Acceleration Cycle Research Articles

Simulation, measurement, and mitigation of beam instability caused by the kicker impedance in the 3-GeV rapid cycling synchrotron at the Japan Proton Accelerator Research Complex

The transverse impedance of eight extraction pulsed kicker magnets is a strong beam instability source in the 3-GeV rapid cycling synchrotron (RCS) at the Japan Proton Accelerator Research Complex. Significant beam instability occurs even at half of the designed 1 MW beam power when the chromaticity ($\ensuremath{\xi}$) is fully corrected for the entire acceleration cycle by using ac sextupole (SX) fields. However, if $\ensuremath{\xi}$ is fully corrected only at the injection energy by using dc SX fields, the beam is stable. In order to study realistic beam instability scenarios, including the effect of space charge and to determine practical measures to accomplish 1 MW beam power, we enhance the orbit particle tracking code to incorporate all realistic time-dependent machine parameters, including the time dependence of the impedance itself. The beam stability properties beyond 0.5 MW beam power are found to be very sensitive to a number of parameters in both simulations and measurements. In order to stabilize a beam at 1 MW beam power, two practical measures based on detailed and systematic simulation studies are determined, namely, (i) proper manipulation of the betatron tunes during acceleration and (ii) reduction of the dc SX field to reduce the $\ensuremath{\xi}$ correction even at injection. The simulation results are well reproduced by measurements, and, as a consequence, an acceleration to 1 MW beam power is successfully demonstrated. In this paper, details of the orbit simulation and the corresponding experimental results up to 1 MW of beam power are presented. To further increase the RCS beam power, beam stability issues and possible measures beyond 1 MW beam power are also considered.

On the Acceleration and Anisotropy of Ions Within Magnetotail Dipolarizing Flux Bundles

AbstractDipolarizing flux bundles (DFBs), earthward propagating structures with enhanced northward magnetic field Bz, are usually believed to carry a distinctly different plasma population from that in the ambient magnetotail plasma sheet. The ion distribution functions within the DFB, however, have been recently found to be largely controlled by the ion adiabaticity parameter κ in the ambient plasma sheet outside the DFB. According to these observations, the ambient κ values of 2–3 usually correspond to a strong perpendicular anisotropy of suprathermal ions within the DFB, whereas for lower κ values the DFB ions become more isotropic. Here we utilize a simple, test particle model to explore the nature of the anisotropy and its dependence on the ambient κ values. We find that the anisotropy originates from successive ion reflections and reentries to the DFB, during which the ions are consecutively accelerated in the perpendicular direction by the DFB‐associated electric field. This consecutive acceleration may be interrupted, however, when magnetic field lines are highly curved in the ambient plasma sheet. In this case, the ion trajectories become stochastic outside the DFB, which makes the reflected ions less likely to return to the DFB for another cycle of acceleration; as a consequence, the perpendicular ion anisotropy does not appear. Given that the DFB ions are a free energy source for instabilities when they are injected toward Earth, our simple model (that reproduces most observational features on the anisotropic DFB ion distributions) may shed new lights on the coupling process between magnetotail and inner magnetosphere.

Quantum radiation by an Unruh-DeWitt detector in oscillatory motion

Quantum radiated power emitted by an Unruh-DeWitt (UD) detector in linear oscillatory motion in (3+1)D Minkowski space, with the internal harmonic oscillator minimally coupled to a massless scalar field, is obtained non-perturbatively by numerical method. The signal of the Unruh-like effect experienced by the detector is found to be pronounced in quantum radiation in the highly non-equilibrium regime with high averaged acceleration and short oscillatory cycle, and the signal would be greatly suppressed by quantum interference when the averaged proper acceleration is sufficiently low. An observer at a fixed angle would see periods of negative radiated power in each cycle of motion, while the averaged radiated power over a cycle is always positive as guaranteed by the quantum inequalities. Coherent high harmonic generation and down conversion are identified in the detector’s quantum radiation. Due to the overwhelming largeness of the vacuum correlators of the free field, the asymptotic reduced state of the harmonics of the radiation field is approximately a direct product of the squeezed thermal states.

