Bunch Shape Research Articles

Bunch Shape Monitor Measurements at the LANSCE Linac

Bunch Shape Monitor Measurements at the LANSCE Linac

Perturbation-minimized triangular bunch for high-transformer ratio using a double dogleg emittance exchange beam line

The longitudinal shape, i.e., the current profile, of an electron bunch determines the transformer ratio in a collinear wakefield accelerator and thus methods are sought to control the longitudinal bunch shape. The emittance exchange (EEX) appears to be promising for creating a precisely controlled longitudinal bunch shapes. The longitudinal shape is perturbed by two sources: higher-order terms in the beam line optics and collective effects and these perturbations can lead to a significant drop of the transformer ratio. In this paper, we analytically and numerically investigate the perturbation to an ideal triangular longitudinal bunch shape and propose methods to minimize it.

Suppression of Emittance Growth Using a Shaped Cold Atom Electron and Ion Source.

We demonstrate precise control of charged particle bunch shape with a cold atom electron and ion source to create bunches with linear and, therefore, reversible Coulomb expansion. Using ultracold charged particles enables detailed observation of space-charge effects without loss of information from thermal diffusion, unambiguously demonstrating that shaping in three dimensions can result in a marked reduction of Coulomb-driven emittance growth. We show that the emittance growth suppression is accompanied by an increase in bunch focusability and brightness, improvements necessary for the development of sources capable of coherent single-shot ultrafast electron diffraction of noncrystalline objects, with applications ranging from femtosecond chemistry to materials science and rational drug design.

Diagnostic technique applied for FEL electron bunches

Diagnostic technique applied for FEL ultrashort electron bunches is developed at JINR-DESY collaboration within the framework of the FLASH and XFEL projects. Photon diagnostics are based on calorimetric measurements and detection of undulator radiation. The infrared undulator constructed at JINR and installed at FLASH is used for longitudinal bunch shape measurements and for two-color lasing provided by the FIR and VUV undulators. The pump probe experiments with VUV and FIR undulators provide the bunch profile measurements with resolution of several femtosecond. The new three microchannel plates (MCP) detectors operated in X-ray range are under development now in JINR for SASE1-SASE 3 European XFEL.

Temporal evolution of longitudinal bunch profile in a laser wakefield accelerator

Due to their ultra-short duration and peak currents in the kA range, laser-wakefield accelerated electron bunches are promising drivers for ultrafast X-ray generation in compact free-electron-lasers (FELs), Thomson-scattering or betatron sources. Here we present the first single-shot, high-resolution measurements of the longitudinal bunch profile obtained without prior assumptions about the bunch shape. Our method allows complex features, such as multi-bunch structures, to be detected. Varying the length of the gas target, and thus the acceleration length, enables an assessment of the bunch profile evolution during the acceleration process. We find a minimum bunch duration of 4.2 fs (full width at half maximum) with shot-to-shot fluctuation of 11% rms. Our results suggest that after depletion of the laser energy, a transition from a laser-driven to a particle-driven wakefield occurs, associated with the injection of a secondary bunch. The resulting double-bunch structure might act as an elegant approach for driver-witness type experiments, i.e. allowing a non-dephasing-limited acceleration of the secondary bunch in a plasma-afterburner stage.

Realizing Ultrafast Electron Pulse Self-Compression by Femtosecond Pulse Shaping Technique.

Uncorrelated position and velocity distribution of the electron bunch at the photocathode from the residual energy greatly limit the transverse coherent length and the recompression ability. Here we first propose a femtosecond pulse-shaping method to realize the electron pulse self-compression in ultrafast electron diffraction system based on a point-to-point space-charge model. The positively chirped femtosecond laser pulse can correspondingly create the positively chirped electron bunch at the photocathode (such as metal-insulator heterojunction), and such a shaped electron pulse can realize the self-compression in the subsequent propagation process. The greatest advantage for our proposed scheme is that no additional components are introduced into the ultrafast electron diffraction system, which therefore does not affect the electron bunch shape. More importantly, this scheme can break the limitation that the electron pulse via postphotocathode static compression schemes is not shorter than the excitation laser pulse due to the uncorrelated position and velocity distribution of the initial electron bunch.

Ampelographic characteristics of Azerbaijani local grape varieties

The article aims to describe some local grapevine varieties cultivated in different areas of Azerbaijan. The cultivars are grown in the ampelographic collection of the Azerbaijani Scientific Research Institute of Viticulture and Wine-making. The report of their ampelographic traits was based on the OIV descriptors list. Comparing cultivars, it has been found that, although there have been similarities in various descriptor traits, most of the characteristics are distinctive of specific cultivars. A considerable polymorphism was found concerning the morphological features of leaves, clusters, berries, as well as considering some physiological and technological characteristics. In more detail, these genotypes differ between each other by the aspect of leaves; the shape, size and structure of bunches; the shape, color and flavor of berries; the productivity indices; the resistance to pests and diseases; the duration of their vegetative period; the sugar and acid contents; and the number of seeds in the berry.

