Bunch Structure Research Articles

LHC-rate beam test of CMS pixel barrel modules

Modules for the CMS pixel barrel detector have been operated in a high rate pion beam at PSI in order to verify under LHC-like conditions the final module design for the production. The test beam provided charged particle rates up to 10 8 cm - 2 s - 1 over the full module area. Bunch structure and randomized high trigger rates simulated realistic operation. A four layer telescope made of single pixel readout chip assemblies provided tracking needed for the determination of the modules hit reconstruction efficiency. The performance of the modules has been shown to be adequate for the CMS pixel barrel.

Superhydrophobic nano-wire entanglement structures

Superhydrophobic nano-wire entanglement structures (NWES) were fabricated by the dipping method, based on an anodization process in oxalic acid. The pore diameter and the depth were influenced by the applied voltage and the anodizing time. To obtain the NWES, polytetrafluoroethylene (PTFT, Teflon®: DuPont™) replication based on the dipping method was used, with a PTFT solution (0.3 wt%). During replication, the polymer sticking phenomenon due to van der Waals interactions creates microscale bunch structures on the nanoscale wire-entanglement structures. This process provides a hierarchical structure with nanostructures on microstructures and enables commercialization. The diameter of the replicated wires was about 40 nm, and their lengths were 22–75 µm according to the anodizing time. The fabricated surface has superhydrophobicity; the apparent contact angle of the PTFT micro and nanostructures is about 160°–170° and the sliding angle is less than 1°.

Regulating yield and wine quality of minimal prunning systems through the application of gibberellic acid

<p style="text-align: justify;">The use of gibberellic acid to increase berry size and to loosen up bunches in the production of seedless table grape varieties has a long history. The use of gibberellic acid on wine grapes, however, is very limited, mainly because some varieties can show substantial losses in bud fertility and thus in commercial yield. We tried to exploit the feature of decreases in bud fertility as a response to gibberellic acid applications (in the form of GA3) to regulate yield and quality aspects of minimally pruned (MP) White Riesling grapevines where other thinning methods have failed. Single applications of 50 mg L-1 GA3 at 500 L ha-1 were used during full bloom in each year from 2002-2004 (MP GA3-02/03/04) in one MP treatment, while the second MP treatment received no GA3 in 2003 (MP GA3-02/04). Treatments were compared with untreated MP vines and with a standard pruned, vertically shoot positioned system (VSP). GA3 applications reduced inflorescence number by about 30-50% the year following treatment, while shoot number remained unchanged. GA3 treated MP vines responded to this type of « thinning » by a 10-28 % increase in berry weight. Total yield of MP vines was reduced by 26-49% the year after first time application approaching VSP yield. Yield of the continuously treated vines (MP GA3-02/03/04) remained comparable to pruned VSP vines up to now (harvest 2005) (about 9-13 tons per ha). Discontinuing the GA3 treatment for one year caused yield to re-approach the one of untreated MP vines the next year. Despite of the increase in berry weight, bunch structure remained less compact as compared to VSP fruit. Sugar levels at harvest of vines treated with GA3 the previous year were similar to sugar levels of VSP vines and superior to untreated MP vines. We found no treatment effect on glycosyl-glucose (bound secondary metabolites, GG) concentration but a slight increase in phenols and titratable acidity the year after GA3 treatment. Sensory evaluation of the resulting wines revealed no or only minimal differences with a slight preference for the least yielding VSP and MP GA3-02/03/04 wines. The outlined strategy seems promising for the production of quality fruit in a highly economic viticultural system.</p>

Longitudinal beam profile measurements at CTF3 using a streak camera

The proposed Compact Linear Collider (CLIC) is a multi-TeV electron-positron collider for particle physics based on an innovative two-beam acceleration concept. A high-intensity drive beam powers the main beam of a high-frequency (30 GHz) linac with a gradient of 150 MV/m, by means of transfer structure sections. The aim of the CLIC Test Facility (CTF3) is to make exhaustive tests of the main CLIC parameters and to prove the technical feasibility. One of the points of particular interest is the demonstration of bunch train compression and combination in the Delay Loop and in the Combiner Ring. Thus, detailed knowledge about the longitudinal beam structure is of utmost importance and puts high demands on the diagnostic equipment.Among others, measurements with a streak camera have been performed on the linac part of the CTF3 as well as on the newly installed Delay Loop. This allowed e.g. monitoring of the longitudinal structure of individual bunches, the RF combination of the beam, the behavior during phase shifts and the influence of the installed wiggler. This article first gives an overview of the CTF3 facility, then describes in detail the layout of the long optical lines required for observation of either optical transition radiation or synchrotron radiation, and finally shows first results obtained during the last machine run this year.

