Mechanical design and characteristics of a superconducting insertion quadrupole model magnet for the Large Hadron Collider

Abstract ---A superconducting insertion quadruple is being developed by KEK in collaboration with CERN for the Large Hadron Collider (LHC) project. The mechanical design of the magnet in which the pre-stress is applied to the coil through thin stainless steel collars inside the yoke, the two halves of which are held together by means of keys, has been validated experimentally by measurements on a short model. The 140 mm long model was assembled from real magnet components in order to simulate the magnet assembly and to evaluate the change in coil pre-stress during assembly and cool-down. A new technique using capacitance pressure transducers was used, which has enabled measurements of the stress distributions in the coil with high accuracy. This paper describes the mechanical design of the quadrupole magnetand results obtained from the short mechanical model. I. I NTRODUCTION A cooperative program to develop the low-β quadrupole magnetshas been established between KEK and CERN as part of the Japanese contribution to the LHC accelerator project which is being built at CERN [1-5]. KEK will provide half of the 32 quadrupole magnetsrequired for the inner triplets. These quadrupolesare key components that are necessary for strong focusingof the high energy proton beams and high luminosity collisions in the physics experiments. The main design goal for the magnet is to provide a field gradient of 240 T/m in a coil aperture of 70 mm, corresponding to a nominal operational field gradient of 200 to 205 T/m at 1.9 K with a superconductor load lineratio of not more than 80 %. The lost particle showersfrom the colliding beams will deposit a power of several watts per meter into the coil windings, and this has to be allowed by the coil design. The design optimization has been based on the use of NbTi superconductor cooled with pressurized superfluid helium at 1.9 K. In this paper, we discuss the reasons for building and testing of a140 mm thick “slice” of the straight part of the quadrupole, shown in Fig. 1, and describe the assembly of the mechanical short model.. The “slice” was built using real magnet components, and was instrumented with capacitance pressure transducers [6]. The model was assembled and cooled to liquid nitrogen temperature. The internal coil pressures were measured and the results compared with the design values [3]. Finally, we compare two techniques of coil modulus measurements, and comment on the choice of the material for the yoke, which has to provide support for the assembly and magnetic forces.