Among the proton accelerator components, neutrons were the highest in scatterers, and the neutron flux decreased as it moved away from the central flux of the proton. This study can be used as a basic data for the evaluation of the radiation necessary for the maintenance and dismantling of proton accelerators.

Driverless Bus Path Tracking Based on Fuzzy Pure Pursuit Control with a Front Axle Reference

Currently, since the model of a driverless bus is not clear, it is difficult for most traditional path tracking methods to achieve a trade-off between accuracy and stability, especially in the case of driverless buses. In terms of solving this problem, a path-tracking controller based on a Fuzzy Pure Pursuit Control with a Front Axle Reference (FPPC-FAR) is proposed in this paper. Firstly, the reference point of Pure Pursuit is moved from the rear axle to the front axle. It relieves the influence caused by the ignorance of the bus’s lateral dynamic characteristics and improves the stability of Pure Pursuit. Secondly, a fuzzy parameter self-tuning method is applied to improve the accuracy and robustness of the path-tracking controller. Thirdly, a feedback-feedforward control algorithm is devised for velocity control, which enhances the velocity tracking efficiency. The proportional-integral (PI) controller is indicated for feedback control, and the gravity acceleration component in the car’s forward direction is used in feedforward control. Finally, a series of experiments is conducted to illustrate the excellent performances of proposed methods.

Diffusion bonding of Cu atoms with molecular dynamics simulations

Diffusion bonding of copper disks is an important step during the assembly of accelerating structures -the main components of power radio-frequency linear accelerators-. During the diffusion bonding copper disks are subjected to pressure at high temperatures. Finding the optimal combination of pressure and temperature will enable an accurate design of manufacturing workflow and machining tolerances. However, required optimization is not possible without good understanding of physical processes developed in copper under pressure and high temperature. In this work, the combined effect of temperature and pressure on closing time of inter-granular voids is examined by means of molecular dynamics simulations. In particular, a nano-void of 3.5–5.5 nm in diameter representing a peak and a valley of surface roughness facing each other was inserted between identical copper grains. The simulations performed at T = 1250 K, the temperature used in experimental condition, and the 300–800 MPa pressure range indicated the dislocation-mediated enhancement of atomic diffusion leading to full void closure.

Prediction of surface roughness in CNC turning by model-assisted response surface method

Various statistical approaches such as classical regression and modern machine learning methods have been applied to measurement data for estimating the status of manufacturing processes, which is now boosted by the movement of Internet of Things (IoT). In this study, we attempt to integrate an analytical tool model of surface roughness and measurement data of CNC turning to develop a modeling approach which does not depend too much on data, but also effectively uses existing analytical models. As in previous researches, we use cutting speed, feed rate, depth of cut and three acceleration components from an accelerometer to predict surface roughness. Co-Kriging method is employed to integrate the above measurements and a well-known model of surface roughness in turning. It was confirmed that the approach improved the prediction accuracy when only small amount of data is available for model construction. Meanwhile, the accuracy of ordinary Kriging method, which only depends on data, is suitable when measurement data sufficiently spans the parameter space, being expected that it may be rare in actual operations. We also attempted to detect outlier of measurements using the Co-Kriging method, which might be a non-trivial task when there is no additional information to evaluate the validity of the measurement data.

Extending the concept of machine acceleration used to model the bubble-particle detachment in flotation. Part 2 – Machine acceleration of solid particles in water

The machine acceleration introduced by H. J. Schulze has been a cornerstone of the bubble-particle (BP) detachment theory. It connects the mean dissipation rate of turbulence energy of water in a flotation machine with the BP detachment. In a recent paper, we scrutinized the theory and recommended its extension to cover both the longitudinal (centrifugation) and transverse (shear) effects of water turbulence. Since there is a significant difference in the densities of water, solid particles, and air bubbles, it is unknown if the available determination of the machine acceleration using the “water particles” is a good approximation for the bubble-particle aggregates. This paper aims to provide an answer to this fundamental question. For simplicity, this paper focuses on the acceleration of solid particles in water. Specifically, we use the Basset-Boussinesq-Oseen equation to quantify the particle acceleration. The correlation method in combination with the isotropic turbulence theory is applied to predict the particle acceleration components for the full range of turbulence length scale. Comparing with Schulze’s model, our recent model shows that the particle inertia should be considered in calculating the machine acceleration, especially for large and/or heavy particles and high energy dissipation rate. Our numerical results show that the machine acceleration decreases with increasing particle size and density and increases with increasing dissipation rate of turbulent kinetic energy and turbulence intensity.

