Beam Envelope Research Articles

Safety Management Method of Coastal Buildings against Typhoon Based on BIM Technology

Xiao, M. and Zhou, X., 2020. Safety management method of coastal buildings against typhoon based on BIM technology. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 539–542. Coconut Creek (Florida), ISSN 0749-0208.The traditional safety management method of building anti wind has great error in calculating the parameters of building anti wind, so a safety management method of coastal building anti typhoon based on BIM Technology is designed. Firstly, the structural column family, structural beam family, floor family, and envelope family are created respectively by using Revit platform. According to the construction drawing, the BIM model of the measured building is established, and the typhoon data is analyzed. Based on the data, the building parameters such as the stable weight of the protective cover block, the weight and thickness of the cushion block stone are calculated to ensure that the coastal building has a good anti typhoon effect. In order to verify the effectiveness of the safety management method, the typhoon simulation experiment was designed, and the traditional method was used as the control group. The experimental results show that three parameters of the traditional method are not up to the minimum standard, and the design methods are all qualified.

Theoretical research on the annular intensive relativistic electron motion focused by coaxial cusped periodic permanent magnetic field

This paper theoretically investigates the motion characteristics of an annular intensive relativistic electron beam (IREB) in a coaxial, smooth waveguide under a cusped periodic permanent magnetic (CPPM) field. The motion of the electron beam clearly exhibits a periodic oscillation in a CPPM. For the effective transmission of an IREB, the structural parameters of the CPPM must be chosen carefully. Based on theoretical analysis, stability conditions are suggested. The influence of the magnetic field phase, strength, and period on the oscillation amplitude of the beam envelope is analyzed, and the criteria for minimal oscillation amplitude are proposed accordingly. Notably, the theoretical formula, used to predict the oscillation period of the beam envelope, is proposed and verified by single-particle and particle-in-cell simulation results.

A compact polarization insensitive all-dielectric metasurface lens for Gaussian to tophat beam shaping in sub-terahertz regime

In this paper, we present a Gaussian to tophat beam shaper (GTBS) based on an all-dielectric metasurface lens for sub terahertz (sub-THz) applications. In order to calculate the required phase profile of the GTBS, we use an analytical procedure based on the geometrical transformation technique. The calculated phase profile is then realized by a silicon (Si) metasurface lens consisting of rectangular-shaped pillars of subwavelength dimensions. Because of large solution domain relative to the operation wavelength, we combined the beam envelope and the finite element methods to simulate the structure with a high precision. By designing an anti-reflection metasurface made up of periodically arranged Si pillars of subwavelength dimensions at the back surface of the beam shaper, we reduced the reflection from the lens surface considerably. The proposed idea is firstly investigated in a two-dimensional (2D) structure composed of an array grooves in a Si substrate and then is extended to three dimensions (3D) by considering a 2D array of subwavelength pillars or holes. The 3D structure is shown to be polarization insensitive. The compactness, ease of fabrication, low transmission loss, polarization independence, and straightforward design of the proposed metasurface beam shaper lens make it a promising choice for the implementation of sub-THz quasi-optical elements especially for standoff imaging systems.

Effects of waveguides on a free-electron laser with two electron beams

AbstractThe effects of the phase variation, the evolution of the electron beam, the evolution of the radiation intensity, and the higher-order modes due to waveguides on a free-electron laser (FEL) oscillator have been analyzed by using two electron beams of different energies based on the proposed FEL facility which is to be operated in the far-infrared and infrared regions. The three-dimensional (3D) effects on a FEL oscillator due to waveguides and higher-order modes were studied using an extended 3D FEL code with two electron beams that we have developed. The effects of the variation on the amplitude of radiation on the electron beam's emittance and energy spreads were also calculated in the case of waveguide for multi-particle and multi-pass numbers by using a new 3D code. The phase variation, the variation in the beam envelope, the evolution of the amplitude, and power were calculated for the fundamental mode. The results were compared with those of the higher-order modes of the wiggler for various TE and TM modes for determining the FEL's performance which is required for high-quality electron beams.

Evolution of a Relativistic Electron Beam for Tracing Magnetospheric Field Lines

Tracing magnetic field-lines of the Earth's magnetosphere using beams of relativistic electrons will open up new insights into space weather and magnetospheric physics. Analytic models and a single-particle-motion code were used to explore the dynamics of an electron beam emitted from an orbiting satellite and propagating until impact with the Earth. The impact location of the beam on the upper atmosphere is strongly influenced by magnetospheric conditions, shifting up to several-degrees in latitude between different phases of a simulated storm. The beam density cross-section evolves due to cyclotron motion of the beam centroid and oscillations of the beam envelope. The impact density profile is ring shaped, with major radius $\sim 22$ meters, given by the final cyclotron radius of the beam centroid, and ring thickness $\sim 2$ meters given by the final beam envelope. Motion of the satellite may also act to spread the beam, however it will remain sufficiently focused for detection by ground-based optical and radio detectors. An array of such ground stations will be able to detect shifts in impact location of the beam, and thereby infer information regarding magnetospheric conditions.

