TRACING BACK MEASURED MAGNETIC-FIELD IMPERFECTIONS ISN LHC MAGNETS BYMEANS OF THE INVERSE PROBLEM APPROACH

After measuring the magnetic field of a model or prototype superconduc ting magnet for the Large Hadron Collider (LHC) an inverse field probl em is formulated in order to explain the origin of the content of unwa nted multipole terms. The inverse problem solving is done by means of a least-squares minimization using the Levenberg-Marquard algorithm. A lthough the uniqueness of the results remains uncertain, useful insigh ts into the causes of measured field imperfections can be deduced. A m odel dipole magnet, a main quadrupole prototype and a combined dipole- sextupole corrector magnet are given as examples.