AB-CO TC / J. Wenninger1 MCB orbit correctors  There are 752 MCBH(V) SSS orbit corrector circuits.  Individually powered by a ± 60 A, ± 8 V converter.  PCs installed in the tunnel (radiation).  PCs are in production today.  The design MTBF is 100’000 hours   1 failure in operation every 100 hours.  Assuming ½ MCBs have significant kicks, we may get 1 MCB- induced beam loss per week due to our orbit tight tolerances !

AB-CO TC / J. Wenninger2 Crowbar In case of PC failure the magnet is shorted and discharged through a crowbar. Time constants :  without crowbar seconds  with crowbar seconds - mostly due to 100 m  resistors

AB-CO TC / J. Wenninger3 Remedies  The orbit FB could save the beam :  The FB must switch in a compensating scheme based on nearby correctors (or equivalent)  reduce effect to a local bump.  The FB must be informed rapidly – time scale of 1 second or less.  The circuit time constants should be as long as possible.  With the 2 crowbar resistors the situation is very tight…  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 !

AB-CO TC / J. Wenninger4 Can we remove 1 or both crowbar resistors ?  Meeting with all concerned parties (AB & AT) :  The crowbar resistors have no role in protecting the magnets. The magnets are self-protected.  Motivation behind resistors seems to be a shorter circuit discharge time.  PC tests performed without crowbar resistors by AB/PO indicate that the resistors can be removed.  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.