Beam matching with space charge in energy recovery linacs

Abstract Matching with space charge of an Energy-Recovery Linac (ERL) arc into the subsequent RF structure is essential to preserve beam quality. We show how to match beam envelopes and dispersion along the bends and recirculation arcs of an ERL, including space charge forces, in order to adjust the beam to the parameters of the subsequent RF structure. For a qualitative analysis, we show that one can use a beam matrix approach together with the smooth focusing approximation but with longitudinal–transverse coupling. It is also shown that the space-charge-modified dispersion plays a key role for the adjustment of the momentum compaction R 56 required for both the isochronous and the non-isochronous recirculation mode of an ERL. In this work, a simple coupled transverse–longitudinal beam matrix approach for matching with space charge is employed and compared with particle tracking simulations using ELEGANT. As an example case, we use the 5 MeV low-energy, 18 0 ° injection arc, which also works as a bunch compressor, and matched to the subsequent first RF structure of the projected multi-turn Mainz Energy-recovering Superconducting Accelerator (MESA).

Data-driven cross-talk modeling of beam losses in LHC collimators

The Large Hadron Collider at CERN is equipped with a collimation system to intercept potentially dangerous beam halo particles before they damage its sensitive equipment. The collimator settings are determined following a beam-based alignment procedure, in which the collimator jaws are moved towards the beam until losses appear in the beam loss monitors. When the collimator reaches the beam envelope, beam losses propagate mainly in the direction of the beam and are, therefore, also observed by other nearby beam loss monitors. This phenomenon is known as cross talk. Due to this, collimators are aligned sequentially to be able to identify which losses are generated by which collimator, such that any cross talk across beam loss monitors positioned close to each other is avoided. This paper seeks to quantify the levels of cross-talk observed by beam loss monitors when multiple collimators are moving, to be able to determine the actual beam loss signals generated by their corresponding collimators. The results obtained successfully predicted the amount of cross-talk observed for each of the cases tested in this study. This was then extended to predict loss map case studies and the proton impacts at each collimator by comparing them to simulations.

Experimental characterisation of a proton kernel model for pencil beam scanning techniques

The aim of this work is to perform Monte Carlo simulations of a proton pencil beam scanning machine, characterise the low-dose envelope of scanned proton beams and assess the differences between various approximations for nozzle geometry. Measurements and Monte Carlo simulations were carried out in order to describe the dose distribution of a proton pencil beam in water for energies between 100 and 220 MeV. Dose distributions were simulated by using a Geant4 Monte Carlo platform (TOPAS), and were measured in water using a two-dimensional ion chamber array detector. The beam source in air was adjusted for each configuration. Double Gaussian parameterisation was proposed for definition of the beam source model in order to improve simulations starting at the nozzle exit. Absolute dose distributions and field size factors were measured and compared with simulations. The influence of the high-density components present in the treatment nozzle was also investigated by analysis of proton phase spaces at the nozzle exit. An excellent agreement was observed between experimental dose distributions and simulations for energies higher than 160 MeV. However, minor differences were observed between 100 and 160 MeV, suggesting poorer modelling of the beam when the full treatment head was not taken into account. We found that the first ionisation chamber was the main cause of the tail component observed for low proton beam energies. In this work, various parameterisations of proton sources were proposed, thereby allowing reproduction of the low-dose envelope of proton beams and excellent agreement with measured data.

Study of orbit properties and intense beam dynamics in a high current separated sector proton cyclotron

This paper outlines a simple method based on analytical formulations to find out the physics design of a separated sector cyclotron. Formulations are developed to determine the magnet sector shape and equilibrium orbit properties for a chosen orbital frequency and a peak magnetic field in the magnet sector. Stability analysis of single particle motion without space charge effect has been performed and allowed values of sector angles are determined. The dynamics of space charge dominated beam in the separated sector proton cyclotron are explored by using beam envelope equations that includes radial and longitudinal coupling. Evolution of the rms beam envelopes and emittances has been studied as a function of the beam current for various sector geometry. The envelope equations and perturbed equations of motion around the matched beam envelopes have been utilized to obtain the matched beam conditions at different values of the beam current.

