A. P. AT-CRG, 21 October MP3 21 October 2009 Gas flow control valves for current leads brief overview A. Perin, TE-CRG

A. P. AT-CRG, 21 October CL gas flow control valves operation Electromagnetic proportional valves -Pulse width modulation command signal, no feedback, sensitive to DP - specified DP 50 mbar. Actual 150 mbar – 200 mbar In current setting, essentially on/off valve switching at 2% input signal. Expected for normal behaviour without tuning : oscillating around 2% Tuning of control electronics is possible to obtain a better regulation profile

A. P. AT-CRG, 21 October Quasi on/off operation (13kA Jan 2008) Current ramp to 9800 A

A. P. AT-CRG, 21 October Regulation in quasi on/off mode: 600A 51 K 49 K 4 % 2 % 30 min Cryostart: 46 < TT891 < 54 Cryomaintain: TT891 < 60 K

A. P. AT-CRG, 21 October A CL control valves operation: appearance of hysteresis due to friction Normal behaviour 5% - 7 % 30 %

A. P. AT-CRG, 21 October Effect of excessive hysteresis on temperature regulation (600A) Cryostart: 46 < TT891 < 54 Cryomaintain: TT891 < 60 K Valve with excessive hysteresis Valve with normal behaviour - Valve position - temperature - Valve position - temperature

A. P. AT-CRG, 21 October Findings and measures taken Findings of 2008 run - without specific tuning of the electronics the valves regulate essentially in on/off mode. All 2008 commissioning operation were performed in this mode. - in 2008 a small proportion (about 4 %) of the 600 A valves showed the appearance of increased hysteresis. - an investigation was lauched in collaboration with the manufacturer and the cause was traced to the presence of small metallic particles in the moving parts. - the particles appeared to have come from the the cryogenic piping (line D, etc.) - the corrective actions were to replace the defective valves with clean ones. This allowed continuous operation for several months. - also a small number (2%) of 6 kA regulation valves showed problems - leaky valves: all solved - difficult regulation: not all solved, 3 valves still impossible to regulate within required limits - some valves that were ok during tests in lab show non nominal behaviour! Measures taken: - all valves equipped with 40 microns filters ( 6KA and 13 kA equipped with 10 microns filters due to manufacturing error) - ordered 90 spare 600A valves and A piping assemblies. - all 600A valves were tuned for proportional operation Findings in may-june A valves are more sensitive due to the electronics tuning (but also smoother regulation) - several cases of valves that were failing even after having been cleaned. Thorough investigation led to the discovery of fine particles in some of the piping. Therefore all valves and piping are now cleaned intensively.

A. P. AT-CRG, 21 October Findings and measures taken Further findings - failure rate of uncleaned valves about 13% of valves corresponding to 53% of the 4-valves assemblies that were replaced with clean ones. All types of DFBs affected. - degradation observed also for cleaned and reinstalled valves (3.1 % to date, coresponding to 10% of 4-valves assemblies) Status - replacement capacity approx. 10 x 4 valves / week - 1 sector / week on average Current corrective strategy - when possible replace all 600A valves of a DFBA LCM (done in DFBAB,. DFBAI, DFBAA, DFBAP) - if not possible. Cure the defective valves only that do not allow the correct regulation of temperature. - intervene on demand for further failing valves. - replacement of valves requires the cryo and electrical consignation of the DFB (approx. 1 day total time including intervention) Possible corrective actions on 600A without replacing the valves: different tuning of electronics - change the command signal frequency: tested in DFBAD LCM (19.10), restored correct operation of 7 valves out of 8 - change back to on/off (2008 like) operation mode: tested in DFBAE (19.10), restored correct operation of 4 valves of of 4 - durability to be validated. Investigations continue towards long term reliable solution.