Single Bunch Research Articles

Coherent emission from a bunched electron beam: superradiance and stimulated-superradiance in a uniform and tapered wiggler FEL

We outline fundamental coherent radiation processes from a charge particles beam: Spontaneous Superradiance (SR), Stimulated Superradiance (ST-SR), and in the context of undulator radiation: Tapering-Enhanced Superradiance (TES) and Tapering-Enhanced Stimulated Superradiance Amplification (TESSA). Both single bunch and periodic bunching (in phasor and spectral Fourier frequency formulations) are considered in a model of radiation mode expansion.

Nonlinear structure of the wakefield generated by relativistic intense ion bunch

The resonant excitation of the nonlinear wakefield by a single proton bunch is investigated with the parameters characteristic of the AWAKE experiment. It is shown that obtained structure of the wakefield at a distance more than twenty periods behind the driver proton bunch can be suitable for the side injection and further acceleration of the witness electron bunch in the wakefield.

Correlation Between Substrate Morphology and the Initial Stages of Epitaxial Organic Growth: PTCDA/Ag(111)

We have investigated the initial growth of the first two epitaxial layers of PTCDA on a Ag(111) surface consisting of a distribution of flat (111) terraces, separated by single atomic steps or step bunches with a few point defects. By utilizing the low-energy electron microscopy (LEEM) technique in both bright and dark field modes, we are able not only to follow the growth of the first layers but also to distinguish between different rotational and mirror domains and their influence on the growth of subsequent layers. Thus, we learn much about diffusion lengths and barriers, domain sizes, and about the influence of domain boundaries and nucleation centers. The results give deep insight into the growth dynamics, the influence of step orientation, and the quality of the resulting epitaxial layers and lead to the conclusion that the morphology of the substrate surface is likely to be the most influential parameter for the homogeneity of epitaxial layers.

Optimized stability of a modulated driver in a plasma wakefield accelerator

AbstractWe analyze the transverse stability for a configuration of multiple Gaussian bunches subject to the self-generated plasma wakefield. Through a semi-analytical approach we first study the equilibrium configuration for the modulated beam and then we investigate the evolution of the equilibrium configuration due to the emittance-driven expansion of the beam front that results in a rigid backward shift. The rear-directed shift brings the modulated beam out of the equilibrium, with the possibility for some of the bunch particles to be lost with a consequent deterioration of the driver. We look therefore for the proper position of the single bunches that maximize the stability without severely affecting the accelerating field behind the driver. We then compare the results with three-dimensional particle in cell simulations.

Towards a Practical Multi-Meter Long Dielectric Wakefield Accelerator: Problems and Solutions

A multi-meter long collinear dielectric wakefield accelerator is considered, and it is shown that a single bunch breakup instability is a major limiting factor for obtaining highly efficient energy transfer from the drive bunch to the main bunch. Different methods for instability suppression are studied. Numerical simulations using a 6D particle tracking computer code are performed and tolerances to various errors are defined.

Observation of Electron Cloud Instabilities and Emittance Dilution at the Cornell Electron-Positron Storage Ring Test Accelerator

Electron cloud related emittance dilution and instabilities of bunch trains limit the performance of high intensity circular colliders. One of the key goals of the Cornell electron-positron storage ring Test Accelerator (CesrTA) research program is to improve our understanding of how the electron cloud alters the dynamics of bunches within the train. Single bunch beam diagnotics have been developed to measure the beam spectra, vertical beam size, two important dynamical effects of beams interacting with the electron cloud, for bunch trains on a turn-by-turn basis. Experiments have been performed at CesrTA to probe the interaction of the electron cloud with stored positron bunch trains. The purpose of these experiments was to characterize the dependence of beam-electron cloud interactions on the machine parameters such as bunch spacing, vertical chromaticity, and bunch current. The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 1) a gated beam position monitor (BPM) and spectrum analyzer to measure the bunch-by-bunch frequency spectrum of the bunch trains; 2) an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this paper we report on the observations from these experiments and analyze the effects of the electron cloud on the stability of bunches in a train under many different operational conditions.