Roughness effects on the second-order turbulence statistics in oscillatory flows

Effects of roughness on the near-bed turbulence characteristics in oscillatory flows are studied by means of particle-resolved direct numerical simulations (DNS). Two particle sizes of diameter 375 and 125 in wall units in a very rough turbulent flow regime are studied. A double-averaging technique is employed to study the nature of the wake field, i.e., the spatial inhomogeneity at the roughness length scale. This introduced dispersive stresses along with additional production and transport terms in the double-averaged Reynolds stress budget, indicating alternate pathways of turbulent energy transfer mechanisms. While overall nature of the elementary processes responsible for energy transport in both flow cases remains identical, there are some discernible differences with regards to the near-bed turbulence structure. It is shown that the roughness modulates the near-bed turbulence, distorts and breaks the streamwise horseshoe structures, and therefore reduces the large-scale anisotropy; a result of redistribution of energy from streamwise component to other two components of the Reynolds stress and is illustrated by studying their individual budgets. In comparison to the small diameter, such effects are found to be significant in the case of large diameter particle-bed. In addition, redistribution of energy in the large diameter particle case shows reduced dependence on the flow oscillations, while for the small diameter particle it is more pronounced towards the end of an acceleration cycle.

Social Acceleration vs. Slowdown: Who Became Less Busy in Korea? and Why?

IntroductionTimelessness, or the sense of not having enough time, is what many people in contemporary societies complain about. This experience of shortage has been noted as one of the most significant phenomena in modern history (Gershuny 2005; Rosa 2013; Szollos 2009). If the sense of rushed is a defining feature of modern society, the Korean case may be especially useful to consider, in light of the rapid pace at which Korean society modernized. Indeed, in recent periods, pressure trends have been a topic of widespread concern in Korea, calling for scientific attention to be paid to Koreans' experience of and stresses related to pressure.This study deals with how people feel about their and how that feeling has changed over the last decades in Korea. We explore significant factors, such as education attainment, employment role and parental role that have been identified in social acceleration discourse (Rosa 2003; Rosa 2010a; Rosa 2010b; Rosa 2013; Roxburgh 2002). And we conduct several analyses to examine how those factors contribute to perceived pressure (PTP) in the Korean context. The findings from this study may be useful in describing changing notions about and the experience of in contemporary society.For much of history, was considered as a phenomenon of nature, aligned with the rhythms of seasons or the cycles of human life. However, with the emergence of clock-based time, it has been separated from nature and the biological cycle (Rosa 2010b, pp. 1-29). Time is now considered as a resource, or even equivalent to currency (time is money); we consume time, deploy it, or exhaust it. Contemporary technology and social practices are based upon the time-saving and high-speed framework (Wajcman 2008, pp. 60-62). According to the high-speed modernity literature, the social acceleration cycle is achieved by the combination of three factors, namely technological innovation, accelerated change at the societal level, and changes in the pace of life (Rosa 2010a, p. 33).According to Hartmut Rosa, social acceleration not only impact daily routine but also touches individual perception of and the way people handle (Rosa 2013, pp. 13-19). Indeed, several empirical studies have identified how technology development and societal changes (increases in work competition, rates of economic growth, automobile ownership, and use of speedy devices) affect the pace of everyday life (Roxburgh 2002; Teuchmann, Totterdell and Parker 1999; Wajcman 2008). Rosa has observed that maintaining the pace of life is like standing on the sliding rooftop (Rosa 2010a, pp. 87-88). That is, people need to balance their pace of life against the demands of fast-changing society; by failing to do so, they slip off the inclined roof, risking social exclusion and alienation.Keeping pace with social change and efforts to synchronize with disruptions that often result from change can be very stressful. Recent empirical studies report that time-related stress, described as feeling rushed, hurriedness, and feeling busy, can have direct or indirect impact on psychological as well as physical health outcomes (Roxburgh 2012; Sullivan 2007; Szollos 2009). It is therefore crucial in contemporary societies to examine the relationship between health outcomes time-related stress.Arguments have also emerged in the literature that there are several types of resisting force that create delay or actually decelerate the speed of social change. Natural disasters (e.g., heavy snow, floods, etc.), long distances, illness, and pregnancy tend to limit the effects of speedy innovations (Rosa 2010a, p. 34). Human societies have mostly overcome those types of hurdles so far. Recent social movements, however, have intentionally resisted this on-going social process by introducing the idea of time escape. This emphasizes that caring, sharing, and building memories are the essence of human nature and that they take and energy (Urry 2010; Yee and Chang 2009). …