Homoepitaxial Growth on a 4H‐SiC C‐Face Substrate

AbstractHomoepitaxial growth on a 4H‐SiC carbon face (C‐face) was investigated. The C‐face showed a similar site‐competition phenomenon to that seen on a 4H‐SiC Si‐face. This site‐competition phenomenon was distinctly sensitive to growth pressure. The surface morphology of the C‐face epitaxial layer was sensitive to surface imperfections on the substrate. The growth window of 4° off‐axis, C‐face substrates was shown to be wider than that of the corresponding Si‐face. A specular surface morphology without a bunched step structure was obtained over a whole 2 inch C‐face substrate with a vicinal off‐angle of 0.5°.

Complicated surface structure of flower-like bunches of LiV0.1Mn1.9O4 nanofibers

LiV0.1Mn1.9O4 nanofibers were synthesized via a conventional solid-state reaction. The nanofibers tend to form bunches with flower-like shapes. Since this interesting form provides a 3D structure, surface analysis of such flowers is of particular interest and was performed by means of small-angle X-ray scattering (SAXS) via the concept of fractal geometry. The results obtained from experimental measurements suggested a fractal dimension close to 3, which is indicative of a 3D structure. This provides an excellent accessibility of the material for diffusion-based reactions, since diffusion within the material is easy through such ordered nanofibers.

Terahertz radiation as a bunch diagnostic for laser-wakefield-accelerated electron bunches

Experimental results are reported from two measurement techniques (semiconductor switching and electro-optic sampling) that allow temporal characterization of electron bunches produced by a laser-driven plasma-based accelerator. As femtosecond electron bunches exit the plasma-vacuum interface, coherent transition radiation (at THz frequencies) is emitted. Measuring the properties of this radiation allows characterization of the electron bunches. Theoretical work on the emission mechanism is presented, including a model that calculates the THz wave form from a given bunch profile. It is found that the spectrum of the THz pulse is coherent up to the 200 μm thick crystal (ZnTe) detection limit of 4THz, which corresponds to the production of sub-50fs (rms) electron bunch structure. The measurements demonstrate both the shot-to-shot stability of bunch parameters that are critical to THz emission (such as total charge and bunch length), as well as femtosecond synchronization among bunch, THz pulse, and laser beam.

Morphology of female reproductive tract of the predator Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) fed on different diets

The morphology of the reproductive tract of Podisus nigrispinus (Dallas) females fed with Alabama argillacea (Hübner) larvae, artificial diet, Tenebrio molitor L. larvae or Musca domestica L. larvae were studied. The reproductive tract of females of this species presented yellow coloration and independent of the diet, each ovary had seven ovarioles joined through terminal filaments and forming a bunch shape structure. The histological data revealed that the ovary of P. nigrispinus was of meroistic telotrophic type, with each individual ovariole divided in a terminal filament, a tropharium (trophic chamber), a vitellarium, and a pedicel. The prey type affected the development and morphometry of these structures. Females of P. nigrispinus fed with 3rd or 5th instar larvae of cotton leafworm (A. argillacea) presented developed ovaries with ovarioles showing a great number of oocytes in advanced stages of development. Females fed with artificial diet presented atrophic ovaries and ovarioles practically without oocytes. Females fed with T. molitor or M. domestica showed ovaries in intermediary stage of development. The central ovariole was longer in females fed with 5th instar larvae of cotton leafworm and shorter in those fed with artificial diet. Most developed oocytes were observed in ovaries of females fed with 5th or 3rd instar larvae of cotton leafworm, and the majority of atrophic oocytes were found in females fed with artificial diet.

Control of Nano-Step Structures on Sapphire Wafer Surface by Focused Ion Beam Processing

Nano-dots array whose diameter and interval were approximately 200 nm and 750 nm, respectively, were made parallel to the atomic step edges on sapphire wafers by focused ion beam (FIB) system. Upon annealing a bunched multi-steps structure formed at regularintervals and straight because the steps were pinned at the nano-dots. The step heights andterrace widths were approximately 2.0 nm, 700 nm in off-angle 0.15° and 10.0 nm, 350 nm in off-angle 1.0°, respectively.