Development of the bunch-by-bunch beam position acquisition system based on BEEcube

In this paper, we report the development of a bunch-by-bunch beam position acquisition system. Through a wideband synthesizer of PLL, the system realizes synchronous clock of bunch signal. Based on the high-performance FPGA hardware DAQ environment, four-channel raw data of beam signal can be achieved. Test results in the SSRF storage ring show that the system can obtain beam position of single bunch with the resolution of 10 μm and multi-bunch instability can be observed.

Conceptual design and modeling of a six-dimensional bunch merging scheme for a muon collider

A high luminosity muon collider requires single, intense, muon bunches with small emittances: just one of each sign. An efficient front end and a cooling channel have been designed and simulated within the collaboration of the Muon Accelerator Program. The muons are first bunched and phase rotated into 21 bunches, and then cooled in six dimensions. When they are cool enough, they are merged into single bunches: one of each sign. The bunch merging scheme has been outlined with preliminary simulations in previous studies. In this paper we present a comprehensive design with its end-to-end simulation. The 21 bunches are first merged in longitudinal phase space into seven bunches. These are directed into seven ``trombone'' paths with different lengths, to bring them to the same time, and then merged transversely in a collecting ``funnel'' into the required single larger bunches. Detailed numerical simulations show that the 6D emittance of the resulting bunch reaches the parameters needed for high acceptance into the downstream cooling channel.

Controlled electron bunch generation in the few-cycle ultra-intense laser–solid interaction scenario

The generation of Maxwellian or exponentially decaying spectra in the interaction of ultra-intense ultra-short laser pulses with solid foils is very general observation both in experiments and simulations. Yet, the physical origin of this observation is not well understood. For a very idealized situation of plane wave, plane and cold target interaction, we show that both randomization between individual electron bunches accelerated by the laser through the plasma as well as randomization during a single bunch are not observable in particle-in-cell simulations. Hence they are not accountable for the apparent thermalization (exponential spectrum).

Observation of Wakefield Suppression in a Photonic-Band-Gap Accelerator Structure.

We report experimental observation of higher order mode (HOM) wakefield suppression in a room-temperature traveling-wave photonic-band-gap (PBG) accelerating structure at 11.700GHz. It has been long recognized that PBG structures have the potential for reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in a room-temperature PBG structure was conducted in 2005. Since then, the importance of PBG accelerator research has been recognized by many institutions. However, the full experimental characterization of the wakefield spectrum and demonstration of wakefield suppression when the accelerating structure is excited by an electron beam has not been performed to date. We conducted an experiment at the Argonne Wakefield Accelerator test facility and observed wakefields excited by a single high charge electron bunch when it passes through a PBG accelerator structure. Excellent HOM suppression properties of the PBG accelerator were demonstrated in the beam test.

A preliminary design of the collinear dielectric wakefield accelerator

A preliminary design of the multi-meter long collinear dielectric wakefield accelerator that achieves a highly efficient transfer of the drive bunch energy to the wakefields and to the witness bunch is considered. It is made from ~0.5m long accelerator modules containing a vacuum chamber with dielectric-lined walls, a quadrupole wiggler, an rf coupler, and BPM assembly. The single bunch breakup instability is a major limiting factor for accelerator efficiency, and the BNS damping is applied to obtain the stable multi-meter long propagation of a drive bunch. Numerical simulations using a 6D particle tracking computer code are performed and tolerances to various errors are defined.

Influence of berry diameter and colour on some determinants of wine composition ofVitis vinifera L. cv. Riesling

Background and Aims To successfully use berry sorting in winemaking, it is crucial to understand the interaction of physical and chemical composition of berries. The aim of this study was to investigate the relationship between berry diameter and colour and aspects of wine composition, such as titratable acidity, aroma compounds and phenolic substances of Vitis vinifera L. cv. Riesling. Methods and Results In a first trial, berries were sorted into three berry diameter classes with equal TSS concentration and vinified by 70 mL scale fermentation. In a second trial, berries from each of two diameter classes with equal TSS concentration were sorted by berry colour to obtain samples of low a* value and high a* value berries for the respective diameter class, and vinified. In the first trial, wines from smaller berries had lower titratable acidity and a lower concentration of malic acid. In the second trial, wine obtained from berries with higher a* values showed a higher concentration of free C13-norisoprenoids as well as free and glycosylated monoterpenes. Wines from smaller berries in this trial showed a higher concentration of norisoprenoids and a lower pH. Conclusions Berry diameter and colour are highly variable within single vineyards, vines and single bunches. Sorting by berry size or colour will lead to wines with a pronounced difference in aroma compounds, acidity and α-amino nitrogen. Significance of the Study This study shows the relationship between berry diameter or colour and wine quality aspects such as acidity and aroma. Understanding this relationship will assist winemakers to conduct targeted berry sorting.