Smart traffic-scenario compressor for the efficient electrical simulation of mass transit systems

The electrical infrastructure of DC-electrified mass transit systems (MTSs) is currently under review. The improvement of MTS infrastructure is commonly tackled by means of optimisation studies. These optimisers usually take large times to obtain their solutions, mainly due to the traffic scenarios that must be taken into account.The optimisation time may be reduced by increasing the sampling time used to obtain the traffic scenarios. However, due to the fast acceleration and braking cycles in MTSs, it is not clear to which extent the sampling time may be increased. In the majority of cases, this parameter is simply set to 1s.To tackle this concern, this paper presents a compression algorithm which makes it possible to thoroughly reduce the number of snapshots to be included in a given traffic scenario with good energy-saving accuracy figures. The traffic-scenario compressor presented is performed in two stages: a first step finds clusters of similar snapshots in the uncompressed traffic scenario; then a second stage searches for a specific set of trains’ positions and powers that may be directly included in the traffic model used in the optimisation study.The results obtained have shown that the compressor makes it possible to obtain an 80% optimisation-time reduction for a given traffic scenario with a total energy-saving error lower than 5%.

Vestibular Perceptual Thresholds Increase above the Age of 40.

We measured vestibular perceptual thresholds in 105 healthy humans (54F/51M) ranging from 18 to 80 years of age. Direction-recognition thresholds were measured using standard methods. The motion consisted of single cycles of sinusoidal acceleration at 0.2 Hz for roll tilt and 1.0 Hz for yaw rotation about an earth-vertical axis, inter-aural earth-horizontal translation (y-translation), inferior–superior earth-vertical translation (z-translation), and roll tilt. A large subset of this population (99 of 105) also performed a modified Romberg test of standing balance. Despite the relatively large population (54F/51M), we found no difference between thresholds of male and female subjects. After pooling across sex, we found that thresholds increased above the age of 40 for all five motion directions investigated. The data were best modeled by a two-segment age model that yielded a constant baseline below an age cutoff of about 40 and a threshold increase above the age cutoff. For all subjects who passed all conditions of the balance test, the baseline thresholds were 0.97°/s for yaw rotation, 0.66°/s for 1-Hz roll tilt, 0.35°/s for 0.2-Hz roll tilt, 0.58 cm/s for y-translation, and 1.24 cm/s for z-translation. As a percentage of the baseline, the fitted slopes (indicating the threshold increase each decade above the age cutoff) were 83% for z-translation, 56% for 1-Hz roll tilt, 46% for y-translation, 32% for 0.2-Hz roll tilt, and 15% for yaw rotation. Even taking age and other factors into consideration, we found a significant correlation of balance test failures with increasing roll-tilt thresholds.

Acceleration of electrons by a laser pulse at its output onto an optical surface of the vacuum – transparent medium interface. Laser synchrotron

We consider the electron dynamics in the field of an electromagnetic wave produced at the vacuum – transparent medium interface upon reflection from the boundary, close to total internal reflection. The propagation velocity of a constant phase of the electromagnetic wave along the interface can vary from to infinity ( is the speed of light in vacuum, and is the refractive index of the medium at the interface). In this case, there emerge regions of positive and negative phases of the field with wavelengths, approximately equal to half the wavelength of the original laser beam, which can propagate at a speed close to that of light in vacuum. If a beam of relativistic electrons propagates along the surface, they can gain energy and accelerate, as well as radiate. With closed trajectories of electron motion, a laser synchrotron will be implemented as a result of many acceleration cycles.

