Vertical Steering Research Articles

3D beamforming: Performance improvement for cellular networks

The beam pattern of a mobile communication base station has significant impact on the performance of a cellular network. Three-dimensional (3D) beamforming combines the horizontal beam pattern adaptation, as applied for beamforming and multiple input multiple output (MIMO) schemes, with a vertical antenna pattern adaptation. The recent availability of new flexible antenna techniques enables a fully dynamic antenna pattern adaptation which can be specified per resource block and user equipment (UE), and makes 3D beamforming practically feasible. This paper describes the basic principles of 3D beamforming, including the impact of downtilt adaptation on the physical layer as well as the potential of its combination with beam coordination involving the media access control (MAC) layer. Our investigations assumed the vertical main lobe of the beam pattern was geometrically pointed towards the UE. We discuss a number of different realization options and simulation results including a Bell Labs field trial with vertical beam steering. Using wireless systems with state of the art Long Term Evolution (LTE) signal format and including the lightRadio™ antenna array, our trials in the Stuttgart testbed verified the basic predicted properties and potential advantages of 3D beamforming.

Alternate phase focusing in sequence of independent phased resonators as superconducting linac boosters

Theoretical study of an alternate phase focusing (APF) structure, realized in a long chain of double gap quarter wave resonators, capable of accelerating heavy ions from 1.3 to $7\text{ }\text{ }\mathrm{MeV}/\mathrm{u}$ has been carried out. Mathieu-Hill stability analysis for the focusing periods consisting of independent resonators with phase variation satisfying square-wave law has been used to evaluate parameters such as the electric field and phase for the resonators. Furthermore, a smooth approximation method taking into account the acceleration in the linac has been employed to find out the rf bucket parameters (energy and phase width acceptance) of the focusing periods. Corroborative particle tracking (longitudinal and transverse) has been carried out using simulated 3D fields for double gap quarter wave resonators (QWR). Steering effects in QWRs over the period have also been studied. In one APF period, the individual phase of resonators changes sign resulting in a vertical steering kick in a particular direction, which is less as compared to the case where all the individual resonators operate in the same phase.

A preliminary study of the feasibility of using superconducting quarter-wave resonators for accelerating high intensity proton beams

The superconducting (SC) cavities currently used for the acceleration of protons at a low velocity range are based on half-wave resonators. Due to the rising demand on high current, the issue of beam loading and space-charge problems has arisen. Qualities of low cost and high accelerating efficiency are required for SC cavities, which are properly fitted by using SC quarter-wave resonators (QWR). We propose a concept of using QWRs with frequency 162.5 MHz to accelerate high current proton beams. The main factor limiting SC QWRs being applied to high current proton beams is vertical beam steering, which is dominantly caused by the magnetic field on axis. In this paper, we intend to analyze steering and eliminate it to verify the qualification of using QWRs to accelerate high intensity proton beams.

Animals in the administrative zoo: organizational change and agency autonomy in Germany

Although Germany does not figure among the ‘forerunners’ of managerial reforms of the public sector, it has a long tradition of agencies and non-departmental bodies at the federal level. Over time, the federal administration has developed into a highly differentiated ‘administrative zoo’ with a large number of species, questioning the image of a well-ordered German bureaucracy. The article addresses organizational changes among non-ministerial agencies during the past 20 years and ministry—agency relations, drawing on data from a comprehensive survey of the federal administration. The structural changes we observe are neither comprehensive nor planned; they are much more evolutionary than revolutionary, driven by sectoral policies and not by any overall agency policy, supported more by regulatory than by managerial reforms, and most of the changes are horizontal mergers or successions of existing organizations, while we find almost no evidence for hiving-off from ministries to agencies. At the same time, federal agencies report a lot of bureaucratic discretion, whereas they perceive substantial levels of ‘red tape’ due to administrative regulations. We also find that traditional, hierarchical modes of ministerial oversight are still dominating; only few agencies have performance agreements with measurable goals.Points for practitionersThe article will be of interest to practitioners concerned about the nature and direction of organizational change within government, especially about processes of horizontal and vertical differentiation and steering. It demonstrates that even in a highly developed and classical bureaucratic administrative system such as Germany there is and has for a long time been a large variety of governmental agencies that enjoy a considerable amount of autonomy. At the same time there is continuous change and adaptation to new circumstances, even though all this has very little to do with international modernization trends such as New Public Management or comprehensive agencification.

