[BTeam] Fwd: CEBAF/Cryo Status

[Arne Freyberger]

Time to start thinking about a 6GeV program.  What are the issues? 
Shunts?  What else?

Arne


-------- Forwarded Message --------
Subject: 	CEBAF/Cryo Status
Date: 	Sat, 28 Mar 2015 13:26:22 -0400
From: 	Arne Freyberger <freyberg at jlab.org>
To: 	Hugh Montgomery <mont at jlab.org>, mike dallas <mdallas at jlab.org>, 
Bob McKeown <bmck at jlab.org>, Andrew Hutton <Andrew at jlab.org>, Fulvia 
Pilat <pilat at jlab.org>, rode >> Claus Rode <rode at jlab.org>, Allison Lung 
<lung at jlab.org>, Leigh Harwood <harwood at jlab.org>, Rolf Ent 
<ent at jlab.org>, rossi patrizia <rossi at jlab.org>, Mary Logue 
<logue at jlab.org>, Bob May <may at jlab.org>, Will Oren <oren at jlab.org>, Tim 
Michalski <michalsk at jlab.org>, Rusty Sprouse <sprouse at jlab.org>, Rolf 
Ent <ent at jlab.org>, rossi patrizia <rossi at jlab.org>, 'Javier Gomez' 
<gomez at jlab.org>, Cynthia Keppel <keppel at jlab.org>, Volker Burkert 
<burkert at jlab.org>, Eugene Chudakov <gen at jlab.org>
CC: 	Jonathan Creel <creel at jlab.org>



This is a summary email from Arne and Jonathan.

Cryo recovery efforts since the power outage Wednesday have not converged.

*CHL2->SCN->NorthLinac*: has gone through several 2K pumpdowns only to 
trip an hour or so after achieving 2K.  The CHL2->SCN hardware is in 
working order.  Analysis indicates the cause of these trips appears to 
be contamination plugging across the 2K to 4K heat exchanger in the 
bottom of the SCN cold box. This is forcing them them to operate at or 
near their surge curves. This problem coupled with the previous 
contamination problem with SCN cold compressor 2 seems to indicate that 
we had a significant amount of contamination enter the system or move in 
the system during the multi-hour power outage. The SCN must be warmed up 
and decontaminated in order to support any 2K operation.

*CHL1->SCM->SouthLinac:*  has not been able to pump down to 2K.  
Evidence is mounting that there is a likely physical problem with cold 
compressor #4 (CC4) in the SCM.  CC4 went through an unusual trip during 
the first pump down attempt after the power outage, the controller 
responding as it should but the hardware ramped from 500Hz to 0Hz in a 
very abrupt fashion. The magnetic bearings for CC4 will no longer 
levitate the compressor wheel. The coils are drawing maximum current but 
the internal hardware is not moving. The coil resistances appear normal. 
The CC4 and CC5 mag bearing control cables were switched during trouble 
shooting.  Either mag bearing cabinet can successfully levitate CC5 but 
neither mag bearing cabinet can successfully levitate CC4.  This leads 
to the conclusion that there is likely something physically wrong with 
CC4. This is a single point of failure; CC4 can not be by-passed.  The 
SCM must be disconnected and warmed up in order to access the compressor 
to determine what happened and carry out any repairs. Cryo is performing 
some final checks on CC4 and developing plans for an SCM warm up which 
could last several weeks to months in duration.

*Short Term:* No beam  operations this weekend and probably for the next 
week or two.  Cryo will continue to assess the CC4 problem. Cryo is 
formulating plans this weekend which they will review with Ops on Monday 
morning to formulate a revised schedule.

*Long Term (Plan B):*   There are options on the table if CHL1->SCM is 
not available.   These options include, but there may be others:

 1. Configuring both CEBAF LINACS to 2K on CHL2->SCN   and establishing
    a 5-6GeV CEBAF.   Hall-A has some 2GeV data and HPS data can be
    accommodated by this configuration, Hall-D could do some
    commissioning activities with a 6GeV beam.
 2. Extending the run well beyond  the May 4th scheduled end date, this
    will result in a tremendous amount of UIM/CHL2 and other contractual
    changes.   But it would retain the physics weeks.


Arne and Jonathan

-- 
Arne Freyberger
Director of Accelerator Operations
Jefferson Lab
12000 Jefferson Avenue      Cell: (757) 876-6289
Postal Suite 19             Email:freyberg at jlab.org  
Newport News, VA 23606



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