First demonstration of optics measurement and correction during acceleration with beta-squeeze in a high energy collider

Setting up collisions in high energy circular colliders requires beam acceleration and “beta-squeeze”. The latter produces small beam sizes, and hence, high luminosity by applying strong focusing with quadrupoles near the interaction points. At the Relativistic Heavy Ion Collider (RHIC), these two processes, beam acceleration and beta-squeeze, have been performed simultaneously during recent years. In the past, beam optics correction at RHIC has only taken place at injection and at final energy, with interpolation of corrections partially into the acceleration cycle. Recent measurements of the beam optics during acceleration and squeeze have evidenced significant beta-beats that, if corrected, could minimize undesirable emittance dilutions and maximize the spin polarization of polarized proton beams by avoiding the high-order multipole fields sampled by particles within the bunch. We recently demonstrated beam optics corrections during acceleration at RHIC. As a valuable by-product, these corrections minimized the beta-beat at the profile monitors, so providing more accurate measurements of the evolution of the beam emittances during acceleration.

Analysis of Shock Waves and Speed Peak Propagations in Car-Following Conditions from Start to Stop within Short Distances

The car-following platoon consisted of ten vehicles with the leading vehicle initiating perturbations on a test-track. Vehicle movements varied based on the speed patterns initiated by the leading vehicle with each data set including a cycle of stop, acceleration, car-following, deceleration, and complete stop. Shock waves are normally used for stop and go conditions at a fixed location, however this study focused on observing repeated shock waves created by the same group of drivers repeatedly. As well as studying the vehicle trajectories in microscopic level, speed wave propagations among the vehicles were also studied considering asymptotic stability in the car-following platoon. After carefully reviewing the stop and go vehicle trajectories, it was found that there is a discrepancy between actual vehicle trajectories and hypothetical uniform traffic flows in the shock wave theory derived from the macroscopic traffic model especially in the case of short distances.

New Method for a Continuous Determination of the Spin Tune in Storage Rings and Implications for Precision Experiments.

A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune-defined as the number of spin precessions per turn-is given by ν(s)=γG (γ is the Lorentz factor, G the gyromagnetic anomaly). At 970 MeV/c, the deuteron spins coherently precess at a frequency of ≈120 kHz in the Cooler Synchrotron COSY. The spin tune is deduced from the up-down asymmetry of deuteron-carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the order 10^{-8}, and to 1×10^{-10} for a continuous 100 s accelerator cycle. This renders the presented method a new precision tool for accelerator physics; controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring.

A reservoir trap for antiprotons

We have developed techniques to extract arbitrary fractions of antiprotons from an accumulated reservoir, and to inject them into a Penning-trap system for high-precision measurements. In our trap-system antiproton storage times >1.08 years are estimated. The device is fail-safe against power-cuts of up to 10h. This makes our planned comparisons of the fundamental properties of protons and antiprotons independent from accelerator cycles, and will enable us to perform experiments during long accelerator shutdown periods when background magnetic noise is low. The demonstrated scheme has the potential to be applied in many other precision Penning trap experiments dealing with exotic particles.

Racetrack-shape fixed field induction accelerator for giant cluster ions

A novel scheme for a racetrack-shape fixed field induction accelerator (RAFFIA) capable of accelerating extremely heavy cluster ions (giant cluster ions) is described. The key feature of this scheme is rapid induction acceleration by localized induction cells. Triggering the induction voltages provided by the signals from the circulating bunch allows repeated acceleration of extremely heavy cluster ions. The given RAFFIA example is capable of realizing the integrated acceleration voltage of 50 MV per acceleration cycle. Using 90\ifmmode^\circ\else\textdegree\fi{} bending magnets with a reversed field strip and field gradient is crucial for assuring orbit stability in the RAFFIA.