Design of a Multi-Element Corrector Magnet for the Storage Ring NewSUBARU

A design for a multi-element octupole-base corrector magnet is presented. The new corrector magnet will be installed in the electron storage ring NewSUBARU in place of vertical steering (skew dipole) magnets. The new magnet uses coil windings to produce the skew quadrupole, skew sextupole, normal octupole, and skew dipole fields. The skew dipole element is used to achieve vertical steering. The skew quadrupole and the skew sextupole elements are for the resonance correction. The normal octupole element is used to control the higher order dispersion function and the higher order momentum compaction factor. In this design the main coil is wound around the return yoke instead of the pole. We expect improvement of the beam lifetime and injection efficiency during normal operation as well as improved isochronism during extreme quasi-isochronous operation. In designing the magnet, careful consideration is given to field interference caused by a neighboring magnet, which is in close proximity to the corrector magnet. The magnetic field with field interference is calculated using OPERA-3D.

Vehicle steering returnability with maximum steering wheel angle at low speeds

In this paper, an analytical model with suitable vehicle parameters, together with a multi-body model is proposed to predict steering returnability in low-speed cornering with what is expected to be adequate precision as the steering wheel moves from lock to lock. This model shows how the steering response can be interpreted in terms of vertical force, lateral force with aligning moment, and longitudinal force. The simulation results show that vertical steering rack forces increase in the restoring direction according to steering rack displacement for both the inner and outer wheels. As lateral forces due to side-slip angle are directed toward the medial plane of the vehicle in both wheels, the outer wheel pushes the steering wheel in the returning direction while the inner wheel does not. In order to improve steering returnability, it is possible to increase the total steering rack force in both road wheels through adjustments to the kingpin axis and steering angle. This approach is useful for setting up a proper suspension geometry during conceptual chassis design.

Off-axis neutral beam current drive for advanced scenario development in DIII-D

Modification of the two existing DIII-D neutral beamlines is planned to allow vertical steering to provide off-axis neutral beam current drive (NBCD) peaked as far off-axis as half the plasma minor radius. New calculations for a downward-steered beam indicate strong current drive with good localization off-axis so long as the toroidal magnetic field, BT, and the plasma current, Ip, point in the same direction. This is due to good alignment of neutral beam injection (NBI) with the local pitch of the magnetic field lines. This model has been tested experimentally on DIII-D by injecting equatorially mounted NBs into reduced size plasmas that are vertically displaced with respect to the vessel midplane. The existence of off-axis NBCD is evident in the changes seen in sawtooth behaviour in the internal inductance. By shifting the plasma upwards or downwards, or by changing the sign of the toroidal field, off-axis NBCD profiles measured with motional Stark effect data and internal loop voltage show a difference in amplitude (40–45%) consistent with differences predicted by the changed NBI alignment with respect to the helicity of the magnetic field lines. The effects of NBI direction relative to field line helicity can be large even in ITER: off-axis NBCD can be increased by more than 30% if the BT direction is reversed. Modification of the DIII-D NB system will strongly support scenario development for ITER and future tokamaks as well as provide flexible scientific tools for understanding transport, energetic particles and heating and current drive.

Superconducting Combined Function Magnet System for J-PARC Neutrino Experiment

The J-PARC Neutrino Experiment, the construction of which starts in JFY 2004, will use a superconducting magnet system for its primary proton beam line. The system, which bends the 50 GeV 0.75 MW proton beam by about 80 degrees, consists of 28 superconducting combined function magnets. The magnets utilize single layer left/right asymmetric coils that generate a dipole field of 2.6 T and a quadrupole field of 18.6 T/m with the operation current of about 7.35 kA. The system also contains a few conduction cooled superconducting corrector magnets that serve as vertical and horizontal steering magnets. All the magnets are designed to provide a physical beam aperture of 130 mm in order to achieve a large beam acceptance. Extensive care is also required to achieve safe operation with the high power proton beam. The paper summarizes the system design as well as some safety analysis results.

