Go to the LArIAT BeamOverview - Synoptic Viewer window and click on the "TO TPC OVERVIEW" box on the cryostat cartoon.
Click on the flower in the red Cathode box.
This brings up the LArIAT_CathodeHVMonitor window:
Monitoring drift HV¶
The LArIAT_CathodeHVMonitor window will produce a plot in time of the voltage readback (red line E:GMV), and the step voltage (blue). The most recent value of these voltages are listed on the left of the window. E:GMV is the actual output voltage. The "step voltage" is the desired voltage setting. These should agree within noise limits. If not, please check out "What to do if the Step voltage does not agree with the readback value (E:GMV)."
Changing drift HV
Follow these instructions if HV LAr level interlock has disabled power supply output¶
If you plan to return to an initial voltage, please take note of the settings before making changes.
In the LArIAT_CathodeHVMonitor window, click the symbol in the bottom right corner of the window.
This brings up a pop up menu to enable changing settings for some period of time. Choose an appropriate time scale. Now click back on the main window. Click the lighter blue small square in the SET VOLTAGE blue rectangle.
A window will pop up that will allow you to enter the desired voltage in volts. The default cathode HV value is 23500 V. Do not go above 25000 V without prior approval. As an example, if the you wish to ramp the HV down to zero, put 0 in the window and click "OK". The ramp will then start. The target voltage in the graph (green line) will make a point at 0 V and the voltage will start to ramp toward that value.
What to do if the Step voltage does not agree with the readback value (E:GMV)¶
Case 1: Read back is 0 V and it should not be.
Solution 1: Set the Target HV to voltage 0 V following the above instructions. Call experts. Don't touch the power supply.