[Hallb-engineering] Engineering Meeting Tomorrow -- Apr. 20

[Saptarshi Mandal]

Hi All,

We will have an engineering meeting at the regular time tomorrow. People 
familiar with the control systems used in the hall should be present. 
Please read the email from Andy below.

Saptarshi

-------- Original Message --------
Subject: Eng mtg tomorrow-re epics failure and IBC magnet quench
Date: Thu, 19 Apr 2012 12:31:03 -0400
From: A.M.  Sandorfi<sandorfi at jlab.org>
To:<miller at jlab.org>
CC: Krister Bruhwel<bruhwel at jlab.org>, burkert<burkert at jlab.org>,
     David Kashy<kashy at jlab.org>, Christopher Bass<cbass at jlab.org>,
      "mlowry at jlab.org"  <mlowry at jlab.org>

Hi Bob,
I gather Dave is away tomorrow and in such circumstances the Engineering
meeting is often cancelled. Volker has asked that we hold at least a
mini-meeting, particularly with the people familiar with the control systems
used in the hall, to discuss what can be done to avoid another event like
last night when the epics signals froze and the helium supply was cut to the
IBC. A brief history of last night's event is below.

I've copied Krister; please pass this on to whomever is appropriate.

Thanks,...Andy




_______________
   at about 17:25 EPICS communications stopped;
- epics alarm on alarm handler eventually went off, but probably not until
epics came back.

- the supply valve on the buffer dewar, EV8215, regulates LHe flow to
the IBC by looking at the liquid level in the cryostat. The last good value
read by epics happened to be high, so it began to close EV8215. Since the
level value remained constant, it continued to close until 18:45 when epics
signals returned.
- while the supply valve was closing, the level in the IBC LHe bath was
dropping, although the apparent epics value was a flat line at the last
17:25 value.
- at 18:45 epics signals came alive again, the IBC LHe bath level
registered only 38%, and the EV8215 valve immediately opened. Since the
transfer line from the buffer dewar to the IBC had by now warmed, the LHe
flow from the opening of EV8215 boiled in the transfer line and the
expanding gas blew the IBC bath level down further, reaching 30% at 18:58.
- when epics came alive, the nose temperature was 5K and rising.
- by this time the solenoid magnet in the IBC nose, which was at 0.9 tesla
and 46 amps, was completely uncovered and no longer cooled. This caused a
quench, at about 18:55.
- mix1 =>  spiked to about 3 K

- polarizations dropped by about 40% !


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