Magnet system for the KEKB main ring

Abstract KEKB is a two-ring electron–positron collider with asymmetric energies of 8 and 3.5 GeV to study CP violation in B meson decay. In KEKB, there are 21 types of magnets; about 1600 in total. About 430 dipole and quadrupole magnets were recycled from TRISTAN, the preceding program. All quadrupole magnets are equipped with vertical and horizontal steering dipole magnets. The number of steering magnets is about 1700. There are 212 sextupole magnets, and all of them are fixed on remotely controlled movers to adjust their positions to the beam passage. All main dipole magnets have back-leg coils to steer beams precisely. All quadrupole and sextupole magnets are equipped with correction coils to have a capability for beam-based alignment. Also one-turn coils are installed as well to each magnetic pole of the main magnets to monitor the magnetic flux in the case of trouble. The magnetic field in all magnets was measured and its quality strictly checked. After field measurement, the magnets were installed and precisely aligned. A cooling water system and a power supply system for these magnets were constructed. Magnet design was started in 1994, and construction of the two rings was completed in November 1998. The parameters of the magnets and the construction of the KEKB magnet system are described. Some of the problems experienced during this construction work are also presented.

Correction multipoles for the high current operation of the Heavy Ion Synchrotron SIS

An upgrade program is under way to fill the Heavy Ion Synchrotron SIS up to the space charge limit at injection energy (e.g., 2/spl middot/10/sup 11/ Ne/sup 10+/ ions and 4/spl middot/10/sup 10/ U/sup 73+/ ions). One part of the program entails the construction of corrector multipoles for fine tuning of the synchrotron. Four normal quadrupoles are foreseen to compensate gradient errors of the 36 main quadrupoles in the ring, while eight skew quadrupoles will be used for the correction of tilt errors of the main quadrupoles. The skew quadrupoles will also be used to improve the multiturn injection efficiency, by linear coupling of the horizontal and vertical phase spaces. Two skew sextupoles will be provided to compensate sextupole components of the short, large aperture vertical steering magnets in the ring. Two technical restrictions had to be fulfilled. First, the space occupied by the correctors must be minimal. Therefore, the correction magnets will be constructed with a number of concentrically arranged multipole correction windings in the same magnet housing. Second, these magnets must be mounted around the beam line vacuum chamber, to avoid breaking the vacuum during their installation. Different possible configurations were investigated by computer simulation with respect to their field quality. Installation of the magnets is planned for the winter shut down of 2001/2002.

Environmentally adaptive sonar system

The vertical beamwidth of the received beam of a return signal of a sonar system is adaptively modified as a function of water depth, altitude and range. The received beam is also vertically steered as a function of altitude and is steered at least once prior to the adaptive modification of the beamwidth. The vertical aperture is thereafter grown as a function of range by increasing the number selected elements in the hydrophone array. This is achieved by dynamically controlling a vertical beamformer by controlling the number of elements selected and the vertical steering angle in response to sensors which provide, among other things, data as to water depth, altitude or sonar depth, platform dynamics, and sonar range/time.

Magnetic design of trim excitations for the Advanced Light Source storage ring sextupole

The Advanced Light Source (ALS) storage ring sextupole is a unique multi-purpose magnet. It is designed to operate as a sextupole with three auxiliary trim modes: horizontal steering, vertical steering, and skew quadrupole. A perturbation theory for iron-dominated magnets developed by Klaus Halbach (1969) provides the basis for this design. The three trim excitations are produced by violating sextupole symmetry and are thus perturbations of the normal sextupole excitation. The magnet was designed such that all four modes are decoupled and can be excited independently. This paper discusses the use of Halbach's perturbation theory to design the trim functions and to evaluate the primary asymmetry in the sextupole mode, namely, a gap in the return yoke to accommodate the vacuum chamber.

Simultaneous scanning of the revolver undulator and monochromator at BL-19A of the Photon Factory

The revolver undulator beam line BL-19A at the Photon Factory has been constructed to be dedicated to the solid-state research and laid out for photon energy from 20 to 250 eV. To cover a wide spectral range by the maximum intensity of a first harmonics of undulator radiation, the simultaneous scanning of the undulator magnet gap and the monochromator has been accomplished in the normal user beam time. A displacement of the positron beam induced by scanning the undulator magnet gap are corrected using vertical and horizontal steering magnets at both ends of the undulator. The degradation of the beamline by the high heat loading was considerably reduced by adopting SiC substrate mirrors and gratings.

Orbit distortion due to UVSOR wiggler

A three-pole wiggler with a maximum magnetic field of 4 T was installed in the UVSOR electron storage ring. The insertion effect on the tune and the closed orbit of the stored beam is not negligible. The measured tune shifts are in good agreement with the values estimated from results of the magnetic field measurement. Compensation of the vertical closed orbit distortion due to misalignment of coils of the wiggler was tried with a vertical steering magnet. However, compensation is not perfect at the maximum excitation level because the distance between the steering magnet and the wiggler is not sufficiently short.