Short-bunch generation from an rf photoinjector with injection phase compensation

A radio-frequency photoinjector is widely used for generating picosecond-femtosecond electron bunches. During particle acceleration, the electron bunch shape varies under the influence of both the acceleration fields and space charge fields. To restore a distorted electron bunch, we propose an injection phase compensation technique for the electrons by illuminating the photocathode with a pulse-front-corrected laser pulse. Using an S-band 1.6-cell photoinjector as an example, our study shows that the proposed technique can generate nearly undistorted electron bunches up to a bunch rate of a few hundred terahertz.

PROPERTIES OF TWO INTERSPECIES GRAPEVINE HYBRIDS FROM SERBIA

During the 1960s, many Serbian research institutions initiated activities to create new grapevine cultivars. The Faculty of Agriculture in Belgrade has so far created a total of 23 cultivars. Of that number, 15 cultivars are intended for fresh consumption, and 8 for wine production. Planning hybridization is the most important method for creating new grapevine cultivars. This paper presents the results of a five-year investigation of important agro-biological and technological properties of two interspecific hybrids (19574 and 19295). The investigated hybrids in 2012 were reported to the Commission for the recognition of new cultivars of grapevine. The hybrid 19574 was obtained from the cross of ?Seyve Villard 18315? × ?Muscat Hamburg?, and the hybrid 19295 was obtained from the cross of ?Muscat Hamburg? × ?Seedling 108?. Both hybrids are intended for fresh consumption and have hermaphrodite flowers, cylindrical-conical bunch shape, and ?Muscat? flavor. Skin color of the hybrid 19574 is green-yellow, and the color of the hybrid 19295 is dark-red-purple. The hybrid 19574 ripens in late September and has an average yield of 4.6 kg/vine, and the hybrid 19295 ripens in the first decade of October and has an average yield of 4.2 kg/vine. Sugar content of must in the hybrid 19574 was 21.2%, and the total acid content was 7.63 g/L, while sugar content of must in the hybrid 19295 was 19.6%, and the total acid content was 6.58 g/L. Both tested hybrids showed high to very high level of resistance to Plasmopara viticola, Erysiphe necator and Botrytis cinerea.

Electron Bunch Shape Measurements Using Electro-optical Spectral Decoding

Longitudinal diagnostics of the electron bunch shapes play a crucial role in the operation of linac-based light sources. Electro-optical techniques allow us to measure the longitudinal electron bunch profiles non-destructively on a shot-by-shot basis. Here we present results from measurements of electron bunches with a length of 200-900 fs rms at the Swiss FEL Injector Test Facility. All the measurements were done using an Yb-doped fibre laser system (with a central wavelength of a 1050nm) and a GaP crystal. The technique of electro-optical spectral decoding (EOSD) was applied and showed great capabilities to measure bunch shapes down to around 370 fs rms. Measurements were performed for different electron energies to study the expected distortions of the measured bunch profile due to the energy-dependent widening of the electric field, which plays a role for low beam energies below and around 40 MeV. The studies provide valuable input for the design of the EOSD monitors for the compact linear accelerator FLUTE that is currently under commissioning at the Karslruhe Institute of Technology (KIT).

THz wiggler applied for measurements of electron bunch longitudinal structure in FEL

The infrared undulator manufactured at JINR and installed at FLASH in 2007 is used for longitudinal bunch shape measurements in the range of several tenths of a micrometer. The presented electromagnetic wiggler is intended for generating a narrow-band THz radiation to measure the longitudinal electron bunch structure in FELs with an electron energy of several tens of MeV. This is a planar electromagnetic device with six regular periods, each 30 cm long. The K parameter is varied in the range 0.5–7.12 corresponding to the range B = 0.025–0.356 T of the peak field on the axis. The wiggler is simulated for 19.8 MeV/c corresponding to the possible FEL option at PITZ. The wavelength range is 126 μm − 5.1 mm for this electron beam momentum. The 3D Opera simulations of the THz wiggler are discussed. A new PITZ photocathode laser system is proposed for the optimized performance of the high-brightness electron beam. The main goal is a production of 3D ellipsoidal electron bunches with homogeneous charge density. The electromagnetic wiggler is supposed to be used for measuring the longitudinal shape of these electron bunches.