Continuous monitoring of snowpack displacement at high spatial and temporal resolution with terrestrial radar interferometry

AbstractTerrestrial radar interferometry is used in geotechnical applications for monitoring hazardous Earth or rock movements. In this study, we use it to continuously monitor snowpack displacements. As test site, the Dorfberg slope at Davos, Switzerland, was measured continuously during March 2014. The line of sight displacement was retrieved at a spatial resolution of millimeter to centimeter and a temporal resolution of up to 1 min independent of visibility. The results reveal several temperature‐driven diurnal acceleration and deceleration cycles. The initiation of a small full‐depth glide avalanche was observed after 50 cm total differential displacement. The maximum measured displacement of another differential glide area reached 43 cm/h without resulting in a full‐depth avalanche even after a total measured differential displacement of 4.5 m. In regard of the difficulty to predict full‐depth glide avalanches on the regional scale, the presented method has big potential for operational snow glide monitoring on critical slopes.

Luminosity Determination for the Deutron--Deutron Reactions Using Free and Quasi-free Reactions with WASA-at-COSY Detector

Two methods of the luminosity determination for the experiment performed by WASA collaboration to search for 4 He- bound state are presented. During the measurement the technique of continous change of the beam momentum in one accelerator cycle (called ramped beam) was applied. This imposes the requirement to determine not only the total integrated luminosity, but also its variation as a function of the beam momentum.

Thresholds for self-motion perception in roll without and with visual fixation target--the visualvestibular interaction effect.

The purpose of this study was to establish the selfmotion perception threshold, in roll, in the visualvestibular interaction (VVI) state, creating an oculogyral illusion, and to compare this threshold to the self-motion perception threshold in darkness. A further aim was to investigate the dynamics of the threshold at a low frequency range (0.1-1 Hz) of sinusoidal rotation. Seven healthy subjects were tested. A motion platform was used to generate motion. Single cycles of sinusoidal acceleration at four frequencies (0.1, 0.2, 0.5 and 1 Hz) were used as motion stimuli. To avoid otolith stimulation, subjects were rotated about a vertical axis in supine position. To evoke an oculogyral illusion subjects were instructed to fixate their gaze on a cross-shaped object aligned with their head, which rotated with them. The results show a lowering of the self-motion perception threshold in the VVI state, significant for the frequencies 0.1 and 0.2 Hz (p<0.05). In all the subjects, visual fixation on the cross evoked an oculogyral illusion. The threshold in both tested conditions was frequency dependent: it decreased with increasing frequency values. However, this effect was consistently stronger in darkness across all frequencies (p<0.05). In conclusion, the application of sinusoidal rotation during roll at low frequencies in the VVI condition evokes oculogyral illusion. This interaction lowers the self-motion perception threshold compared to that measured during rotation in darkness. This testing method could be of practical benefit in clinical application for revealing brain dysfunction involving integrative mechanisms of perception.

Field Investigation of Vehicle Acceleration at the Stop Line with a Dynamic Vision Sensor

This article presents a study of vehicle acceleration measurements at the stop line of a traffic light in an urban environment. Accurate representation of vehicle acceleration behavior is an important parameter to traffic simulation tools especially when the emissions related to the simulated traffic need to be calculated. A smart eye traffic data sensor (TDS) system was used to record the vehicle trajectories. This device is based on dynamic vision sensor technology that features 1 millisecond temporal resolution, wide dynamic range of 120 dB of illumination, zero-redundancy and asynchronous data output. The trajectories of the detected vehicles from the vision sensor temporal contrast event data have been manually annotated in a space-time representation using a graphical tool. From these extracted trajectories the acceleration of the vehicles has been calculated. We present results of acceleration distributions obtained from over 300 passenger-car acceleration cycles observed in the field. The measurements focus on the first phase of acceleration from the stop line up to a maximum speed of 40 km/h. The results are compared to the results from a traffic micro simulation tool obtained for a similar stop line scenario. The results will be used in the traffic micro-simulation that serves as a basis for a decision support tool for adaptive traffic management developed in the CARBOTRAF FP7 EU project.

