I like to document the requests from the etof group and the response from the TPCgroup.

Response from Alexei and TPC group April 26

Dear All,
I repeat eTOF leak rate on 04.24.19 and  it is less than ~ 30cc/min. I arra
nged SF6 flow ready for e-TOF detector. Also I verified e-TOF air blower performance- looks reasonable to blow out any leaks for eTOF. Appropriate pap
erwork for CAD was done at the beginning of run 2019.
Geary was informed yesterday and promised to consult witheTOF group  in Ger many. After his word I'll start SF6 flow and will put appropriate note in the logbook.
Below it is a request form eTOF group initiated...
Thank you,
Alexei

April 22 request from eTOF group
Ops group:

Current eTOF DAQ problems not withstanding, eTOF would likely perform a little better if the gas mixture contained 1/2% SF6, the same as the MTD ran in previous years. It might help in preventing the type of damage the eTOF has sustained from beam excursions.

A calculation of the risk to the TPC:

eTOF supports a 30 ccm flow to the bubbler, indicating the maximum leak rate inside the pole tip is 30 ccm. At 1/2% SF6, the SF6 flow behind the pole tip is a maximum of 0.15 ccm.

The air blowers provide 500 cfm = 14158400 ccm behind the east pole tip.

Not counting on any other air diffusion from behind the pole tip, the indicated steady state SF6 content in the air behind the pole tip is 0.15 / 14158400 =
1 part in 10^8.

The air content in the TPC gas is 125 parts in 10^6. (If it is still the same as in 2012.) If all the TPC air came from the east pole tip air, the SF6 content in the TPC would be 125 parts in 10^14, or 1.25 parts in 10^12.
The danger level for SF6 in the TPC is 1 part in 10^9.
I think we should consider adding SF6 to the eTOF gas now. Alexei could verify during maintenance Wednesday that eTOF still supports the bubbler at about 30 ccm flow.

-Geary

In June 6 2019 it was requested to increase the rate to 1%. Alexei agreeed to this after having checked the etof leak rate
and under condition that the blower was on.