A simple method for the determination of the structure of ultrashort relativistic electron bunches

In this paper we propose a new method for measurements of the longitudinal profile of 100 fs electron bunches for X-ray Free Electron Lasers (XFELs). The method is simply the combination of two well-known techniques, which where not previously combined to our knowledge. We use seed 10-ps 1047 nm quantum laser to produce exact optical replica of ultrafast electron bunches. The replica is generated in an apparatus which consists of an input undulator (energy modulator), and the short output undulator (radiator) separated by a dispersion section. The radiation in the output undulator is excited by the electron bunch modulated at the optical wavelength and rapidly reaches 100 MW-level peak power. We then use the now-standard method of ultrashort laser pulse-shape measurement, a tandem combination of autocorrelator and spectrum (FROG—frequency resolved optical gating). The FROG trace of the optical replica of electron bunch gives accurate and rapid electron bunch shape measurements in a way similar to a femtosecond oscilloscope. Real-time single-shot measurements of the electron bunch structure could provide significant information about physical mechanisms responsible for generation ultrashort electron bunches in bunch compressors. The big advantage of proposed technique is that it can be used to determine the slice energy spread and emittance in multishot measurements. It is possible to measure bunch structure completely, that is to measure current, energy spread and transverse emittance as a function of time. We illustrate with numerical examples the potential of the proposed method for electron beam diagnostics at the European XFEL.

Experimental results on electron beam combination and bunch frequency multiplication

The aim of the CLIC Test Facility CTF3 at CERN is to demonstrate the feasibility of the key points of the two-beam acceleration based compact linear collider study. In particular, it addresses the efficient generation of a drive beam with the appropriate time structure of the electron bunches in order to produce high power rf pulses at a frequency of 30 GHz. This time structure requires a high bunch repetition frequency. It is obtained by successive injections of bunch trains into an isochronous ring using transversely deflecting rf structures. The major goal of the now completed first phase of the CTF3 was to achieve the bunch train combination at low charge. In this paper, we give a description of the project and summarize the experimental results, with a focus on the successful bunch frequency multiplication for various factors up to 5.

A detector of bunch time structure for cw heavy-ion beams

The manuscript describes the design, commissioning and performance of a new device for the measurement of bunch time structure of heavy-ion beams. The Bunch Length Detector (BLD) has been developed, constructed and installed at the Argonne Tandem Linear Accelerating System, a superconducting linac. The BLD is a wire scanning detector based on the analysis of secondary electrons produced by the primary beam hitting a target wire. The device provides measuring of bunch phase spectrum for ion beams in a wide range of energies, intensities and species in cw mode with up to 20 ps resolution.

In situ observation of step-terrace structures on MOVPE grown InP(0 0 1) by using grazing X-ray scattering

Step-terrace structures on MOVPE grown InP(0 0 1) surface were investigated by using grazing X-ray scattering. After buffer layers were formed on the substrate, X-ray scattering profiles were measured in the same chamber without exposing the sample to air. Small peaks were observed at the tail of the specular reflections, suggesting the in-plane periodicity of surface morphology. The azimuth angle dependence of peak position suggests a one-dimensional structure on the surface, and considering the AFM images of the sample, the bunched step-terrace structure toward [1 0 0] is the reason of this structure. Analyses based on a simple grating approximation shows the period of the one-dimensional structure is about 550 nm, which is consistent with the spacing value determined from AFM images.

Coherent X-ray imaging and microscopy opportunities with a diffraction-limited Energy Recovery Linac (ERL) synchrotron source

A proposed Energy Recovery Linac (ERL) x-ray source at Comell would be a 5-7 GeV synchrotron facility based on the energy-recovery principle with a superconducting linac. Because of its ultra-small round electron source and ultra-short but flexible bunch structure, the ERL has the potential to produce subpicosecond ultra-bright diffraction-limited hard x-ray beams that are superior to those from existing storage rings, and would enable new scientific experiments that are difficult or impossible to perform today. In this paper, we discuss the transverse coherence properties of the ERL source and show how these properties could benefit various x-ray microscopy applications that require a highly coherent and intense x-ray beam. These applications include full coherent illumination of wide-aperture zone-plate optics for scanning x-ray microscopy, diffraction-limited coherent phase-contrast microscopy and tomography, fully coherent hard x-ray diffraction microscopy, and large-coherence-area x-ray holography techniques.

