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Optics Studies for the Cern Proton Synchrotron: Linear and Nonlinear Modelling Using Beam Based Measurements
| Content Provider | Semantic Scholar |
|---|---|
| Author | Giovannozzi, Massimo Martini, Marcello |
| Copyright Year | 2003 |
| Abstract | The CERN Proton Synchrotron machine is built using combined function magnets. The control of the linear tune as well as the chromaticity in both planes is achieved by means of special coils added to the main magnets, namely two pole-face-windings and one figure-of-eight loop. As a result, the overall magnetic field configuration is rather complex not to mention the saturation effects induced at top-energy. For these reasons a linear model of the PS main magnet does not provide sufficient precision to model particle dynamics. On the other hand, a sophisticated optical model is the key element for the foreseen intensity upgrade and, in particular, for the novel extraction mode based on adiabatic capture of beam particles inside stable islands in transverse phase space. A solution was found by performing accurate measurement of the nonlinear tune as a function of both amplitude and momentum offset so to extract both linear and nonlinear properties of the lattice. In this paper the measurement results are presented and the derived optical model is discussed in detail. PS LATTICE AND MAIN MAGNET The PS lattice consists of ten super-periods each made of ten combined function magnets 4.4 m long, interlaced with eight 1.6 m and two3.0 m drift spaces [1]. Every magnet is composed of two half-units, each made of five blocks with small gaps in between, with gradients of opposite sign ( |G| = 5.2 T/m), separated by a central junction. The control of the tunes and chromaticities is obtained by means of the three currents of the pole-face winding and figure-of-eight loop devices located on the magnet poles. As an example, the layout of a PS magnet unit in the extraction region is shown in Fig. 1. The latest PS magnetic field measurements using Hall probes were undertaken in 1992 [2] for different settings of the currents in the main coil, pole-face and figure-of-eight loop windings. The data of the vertical field, including measurements of the central field, the end and lateral stray fields, as well as the field in the junction between the two half-units, produced a discrete 2D field map [2]. The field measurements were carried out in a Cartesian co-ordinate frame (see Fig. 1 for its definition). In this reference system a regular mesh is defined and for each point in the mesh the value of By was measured in the median plane. The step size is 20 mm along the longitudinal zaxis and 10 mm along the radial x-axis. The mesh extends from −2.55 m to 2.73 m and from−70 mm to 310 mm in the longitudinal and radial directions respectively. As an example, the fitted 2D field map for the 26 GeV/c working point is shown in Fig. 2 (see Ref. [3] for more details). When the effect of the additional coils is taken into account, Figure 1: Layout of the PS magnet unit 16 (upper part). The vacuum pipes for both the circulating beam and the extracted one are visible. The cross sections of the entry face (open gap) and exit face (closed gap) are shown on the lower left and lower right respectively. nonlinear field components have to be considered. Multipolar components may be derived from the measured field map to model the machine lattice. However, they hold only for the specific set of currents in the pole-face and figureof-eight loop windings. Unfortunately, these values change according to the machine setting, thus a magnetic measurement is required for each new working point, which is not possible in practise. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://accelconf.web.cern.ch/accelconf/p03/PAPERS/RPAG012.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
