Design of the superconducting quadrupoles for the LEP200 low-beta insertions

The low-beta insertions in the LEP (Large Electron-Positron Collider) have been instrumental to the initial success of this machine. The most powerful focusing elements of the insertions are the eight 2-m-long superconducting quadrupoles embedded into either side of the four experiments. Over the next years, the LEP200 project will take the machine energy up to above 90 GeV, requiring that the final quadrupoles be strengthened. New quadrupoles have been designed for this purpose, and an order placed with industry for their fabrication. Thanks in part to the higher-performance NbTi conductor now available, it has been possible to retain the external dimensions of the present units. Nevertheless, in order to achieve the required 50% increase in integrated gradient, a number of significant changes have had to be made to the design of the magnet itself. The authors describe the magnetic and mechanical design of the new 60 T/m 120 mm diameter warm bore quadrupoles for the LEP200