Fully 3-D Integrated Pixel Detectors for X-Rays

The vertically integrated photon imaging chip (VIPIC1) pixel detector is a stack consisting of a 500-μm-thick silicon sensor, a two-tier 34-μm-thick integrated circuit, and a host printed circuit board (PCB). The integrated circuit tiers were bonded using the direct bonding technology with copper, and each tier features 1-μm-diameter throughsilicon vias that were used for connections to the sensor on one side, and to the host PCB on the other side. The 80-μm-pixel-pitch sensor was the direct bonding technology with nickel bonded to the integrated circuit. The stack was mounted on the board using Sn-Pb balls placed on a 320-μm pitch, yielding an entirely wire-bond-less structure. The analog front-end features a pulse response peaking at below 250 ns, and the power consumption per pixel is 25 μW. A successful completion of the 3-D integration is reported. In addition, all pixels in the matrix of 64 x 64 pixels were responding on well-bonded devices. Correct operation of the sparsified readout, allowing a single 153-ns bunch timing resolution, was confirmed in the tests on a synchrotron beam of 10-keV X-rays. An equivalent noise charge of 36.2 e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> rms and a conversion gain of 69.5 μV/e with 2.6 e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> rms and 2.7 μV/e rms pixel-to-pixel variations, respectively, were measured.

Characterization of pseudosingle bunch kick-and-cancel operational mode

Author(s): Sun, C; Robin, DS; Steier, C; Portmann, G | Abstract: Pseudosingle-bunch kick-and-cancel (PSB-KAC) is a new operational mode at the Advanced Light Source of Lawrence Berkeley National Laboratory that provides full timing and repetition rate control for single x-ray pulse users while being fully transparent to other users of synchrotron radiation light. In this operational mode, a single electron bunch is periodically displaced from a main bunch train by a fast kicker magnet with a user-on-demand repetition rate, creating a single x-ray pulse to be matched to a typical laser excitation pulse rate. This operational mode can significantly improve the signal to noise ratio of single x-ray pulse experiments and drastically reduce dose-induced sample damage rate. It greatly expands the capabilities of synchrotron light sources to carry out dynamics and time-of-flight experiments. In this paper, we carry out extensive characterizations of this PSB-KAC mode both numerically and experimentally. This includes the working principle of this mode, resonance conditions and beam stability, experimental setups, and diagnostic tools and measurements.

MPX Detectors as LHC Luminosity Monitor

A network of 16 Medipix-2 (MPX) silicon pixel devices was installed in the ATLAS detector cavern at CERN. It was designed to measure the composition and spectral characteristics of the radiation field in the ATLAS experiment and its surroundings. This study demonstrates that the MPX network can also be used as a self-sufficient luminosity monitoring system. The MPX detectors collect data independently of the ATLAS data-recording chain, and thus they provide independent measurements of the bunch-integrated ATLAS/LHC luminosity. In particular, the MPX detectors located close enough to the primary interaction point are used to perform van der Meer calibration scans with high precision. Results from the luminosity monitoring are presented for 2012 data taken at sqrt(s) = 8 TeV proton-proton collisions. The characteristics of the LHC luminosity reduction rate are studied and the effects of beam-beam (burn-off) and beam-gas (single bunch) interactions are evaluated. The systematic variations observed in the MPX luminosity measurements are below 0.3% for one minute intervals.

Broadband impedance calculations and single bunch instabilities estimations of of the HLS-II storage ring**Supported by Natural Science Foundation of China (11175182, 11175180)

The upgrade project of the Hefei Light Source storage ring is under way. In this paper, the broadband impedances of resistive wall and coated ceramic vacuum chamber are calculated using the analytic formula, and the wake fields and impedances of other designed vacuum chambers are simulated by CST code, and then a broadband impedance model is obtained. Using the theoretical formula, longitudinal and transverse single bunch instabilities are discussed. With the carefully-designed vacuum chamber, we find that the thresholds of the beam instabilities are higher than the beam current goal.

