[Esr-users] ESR Hall update

[Jonathan Creel]

There seemed to be some confusion over the ESR/Hall problem last night.

The original 12GeV plan was Hall D plus any two other Halls. The 
projected loads in the Halls matched well with the capacity of the ESR. 
When the proposal was changed to support Hall D plus three Halls it was 
determined the ESR would likely need to run at its very highest capacity 
and would also require constant support from the CHL to meet the needs 
of the loads. There would be no margin.

It has been widely disseminated that this would have a several side effects.

First, operating the ESR at full capacity will lower its reliability. 
The ESR was originally build in 1978 for the ESCAR project and was 
decommissioned and installed here at JLab in 1994. The plant is aging 
and operating it at its highest capacity for extended periods will have 
an impact.

Second, the Halls are all essentially manifolded together at the ESR. 
Operating the system at the highest capacity makes the ESR and the Halls 
very susceptible to collateral problems in any one Hall. With the warm 
compressors processing the large quantities of helium gas molecules 
flowing through the system there is little compressor margin to 
instantly react to process the extra gas molecules that are generated 
during magnet quenches or fast dumps. The result is that a significant 
event in one Hall will instantly raise the helium return pressures for 
all Halls and the ESR plant. If this pressure rise is high enough the 
magnets in the other Halls will shutdown or fast dump. If the 
disturbance is large enough the increased return pressures effect the 
ESR plant operation and pressurizes the dewar which leads to turbine 
shutdowns to protect the equipment from damage. This is the scenario 
that occurred last night.

Third, following a ESR trip, it has been disseminated that two of the 
Halls would be recovered fairly quickly but as the load increases on the 
plant the third Hall does not have access to any extra capacity to 
cooldown fast. For this reason the the third Hall will require from one  
to several days to recover depending on the length of time the plant was 
shutdown. This is the scenario that happened overnight with Hall C. We 
pre-determine the recovery priorities based on an email sent to us by 
Physics.

In summary, the events at the end station essentially followed the 
predictions and recovery went as expected. We are working with Physics 
to see if there are any lessons learned can be applied to the future.

Thanks

-- 
Jonathan Creel
Cryogenics Engineering and Operations Department Head and Senior Electrical Engineer
Thomas Jefferson National Accelerator Facility
12000 Jefferson Avenue, Newport News, Virginia, 23602
Phone (757)269-5925