Braking System Modeling and Brake Temperature Response to Repeated Cycle

Braking safety is crucial while driving the passenger or commercial vehicles. Large amount of kinetic energy is absorbed by four brakes fitted in the vehicle. If the braking system fails to work, road accident could happen and may result in death. This research aims to model braking system together with vehicle in Matlab/Simulink software and measure actual brake temperature. First, brake characteristic and vehicle dynamic model were generated to estimate friction force and dissipated heat. Next, Arduino based prototype brake temperature monitoring was developed and tested on the road. From the experiment, it was found that brake temperature tends to increase steadily in long repeated deceleration and acceleration cycle.

Kinematic analysis of 24-hour recording of walking pattern in patients with vascular parkinsonism

Background: There is a need to define the basic characteristics of various kinematic parameters recorded during walking in patients with vascular parkinsonism (VP). The present study was designed to determine the kinematic features of walking in VP patients. For this purpose, gait acceleration and gait cycle were recorded continuously over 24-h period of daily living in VP patients, patients with Parkinson's disease (PD), and healthy subjects. Methods: We used our newly developed 24-h monitoring device, the portable gait rhythmogram, which records gait during walking, and computes gait-induced accelerations with pattern matching algorithm. We studied nine VP patients with history of multiple lacunar infarcts (mean age ± standard deviation (SD): 72.6 ± 5.0 years, 7 men), 39 PD patients (mean age ± SD: 70.8 ± 5.8 years, 18 women), and 15 normal control subjects (mean age ± SD: 67.9 ± 4.7 years, 9 men). Results: The “amount of overall movements per 24 h” was lower in VP and PD, compared with the control, with no significant differences between the two groups. Gait acceleration during walking was significantly lower (p < 0.01 in each case), while the gait cycle was the same in VP and PD patients compared with the control. Conclusions: The results suggest that deficit in force production and preservation of gait rhythm are common features of walking patterns in VP and PD patients.

NON-THERMAL ELECTRON ACCELERATION IN LOW MACH NUMBER COLLISIONLESS SHOCKS. I. PARTICLE ENERGY SPECTRA AND ACCELERATION MECHANISM

Electron acceleration to non-thermal energies in low Mach number (M<5) shocks is revealed by radio and X-ray observations of galaxy clusters and solar flares, but the electron acceleration mechanism remains poorly understood. Diffusive shock acceleration, also known as first-order Fermi acceleration, cannot be directly invoked to explain the acceleration of electrons. Rather, an additional mechanism is required to pre-accelerate the electrons from thermal to supra-thermal energies, so they can then participate in the Fermi process. In this work, we use two- and three-dimensional particle-in-cell plasma simulations to study electron acceleration in low Mach number shocks. We focus on the particle energy spectra and the acceleration mechanism in a reference run with M=3 and a quasi-perpendicular pre-shock magnetic field. We find that about 15 percent of the electrons can be efficiently accelerated, forming a non-thermal power-law tail in the energy spectrum with a slope of p~2.4. Initially, thermal electrons are energized at the shock front via shock drift acceleration. The accelerated electrons are then reflected back upstream, where their interaction with the incoming flow generates magnetic waves. In turn, the waves scatter the electrons propagating upstream back toward the shock, for further energization via shock drift acceleration. In summary, the self-generated waves allow for repeated cycles of shock drift acceleration, similarly to a sustained Fermi-like process. This mechanism offers a natural solution to the conflict between the bright radio synchrotron emission observed from the outskirts of galaxy clusters and the low electron acceleration efficiency usually expected in low Mach number shocks.