Multipole Errors Research Articles

Conceptual design of a 70 mm aperture quadrupole for LHC insertions

Due to their detrimental effect on the Large Hadron Collider (LHC) dynamic aperture, the random multipole errors of the LHC insertion quadrupoles need to be lower by a factor of five than the corresponding errors in the lattice. For achieving this level of random errors, the authors propose to increase the aperture of the insertion quadrupoles. A novel approach for achieving a quadrupole strength of 250 T/m in an aperture of 70 mm, based on a graded multilayer coil wound from NbTi conductor cooled at 1.8 K, has been investigated. The design concept of the coil, which incorporates a shell-like structure composed of a high current density block imbedded in a low density shell, is developed. The coil design, parameters of the superconducting cable, and the yoke and collar design are described, both for a two-in-one and a single quadrupole geometries. >

A beam tracking of a compact storage ring using superconducting bending magnets

The tolerances of imperfections of superconducting bending magnets in a compact storage ring have been estimated. The storage ring, which is under construction, is a race-tracked type with combined function bending magnets. A tracking code ‘‘providence,’’ which calculates a particle’s orbit with a numerical integration of exact equations of motion has been used. The results of calculating dynamic apertures with modelized three-dimensional (3-D) magnetic fields show that multipole errors must be suppressed with (sextupole errors) ≤20[T/m2], (octupole errors) ≤110[T/m3], where the dynamic aperture is defined as a stable amplitude area with nominal aperture limitation in this paper. The dynamic aperture with actual magnetic fields has been also calculated. The result shows that the superconducting bending magnets have enough good field regions, and that the ring has a sufficient dynamic aperture: ‖x‖≂30 mm and ‖y‖≂50 mm.

A general formalism for quasi-local correction of multipole distortions in periodic transport systems

We generalize a new concept of local correction of nonlinearities due to multipole content by giving it a mathematical description. We present a general method which allows for a general reduction of all the distortions produced by a given set of multipole errors. The method can be applied to correct an arbitrary distribution of multipole errors in any transport system, such as transport lines, linacs, synchrotrons and storage rings, and can solve formidable nonlinearity problems in such large transport systems as the SSC and LHC synchrotrons.

Random Errors in the Magnetic Field Coefficients of Superconducting Magnets

Random errors in the multipole magnetic coefficients of superconducting magnet have been of continuing interest in accelerator research. The Superconducting Super Collider (SSC) with its small magnetic aperture only emphasizes this aspect of magnet design, construction, and measurement. With this in mind, we present a magnet model which mirrors the structure of a typical superconducting magnet. By taking advantage of the basic symmetries of a dipole magnet, we use this model to fit the measured multipole rms widths. The fit parameters allow us then to predict the values of the rms multipole errors expected for the SSC dipole reference design D, SSC-C5. With the aid of first-order perturbation theory, we then give an estimate of the effect of these random errors on the emittance growth of a proton beam stored in an SSC. 10 refs., 6 figs., 2 tabs.