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TY - CONF AU - Gupta, R.C. AU - Anerella, M. AU - Cozzolino, J.P. AU - Jain, A.K. AU - Muratore, J.F. AU - Wanderer, P. ED - Petit-Jean-Genaz, Christine ED - Arduini, Gianluigi ED - Michel, Peter ED - Schaa, Volker RW TI - Iron Shims outside the Helium Vessel to Adjust Field Quality at High Fields J2 - Proc. of IPAC2014, Dresden, Germany, June 15-20, 2014 C1 - Dresden, Germany T2 - International Particle Accelerator Conference T3 - 5 LA - english AB - This paper describes the development and demonstration of a novel technique of adjusting measured field quality at the design field in superconducting magnets. The technique is based on placing iron shims of variable stack thicknesses, variable width and/or variable length on the outer surface of the stainless steel shell at strategic locations. Since the shims are placed outside the helium vessel, adjustments can be made without involving major operations such as opening the helium vessel. It is a simple and economical technique which is suitable for long magnets with a fast turn-around. This allows one to reduce field errors well beyond the normal construction errors. The technique has recently been successfully applied in two 3.8 T, 80 mm aperture, 9.45 m long dipoles. These magnets were built at Brookhaven National Laboratory (BNL) for the APUL project (Accelerator Project to Upgrade the LHC) as a part of US contribution to LHC. The paper will present the design, measurement and adaptation of this technique which, when used in combination with the coil shims, produced near zero sextupole harmonic at high fields and small harmonics throughout the range of operation. PB - JACoW CP - Geneva, Switzerland SP - 2734 EP - 2736 KW - sextupole KW - dipole KW - operation KW - insertion KW - quadrupole DA - 2014/07 PY - 2014 SN - 978-3-95450-132-8 DO - 10.18429/JACoW-IPAC2014-WEPRI101 UR - http://jacow.org/ipac2014/papers/wepri101.pdf ER -