MCB orbit correctors There are 752 MCBHV SSS

MCB orbit correctors Ø There are 752 MCBH(V) SSS orbit corrector circuits. Ø Individually powered by a ± 60 A, ± 8 V converter. Ø PCs installed in the tunnel (radiation). Ø PCs are in production today. Ø The design MTBF is 100’ 000 hours Ø 1 failure in operation every 100 hours. Ø Assuming ½ MCBs have significant kicks, we may get 1 MCBinduced beam loss per week due to our orbit tight tolerances ! 11. 12. 2003 AB-CO TC / J. Wenninger 1

Crowbar In case of PC failure the magnet is shorted and discharged through a crowbar. Time constants : Ø without crowbar 85 -130 seconds Ø with crowbar 30 -35 seconds - mostly due to 100 m resistors 11. 12. 2003 AB-CO TC / J. Wenninger 2

Remedies Ø The orbit FB could save the beam : Ø The FB must switch in a compensating scheme based on nearby correctors (or equivalent) reduce effect to a local bump. Ø The FB must be informed rapidly – time scale of 1 second or less. Ø The circuit time constants should be as long as possible. Ø With the 2 crowbar resistors the situation is very tight… Ø From MP point of view, the MCBs are slow enough even with crowbar resistors not to present a major problem. But the slow is beautiful for MP slower is better ! 11. 12. 2003 AB-CO TC / J. Wenninger 3

Can we remove 1 or both crowbar resistors ? Ø Meeting with all concerned parties (AB & AT) : Ø The crowbar resistors have no role in protecting the magnets. The magnets are self-protected. Ø Motivation behind resistors seems to be a shorter circuit discharge time. Ø PC tests performed without crowbar resistors by AB/PO indicate that the resistors can be removed. Ø Implications for electrical safety, since it takes then ~ 10 minutes for the current to go from 60 to below 1 A for the slowest elements. need a rapid decision since the PCs are in production. ECR will be prepared this week. 11. 12. 2003 AB-CO TC / J. Wenninger 4