IV. FEE and MWC VOLTAGES

 

 

The low voltage power supplies for the TPC FEE’s and MWC front end cards can be powered on/off remotely using separate slow controls GUI’s.

 

FEE’s

 

The FEE power supplies are located in racks 2B1-2B4 and 2B6-2B9 on the south platform.  Rack 2B5 has the VME crate and CPU. To turn on:

 

1. Select Desktop # 4 (FEE)

 

2. On the top level GUI, click on the FEE Voltage icon.

 

3. For each supersector, power supplies N1 and N2 are for the inner sector readout boards.  (RDO’s) and N3-N6 are for the outer sectors. The power supplies can be turned on individually or by rack (three supersectors) or by east or west end, or for the whole TPC. (The power supplies come on in sequence to avoid power surges.) Click “on” for your selection.

 

4. To turn the FEE’s off, click the appropriate “off” button. In normal operation, the FEE’s should be left off unless the TPC is taking data (especially if the experiment is not manned after hours). In addition:

 

THE FEE AND MWC POWER SUPPLIES MUST BE TURNED OFF WHEN THE MAGNET IS RAMPING UP OR DOWN!

 

MWC’s

 

The MWC cards are used in the trigger and are powered separately. The power supplies are located in Rack 1B3 on the south platform.

 

EVEN IF THE MWC ARE NOT BEING USED FOR THE TRIGGER THEY STILL SHOULD BE POWERED ON DURING DATA TAKING, since they terminate the TPC anode wires.

 

1. Select Desktop #4 (FEE)

 

2. On the top level GUI, click on the “MWPC LVPS” icon.

 

3. Click on the global on button.

 

4. The same caveats apply as for the FEE’s. Turn the MWC off when not taking data and during magnet ramps.

 

INTERLOCKS

 

1. Air blower: At the bottom of each rack there is an air blower which supplies cooling air for each power supply in that rack. Inside each blower, there is an air flow switch so that if the blower stops, all the power supplies in that rack are turned off.  If one rack of power supplies won’t come on, that is probably the reason.  It would require an access to fix this.

 

 

2. TPC water skid:  The cooling water for all TPC electronics is supplied by the TPC water skid located in the second floor utility room at STAR (east end of assembly building.) The skid is designed to supply water at a temperature of 75 ° F.  The skid exchanges its heat with the STAR Modified Chilled Water (MCW) which is the same water that cools the platform and DAQ racks. Typically, the MCW temperature needs to be 60 – 62 °F for the TPC skid to maintain its setpoint when the FEEs are powered.

 

The FEE and MCW power supplies are interlocked so that if the flow stops the power supplies turn off. This is done automatically through the TPC interlock system. There are five flowmeters for the TPC. The flow rates are displayed on a panel in Rack 2A9 and also on the Interlocks GUI (Desktop 7).(For more information on the interlock system, see the TPC Interlocks Manual.

 

Problems with the TPC water skid, MCW etc need to be addressed by a STAR shift leader who will contact the appropriate experts (pump room, STAR ops, TPC etc)

 

TEMPERATURE MONITOR

 

Thermocouples (120 total) have been placed on the TPC FEE/RDO cooling manifolds to monitor the temperature. The readings from these thermocouples are recorded by a PC which is located in Rack 2A4 on the platform. To see the current readings and view past history, use Netscape or Explorer to go to http://tpctemp.star.bnl.gov/ The readings are updated every few seconds, and at the bottom of the page it is possible to pull up a graph of any individual thermocouple (or the average) for the past hours or days.

 

NOTE: IT IS VERY IMPORTANT TO KEEP THE TPC TEMPERATURE BELOW 80 ° F.  TEMPERATURES ABOVE 80 CAN RESULT IN STRUCTURAL DAMAGE TO THE TPC.  IF IN DOUBT, POWER  OFF THE FEE’SAND CALL AN EXPERT.

 

 

V. GATED GRID

 

The gated grid is a plane of wires above the anodes that, when energized (closed), prevents ionization in the TPC from reaching the anodes. After a valid trigger, the gated grid is opened for a fixed time (currently ~ 60 msec). The gated grid system is located in two crates in Rack Row 2A6, the top crate containing the VME CPU and control modules and the next crate containing the HV drivers. The signal to open the gated grid comes from the TPC TCD located in Rack 1A2 (output J2). It is also possible to open the gated grid continuously (for laser runs etc).

 

TO TURN ON THE GATED GRID:

 

1. Select Desktop # 9 and click on “VME Status” on the top level GUI.

 

2.  Check that crates 2A6-1 (GG Control) and 2A6-2 (GG-driver) are on. If not, turn them on (2A6-1 first). There is a safety interlock for crate 2A6-2 that can prevent it from turning on – if this is the case refer to the TPC Interlock Manual or call an expert.

 

3. Select Desktop #3 (Gating Grid) and click on “Gating Grid” on the top level GUI.  This will bring up the Gating Grid Monitor and control screen.  All sectors should be red.

 

4. Click on the button labeled “Default Sequences”. This will bring up the auto sequence window.

 

5. Click on the button labeled “Grid On”. The status should change from “Idle” to “Downloading Setpoints”. Wait ~ 5 minutes for the voltages to be turned on in sequence. If, after clicking “Grid On” the status remains “idle” it may be necessary to reboot the VME processor. See that section of this manual.

 

6. After the voltages are set, close the sequence window. In the monitor window, all sectors should now be green:

 

 

 

 

7. To check on the voltage setpoints, click on the “expert controls” button. This will open the control window. Click on the “Global Controls” button.

 

8. For normal running, the settings should be:

 

 

 

VGG, VGG hi and VGG lo have been calculated to properly terminate the field cage drift field and should only be changed by an expert. The low and high alarm set points determine when the color field on the monitor screen changes for each sector. Thus, a voltage that deviates 1% from the setpoint will show up as yellow, 2% will be red.

 

To see the actual voltage on an individual sector, click on the button for that sector on the monitor GUI. For each sector, the window looks like:

 

 

To see a strip chart of a monitored voltage, click on the button to the right of that voltage.

 

 

NOTE:  For normal operations, all sectors should be green or yellow. Sectors displaying red should be investigated, and the run stopped. Incorrect voltage on the gated grid causes distortions in the TPC drift field. Contact a TPC expert.

 

TO RUN WITH THE GATED GRID OPEN:

 

For special runs (ie laser) it is possible to run with the gated grid open all the time. If there is beam and the TPC anodes are on then it is necessary to keep this time to a minimum. To open the gate:

 

 

1. On the gated grid monitor GUI, click on the “expert controls” button. This pops up the expert window:

 

 

2. Click on the “Write Disabled” button - it will switch to “Write Enable” Then click on the “Global Control” button to open the global control window. (If “Write Enable” is not on, you can’t make changes to the GG settings.)

 


 

 

 


 

 

 


4. To return to normal running, reverse the process: In the global control window, click on VME Gate Disable, close the window; in the experts window click on the Write Enable button,  and close the experts window.

 

TURNI NG OFF

 

1. On the gated grid monitor GUI, click on the “default sequences” button to open the auto sequences window.

 

2. Click on the “Grid Off” button and close the window. On the monitor window, all the sector color fields should turn red.

 

3. If it is anticipated that the TPC will be off for some time, turn off the GG driver crate (2A6-2).

 

TROUBLESHOOTING

 

Further troubleshooting hints are on the web. Go to the STAR homepage, then Group Documents ->TPC -> Operations. There are two files: Gating Grid Troubleshooting and Replacing Gating Grid Module.