Conversion of the SRS to a higher brilliance lattice (invited)

The SRS at Daresbury has been upgraded by the addition of quadrupoles which reduce the emittance by a factor of 15. In order to do this without disturbing the beamlines, all 16 straight sections were rebuilt. Additional sextupole and octupole magnets were included, as was additional pumping capacity. Completely new beam monitor and vertical steering systems have been incorporated. The SRS was shut down on 1 October 1986 and, after recommissioning, regular scheduled operation for users at the rate of nearly 6000 h per year has been in effect again since June 1987. Scheduled operation is at 2 GeV with the 5T wiggler operational. The gain in brightness is as expected. Maximum beam current at 2 GeV is now 280 mA. Beam lifetime is 20 h at 200 mA. Diffraction patterns of small angle scattering from muscle obtained with an electronic area detector show that with the improved brilliance, diffraction lines corresponding to spacings exceeding 15 000 Å can be clearly resolved. Work is about to start on the provision of a second superconducting wiggler with 6T field feeding five new experimental stations.

High-power steerable short-wave antennas

The theoretical study and model measurements on a high-power, steerable shortwave antenna covers a spherical reflector, a parabolic reflector, and a log-periodic switch-steerable-type antenna. The scale modeling facilities are described and the modeling results are presented. The spherical reflector gives reasonable good azimuth and elevation steering over the shortwave band from 5.8 MHz to 27 MHz. The parabolic reflector gives good azimuth steering, with higher gain but no vertical steering. The log periodic antenna provides a high-gain switch-steerable antenna suitable for over-the-horizon radar detection. >

Violation of Midplane Symmetry in Bending Magnets

Charged particle optics has traditionally been based on the concept of midplane symmetry. Accelerators, beamlines, and spectrometers are often midplane symmetric in their entirety. Departures from midplane symmetry are usually obtained by rotating midplane symmetric components about a longitudinal axis. Misalignments and magnet imperfections introduce non midplane symmetric components into a beam line. Vertical steering and correction of the effect of errors can be accomplished through the deliberate introduction of midplane symmetry violating components in bending magnets. We have worked out the equations of motion and derived the transfer matrix for bending magnets with small midplane symmetry violating field components. The solutions are linearized in the non midplane symmetric magnetic field components.

Computer simulation of spatial filtering of modes by vertical array steering and double symmetrical angles of sight in shallow water propagation

A method is proposed for angular filtering for a selected normal mode by means of a steered array. Examples are given for spatial filtering by a single angle of sight and by association of the symmetrical angle of sight. Calculations were made for the particular case corresponding to previous experiments. Identity between the spatial filtering by amplitude shading with functions of one of the normal modes and by electronic steering with phase-shifters is demonstrated. Possibilities for modal spectroscopy and adaptive filtering are investigated.

The Effect of Large-Scale Structures on the Stability of Coal-Face Steering

Simplified models of piecewise rigid support structures for power-loaders operating on longwall coal-faces are shown to be amenable to analysis by z-transform methods. Such analysis predicts that increasing sufficiently the length of the sub-sections of the structure (compared to the inherent delay within the vertical steering system of the machine) should stabilize the vertical steering of the entire coalface. Increasing the width of the structure to embrace more than two consecutive cut floors is shown analytically to eliminate the need for electronic tilt-feedback in control systems. In general terms, these analytical predictions are shown to hold good in detailed simulations of the system that eliminate the simplifications demanded by the analytical method. The general conclusion of the work is therefore that an increase in the size of support structure segments can potentially reduce the complexity of steering control systems. The size-increase must be substantial, e.g. to four to five times the size of conventional structures.

Modelling the Steering Characteristics of Coal Face Conveyors by Random Signal Testing

A quarter-scale model of a coal cutting machine and armoured flexible conveyor (a.f.c.) system is subjected to random signal testing in an attempt to fit a continuous elastic beam model to the piecewise rigid a.f.c. structure for vertical steering investigations. A roller track, over which the system is hauled at constant speed, is used to provide the random test signal and a systems identification package, SPAID, developed at Sheffield, used to generate the source signal noise and to compute the cross correlation functions relating input and output height profiles. An energy-minimising dynamic-programming model of the a.f.c. is used to guide the choice of experimental parameters.The results yield an equivalent elastic beam stiffness for the loose-coupled a.f.c. structure that is considerably less than that originally anticipated, thus reconciling the hitherto opposing predictions for steering system stability produced by discrete and continuous models. A.f.c. segments are shown to require considerable lengthening to stabilise simple analogue steering controllers.