• R. Denz, K. Dahlerup-Petersen, F. Formenti, K.H. Meß, A.P. Siemko, J. Steckert, L. Walckiers
  CERN, Geneva
• J. Strait
  Fermilab, Batavia

Prior to the re-start of the Large Hadron Collider LHC in 2009 the protection system for superconducting magnets and bus bars QPS will be submitted to a substantial upgrade. The foreseen modifications will enhance the capability of the system in detecting problems related to the electrical interconnections between superconducting magnets as well as the detection of so-called symmetric quenches in the LHC main magnets. The paper will describe the design and implementation of the new protection layers and report as well on the commissioning of the system and first operational results.

• J. Strait
  Fermilab, Batavia
• R. Bailey, M. Bednarek, B. Bellesia, N. Catalan-Lasheras, K. Dahlerup-Petersen, R. Denz, C. Fernandez-Robles, R.H. Flora, E. Gornicki, M. Koratzinos, M. Pojer, L. Ponce, R.I. Saban, R. Schmidt, A.P. Siemko, M. Solfaroli Camillocci, H. Thiesen, A. Vergara-Fernández
  CERN, Geneva
• Z. Charifoulline
  RAS/INR, Moscow
• P. Jurkiewicz, P.J. Kapusta
  HNINP, Kraków

The incident of 19 September 2008 at the LHC was apparently caused by a faulty inter-magnet splice of about 200 nOhm resistance. Cryogenic and electrical techniques have been developed to detect other abnormal splices, either between or inside the magnets. The quench protection system is used in a special mode to measure the voltage across each magnet with an accuracy better than 0.1 mV, allowing internal splices with R > 10 nOhm to be detected. Since this system does not cover the bus between magnets, the cryogenic system is used in a special configuration* to measure the rate of temperature rise due to ohmic heating. Accuracy of a few mK/h, corresponding to a few Watts, has been achieved. This allows detection of excess resistance of more than a few tens of nOhms in a cryogenic sub-sector (2 optical cells). Follow-up measurements, using an ad-hoc system of high-accuracy voltmeters, are made in regions identified by the cryogenic system. These techniques have detected two abnormal internal magnet splices of 100 nOhms and 50 nOhms respectively. In 2009, this ad-hoc system will be replaced with a permanent one which will monitor all splices at the nOhm level.

*L. Tavian, Helium II Calorimetry for the Detection of Abnormal Resistive Zones in LHC Sectors, this conference.