• F. Formenti, Z. Charifoulline, G.-J. Coelingh, K. Dahlerup-Petersen, R. Denz, A. Honma, E. Ravaioli, R. Schmidt, A.P. Siemko, J. Steckert
  CERN, Geneva
• SF. Feher, R.H. Flora, H. Pfeffer
  Fermilab, Batavia

Two events, oc­cur­ring in 2008 dur­ing com­mis­sion­ing of the LHC cir­cuits, lead to fun­da­men­tal changes to the scope of cir­cuit pro­tec­tion. The dis­cov­ery of aper­ture-sym­met­ric quench­es and the ac­ci­den­tal rup­ture at 9kA of an in­ter­con­nect­ing bus­bar re­sult­ed in an emer­gen­cy pro­gram for de­vel­op­ment and im­ple­men­ta­tion of new pro­tec­tion fa­cil­i­ties. The new scheme com­pris­es a dis­tribut­ed bus­bar su­per­vi­sion sys­tem with early warn­ing ca­pa­bil­i­ties based on high-pre­ci­sion splice re­sis­tance mea­sure­ments and sys­tem in­ter­locks for rapid de-ex­ci­ta­tion of the cir­cuit in case of a sud­den splice re­sis­tance in­crease. The de­vel­oped sym­met­ric quench de­tec­tors are dig­i­tal sys­tems with ra­di­a­tion-re­sis­tant FPGA logic con­trollers, hav­ing mag­net heater fir­ing ca­pa­bil­i­ties. This pro­gram suc­cess­ful­ly al­lowed a safe re-pow­er­ing of the col­lid­er. The con­cept of the new elec­tron­ics boards and the pow­er­ing mod­ules will be de­scribed. More than 14'600 extra ca­bles and 6'000 new de­tec­tor and con­trol cards were added to the ex­ist­ing QPS sys­tem. A first eval­u­a­tion of the sys­tem per­for­mance as well as a num­ber of in­ter­est­ing dis­cov­er­ies made dur­ing the com­mis­sion­ing will be pre­sent­ed.