Study on the formation and growth of potassium titanate whiskers

In this paper, K2Ti2O5 single crystals, K2Ti4O9 whiskers and K2Ti6O13 whiskers are synthesized form the anatase-K2CO3 starting materials by the heating calcination and the corresponding morphologic and structural evolution of products are observed. After dissolving non-crystalline hydrosoluble products contained in sinters, the morphologic difference between the original sinter and the whiskers in it shows the sinter microstructure. The further analysis to crystal components in sinters and to the phase diagram proves that K2Ti4O9 whiskers are firstly formed in K2Ti2O5 crystals and there only exists the phase transformation from K2Ti4O9 whiskers with layered crystal structure to~K2Ti6O13 whiskers with tunnel crystal structure. The K2O-rich liquid melt generated from K2Ti2O5 crystals (/and K2Ti4O9 whiskers) coats on the surface of K2Ti4O9 whiskers (/and K2Ti6O13 whiskers), which makes the sinters taking on the layer-by-layer structure (/and the bunch structure). The formation and growth of whiskers is dictated by the K2O-rich non-crystalline hydrosoluble melt generated in phase transformations from solid to liquid-solid and its split effect induced by the orientation melting. A generalized “liquid melt inducing” mechanistic model explaining the formation and growth of potassium titanate whiskers was proposed.

Vapour–liquid–solid mechanism for the growth of SiC homoepitaxial layers by VPE

In order to reach fast growth regime, we have investigated the SiC homoepitaxial growth on off-axis 4H-SiC substrates from a vapour–liquid–solid (VLS) mechanism in a vertical cold wall CVD reactor. The experiments involved silane and propane diluted in hydrogen as feeding vapour phase and melted silicon as “liquid catalyst”. Growth rates up to 25 μm/h at 1500°C and 35 μm/h at 1600°C with a bunched step-terrace structure are demonstrated in such a system. The formation and stability of the VLS equilibrium is discussed with respect to the experimental parameters and a first approach of the mechanism is proposed.

Electro-optical measurements of ultrashort 45 MeV electron beam bunch

We have made an observation of 45 MeV electron beam bunches using the nondestructive electro-optical (EO) technique. The amplitude of the EO modulation was found to increase linearly with electron beam charge and decrease inversely with the optical beam path distance from the electron beam. The risetime of the signal was bandwidth limited by our detection system to ~ 70 ps. An EO signal due to ionization caused by the electrons traversing the EO crystal was also observed. The EO technique may be ideal for the measurement of bunch structure with femtosecond resolution of relativistic charged particle beam bunches.

Observation of hard X-ray pulses with a highly sensitive streak camera

We have developed a highly sensitive X-ray streak camera system, which synchronously operates with the RF signal of the SPring-8 storage ring. The streak camera was installed at an undulator beamline of SPring-8, and the beam loading effect for various electron bunch structures (filling pattern) has been observed. The camera has also been operated as a timing monitor for a synchronization system of synchrotron radiation and a Ti:sapphire laser. The highly sensitive X-ray streak camera system can be used not only as an accelerator diagnosis, but also as a fast temporal detector for beamline applications, such as the observation of fast temporal transitions of diffraction images and relaxation process.

Generation of Sub-picosecond GeV Electron Bunches by Laser Acceleration in Vacuum

The interaction of free electrons with intense laser beams in vacuum was studied using 3D test particle simulation instead of analytically solving the relativistic Newton-Lorentz equation of motions. We found a group of solutions for the equation, which reveal very interesting and unusual characteristics different from any previously reported. The fundamental characteristics of those trajectories are that an electron can be captured into the high-intensity region, rather than expelled from it and that the captured electron can be accelerated to GeV energy with an acceleration gradient of 1–50 GeV/cm. These solutions emerges only when the laser intensity is a0\\gtrsim100, where a0≡eE0/meωc is a measure of the laser intensity. The accelerated GeV electron bunch is a macropulse composed of multiple micropulses, which is analogous to the structure of bunches produced by conventional linacs. The paraxial approximation equations for the Gaussian laser beam used in the simulation are highly accurate and the contribution of the high-order correction is almost negligible when the laser beam width is w0\\geqslant60.

Summary of scenarios working groups

Three scenarios for a neutrino factory were discussed at the workshop. All were based upon muon collider studies differing principally in the proton driver each assumed. Differing assumptions concerning power on target, bunch structure and the use of cooling were ironed out, leaving one basic scenario downstream of the target. A list of R&D topics was compiled and prioritized.