Results from a prototype permanent magnet dipole-quadrupole hybrid for the PEP-II B-factory

Abstract

We describe the construction of a prototype hybrid permanent magnet dipole and quadruple.The magnet consists of two concentric rings of SmzCol, magnetic material 5 cm in len&th. The outer ring is made of 16 uniformly ma&netized blocks assembled as a Halbach dipole and the inner ring has 32 blocks oriented in a similar fashion so as to &enerate a quadruple field. The resultant superimposed field is an offset quadruple field which allows us to center the field on the high-energy beam in the interaction region of the PEP-II B-factory. The dipole blocks are glued to the inside surface of an outer support collar and the quadruple blocks are held in a fixture that allows radial adjustment of the blocks prior to potting the entire assembly with epoxy. An extensive computer model of the magnet has been made and from this model we developed a tunin& al&orithm that allowed us to greatly reduce the n=3-17 harmonics of the ma&net.

Comparison of adjustable permanent magnetic field sources

“…Examples of applications where an adjustable permanent magnet assembly can be used are nuclear magnetic resonance (NMR) apparatus [6], magnetic cooling devices [7] and particle accelerators [8]. The flux density source designed in this paper is dimensioned for a new differential scanning calorime-ter (DSC) operating under magnetic field designed and built at Risø DTU [9], but the general results apply for any application in which a variable magnetic field source is needed.…”

Optimization and improvement of Halbach cylinder design

“…A Halbach cylinder is a long cylinder made of a magnetic material with a bore along the cylinder symmetry axis. The Halbach cylinder can be characterized by three parameters; the internal and external radii, r in and r ex respectively, and the length, L. The magnetic material around the bore is magnetized such that the direction of magnetization at any point is at an angle η = 2θ (1) from the vertical axis (4; 5). This arrangement means that a uniform field will be created across the bore in the vertical direction without creating, in the ideal case, any stray field outside the cylinder.…”

“…Configurations of permanent magnets that produce a strong homogeneous field in a confined region of space and a very weak field elsewhere are useful in many applications such as particle accelerators (1), nuclear magnetic resonance (NMR) apparatus (2) or magnetic cooling applications (3).…”

The magnetic properties of the hollow cylindrical ideal remanence magnet

“…For this design, the remanence is given by As can be seen, the norm of the remanence is uniform throughout the magnet, unlike the case of the ideal remanence magnets discussed above. The Halbach design has been used in a large number of applications including nuclear magnetic resonance (NMR) equipment [7,8], accelerator magnets [9,10], magnetic refrigeration devices [11,12] and medical applications [13]. For the Halbach cylinder, the magnetic flux density generated in the cylinder bore is given as [6] = ( )…”