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[en] Various permanent magnet arrangements to produce a uniform field for NMR tomography are discussed. Standard requirement is a full-body magnet with access diameter of at least 1 m and a non-uniformity of at most 100 ppm within a sphere of 0.5 m diameter. Magnet weight, material price and ease of construction are considered. The conclusion is that permanent magnet systems of reasonable weight and price produce a field of no more than about 0.2 T. A prismatic ferrite magnet design is proposed as the most feasible one. It generates a field of 0.15 T in a 1 m air gap, weighs 21 tonnes and requires about 800 thousand dollars worth of ferrite. (author). 1 ref.; 17 figs.; 2 tabs
[en] The first CBETA magnet to be made using the production run of permanent magnet wedges is the BDH magnet, a “half length BD” to be placed at the start of the first girder of the FFAG return loop. This magnet has identifier number 2731 and is shown in the picture below while being prepared for measurement.
[en] A compact Permanent Magnet Symmetric (PMS) lens which produces the axial magnetic field is studied. The proposed lens has no iron pole piece except for the return poles on both ends. It can produce the magnetic field on the axis more than the remanent field of the magnet material by the perpendicular field superimposition
[en] In this paper we investigate the torque performances of three prototypes of a magnetorheological clutch, whose operation is based on the relative movement of a permanent magnet with respect to a gap filled with magnetorheological fluid, are discussed. The clutch was already been presented by the authors in other papers. The analysed prototypes are based on the same layout and have different sizes (i.e. outer diameter and overall length). Two new performance indices are introduced to evaluate the clutch design, and are proposed as an alternative to the usually employed turn-up ratio for evaluating MR clutches and brakes. Measurements of the transmitted torque in different operating conditions were carried out on a purpose-built test bench. A brushless motor drove the primary shaft of the clutch, while the transmitted torque was measured by a torque-meters up to 1500 rpm. The experimental results are discussed and compared to those expected on the basis of simulations, showing a fairly good agreement. Some geometric parameters were found to have a great influence on the magnet shielding in the disengaged configuration. (paper)
[en] Hall thrusters are one of the most successful electric thrusters for space application that has been developed until now. The Plasma Physics Laboratory of the University of Brasília (UnB) has been developing a Permanent Magnet Hall Thruster (PHALL) for the Brazilian Space Program since 2004. Recently we have achieved important experimental results satisfying our initial goals of generating a force above 40 mN with powers around 620 W. We will discuss in this article possible applications of this thruster to nano and microsatellites with powers above 50 W. Meanwhile, a complete description is given of our present and future installations where the new thruster will be tested; taking advantage of our new 1.5 m diameter vacuum chamber (the old chamber had 0.5 m in diameter), which intends to test our thruster in the most realistic conditions, including mounting and testing on a 3U CubeSat structure, which is where we intend to start testing our thruster in a real mission in space. (paper)
[en] Response is given to various questions on alignment tolerances for the permanent magnet sextupoles (PMS's) in the damping rings. Consideration is given to rotational errors, strength/longitudinal placement errors, transverse placement errors, pitch/yaw or tilt errors, and harmonic field errors. Resulting error limits can be specified in terms of the maximum errors allowed in the distribution
[en] Helicon discharges are known for their ability to produce high densities of partially ionized plasma, their efficiency arising from an unusual mechanism of rf coupling. However, the requirement of a dc magnetic field has prevented their wide acceptance in industry. The use of permanent magnets greatly simplifies helicon sources, and arrays of small sources extend the use of helicons to the processing of large substrates. An eight-tube array was designed and constructed, and its density uniformity measured in a 53x165 cm2 chamber. Three innovations involved (a) the remote field of ring magnets, (b) a low-field density peak, and (c) rf power distribution. High-density plasmas uniform over large areas requires compatibility in all three areas.
[en] A Faraday isolator with a single magneto-optical element is constructed and experimentally tested. It provides the isolation ratio of 30 dB at an average laser radiation power of 650 W. These parameters are obtained by increasing the field intensity in the magnetic system of the isolator and employing a low-absorption magneto-optical element. (elements of laser devices)
[en] Highlights: • Impact on wind turbines due to fifth harmonic and sag content. • Converter topologies considered are two-level and three-level ones. • Controllers are based on PI and fractional-order methods. • New control strategy for the selection of output voltage vectors. • Balancing voltages in the DC-link capacitors. - Abstract: This paper deals with the computing simulation of the impact on permanent magnet synchronous generator wind turbines due to fifth harmonic content and grid voltage decrease. Power converter topologies considered in the simulations are the two-level and the three-level ones. The three-level converters are limited by unbalance voltages in the DC-link capacitors. In order to lessen this limitation, a new control strategy for the selection of the output voltage vectors is proposed. Controller strategies considered in the simulation are respectively based on proportional integral and fractional-order controllers. Finally, a comparison between the results of the simulations with the two controller strategies is presented in order to show the main advantage of the proposed strategy