Pole Face Windings Research Articles

The Magnet Design Study for the FFAG Accelerator

The required magnetic field for the fixed field alternating gradient (FFAG) accelerator is proportional to the k-th power of the orbit radius where k is the field index of the accelerator. Although the field is constant in time, the design of the magnets is more difficult than that of the conventional synchrotron due to the intrinsically nonlinear field. There are several ways to design the FFAG magnet. The "iron pole shape" makes the field by changing the pole gap size along the radius, which is the most conventional and suitable for the compact FFAG. Another way is a "pole face winding" where the field is produced by distributing the coil current along the radius. Although it is a challenging design, a large and high field FFAG is feasible. The third one is a "multipole combination" in which the magnetic field is generated by combining the multipole components of the fields. This could be applied to superconducting magnets. The FFAG has the potential for various applications, and the magnet design of the FFAG should be selected properly for each application.

Superconducting magnet design for Fixed-Field Alternating-Gradient (FFAG) accelerator

The FFAG accelerator requires static fields that increase with radius along the accelerator midplane according to B=B/sub 0/(R/R/sub 0/)/sup 13.4/. The field is generated by equally spaced magnets around the circumference and varies from a maximum of 4.1 T to a minimum of -1.9 T. The general coil design employs cryostable magnets wound with aluminum stabilized superconductor. Each magnet has resistive pole face windings outside of the cryostat to allow for field fine tuning after construction. A set of iron-free coil windings generate the required field distribution.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radial Damping by Octupole for ZGS Beam

Landau damping by the octupolar tune spread is used to prevent the radial blowup of the beam during the acceleration cycle. The octupole field is produced by a set of pole face windings in the ring magnets. The strength of the octupole field, which is controlled by the Zero Gradient Synchrotron (ZGS) programmer, is set to give a tune profile of ?X = 0.83 + 0.008 × a2, where a is the radial coordinate of the aperture in unit of cm. The radial damper feedback system, which has been operating for some years, has been replaced by this octupole, and the radial stability is remarkably improved by the new system.

Pole Face Winding (PFW) Equipment for Eddy Current Correction at the Zero Gradient Synchrotron (ZGS)

The titanium vacuum chambers installed in the ZGS this past summer were equipped with PFW's. In this paper, the operation and monitoring of the windings used to flatten the guide field in the ZGS will be described. The physical and electrical characteristics of the system will be discussed along with a computer program which calculates the magnetic field shape in the vacuum chamber as a function of PFW current and other machine parameters.

The Program Used to Retune the Zero Gradient Synchrotron (ZGS) after the Installation of a New Vacuum Chamber and Pole Face Windings

The Program Used to Retune the Zero Gradient Synchrotron (ZGS) after the Installation of a New Vacuum Chamber and Pole Face Windings

Extension of the CERN ISR Energy by Acceleration of Stacked Beams

The proton beams in the CERN Intersecting Storage Rings (ISR) have been accelerated to achieve colliding beams at 31.4 GeV/c, equivalent to a momentum of above 2000 GeV/c if a conventional accelerator with a stationary target were used. High density stacks were made at 26.5 GeV/c from which a part was rebunched with the maximum available RF voltage. The rebunched beam was kept near central orbit while the magnetic field was gradually increased to its maximum value. The major problem was to keep the betatron oscillation frequencies unchanged while changing the magnetic field thus avoiding any blow-up of the beam due to resonances. The corrections of the highly non-linear saturation effects of the main magnet were achieved by a computer controlled tuning of the field by excitation of the poleface windings and sextupole lenses. Closed orbit corrections were applied throughout the acceleration. Colliding beams with currents above 0.5 A were obtained.