Actigraphic measurement of the upper limbs movements in acute stroke patients

BackgroundStroke units provide patients with a multiparametric monitoring of vital functions, while no instruments are actually available for a continuous monitoring of patients motor performance. Our aim was to develop an actigraphic index able both to identify the paretic limb and continuously monitor the motor performance of stroke patients in the stroke unit environment.MethodsTwenty consecutive acute stroke patients (mean age 69.2 years SD 10.1, 8 males and 12 females) and 17 bed-restrained patients (mean age 70.5 years SD 7.3, 7 males and 10 females) hospitalized for orthopedic diseases of the lower limbs, but not experiencing neurological symptoms, were enrolled. This last group represented our control group. The motor activity of arms was recorded for 24 h using two programmable actigraphic systems showing off as wrist-worn watches. The firmware segmented the acquisition in epochs of 1 minute and for each epoch calculates two motor activity indices: MAe1 (Epoch-related Motor Activity index) and MAe2 (Epoch-related Motor Activity index 2). MAe1 is defined as the standard deviation of the acceleration module and MAe2 as the module of the standard deviation of acceleration components. To describe the 24 h motor performance of each limb, we calculated the mean value of MAe1 and MAe2 (respectively MA1_24h and MA2_24h). Then we obtained two Asymmetry Rate Indices: AR1_24h and AR2_24h to show the motor activity prevalence. AR1_24h refers to the asymmetry index between the values of MAe1 of both arms and AR2_24h to MAe2 values.The stroke patients were clinically evaluated by NIHSS at the beginning (NIHSST0) and at the end (NIHSST1) of the 24 h actigraphic recordings.ResultsBoth MA1_24h and MA2_24h indices were smaller in the paretic than in the unaffected arm (respectively p = 0.004 and p = 0.004). AR2_24h showed a better capability (95% of paretic arms correctly identified, Phi Coefficient: 0.903) to discriminate the laterality of the clinical deficit than AR1_24h (85% of paretic arms correctly identified, Phi Coefficient: 0,698). We also found that AR1_24h did not differ between the two groups of patients while AR2_24h was greater in stroke patients than in controls and positively correlated with NIHSS total scores (r: 0.714, p < 0.001 for NIHSS, IC95%: 0.42–0.90) and with the sub-score relative to the paretic upper limb (r: 0.812, p < 0.001, IC95%: 0.62–0.96).ConclusionsOur data show that actigraphic monitoring of upper limbs can detect the laterality of the motor deficit and measure the clinical severity. These findings suggest that the above described actigraphic system could implement the existing multiparametric monitoring in stroke units.

COMPUTER MODELING OF ACCURACY CHARACTERISTICS OF STRAPDOWN INERTIAL NAVIGATION SYSTEM

Context. The problem of correction for operation of strapdown inertial navigation system used for unmanned aerial vehicle is urgent because of further increased requirements to autonomous flight in blackout zones. The object of the study was to simulate the accuracy characteristics of strapdown inertial navigation system based on known (or given) instrument errors of its sensors. Objective. The goal of the work is to develop a mathematical and computer model of the strapdown inertial navigation system and estimate its accuracy characteristics based on given values of sensor errors. Method. The mathematical and computer models of the strapdown inertial navigation system based on slow, medium and fast cycles are developed. For the simulation of accuracy characteristics, the strapdown inertial navigation system is represented as a set of dynamic and kinematic equations in local tangent plane coordinate system with the Earth’s model taking into account components of gravity acceleration. The models of sensors are developed based on characteristics of low-cost microelectromechanical sensors used onboard. Data fusion algorithms were previously considered and include modified Kalman filter or, for some cases, complimentary filter by compensation scheme, but not considered here in details. Direction cosine matrix for strapdown inertial navigation system algorithms is found by Poisson’s method. Results. The developed models have been realized and simulated in MATLAB+Simulink. Initial parameters (errors of the primary information sensors and the flight conditions) during simulation have been varied: medium, high and low latitudes; direction of flight (along and across the meridian; on and against the direction of rotation of the Earth). Conclusions. The developed models and their simulations have been compared with actual testing results of strapdown gyrovertical СБКВ-П2А and confirmed the validity. It allow us to recommend them for use in designing strapdown inertial navigation system of unmanned aerial vehicle, as well as for experimental study of innovative data fusion algorithms for integrated satellite and inertial navigation system.

