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Frederick Gray, 11/21/2020 06:44 PM


Preping the hardware for data taking

LAST UPDATE: Nov. 21, 2020.

Contact Fred Gray () or the detector on-call for any feedback, question, request.

This wiki contains the instructions for the shifters to collect data with the Fiber Harps. The instructions are separated in two steps:

  • turn on the Fiber Harps Bias Voltage
  • insert the Fiber Harps and collect calibration and measurement data

The Fiber Harps system is made of two pairs of harps. Each pair is made of a Y-profile and a X-profile harp. One pair is located at 180 degree in the ring and the second pair is located at 270 degree in the ring.

You need to read this document entirely before doing anything to make sure you understand the big picture.

1. Turn on the Bias Voltage

You need the Bias Voltage to be turned on, and with a high enough value, to collect data. There won't be any useful data from the harps if the Bias Voltage is off. This section explains how to turn it on/off and adjust the value.

ssh to the beagle bone

There is a beagle bone that controls the Bias Voltage power supply, you need to connect to it.

First, ssh to the g2be1 machine. You can do it from any machine in the control room:

ssh daq@g2be1 

Then you will ssh to the beagle bone board:

ssh daq@192.168.26.21 

the password is 'harp4Precess'.

Check which supply is connected to which harp

There are two power supplies and two pairs of harps. Every time the beagle bone is powered-cycle, the supply / harp pair association is reset. Thus, you first want to check which supply is connected to which harp by running in order, if needed, to configure independently the two pairs of harps. The command is:

./bk_command0.py 'SYST:ADDR?' 

and

./bk_command1.py 'SYST:ADDR?' 

The two possible outputs are 27 and 18, which previously referred respectively to the harps pair at 270 degree in the ring and the harps pair at 180 degree. For instance if the output is:

root@Regis-RangerBone:~# ./bk_command0.py 'SYST:ADDR?'
27

it meant that supply 0 is connected to the 270 degree Harp. So if you wanted to configure the 270 degree harps pair you would use the supply 0.

Set the current limit on the harps

The current limit must be set to 5 mA (0.005 A) before turning on the bias voltage. <bf> If it is not set, a fuse that is in series with the bias supply output will be blown by the inrush current that charges the capacitors on the SiPM boards. </bf>. To do this, run:

root@Regis-RangerBone:~# ./bk_command1.py 'SOUR:CURRENT 0.005'
0.0000

root@Regis-RangerBone:~# ./bk_command0.py 'SOUR:CURRENT 0.005'
0.0000

Check if the Bias Voltage is on or off

The next step is to check if the Bias Voltage is on or off. To do so, run:

root@Regis-RangerBone:~# ./bk_command1.py 'MEAS:VOLT?'
0.0000

root@Regis-RangerBone:~# ./bk_command0.py 'MEAS:VOLT?'
0.0000

In this example both pairs of harps are turned off. The output of the commands we just ran is the delivered Bias Voltage to the harps in V. You should expect 0 V when the harps are turned off and a value ranging from 67 to 70 V when the harps are turned off.

Set the Bias Voltage

There are two steps to turn on the harps: first you want to set the Bias Voltage value (set point), second you want to deliver the set point Bias Voltage. To set the Bias Voltage:

./bk_command0.py 'SOUR:VOLT 68'
./bk_command1.py 'SOUR:VOLT 68'

which would set the Bias Voltage of the two pairs of harps to 68 V. Use this value by default if no other is provided to you.

Important: if using 68 V by default. Make sure from the Fiber Harp DQM (see bottom of this page for the DQM guide) that the signal is clearly visible and also not obviously clipping (the first turn might be clipping and it is alright for now). The Bias Voltage ideally should be tweaked for any change in the beam intensity if the change is large enough. A large change is definitely when going from a proton beam to a muon-only beam.

Turn on the Bias Voltage

Since you have set the Bias Voltage, you can now turn it on:

./bk_command0.py 'OUTP 1'
./bk_command1.py 'OUTP 1'

To check that it worked, run again:

root@Regis-RangerBone:~# ./bk_command1.py 'MEAS:VOLT?'
68.0000

root@Regis-RangerBone:~# ./bk_command0.py 'MEAS:VOLT?'
68.0000

and you should see the set point Bias Voltage you set. You are know ready to do things, i.e. insert the harps into the beam!!

2. Enable digitizer readout

To enable digitizer crate 26:
  • Stop the run.
  • Edit the ODB key "/Equipment/AMC1326/Common/Enabled" to be "y"
  • Press "restart fast frontends."
  • Wait a little bit and then restart from the Programs page any frontends that didn't restart properly on their own.

The fiber harp DQM can also be restarted at this point.

When finished with the fiber harps, these steps can be reversed:
  • Stop the run.
  • Edit the ODB key "/Equipment/AMC1326/Common/Enabled" to be "n"
  • Press "restart fast frontends."
  • Wait a little bit and then restart from the Programs page any frontends that didn't restart properly on their own.

The AMC1326 crate should normally be disabled for production data, and only turned on for special runs where the fiber harps are being used.

3. Insert/Retract/Rotate the harps into the beam

To insert / retract / rotate the harps, you will use the MIDAS Fiber Harp Control web-page. You need the Fiber Harp Control front-end to be running; it should normally be left running all the time. You will find the web-page under:

g2be1:8080/CS/FiberHarpControl

You will use the buttons "Insert", "Retract", "Calibrate", "Measure". Hopefully the names are self explanatory. You might need to try twice when pushing a button. There is a little bit of flakiness to the system.

Important do no retract the harps if there are in calibrate position!! Rotate them back into measure position.

When you are done, you need to retract the harps and leave them there. Then turn off the Bias Voltage (next section). Never left the harps inserted without a good reason.

MIDAS Insertion Alarm

As of now, when one Harp is inserted, MIDAS will raise an Alarm which will cause you troubles. This issue should be fixed in the future. For now, every time the Harps are being inserted, the Fiber Harps MIDAS alarms should be disabled. To do so: go to the 'Alarns' page of MIDAS, find the lines: 'FiberHarp180Y', 'FiberHarp180X', 'FiberHarp270Y', 'FiberHarp270X'. Click one at a time on each and every one and change the line 'Active y' to 'Active n'. Do not forget to re-enable the alarms when you are done.

4. Turn off the Bias Voltage

Once you are done, you should turn off the Bias Voltage and set it to zero:

./bk_command0.py 'OUTP 0'
./bk_command1.py 'OUTP 0'
./bk_command0.py 'SOUR:VOLT 0'
./bk_command1.py 'SOUR:VOLT 0'

Typical Fiber Harps run

For Fiber Harps data collection, you will typically do the following things chronologically:

  • Configure and turn on the Bias Voltage checking the read-out
  • Insert the 4 harps into the beam
  • Rotate the 4 harps into calibrate position to collect calibration data
  • Rotate the 4 harps into measure position to collect measurement data
  • Rotate the 4 harps into calibrate position to collect a second calibration data set
  • Rotate the 4 harps into measure position
  • Retract the 4 harps
  • Turn off the Bias Voltage

Important: you want to write an elog entry for every item of the list above. Also, you want one dedicated elog entry to keep track of which MIDAS run number is what (either wait until the end of the measurement campaign to post the entry or use the "add comment" for each new run). For each run you typically want to give the information:

  • Run number
  • Fiber Harps in calibrate or measure
  • Kickers set point
  • Quads HV