A DIRC Water Plant Digest for Commissioners

If you're looking for some information on the procedure to be followed after a SOB dump, just go here.

This document does not aim at describing in a complete and detailled way the DIRC Water plant. It just summarizes a few information gathered here and there which may be useful for DIRC oncall experts. For a more precise and technical view of this essential DIRC component, the water plant experts, Jerry Va'Vra and Matt MacCulloch, should be contacted.

The DIRC water plant is a complex and sensitive hardware system: therefore, DIRC oncall experts should not attempt to fix problems or operate any of its components without specific instructions. Our main jobs are the following:

The most urgent problems which may occur are the following: Otherwise, nothing really serious should occur on a day timescale: the water quality (transmission, bacteria level) deteriorates very slowly and the system can run with the pump off during several hours. In particular, if we get a page outside 'normal hours' (6am → 9pm on week days and 9am → 9pm on weekends and holiday periods), we should estimate whether the problem needs to be fixed urgently or if it can wait the next day -- which is likely.

Other sections of the ops. manual are dealing with the pumps of the DIRC water system. Read them carefully if one of these pumps stops working and strictly follow the instructions they provide.

The water tank

Ultra-pure water is permanently circulating in the SOB whose volume is about 6000l. Filters are used to stop dust particles and to remove ions from water; UV-light is used to to kill bacteria. One pump makes the water circulating and the other one is degasing the water.
The nominal water level is around 5.4m -- this number is indirectly measured via a Bernouilli-like relation. If the level would reach 5.3m/5.2m, it would trigger a yellow/red alarm on the ALH.
A gauge is glued on the tank to show the interval in which the water level is expected to fluctuate during normal operations. The water level is expected to fluctuate for various reasons: temperature variations, BaBar doors being opened or closed etc.
If the water level is found outside this range, the DIRC water experts should be contacted. Before doing this, check for any sign of water leak, either on the IR2 floor (if accessible!) or in the moisture sensors. Those devices will likely trigger some alarm in case of a real leak.

:Picture of the DIRC water tank:
DIRC water tank

If the circulating pump stops, the water will start decreasing in the SOB. This should trigger a red alarm in the ALH and the DIRC oncall expert should be paged automatically. After the pump gets restarted, the water level should come back to its nominal value in a few minutes.
To have a better understanding of the water level evolution with the circulating pump off, a test was setup mid-November 2005 before the startup of Run 5b. The circulating pump was stopped manually and the evolution of the water level and of other water plant parameters were monitored during 5 or 6 hours. A detailled summary of the test can be found here.
Its main results are the following: after an initial drop of ~3-4 cm (the water level was 5.38m when the test started), the water went down slowly at a rate of ~7-8 cm/h. The yellow alarm level was reached after 50 minutes. At that level, the decrease rate was slowly going down. About half an hour later, the rate increased again; 20 minutes later, the water level reached a plateau at ~5.22m, i.e. two centimeters (!) above the red alarm level. Then, the water level stayed stable during the next three hours before the test was ended.
The water level evolution is thought to reflect the geometry on top of the SOB. The plateau should correspond to the moment when the water reaches the top of the main SOB volume -- in that area, you need to drop a large volume of water to see a change in the measured level.
Therefore, if the circulating pump breaks during the night, the water level should remain quite stable after an initial drop. Unless the red alarm level is reached, fixing the problem should wait for the next morning.

The degasing pump is connected to a SIAM as there is no other way to detect that it stopped working. Therefore, its failure would immediately trigger a red alarm on the ALH.

The dump system

The infiltration of water (SOB water leaking in some bar box or moisture condensation) could damage some components of BaBar, in particular the EMC crystals. Therefore, the DIRC has designed and implemented a complex system to avoid humidity (nitrogen flow in the bar boxes and on top of the SOB). If a significant leak is detected, the water in the SOB would be dumped in a few minutes -- to be compared to the refill time, about 10 hours without including the investigation required to understand and fix the origin of the leak.
Actions on or involving the dump system should only be done by the DIRC water experts. Yet, if you're oncall and if you're wondering whether the water dump has occured, there are two quick ways to check that it was not the case...

Water epics panel

The information on the water system is summarized in a dedicated epics panel, reachable from the main BaBar epics panel: 'BaBar Online Detector Control' → 'DRC' button → 'Water'.

:DIRC water epics panel:
DIRC water epics panel

Its data reach the drc-mon IOC through VSAM boards located in this crate. A dead VSAM would have a red light on its front panel and would prevent the IOC from booting. When you change a VSAM, make sure that you're not disturbing the other VSAM connections which are somewhat loose. If a connector gets unplugged, the information displayed on the corresponding epics panel will be crazy.

The list of epics variables related to the water system (as of 2006/06/22) can be here.


Nicolas Arnaud
Last modified: Thu Jun 22 13:27:19 PDT 2006