Measurement of beam steering and RF defocusing effect for a quarter-wave resonator

Quarter-wave resonators (QWRs) are being widely used in linear accelerators (linac) for acceleration of ions with low-[Formula: see text] velocity. Two effects of this kind of cavities are beam steering effect and RF defocusing effect caused by geometric asymmetry. Measurement for the two effects has been conducted by using beam position monitors (BPMs) and wires for a QWR type buncher whose frequency is 162.5[Formula: see text]MHz at Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS). Since experiment and simulation matches well, beam central position and beam envelope could be predicted in simulation code, which is beneficial for high-intensity proton accelerator design and commissioning.

Implementation of a stable, high-power optical lattice for quantum gas microscopy.

We describe the design and implementation of a stable high-power 1064 nm laser system to generate optical lattices for experiments with ultracold quantum gases. The system is based on a low-noise laser amplified by an array of four heavily modified, high-power fiber amplifiers. The beam intensity is stabilized and controlled with a nonlinear feedback loop. Using real-time monitoring of the resulting optical lattice, we find the stability of the lattice site positions to be well below the lattice spacing over the course of hours. The position of the harmonic trap produced by the Gaussian envelope of the lattice beams is stable to about one lattice spacing and the long-term (six-month) relative root-mean-square stability of the lattice spacing itself is 0.5%.

Optimal matching control of a low energy charged particle beam in particle accelerators

Particle accelerators are devices used for research in scientific problems such as high energy and nuclear physics. In a particle accelerator, the shape of particle beam envelope is changed dynamically along the forward direction. Thus, this reference direction can be considered as an auxiliary &#x201C time &#x201D beam axis. In this paper, the optimal beam matching control problem for a low energy transport system in a charged particle accelerator is considered. The beam matching procedure is formulated as a finite &#x201C time &#x201D dynamic optimization problem, in which the Kapchinsky-Vladimirsky &#x0028 K-V &#x0029 coupled envelope equations model beam dynamics. The aim is to drive any arbitrary initial beam state to a prescribed target state, as well as to track reference trajectory as closely as possible, through the control of the lens focusing strengths in the beam matching channel. We first apply the control parameterization method to optimize lens focusing strengths, and then combine this with the time-scaling transformation technique to further optimize the drift and lens length in the beam matching channel. The exact gradients of the cost function with respect to the decision parameters are computed explicitly through the state sensitivity-based analysis method. Finally, numerical simulations are illustrated to verify the effectiveness of the proposed approach.

Optimization of LANSCE proton beam performance for isotope production

The LANSCE Isotope Production Facility (IPF) utilizes a 100-MeV proton beam with average power of 23 kW for isotope production in the fields of medicine, nuclear physics, national security, environmental science and industry. Typical tolerable fractional beam loss in the 100-MeV beamline is 4 ×10−3. Experimental beam study was made to minimize the beam losses. Adjustments to the ion source’s extraction voltage resulted in the removal of tails in phase space. Beam based steering in beamlines led to the reduction of beam emittance growth. Readjustment of the 100-MeV quadrupole transport resulted in the elimination of excessive beam envelope oscillations and removed significant parts of the beam halo at the target. Careful beam matching in the drift tube linac (DTL) provided high beam capture (75%) in the DTL. After improvements, beam losses in the 100-MeV beamline were reduced by an order of magnitude and reached the fractional level of 5×10−4.

Comparison of profile measurements and TRANSPORT beam envelope predictions along the 80-m LANSCE pRad beamline

Here we report a comparison between the simulation of beam phase-space and profile distributions with diagnostic measurements. TRANSPORT, a particle transport code, was used for the prediction of a 800 MeV proton beam envelope from the end of the linac to the proton radiography (pRad) facility (a total length of 80 meters). The beam profile was measured at key positions along the beamline using wire scanners and gated CCD camera systems. These measurements were compared to their respective points along the simulated beamline. The predicted beam envelope and measured data correspond within expected errors.

Bunched Beam Envelope Instability in a Periodic Focusing Channel

The space-charge driven envelope instability presents a great danger in high intensity accelerator design. In this paper, we report on the study of bunched beam envelope instability in a periodic focusing channel using three-dimensional envelope model for a 3D uniform Waterbag distribution and a 3D Gaussian distribution. Our results show that the envelope instability stopband becomes broader with the increase of longitudinal focusing and are not sensitive to the type of distribution. Self-consistent macroparticle simulations using both distributions show similar structure in emittance growth but also extra instability stopbands. The emittance growth from the Waterbag distribution has larger stopband than that from the Gaussian distribution.

