Monitoring and Operation of the BoNuS Detector Gas System

Howard Fenker, 10/11/05

Note: the RTPC windows and cathodes are extremely fragile, and they are pressurized by the flow of gas through the chambers. Too much gas flow can destroy a window or cathode and end the experiment. You may make small adjustments to the flow rate (up to a total max flow of 1000 sccm) without concern. For other valving operations be certain you understand the full impact of what you are about to do before doing it.

The DME bottle is in the Hall-B target gas alcove (out the back door of the counting house, across the road, and to the right). The DME bottle is located in the bottle rack on the left-hand side of this alcove. It is the white low-pressure cylinder and is labeled “Dymel-A”.

You can read the bottle pressure and the delivery pressure on the gauges attached to the regulator on top of the bottle, but note that the pressure in the bottle is temperature dependent and will usually appear to be near zero since the vapor pressure of DME will never be above about 60 psig. The delivery pressure should never (normally) need adjustment, and should remain at about 23 psig.

(The following paragraph describes the DME flow control system in place as of 10/10/05. It will be re-written when the normal DME flow controller is repaired and reinstalled in the hall.)

The DME flow control and measurement apparatus is attached to the DME gas bottle rack. Flow is regulated by a needle valve at the bottom of the ball-type flowmeter (looks like a thermometer), and the flow rate can be read from the digital flowmeter mounted under the needle valve assembly. There are two such flowmeters present, but only the one labeled DME is in use. I suggest you do not even touch the needle valve unless you need to adjust it, as it is very sensitive. If you do adjust the needle valve you can observe the change in flow in the DIGITAL FLOWMETER (not the ball-type flowmeter please!). The digital flowmeter reads directly in sccm (standard cubic centimeters per minute). The desired flow rate is posted here. A wire has been run from this flowmeter, across the road, through the door, and into the B Counting Room so that you can read the DME flowmeter using a voltmeter in the counting room. At a flow of 40_sccm the voltmeter reads 40_millivolts.

Helium is supplied from a pair of bottles on the west side of the Hall-B gas shed. We are presently running this supply at 27 psig. This pressure is set by the Hall-B engineering staff only. The helium flow for the BoNuS detector is controlled by the Qualiflow controller on the BoNuS gas mixing panel in the hall. See here for the current desired flow rate. To adjust the flow rate, use the VNC connection to the gas control computer, and run the Qualiflow control software. The helium controller is attached to COM1. Make sure the screen is set to give you a flow reading in sccm so you can see the flow rate in these units. To set or change the desired flow, however, you must enter the value as a “percent of full-scale” using one of the preset boxes near the bottom of the screen, or by entering a percentage in the “SPECIFIC” box on the right. The full-scale for this control valve is 2000 sccm. Therefore, to set a flow of 160 sccm, for example, you would request 8% of full scale.

You can use the beamline camera to observe the Qualiflow screen on the computer in the hall if it has not gone to sleep. You can also observe the output bubblers from the RTPC using the camera. These bubblers are located under the BoNuS ALTRO electronics crates on the upstream end of the BoNuS support tube. At least a bubble every second or two provides a positive indication of a complete gas circuit, and this is all we need. Both the left and right detectors should bubble at a total flow rate of 200 sccm.

Still needed for this document: how to open the VNC connection to the gas control computer.