The Computation of Poleface Winding Systems Yielding Independent Multipole Fields within the Aperture of Notably Alternating Gradient Synchrotron Magnets

The 28 GeV Proton Synchrotron of CERN (CPS) is now 15 years old. Initially planned as an accelerator for 25 GeV physics, the CPS is developing into the key element of an accelerator complex comprising recently built machines such as the 28 GeV Intersecting Storage Rings (ISR), the 800 MeV PS Booster (PSB), and the 300 GeV SPS now under construction.

Measurement of the Titanium Vacuum Chamber Eddy Current Fields and Pole Face Winding Corrections for the Zero Gradient Synchrotron (ZGS)

The titanium vacuum chambers (TVC) which will be installed in the ZGS are equipped with pole face windings for correction of the eddy current fields. A prototype of the chamber and correction windings has been installed in a spare magnet block test fixture for measurement of the eddy current fields as a function of radial position and time. The ten difference signals from 20 test coils are read into a SEL-810A computer. The computer displays the measured gradient on a scope, either as a function of radial position at a selected time during the magnet pulse or as a function of time at a selected position. Thus, the result of applying compensating pulses to the pole face windings can be shown directly.

The Titanium Vacuum Chamber for the Zero Gradient Synchrotron

An all metal, titanium alloy inner vacuum chamber has been built for the Zero Gradient Synchrotron (ZGS). This chamber has high radiation resistance, high mechanical strength, and provides mountings for pole face windings. The upper and lower surfaces of the chamber consist of 0.012 titanium skins which span the 32 aperture along the 54' length of the octant. These skins are reinforced with radial T-shaped ribs 3/8 high to withstand the design loading of 30 torr. The 20 miles of titanium ribs are diffusion bonded to the skins to provide high strength joints without welding. Eddy-current problems are minimized by using an alloy of high electrical resistivity. Pole face windings mounted in holes in the ribs will be used to correct the effects of the residual eddy currents. Many of the new techniques that were developed for aerospace applications were used to produce and test this chamber. These techniques and the results of the tests will be discussed.

Untersuchungen für ein FFAG-elektronensynchrotron vom radialsektortyp (endenergie um 150 MeV) VIII. Das magnetische Führungsfeld

Zusammenfassung For a FFAG-accelerator the realisation, measuring and correcting of the magnetic guiding field is described. The shape of the pole faces and the form of the pole face windings are given by the magnetic scalar potential. Three methods for calculating the equipotential surfaces are given and the influence of the azimutal field distribution on the form of the equipotential surfaces is investigated. Model magnets scaled 1:2.5 and the measuring equipment are described. The magnetic field errors and the methods for correcting the field are discussed. Based on this model experiments the parameters for an 1:1 magnet are set up. One result of the discussion of these parameters is that the magnet with vertical yokes for the return flux (Sector-magnet) has advantages compared to the magnet with horizontal yokes (Ringmagnet).

The external electron beam of the frascati electron synchrotron

The beam extraction from the Frascati electron synchrotron has been accomplished by exciting the\(\nu _r = \frac{2}{3}\) nonlinear betatron resonance. The second harmonic pattern of the «sextupolar» perturbation in the guiding field which is required to bring the radial oscillations into resonance is introduced by pulsing currents into few wires of the pole face windings of the four quadrants, connected in a loop. In this way the beam is brought into a two-magnet with septum deflecting channel and escapes completely from the magnetic field. The extraction channel is described; the preliminary characteristics of the external beam, the results of measurements on the extraction efficiency and the spill-out times obtained are presented.

Pole Face Windings in the Todai AG Electron Synchrotron

Pole face windings were applied to the Todai AG electron synchrotron to avoid an integral resonance line of betatron oscillations and increase the energy of accelerated electrons which would be lost at 98 MeV. Magnetic fields produced by the pole face windings were calculated by the use of a linear transformation and of an image method, and wee compared with the value measured to give good agreements. The locus of the frequency of the betatron oscillations in the stability pattern was also analysed when the pole face windings were applied, and was compared with experiments. With a rather small power supply, the electron energy of 135 MeV has been obtained.

