[Dsg-rich] Supplemental N2 supply for RICH

[Marc McMullen]

Hi Denny, Bob, Marco C. and Marco M.

As you are aware, the RICH detector requires an uninterrupted gas 
supply. The moisture content of the detector shell volume, which houses 
the Aerogel tiles, increases rapidly with the cessation of N2, as shown 
by the observations presented by Tyler Lemon (DSG RICH contact). The 
maintenance outage, to install the isolation valves (9/21), has 
presented us with information on just how much the humidity in the 
detector volume can change in just 27 minutes. Unfortunately, what 
cannot be measured is the amount of absorption into the tiles, or the 
efficiency degradation due to moisture.

What can be done is taking preventative measures to ensure the safety of 
the detector for future events. To that end, DSG has discussed the 
design and implementation of a secondary N2 supply. In previous 
discussions DSG and Hall B planned to use high pressure LN2 dewars to 
supply the detector during a planned outage. This would still be a 
viable solution for an outage lasting many hours or longer.

For unplanned outages or very short planned outages, a supplementary N2 
circuit (see attached) developed by G. Jacobs and the DSG could use 
multiple high pressure N2 bottles in parallel. Gas flow can be triggered 
using a pressure controlled switch, and check valves will ensure the gas 
flows to the detector instead of back towards the standard N2 source. 
DSG has already procured eight 255cf bottles of N2, which are currently 
located on the gas pad outside of the gas shed. We have calculated 2 to 
3 hours of gas per cylinder at the current flow rate (40Lpm).

Once this plan is approved, DSG can source all necessary components and 
provide diagrams. Hall B Engineering should evaluate the system for 
integration/installation with the current Hall B N2 system, and provide 
all required safety documentation/inspections (including Jlab pressure 
systems compliance). DSG can assist with installation, at the direction 
of the Hall work coordinator to ensure all Hall B/Physics work 
governance procedures are observed.

With pre-assembly, planning, and coordination between Hall B and the 
DSG, work in the hall can be minimized so that installation can be 
completed in a short amount of time.

Regards,

-- 
Marc McMullen Detector Support Group 757-269-7738

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