Equilibrium bunch density distribution with passive harmonic cavities in a storage ring

The MAX IV storage rings, currently under construction in Lund, Sweden, will use third harmonic cavities operated passively to lengthen the bunches and alleviate collective instabilities. These cavities are an essential ingredient in the MAX IV design concept and are required for achieving the final design goals in terms of stored current, beam emittance, and beam lifetime---such performance challenges are in fact common to all recent ultralow emittance storage ring designs and harmonic cavities are currently under consideration in several laboratories. In this paper, we report on parametric studies comparing different harmonic cavity settings in terms of the resulting bunch length, peak bunch density, and incoherent synchrotron frequency spread for the MAX IV 3 GeV ring. The equilibrium longitudinal bunch density distribution was calculated by establishing a self-consistent equation for the bunch form factor, describing the bunch shape. The calculations are fully self-consistent in the sense that not only the amplitude but also the phase of the waves excited by the beam in the harmonic cavity were assumed to be a function of the bunch shape, which allowed us to explore a wide parameter range not restricted to the region close to the conditions for which the first and second derivatives of the total rf voltage are zero at the synchronous phase. Our results indicate that up to a factor 5 increase in rms bunch length is achievable with a purely passive system for the MAX IV 3 GeV ring while keeping a relatively large harmonic cavity detuning, thus limiting the unavoidable Robinson antidamping rate from the fundamental mode of a passively operated harmonic cavity to values below the synchrotron radiation damping rate. The paper is complemented by results of measurements performed in the MAX III storage ring, which showed good agreement with calculations following the fully self-consistent approach.

Analytic calculation of the electric field of a coherent THz pulse

Accelerators can serve as sources for intense THz radiation by producing sub-ps long electron bunches, which generate synchrotron radiation coherently in the THz regime. In this paper, we present an analytic method to calculate the electric field pulse emitted by an electron bunch with arbitrary bunch shape. Our method is applied to a Gaussian bunch as well as a complex bunch profile resulting from a nonlinear beam dynamics simulation.

Transformer ratio studies for single bunch plasma wakefield acceleration

In Plasma Wakefield Acceleration (PWFA) plasma oscillations are driven by ultra relativistic electron beams. The ratio of the maximum accelerating field behind the driving beam (bunch) and the maximum decelerating field inside the driving beam (bunch) is defined as Transformer Ratio, a key parameter that determines the energy gain in particle acceleration. We investigate the transformer ratio for different shapes of a single driving bunch. One dimensional, fluid, relativistic, cold plasma equations have been numerically solved. A complete map of the transformer ratio is obtained by varying: bunch shape, bunch length and density ratio. It is found that the transformer ratio critically depends on the bunch shape and on the density ratio. Moreover both in the linear as well as in the non-linear regime the theoretical limit of 2 for the transformer ratio of a single symmetric bunch can be exceeded using asymmetric bunches in the linear regime as well as symmetric bunches in nonlinear regime.

Noninterceptive method to measure longitudinal Twiss parameters of a beam in a hadron linear accelerator using beam position monitors

A new method of measuring of the rms longitudinal Twiss parameters of a beam in linear accelerators is presented. It is based on using sum signals from beam position monitors sensitive to the longitudinal charge distribution in the bunch. The applicability of the method is demonstrated on the superconducting section of the Oak Ridge Spallation Neutron Source linear accelerator. The results are compared to a direct measurement of the bunch longitudinal profiles using an interceptive bunch shape monitor in the linac warm section of the same accelerator. Limitations of the method are discussed. The method is fast and simple, and can be used to obtain the initial parameters for the longitudinal matching in linear accelerators where interceptive diagnostics are not desirable.

Feasibility study of a single-shot 3D electron bunch shape monitor with an electro-optic sampling technique

We developed a three-dimensional electron bunch charge distribution (3D-BCD) monitor with single-shot detection, and a spectral decoding based electro-optic (EO) sampling technique for a nondestructive monitor enables real-time reconstruction of the three-dimensional distribution of a bunch charge. We realized three goals by simultaneously probing a number of Pockels EO crystals that surround the electron beam axis with hollow and radial polarized laser pulses. First, we performed a feasibility test as a simple case of a 3D-BCD monitor probing two ZnTe crystals as EO detectors installed on the opposite angle to the electron beam axis and confirmed that we simultaneously obtained both EO signals. Since the adopted hollow probe laser pulse is not only radially polarized but also temporally shifted azimuthally, some disorders in the radial polarization distribution of such a laser pulse were numerically analyzed with a plane-wave expansion method. Based on the above investigations, the 3D-BCD monitor is feasible both in experimental and numerical estimations. Furthermore, we previously developed a femtosecond response organic crystal as a Pockels EO detector and a broadband probe laser ($\ensuremath{\ge}350\text{ }\text{ }\mathrm{nm}$ in FWHM); the 3D-BCD monitor realizes 30- to 40-fs (FWHM) temporal resolution. Eventually, the monitor is expected to be equipped in such advanced accelerators as XFEL to measure and adjust the electron bunch charge distribution in real time. The 3D-BCD measurement works as a critical tool to provide feedback to seeded FELs.

