Short Straight Sections Research Articles

How to mimic the shapes of plant tendrils on the nano and microscale: spirals and helices of electrospun liquid crystalline cellulose derivatives

We show that suspended nano and microfibres electrospun from liquid crystalline cellulosic solutions will curl into spirals if they are supported at just one end, or, if they are supported at both ends, will twist into a helix of one handedness over half of its length and of the opposite handedness over the other half, the two halves being connected by a short straight section. This latter phenomenon, known as perversion, is a consequence of the intrinsic curvature of the fibres and of a topological conservation law. Furthermore, agreement between theory and experiment can only be achieved if account is taken of the intrinsic torsion of the fibres. Precisely the same behaviour is known to be exhibited by the tendrils of climbing plants such as Passiflora edulis, albeit on a lengthscale of millimetres, i.e., three to four orders of magnitude larger than in our fibres. This suggests that the same basic, coarse-grained physical model is applicable across a range of lengthscales.

Upgrade of NewSUBARU with Superconducting Magnets

There is an attractive possibility that the critical energy of synchrotron radiation of the NewSUBARU can be increased by introducing superconducting (SC) magnets in the storage ring. In this paper, the effect of 5 T SC magnets on lattice functions of the ring is discussed. There are two possibilities of introducing the SC magnets: one is by replacing the inverse bending magnet with a SC magnet and the other is by installing a SC wiggler. With the former, there is negligible effect on the beam optics and the expected vertical tune shift can be easily corrected by adjusting two quadrupole magnets in the short straight section. With the latter, there are no serious problems, but it is necessary that additional quadrupole magnets are placed at both ends of the wiggler in order to reduce the deformation of electron beam optics.

The magnets of the metrology light source in Berlin-Adlershof

The German National Metrology Institute (PTB) in close cooperation with BESSY II (Berlin) is currently carrying out the construction the low-energy “Metrology Light Source” (MLS). Constructions of the MLS facility are in progress and nearly finished [1]. The user operation is scheduled to begin of 2008. Dedicated to metrology and technology development in the UV and EUV spectral range the MLS will close the gap that is existent since the shutdown of BESSY I [2]. A 100 MeV microtron will provide the electrons for the MLS. The MLS magnetic ring with a circumference of 48 m consists of eight bending magnets, 24 quadrupole magnets, 24 sextupole magnets and four octuple magnets, and has two long and two short straight sections. The MLS magnets have been produced by the Budker Institute for Nuclear Physics, Novosibirsk, Russia [3,4]. The electron energy is ramped to the desired value between 200 and 600 MeV. The expected lifetime for electron energy between 200 and 600 MeV at maximum beam current of 200 mA is between 1 and 10 h, respectively.

Electrical and Magnetic Performance of the LHC Short Straight Sections

The Short Straight Section (SSS) for the Large Hadron Collider arcs, containing in a common cryostat the lattice quadrupoles and correction magnets, have now entered series production. The foremost features of the lattice quadrupole magnets are a two-in-one structure containing two 56 mm aperture, two-layers coils wound from 15.1 mm wide NbTi cables, enclosed by the stainless steel collars and ferromagnetic yoke, and inserted into the inertia tube. Systematic cryogenic tests are performed at CERN in order to qualify these magnets with respect to their cryogenic and electrical integrity, the quench performance and the field quality in all operating conditions. This paper reports the main results obtained during tests and measurements in superfluid helium. The electrical characteristics, the insulation measurements and the quench performance are compared to the specifications and expected performances for these magnets. The field in the main quadrupole is measured using three independent systems: 10-m long twin rotating coils, an automatic scanner, and single stretched wire. A particular emphasis is given to the integrated transfer function which has a spread of around 12 units rms in the production and is a critical issue. The dodecapole harmonic component, which required trimming through a change in coil shims, is also discussed. Finally, the magnetic axis measurements at room temperature and at 1.9 K, providing the nominal vertical shift for installation are reported

Warm and Cold Magnetic and Mechanical Alignment Tests of LHC Short Straight Sections

This paper contains a summary of the results of the magnetic and mechanical alignment tests performed at CERN on the first 111 arc Short Straight Sections. These include the mechanical axis of the Cold Bore Tube at room temperature, the magnetic axis of main quadrupoles and correctors at both room and cryogenic temperature, and the field direction of the main quadrupoles. The measurements show that the quality of the assemblies is generally within the requirements for the machine

Performance of the Room Temperature Systems for Magnetic Field Measurements of the LHC Superconducting Magnets