Resonant Extraction from the 1 GeV Frascati Electron Synchrotron

The 1000MeV electron beam has been extracted from the Frascati Constant Gradient Synchrotron (t) on February 11, 1965 by exciting the 2 radial betatron oscillations/3 revolutions resonance (2). The first successful extraction ~rials were made at 400MeV on November 23, 1964. In this method, pulsed currents are fed at the end of the acceleration cycle into few wires of the pole face windings, connected in a noninduetive loop (see Fig. 1), in order to obtain the eight regenerative (~ • regions~> of ref. (2). This perturbation is strongly nonlinear: the corresponding ABz(x) variat ion is represented in Fig. 2.

General description and operating characteristics of the Berkeley 88-inch cyclotron

The Berkeley 88-inch cyclotron is a variable-energy spiral-ridge machine with an electrostatic deflector for beam extraction. This accelerator was designed to satisfy the needs of the nuclear chemistry and low-energy physics groups, for variable-energy beams of a variety of ions. It will accelerate protons up to 50 MeV, douterons up to 65 MeV, and heavier ions up to corresponding energies. The machine is expected to produce an external beam of 100 to 200 μA. The r.f. has a frequency range of 5.5 to 16.5 Mc/s and a working voltage of 70 kV, dee to ground. The single-dee construction permits operation on the third harmonic mode, which in effect gives another factor of 3 in frequency range. The magnet has three flat hills on each pole, which produce a maximum magnetic-field spiral angle of approximately 55 deg. The iron gap between hills is 7.5 in., between valleys, 11.8 in. The maximum average field is 17 kG, with an effective flutter of ± 3 kG. Pole-face windings are provided for trimming the magnetic field. The first internal beam was obtained in December 1961. Subsequent internal-beam studies with alphas at 12 kG (65 MeV) show a well-behaved beam out to full radius. The beam has not yet been extracted with the electrostatic deflector.

Calculation of cyclotron trim-coil currents for field optimization by linear programming methods

Determination of the current settings in the circular pole-face windings of fixed-frequency cyclotrons for optimization of the magnetic field may be solved with the mathematical technique of linear programming. The resulting fields are optimal with regard to particle phase lag as well as radial and vertical stability, and the currents do not exceed preassigned limits.

Pole-Face Windings. Part I—Design

At fields over 10 000 gauss the effects of saturation in the Cosmotron magnet cause deterioration of the field pattern which rapidly becomes serious enough to cause complete loss of the proton beam. This pattern can be restored adequately up to 14 000 gauss by passing current through single-layer windings on the faces of the magnet poles. Peak correction current required at 14 000 gauss is about 300 amp per radial inch of each winding. The pole-face winding returns are so arranged that the winding is almost completely decoupled from the main magnetizing winding. The windings and their power supplies are in place but are not yet energized. Several turns of the winding are used in a self-powered correction for the distortion of the magnetic median surface at injection fields.

Eddy-Current Phenomena in the Cosmotron

In the Cosmotron magnet, eddy currents in the half-inch laminations cause no serious effects except for a small increase in n value at injection time. This increase needs no correction since it is compensated by the reversed slope of the remanent field. Analyses of eddy-current effects in other metallic components of the Cosmotron are included, for example, in the pole-face windings and in the stainless steel vacuum chamber. Serious shifts in the magnetic median surface result from eddy currents that arise when either inner or outer vertical wall of the vacuum chamber is misaligned.

Pole-Face Windings. Part II—Fabrication

The pole-face windings, for correction of saturation effects in the Cosmotron magnet, were wrapped in Fiberglas tape and then cast in a polyester-resin laminate. The process of fabrication and the materials used for casting are described.

Equivalent circuits for the hunting of electrical machinery

UNTIL recently the study of damping torque has been confined to synchronous machines and rotary converters. Operation of these machines without hunting has been obtained by the use of properly designed amortisseur or pole-face windings.