PHYSICOCHEMICAL AND FUNCTIONAL DIFFERENTIATION OF DESSERT AND COOKING BANANA DURING RIPENING - A KEY FOR UNDERSTANDING CONSUMER PREFERENCES

ISHS VII International Symposium on Banana: ISHS-ProMusa Symposium on Bananas and Plantains: Towards Sustainable Global Production and Improved Use PHYSICOCHEMICAL AND FUNCTIONAL DIFFERENTIATION OF DESSERT AND COOKING BANANA DURING RIPENING - A KEY FOR UNDERSTANDING CONSUMER PREFERENCES

Stability of longitudinal bunch length feedback for heavy-ion synchrotrons

feedback systems to increase the stability and to improve the beam quality. In the longitudinal direction, important modes are the coherent longitudinal dipole and quadrupole oscillation. In this paper we present a new and rigorous approach to analyze the longitudinal feedback to damp these modes. The results are applied to the rf feedback loop at GSI that damps the quadrupole mode. The stability analysis is compared with simulations and is in good agreement with results of a beam experiment. Finally, we summarize practical implications for the operation of the feedback system regarding performance and stability. n ¼ 0. Early investigations of feedback for this mode are found in Refs. (6,7). Since then, considerable progress of digital hardware such as FPGAs has been made and most of the newly developed feedback systems rely on digital hardware. Recent works for the damping of the quadrupole mode are Refs. (8-10) for electron machines, Ref. (11) for a proton synchrotron, Ref. (12) for a heavy-ion collider, and Ref. (13) at GSI for a heavy-ion synchrotron. Thenew contributionof thispaper is arigorous approach for the modeling and analysis of the feedback loop, taking into account also nonlinearities due to the accelerating rf voltage. The structure of the paper is as follows. Section II describes the single-particle longitudinal dynamics in heavy-ion synchrotrons and basic notations. The bunch shape oscillations are defined and the control problem is formulated. In Sec. III, a feedback model for the bunch length oscillations is derived. The modeling approach is based on moments and is applicable for quite general non- linear accelerating voltages. Because the moments are not readily available for measurements, it is shown how they can be obtained from the measured beam current signal. The presented results are used to derive the closed-loop dynamics of a specific setup for the heavy-ion synchrotron SIS18 at GSI. The stability and performance of the feed- back is analyzed in Sec. IV. The analytical calculations are compared with nonlinear macro particle tracking simula- tions (cf. (14-16)) and experimental measurements. A tuning rule for the feedback is presented in Sec. V, the practical implications of the results are discussed in Sec. VI, and a conclusion is given in Sec. VII.

Generating High-Power Short Terahertz Electromagnetic Pulses with a Multifoil Radiator

We describe a multifoil cone radiator capable of generating high-field short terahertz pulses using short electron bunches. Round flat conducting foil plates with successively decreasing radii are stacked, forming a truncated cone with the z axis. The gaps between the foil plates are equal and filled with some dielectric (or vacuum). A short relativistic electron bunch propagates along the z axis. At sufficiently high particle energy, the energy losses and multiple scattering do not change the bunch shape significantly. When passing by each gap between the foil plates, the electron bunch emits some energy into the gap. Then, the radiation pulses propagate radially outward. For transverse electromagnetic waves with a longitudinal (along the z axis) electric field and an azimuthal magnetic field, there is no dispersion in these radial lines; therefore, the radiation pulses conserve their shapes (time dependence). At the outer surface of the cone, we have synchronous circular radiators. Their radiation field forms a conical wave. Ultrashort terahertz pulses with gigawatt-level peak power can be generated with this device.

Calculations of operating schemes for a passive harmonic cavity in HLS- II

A passive higher harmonic cavity (HHC) will be used in the Hefei Light Source II Project (HLS- II) to lengthen the bunch and consequently increase the beam lifetime dominated by Touschek scattering. The effects of constant voltage and constant detuning have been calculated and compared over the operating current from 0.4 to 0.2 A on the bunch lengthening for the passive normal conducting harmonic cavity system in HLS- II. The results show that the bunch shape has less change and the lifetime improvement factors are not less than 2.7 over the beam currents for the constant voltage case. The constant voltage operating scheme may be applied to our machine.