The LHC will be composed of 1232 horizontally curved, 15-meter long, superconducting dipole assemblies and 474 Short Straight Sections containing various types of quadrupoles. These magnets are manufactured by several European companies and half of them are currently produced. The field quality at room temperature is strictly monitored to guide and validate the assembly at different stages of the production in the industry. Dipoles and quadrupoles are measured with two different rotating coil systems. These "moles" travel inside the 50 mm aperture and accurately measure the field and gradient strength integrated over the length, the field direction and high order harmonics. We describe here these two systems, their performance and the experience gained through the two first years of operation

Axis Measurements, Field Quality and Quench Performance of the First LHC Short Straight Sections

The series testing at 1.9 K of the 360 Short Straight Sections (SSS) for the Large Hadron Collider have started at CERN in September 2003. The SSS contain the lattice quadrupoles and correction magnets in a common cryostat. The lattice quadrupoles feature two collared coils with 56 mm bore assembled in a common yoke. The coils are wound in two-layers from 15.1 mm wide NbTi cable, insulated with polyimide tape. The paper reviews the main test results performed in superfluid helium. The magnetic field and magnetic center position of the quadrupoles and associated correctors were measured with two independent systems, namely an automated scanner and a single stretched wire technique. The quench training, the field quality and the magnetic alignment measurements are presented and discussed in terms of the specifications and expected performances of these magnets in the LHC. We discuss in detail the field quality in terms of multipole errors measured at injection and nominal field and decomposed into geometric and persistent current magnetization errors. Warm/cold correlation for the geometric multipoles and the magnetic axis is also presented.

Results of Magnetic Axis Measurements on a Prototype Main Lattice Quadrupole for the LHC

More than 470 twin aperture lattice quadrupoles are needed for the large hadron collider (LHC) under construction at CERN. The lattice quadrupole, assembled with correction magnets in its helium enclosure - the cold mass and integrated in a common cryostat called the short straight section (SSS). All SSS cold mass prototypes have been developed and built by CEA (Saclay) in collaboration with CNRS (Orsay, France). The last SSS prototype (SSS5) was used to investigate the behavior of the magnetic axis through various steps of the installation cycle for the series quadrupoles: including transportation, thermal-cycles, and being lowered into the tunnel. Results of extensive measurements before and after each of these stages are presented here, showing that the effect of transport is weak and within the window of measurement resolution. Also shown is that the long-term stability observed during two years is comparable with the requirements from magnet tolerances. To minimize systematic errors, all tests were performed with two independent measurement systems: single-stretched wire (SSW) and automated scanner. A brief description of these systems is given, concentrating mostly on their accuracies. In addition, establishment of a reliable cold-warm correlation for the magnetic axis position is a very important issue because it can reduce the percentage of cold tests. Though this correlation will be based on proper statistics at the beginning of series production, magnetic axis behavior during thermal-cycle has been investigated for the SSS5 prototype, and these results are also presented.

Pressure Losses and Flow Maldistribution in Ducts with Sharp Bends

Pipelines and ducting systems used in process industry applications are characterized by large sizes, sharp bends and successive bends connected by short straight sections. Systematic studies of such flow situations have not been reported in the literature and the design of such ducting systems is based on rules of thumb and scaled-model testing. Taking advantage of the potential size-insensitivity of CFD-based calculations, a large number of calculations of typical flow situations has been carried out in the present study to address such issues as the optimum location of guides vanes, the influence of an upstream bend on the loss coefficient and the scaling laws for proper extrapolation of laboratory results to industrial scale applications. It is shown that the ideal radial location of a vane for a square duct is given by (RiRo)0.5 and that the influence of an upstream bend on the loss coefficient is beneficial in most cases. Thus, the calculation of bend losses treating each bend as being isolated is likely to be conservative. The velocity profile is uniformly improved by the use of vanes. The loss coefficient is not very sensitive to the fluid scaling, but the effect of wall roughness has to be considered carefully in scaled-down conditions.

Numerical calculation of neutron fluxes at the exit of a complex neutron-guide system at IRI, Delft

A numerical method of calculation of the neutron flux for a complex guide system is described. A feature of the given calculation method is the “short section approximation” based on dividing the guide into many short straight sections, which simplifies the ray-tracing algorithm and the input of the complex geometry parameters into the calculation program. The accuracy of the numerical method is discussed. This method was used for the calculation of the neutron flux at the exit of a new neutron guide system at the Interfaculty Reactor Institute of the Hoger Onderwijs Reactor. Calculations showed that to minimize flux losses to 50% it is necessary that the reflectivity of a NiMo/Ti supermirror ( m=2) at twice the critical angle of nickel should not be lower than 90%. The mean step between channels of the neighbouring optical sections should not exceed 0.02 mm and the waviness of the optical section walls should not exceed 0.5 mrad. The measured flux intensities at the exit of the neutron guide system showed quite a good correspondence to the calculated values.

