Forward Multi-Wire Proportional Chambers Shift

The Multi-Wire Proportional Chambers

The Forward Multi-Wire Proportional Chamber (FMWPC) system consists of six planes interspersed between iron absorbers, which are located downstream of the FCAL on the downstream platform. Each plane consists of 144 sense wires, operating at the nominal +1800 V. The preamps, located on the chambers are powered with +/- 5 V. The table provides a summary of the basic chamber properties. Additional details can be found in the MWPC Construction Report.

MWPC Characteristics

Parameter	Value
sensitive area	60 x 60 inch2
sense wire pitch	0.4 inch
wire plane to cathode plane distance	0.4 inch
size of central deadened region	10 x 10 cm2
wire arrangement	planar, with field wires between sense wires
sense wire diameter	20 um
field wire diameter	.003” non-central region, .004” central region
sense wire voltage	typically +1800 Volt
field wire voltage	ground
cathode plane voltage	ground
operating gas	90:10 argon:CO2 by volume, flowing at 5 cc/s
typical chamber gain	about 100,000
maximum drift time	about 570 ns
number of electronic channels per chamber	144

Routine operation

Fig. 1. FMWPC HV, LV GUI panel.

The most important task for the shift workers is to monitor the parameters (using GUIs) and report any changes from the normal operation for the following FMWPC related subsystems: High Voltage, Low Voltage and Gas system. A description of how to bring up the corresponding GUI screens and how to operate them can be found in the Section Slow Controls. The HV and LV subsystems have a common GUI. The GUIs are designed to show green color if all the parameters in a certain subsystem/subgroup are within their operating limits. If any of the parameters is out of limits the background for the corresponding subsystem/subgroup will turn red. An example the GUI is shown in Figs. 1 for normal operating conditions.

The shift workers are allowed, using the GUI, to turn ON and OFF all the HV and LV systems, as well as parts of them or the individual channels. Instructions how to do this are given in Section Slow Controls, but the general rule is either to bring the pop-up menu with left click on the group title (like "ALL OFF ALL HV / LV") or to click on the individual channel knob (the knob title shows the action to be taken after pressing it). For example, in case a HV channel trips, one should press the corresponding channel knob once (acknowledging the trip) and then again to turn it on. The corresponding voltage parameters, like ramp up/down rates, trip currents, set voltage values etc. should not be changed by the shift workers. The restoration of voltage settings to nominal operation can be accomplished using the top right button "SAVE/RESTORE."

The FMWPCs operate with pre-mixed 90/10 Ar/CO2 bottles located in the gas racks outside the hall. The gas flow to each plane is controlled locally via manually adjustable flow meters located on each chamber. The flow rate will be set at the beginning of the run by experts, but the flow rate can be viewed remotely with the "halldaxis7"??? hall camera. For instructions how to operate the camera, refer to Section Slow Controls. The shift the workers should record the gas flow for each chamber once per shift.

Operations beyond what is specified above shall only be performed by the system expert or under his/her direction.

Interlocks

The HV and LV modules are set to immediately turn off the voltage if the current exceeds the corresponding limit. Setting the voltage channel back should be done only manually by the operator.

Expert personnel

The individuals responsible for the operation of the FMWPCs are shown in the following table. Problems with normal operation of the FDC should be referred to those individuals and any changes to their settings must be approved by them. Additional experts may be trained by the system owner and their name and date added to this table.

Table: Expert personnel for the FMWPC and CTOF systems

Name	Extension	Date of qualification
Beni Zihlmann	269-5310	May 20, 2022