3-D Numerical Analysis of Smith–Purcell-Based Terahertz Wave Radiation Excited by Effective Surface Plasmon

At lower frequency regime, altering the surface structure modifies the characteristics of propagating effective surface plasmons (ESPs), particularly their interaction with light. Movement of an electron beam in the proximity of the surface of a structured metallic grating excite these ESPs, which due to existence of a velocity phase match, they are able to emit terahertz (THz) waves known as Smith–Purcell (SP) radiation. By introducing a femtosecond perturbation (a single electron bunch), the important characteristics of a desired grating are revealed. Through our 3-D investigations, we find the incoherent THz radiation frequency span, and moreover we confirm that the frequency of the ESP is always less than the minimum SP frequency. Additionally, we find that the maximum of signal amplitude is distributed around 90°, only if the grating width is comparable to the longest SP wavelength. Also we learned that by increasing the grating length, the magnitude and spectral resolution of the radiation increases too. In order to study the coherent (superradiant) radiation, we use a train of electron bunches with variable bunch-to-bunch distances, and we calculate the radiation angle of the coherent SP signal. Simulations on the generation of SP radiation at THz frequencies are performed with the help of the 3-D particle-in-cell (PIC) finite integral (FI) method, in which the results agree very well with previously reported 2-D simulations.

Design studies and commissioning plans for plasma acceleration research station experimental program

Plasma acceleration research station is an electron beam driven plasma wakefield acceleration test stand proposed for CLARA facility in Daresbury Laboratory. In this paper, the interaction between the electron beam and the plasma is numerically characterised via 2D numerical studies by using VSIM code. The wakefields induced by a single bunch travelling through the plasma were found to vary from 200 MV/m to 3 GV/m for a range of bunch length, bunch radius, and plasma densities. Energy gain for the particles populating the bunch tail through the wakefields driven by the head of the bunch was demonstrated. After determining the achievable field for various beams and plasma configurations, a reference setting was determined for further studies. Considering this reference setting, the beam quality studies were performed for a two-bunch acceleration case. The maximum energy gain as well as the energy spread mitigation by benefiting from the beam loading was investigated by positioning the witness and driver bunches with respect to each other. Emittance growth mechanisms were studied considering the beam-plasma and beam-wakefield interactions. Eventually, regarding the findings, the initial commissioning plans and the aims for the later stages were summarised.

Single bunch transverse instability in a circular accelerator with chromaticity and space charge

The transverse instability of a bunch in a circular accelerator is elaborated in this paper. A new tree-modes model is proposed and developed to describe the most unstable modes of the bunch. This simple and flexible model includes chromaticity and space charge, and can be used with any bunch and wake forms. The dispersion equation for the bunch eigentunes is obtained in form of a third-order algebraic equation. The known head-tail and TMCI modes appear as the limiting cases which are distinctly bounded at zero chromaticity only. It is shown that the instability parameters depend only slightly on the bunch model but they are rather sensitive to the wake shape. In particular, space charge effects are investigated in the paper and it is shown that their influence depends on sign of wake field enhancing the bunch stability if the wake is negative. The resistive wall wake is considered in detail including a comparison of single and collective effects. A comparison of the results with earlier publications is carried out.

A high-throughput UHPLC MS/MS method for evaluation of tartaric and malic acid concentration in individual grapevine berries

Background and Aims The chemical composition of grape berries during development exhibits large variation within a single bunch. To monitor the change in the concentration of tartaric acid and malic acid between individual berries, a high-throughput method using UHPLC-MS/MS was developed to quantify these acids in berry extracts. Methods and Results The results from analysis of single-vine datasets indicated that there was a large variation in the concentration of tartaric acid and malic acid between individual berries and also between bunches of berries across a vine. From these data, an optimum sampling size of 30 berries per vine was determined, which has an estimated standard error under 10% of the expected average berry acid concentration. Conclusions A high-throughput UHPLC-MS/MS method using the stable isotope dilution analysis has been developed to quantify tartaric acid and malic acid in individual berry extracts and extracts prepared from samples of multiple berries. Significance of the Study This method enabled the study of variation in acid concentration and content between individual berries. This makes it possible to quantify the variation in the acids at several levels (berries, bunches and plants) and to recommend ideal sampling sizes for data collection in vineyards.