Classification of Space-Charge Resonances and Instabilities in High-intensity Linear Accelerators

As the beam intensity increases in modern high-power accelerators, self-field effects of the beam become significant and it is the utmost goal to minimize the beam loss of halo particles by avoiding or minimizing contributions of various halo mechanisms. There are two distinct families of space-charge halo mechanisms in high-intensity linear accelerators, and yet they need to be differentiated: resonances (single particle resonances or incoherent resonances) and instabilities (parametric resonances or coherent resonances). What we call resonances are resonances of the beam particle excited through the space-charge nonlinear multipoles. What we call instabilities (or envelope instabilities) are instabilities of the beam envelope. Instabilities are also called parametric resonances because they are parametric resonances of the envelope equation. They would better be called envelope parametric resonances to distinguish them from particle parametric resonances. Resonances and instabilities may look alike in the phase space, and yet they have distinct differences. Instabilities (or envelope parametric resonances) do not have the resonant frequency component. Various orders of resonances and instabilities are presented along with the beam distributions with which the particular mechanism is observed.

Extraction channel design based on an equivalent lumped parameter method for a SCC-250 MeV superconducting cyclotron

A SCC-250 MeV cyclotron, producing a 250 MeV proton beam, is under development in Huazhong University of Science and Technology (HUST) for proton therapy. The magnetic flux density, as a function of radius, decreases rapidly in the beam extraction region, which increases the radial beam size continuously along the extraction orbit. In this paper, an extraction channel inside the SCC-250 MeV is designed to control the beam size using passive magnetic channels. An equivalent lumped parameter method is used to establish the model of the extraction channel in the complex fringe magnetic field of the main magnet. Then, the extraction channel is designed using the lattice design software MADX. The beam envelopes are verified using particle tracing method. The maximum radial size of 6.8 mm and axial size of 4.3 mm meet the requirements of the extraction from the SCC-250 MeV.

Source-to-accelerator quadrupole matching section for a compact linear accelerator.

Recently, we presented a new approach for a compact radio-frequency (RF) accelerator structure and demonstrated the functionality of the individual components: acceleration units and focusing elements. In this paper, we combine these units to form a working accelerator structure: a matching section between the ion source extraction grids and the RF-acceleration unit and electrostatic focusing quadrupoles between successive acceleration units. The matching section consists of six electrostatic quadrupoles (ESQs) fabricated using 3D-printing techniques. The matching section enables us to capture more beam current and to match the beam envelope to conditions for stable transport in an acceleration lattice. We present data from an integrated accelerator consisting of the source, matching section, and an ESQ doublet sandwiched between two RF-acceleration units.

Beam dynamics pre-design with KONUS principle for the DTL of SPPC p-Linac

As the Higgs bosons were observed on the LHC in 2012, a two-stage particle collider program named CEPC-SPPC is proposed for precise measurement of Higgs properties and exploring the new physics models. In order to deliver a 2.1-TeV proton beam into the Super Proton–Proton Collider (SPPC), the injector chain will use a 1.2-GeV proton linac (p-Linac) and three synchrotrons of p-RCS, MSS and SS. This paper focuses on the preliminary conceptual design of the DTL within the p-Linac and mainly concerns about the beam dynamics studies. Taking advantages of the KONUS principle and LORASR code, a 325 MHz, 50.65 MeV DTL design which is composed of three tanks in 15.6 m will be presented. The whole DTL contains 129 gaps for beam acceleration, one quadruple doublet which is behind the buncher and eight quadruple triplets of which three are located after each tank, respectively. The aims of this pre-study are to optimize the acceleration electric field distribution together with the focusing magnetic field parameters, enhance the beam transmission quality of beam envelopes, particle distribution and energy spread, then improve the DTL performance in terms of transmission efficiency and so on. The results of the analyses show that the DTL pre-design achieves 16.8 times high energy gain and meets all the p-Linac requirements well.

Three-dimensional envelope instability in periodic focusing channels

The space-charge driven envelope instability can be of great danger in high intensity accelerators and was studied using a two-dimensional (2D) envelope model and three-dimensional (3D) macroparticle simulations before. In this paper, we propose a three-dimensional envelope instability model to study the instability for a bunched beam in a periodic solenoid and radio-frequency (RF) focusing channel and a periodic quadrupole and RF focusing channel. This study shows that when the transverse zero current phase advance is below $90$ degrees, the beam envelope can still become unstable if the longitudinal zero current phase advance is beyond $90$ degrees. For the transverse zero current phase advance beyond $90$ degrees, the instability stopband width becomes larger with the increase of the longitudinal focusing strength and even shows different structure from the 2D case when the longitudinal zero current phase advance is beyond $90$ degrees. Breaking the symmetry of two longitudinal focusing RF cavities and the symmetry between the horizontal focusing and the vertical focusing in the transverse plane in the periodic quadrupole and RF channel makes the instability stopband broader. This suggests that a more symmetric accelerator lattice design might help reduce the range of the envelope instability in parameter space.