A design of an electron driven positron source for the internationallinear collider

We designed an electron-driven positron source for the International Linear Collider (ILC). The parameters of the source were chosen to obtain the required positron yields for ILC considering the heat stress in the positron target and accelerator components. In this report, we showed the feasibility of the electron-driven positron source in terms of the heat stress of the accelerator components, the positron yield estimate for realistic conditions such as beam loading to the acceleration, as well as the status of the R&D of the target system.

Distributed guidance law design for multi-UAV multi-direction attack based on reducing surrounding area

In this paper, two cooperative guidance laws based on the encircled area around a target by multi-attacker are designed to deal with the problem of cooperative encirclement and simultaneous attack under condition of both known target acceleration and unknown target acceleration, which guarantees that the attackers hit the target from every prescribed angle and achieve the best effect. The acceleration components along the attacker-target line of sight in novel guidance laws can reduce the relative remaining distance between each of the attackers and the target at the same speed, thus completing simultaneous attack and avoiding the calculation of the remaining time. The components of the guidance laws perpendicular to the attacker-target line of sight can make the normal overload of relative motion zero, so that the trajectory will be smooth and the collision problem within the attacker can be avoided. Simulation results verified the practicability of the novel guidance laws.

Molybdenum Oxides Coatings for High Demanding Accelerator Components

Large electric gradients are required for a variety of new applications, notably including the extreme high brightness electron sources for X-ray free electron lasers (FELs), radio-frequency (RF) photo-injectors, industrial and medical accelerators, and linear accelerators for particle physics colliders. In the framework of the INFN-LNF, SLAC (USA), KEK (Japan), UCLA (Los Angeles) collaboration, the Frascati National Laboratories (LNF) are involved in the modelling, development, and testing of RF structures devoted to particles acceleration by high gradient electric fields of particles through metal devices. In order to improve the maximum sustainable gradients in normal-conducting RF-accelerating structures, both the RF breakdown and dark current should be minimized. To this purpose, studying new materials as well as manufacturing techniques are mandatory to identify better solutions to such extremely requested applications. In this contribution, we discuss the possibility of using a dedicated coating on a solid copper sample (and other metals) with a relatively thick film to improve and optimize breakdown performances and to minimize the dark current. We present here the first characterization of MoO3 films deposited on copper by pulsed-laser deposition (PLD).

Vestibulo-ocular reflex characteristics during unidirectional translational whole-body vibration without head restriction

The vestibulo-ocular reflex (VOR) plays a crucial role in ocular stability. However, VOR characteristics under realistic whole-body vibration conditions, particularly without head restriction, remain unclear. The aim of this study was to characterise the VOR over a wide range of whole-body vibration frequencies (0.7–10 Hz), such as occur when driving a car. Eye and head movements were measured in response to unidirectional translational whole-body vibration that resembled actual vehicle vibrations. The VOR was then modelled by regressing eye velocity data on multiple head movement components. Results showed that the VOR was explained by angular velocity, linear acceleration, and linear jerk components of the head movements. Because the VOR in response to head linear-jerk components disrupted ocular stability in the current experimental setup, our results suggest that degraded vision in whole-body vibratory environments might be partially attributable to jerky head movements. Practitioner summary: The vestibulo-ocular reflex (VOR) during unidirectional translational whole-body vibration without head restriction was modelled using multiple head movement components, with the aim of characterising the VOR. Results showed that the VOR was explained by angular velocity, linear acceleration, and linear jerk components of head movements.