Engineering of the Ags Snake Coil Assembly*

Foundation module, the complex helical cuts are produced in a more efficient manner. Also, since Pro/E can easily construct variable pitch helixes (see Figure 1) the process of creating the helical paths was greatly simplified. The paths produced in this manner were parametric, meaning they could easily be changed without the need to reconstruct them as the design evolved. A 30% Snake superconducting magnet is proposed to maintain polarization in the AGS proton beam, the magnetic design of which is described elsewhere [1]. The required helical coils for this magnet push the limits of the technology developed for the RHIC Snake coils. First, fields must be provided with differing pitch along the length of the magnet. To accomplish this, a new 3-D CAD system ("Pro/Engineer" from PTC), which uses parametric techniques to enable fast iterations, has been employed. Revised magnetic field calculations are then based on the output of the mechanical model. Changes are made in turn to the model on the basis of those field calculations. To ensure that accuracy is maintained, the final solid model is imported directly into the CNC machine programming software, rather than by the use of graphics translating software. Next, due to the large coil size and magnetic field, there was concern whether the structure could contain the coil forces. A finite element analysis was performed, using the 3-D model, to ensure that the stresses and deflections were acceptable. Finally, a method was developed using ultrasonic energy to improve conductor placement during coil winding, in an effort to minimize electrical shorts due to conductor misplacement, a problem that occurred in the RHIC helical coil program. Each of these activities represents a significant improvement in technology over that which was used previously for the RHIC snake coils. Figure 1. A technique was developed to construct the variable pitch cuts in the tube. Helical surfaces were constructed normal to a cylindrical surface and then intersected with that surface to produce the curves that define the helical portions of the grooves’ paths. Various techniques were used to develop the paths of the coil ends. The end curves along with the helical curves define the basic paths of the grooves (see Figure 2). These basic curves were then projected onto a larger cylindrical surface to produce the remaining curves required to define the variable crosssection sweeps. The completed cuts were then produced using the Pro/Engineer variable section sweep cut functionality (see figure 3). A PROCESS FOR MODELING AGS SNAKE HELICAL COILS Previously, helical coil grooves or blocks were created through a time-consuming process using CAD software. After defining the helical path of each groove, numerous cross-sections of the groove were constructed at intervals along the paths. All cross-sections were manually oriented normal to their helical path during construction. Surfaces were then lofted through these cross-sections and used to perform the cuts necessary to produce the grooves in the basic cylindrical part. This process made changes quite difficult. Where variable pitch helixes were required, separate helixes were constructed and joined. In the coil models all grooves were defined and created in this manner. A typical, completed coil tube produced using this process is shown in Figure 4. Since most of the geometry created using this process is parametric, design changes that would normally require extensive geometry modifications could frequently be accomplished by changing a single parameter, resulting in all subsequent geometry being automatically updated. In an evolving, iterative design such as this, considerable time has been saved as a result of these capabilities. With the use of Pro/Engineer, the process of creating variable pitch helical grooves changed dramatically. Using PTC’s Advanced Surfacing module with the Pro/E _____________________________ *Work supported by the U.S. Department of Energy under Contract No. DE-AC02-98CH10886. #[email protected] Paper submitted to The Particle Accelerator Conference, Portland, OR, May 12-16, 2003 BNL-71449-2003-CP Figure 5. AGS SNAKE COIL TUBE ANALYSIS A three-dimensional finite element structural analysis was done on the inner and outer coil support tubes for the AGS snake magnet to determine the stress and deflections in each tube under the Lorentz forces. A 30 inch long section from the center of each tube was used for the analysis. The calculated azimuthal pressures exerted by each coil block were scaled based on the percentage of the groove depth occupied by the coil windings. The resulting pressure for each block as indicated in Table 2 was applied the full sidewall of the groove. Both ends of the tube were completely constrained and the outside diameter of the tube was constrained in the radial direction. Material was assumed to be aluminum with a Young’s modulus of 10e6 psi. Results shown in figures 6 through 9 indicate a peak stress of 34000 psi for the inner tube and 13000 psi for the outer tube with maximum deflections of .0020 inches and .0016 inches respectively. Figure 2.