11.12.2003 AB-CO TC / J. Wenninger 1

MCB orbit correctorsMCB 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 !

11.12.2003 AB-CO TC / J. Wenninger 2

CrowbarCrowbar

In case of PC failure the magnet is shorted and discharged through a crowbar.

Time constants :

without crowbar 85-130 seconds

with crowbar 30-35 seconds - mostly due to 100 mresistors

11.12.2003 AB-CO TC / J. Wenninger 3

RemediesRemedies

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 !

11.12.2003 AB-CO TC / J. Wenninger 4

Can we remove 1 or both crowbar resistors ?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.