• M. Koratzinos, F.F. Bertinelli, Z. Charifoulline, K. Dahlerup-Petersen, R. Denz, C.E. Scheuerlein, R. Schmidt, A.P. Siemko, A.P. Verweij
  CERN, Geneva
• R.H. Flora, H. Pfeffer, J. Strait
  Fermilab, Batavia

At each in­ter­con­nec­tion be­tween LHC main mag­nets, a low-re­sis­tance sol­der joint must be made be­tween su­per­con­duct­ing ca­bles to pro­vide a con­tin­u­ous cur­rent path through the su­per­con­duc­tor, and be­tween the sur­round­ing cop­per sta­bi­liz­er to pro­vide a cur­rent path in case the cable quench­es. About 10,000 such joints exist in the LHC. An ex­ten­sive cam­paign has been un­der­tak­en to char­ac­ter­ize and map the re­sis­tances of both types of joints. All of the su­per­con­duct­ing cable splices were mea­sured using the en­hanced pro­tec­tion sys­tem of the LHC su­per­con­duct­ing cir­cuits. No high-re­sis­tance su­per­con­duc­tor splices were found above 3 nano-Ohms. Non-in­va­sive mea­sure­ments of the sta­bi­liz­er joints were made at 300K in 5 of the 8 sec­tors, and at 80K in 3 sec­tors. More pre­cise local mea­sure­ments were made on sus­pect in­ter­con­nects that were opened up, and poor joints were re­paired. How­ev­er, it is like­ly that ad­di­tion­al im­per­fect sta­bi­liz­er joints still exist in the LHC. A sta­tis­ti­cal anal­y­sis is used to place bounds on the re­main­ing worst-case re­sis­tances. This sets lim­its on the max­i­mum op­er­at­ing en­er­gy of the LHC, prior to a more ex­ten­sive in­ter­ven­tion.

• 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.

• R.J. Steinhagen, A. Boccardi, A.C. Butterworth, E. Calvo Giraldo, R. Denz, M. Gasior, J.L. Gonzalez, S. Jackson, L.K. Jensen, O.R. Jones, Q. King, G. Kruk, M. Lamont, S.T. Page, J. Wenninger
  CERN, Geneva

The LHC de­ploys a com­pre­hen­sive suite of beam-based feed­backs for safe and re­li­able ma­chine op­er­a­tion. This con­tri­bu­tion sum­maris­es the com­mis­sion­ing and early re­sults of the LHC feed­back con­trol sys­tems on orbit, tune, chro­matic­i­ty, and en­er­gy. Their per­for­mance – strong­ly linked to the as­so­ci­at­ed beam in­stru­men­ta­tion, ex­ter­nal beam per­tur­ba­tion sources and op­tics un­cer­tain­ties – is eval­u­at­ed and com­pared with the feed­back de­sign as­sump­tions.