A system for series magnetic measurements of the LHC main quadrupoles

More than 400 twin aperture lattice quadrupoles are needed for the Large Hadron Collider (LHC) which is under construction at CERN. The main quadrupole is assembled with correction magnets in a common cryostat called the Short Straight Section (SSS). We plan to measure all SSSs in cold conditions with an unprecedented accuracy: integrated gradient of the field within 150 ppm, harmonics in a range of 1 to 5 ppm, magnetic axis of all elements within 0.1 mm and their field direction within 0.2 mrad. In this paper we describe the automatic measurement system that we have designed, built, and calibrated. Based on the results obtained on the two first prototypes of the SSSs (SSS3 and SSS4) we show that this system meets all above requirements.

DEPOSITION OF CESIUM IODIDE PARTICLES IN BENDS AND SECTIONS OF VERTICAL PIPE UNDER SEVERE ACCIDENT CONDITIONS

A relatively small-scale aerosol deposition experiment (called WAVE) in a quartz glass pipe with a 90° bend followed by a short straight section was performed at Japan Atomic Energy Research Institute to investigate the effect of pipe orientation on the cesium iodide (CsI) aerosol deposition. In these basic configurations, the section after the bend was either horizontal, upward and downward, respectively. The upward case showed 5 and 10 times larger CsI mass deposition in the vertical section of pipe than the horizontal and downward configurations, respectively. The experiments were analyzed by coupling a three-dimensional fluid-dynamic and an aerosol behavior codes. The calculations were in reasonable agreement with the measured aerosol mass deposition except for the upward case because the principal CsI deposition mechanism is thermophoresis which depends on the thermal gradient in gas and the gradient was well predicted by the fluid-dynamic code. In order to better predict the deposited mass in vertical section of upward case, Nusselt number which is used for thermophoretic deposition calculation had to be reevaluated carefully by considering the effect of secondary free convection in the vertical pipe which flowed opposite to the main stream.

Status of the 2.5 GeV storage ring ANKA

Ångström Source Karlsruhe (ANKA), a new 2.5 GeV synchrotron light source, is under construction at the Research Center Karlsruhe, Germany (FZK) [1]. This source is dedicated to the fabrication of microstructures (LIGA-technique) and X-ray analysis. It has a circumference of 110.4 m and an emittance of 50 nm rad can be reached. ANKA has four long (6 m) and four short (2.2 m) straight sections. One short section hosts the injection, two the RF cavities. One short section and the four long sections are then free for installation of insertion devices. The injector is a 53 MeV microtron and a 500 MeV booster synchrotron with a repetition rate of 1 Hz.

Construction of the new prototype of main quadrupole cold masses for the arc short straight sections of LHC

Each cold mass of the short straight sections in the eight LHC arcs will contain a 3.25 m long twin aperture quadrupole of a nominal gradient of 223 T/m. This magnet will be aligned in a 5.3 m long inertia tube together with auxiliary magnets on each end. On the quadrupole connection end either a pair of 38 cm long octupole or trim quadrupole magnets will be mounted, on the other end there will be combined sextupole-dipole correctors with a yoke length of 1.26 m. The powering of the main quadrupoles will be assured by two pairs of copper stabilized superconducting bus-bars placed inside the cold mass next to the bus-bars for the main dipole magnets. Each of the two quadrupole apertures will be connected to its quench protection diode. The construction of three prototypes has been entrusted to the CEA/Saclay laboratory, in the frame of the special French contribution to the LHC project. The first cold mass prototype has been completed and warm-measured for its multipole content at CEA. The second cold mass is presently under completion. The paper reviews the experience with the development of the quadrupole coils and cold mass construction and gives the results of the first warm magnetic measurements. An outlook for the series manufacture of the 400 are quadrupole magnets and their cold masses for the LHC machine completes the report.

Improvement of the beam quality by chromaticity correction for wavelength shortening in the NIJI-IV FEL

Electron-beam qualities improved by chromaticity correction in the storage ring NIJI-IV were investigated at the beam energy of 309 MeV. Sextupole–quadrupole–sextupole (SQS) magnets, which were installed in all of the short-straight sections in NIJI-IV, perfectly corrected a horizontal and a vertical chromaticity. This improvement suppressed a head–tail instability, so that higher beam current (∼30 mA) and higher peak-electron density (∼6×10 16 m −3) were available for FEL experiments. The maximum FEL gain was estimated to be about 2.5% at a wavelength of 240 nm. The lasing of an FEL around 300 nm was achieved in March 1998, and the lasing of an FEL at around 240 nm was successfully observed in May 1998. The shortest wavelength of FELs with the NIJI-IV FEL system was 228 nm.

Local Heat/Mass Transfer Characteristics in Rectangular Ducts with a Sharp 180-Deg Turn. Influence of Flow-Inlet Condition.

Heat/mass tranfer characteristics in rectangular cross-sectioned serpentine ducts with a sharp 180-degree turn have been measured by the naphthalene sublimation method, directing special attention to the influence of the flow-inlet condition on the local mass transfer. The test duct has relatively short straight sections, (7.9∼9.1) dh, before and after the turn. Two contrasrive flow-inlet conditions, contracted-flow inlet and uniform-flow inlet, have been tested for three turn clearances at Reynolds number of 3.5×104. The distributions of local Sherwood numbers on all walls of the test ducts are shown in the form of 2-D maps. In the straight section before the turn, the influence of the flow-inlet condition on the local mass transfer characteristics appears very clearly. After the turn section, the local mass transfer is also influenced by the flow-inlet condition in a duct with a large turn clearance. As the turn clearance is decreased, however, the influence of the flow-inlet condition becomes weaker.

Design, fabrication and cold tests of a superferric octupole corrector for the LHC

In the correction scheme of the LHC it is planned to install octupole corrector magnets in the short straight section of the lattice. Initially these correctors were distributed windings on the cold bore tube nested in the tuning quadrupoles. The latter being suppressed a new compact superferric design was chosen for the octupole prototype, suitable for a two-in-one configuration. This prototype was designed by CERN and CEDEX/Spain, built at INDAR/Spain and tested at CEDEX. The paper reports on the design of the prototype, describes the fabrication and assembly and presents the measurement results. Special interest has been taken to design a simple and compact magnet, easy to fabricate and training free below nominal field. First results show the feasibility of the solution which will be finally confirmed by magnetic measurements.

A high field superconducting wiggler for MAX-lab at Lund, Sweden

A three-pole superconducting wiggler magnet comprising six racetrack NbTi coils kept together by iron yokes has been built and is being tested. The magnet will be installed in a 1.5-GeV electron storage ring at the University of Lund (Sweden) in order to achieve X-rays in the 1-3-AA domain. After 11 quenches the central flux density is 4.4 T, which is about 60% of the design value. The helium evaporation is below 5 l/h. The magnet geometry is based on 3-D field calculation with a specified period length below 240 mm. An adjustment current of the side coils ensures a zero integral over the whole field range. Due to the short available straight section in the storage ring, the total system length, i.e., including the cryostat, is limited to 900 mm. >

Lasing in visible of a storage-ring free electron laser at ETL

Lasing at 598 nm of a storage-ring free electron laser (FEL) has been observed at the Electrotechnical Laboratory (ETL), though the output power was weak because of the low gain due to the short straight section of the ring. The storage ring was operated in a 3-bunch mode at 230 MeV instead of a full 18-bunch mode. Coherent instabilities of the stored electron beam was suppressed by exploiting a Landau cavity with the 2nd harmonic of the ring frequency 171.62 MHz. The beam current during the oscillation ranged from 5 mA to 3 mA per bunch. A 1.47 m optical klystron consisting of NEOMAX-35 permanent-magnet blocks has been used to enhance the FEL gain. The number of periods (76 mm) in a usual-undulator section is eight. The round-trip cavity loss of dielectric multilayer mirrors, separated by 5.238 m, was measured to be about 2×10 −4. The laser linewidth was about 0.3 nm, and the peak FEL output power was deduced to be at least 10 mW from a rough measurement.

The flow field and heat transfer near a turbulator

A detailed two dimensional numerical study of the fluid flow and heat transfer near a single turbulator within a short straight section of a turbine blade internal cooling passage is described. Axial distributions of local skin friction, Stanton number and Nusselt number are given, as well as profiles of velocity and temperature and contours of streamfunction. The numerical results are found to compare favorably to the experimental results published by Han et al [1].