Triple GEM Aging Test at GIF++

1) Description of the facility

The GIF++ facility is located in the CERN, north area and is equipped with a powerful 14TBq ¹³⁷Cs source, used for the irradiation purposes. The 100 m² GIF⁺⁺ irradiation bunker has two dependent irradiation zones making it possible to test real size detectors, of up to several m², as well as a broad range of smaller prototype detectors and electronic components. The facility is focused on the characterisation and understanding the long-term operational properties and behaviour of large particle detectors.

2) Description of the experiment

The test currently ongoing at the GIF++ facility aims to prove that the tripe GEM based detectors can sustain high flux rate without affecting its' performance. It is foreseen to accumulate the 240 mC/cm² for each of the mounted chambers. There are two gain maps prepared so far, one for each of the detectors, the next ones will be done once the test is accomplished, which will take place in 2019/2020.

3) Description of the setup

Triple-GEM experimental setup

The new setup has been designed and assembled to host the Triple-GEM chambers.

Details of the new Triple-GEM setup for aging test @ GIF++ facility:

• The dimensions are ~52cm wide, ~174cm high and ~52cm deep;
• The electronics is located in lower part of this set-up outside the cone of the source;
• The setup is fully integrated and moveable to easily remove it from the bunker when needed.

Detector Under Test

GE1/1 - IV generation irradiated chamber ( gas mixture: Ar/CO₂ - 70/30)

• Irradiated chamber @ GIF++ during Jeremie’s aging studies to validate the Triple-GEM technology for GE1/1 project;
• ~55mC/cm² collected in about 6 months of continuous tests.

GE1/1 - V generation NOT irradiated chamber ( gas mixture: Ar/CO₂/CF₄ - 45/15/40)

Pictures of the CMS-GEM setup inside the GIF++ bunker ( backside ):

Pictures of the CMS-GEM setup inside the GIF++ bunker ( frontside ):

The GE1/1 - IV generation irradiated chamber detector under test is placed at ~1m from the source point ( D1 position ):

• half of the chamber is directly in front of the irradiator and is operating under a particle flux just below 10⁸ Hz/cm²;
• the other half, protected by the shielding of the irradiator, receive a flux lower by four orders of magnitude.

The Readout System

In order to measure the gain variations in the GE1/1 detector, two KEITHLEY 6487 pico-ammeters are connected to several sectors of the readout board:

• one pico-ammeter in the irradiated part ( readout sector iφ=2,iη=7 );
• one pico-ammeter in the protected part ( readout sector iφ=2,iη=2 );

The devices are connected in series with a GPIB protocol and controlled with a LabView interface; The anode current is recorded every 5 minutes for each sector.

The GE1/1 chamber was also connected to a MCA in order to measure the energy resolution at different values of the accumulated charge.

4) Procedure

4.1 Powering ON the detector & Recording the data

There are two possibilities of powering the detector ON, same for recording the data. The first option is to enter the GIF++ facility and operate the HV Power Supply in person via the dedicated PC "cmsgemhw".

The second, and preferred option is to operate the PC remotely via "TeamViewer" from the network outside CERN and via "Remote Desktop Connection" tool in case of being logged into the CERN network.

The GEM based detector are fragile pieces of hardware, thus they require the user to be operated in a responsible way. The powering process should be realized in the proper way and the user should never exceed agreed working HV point without discussing it with the contact person, responsible for the setup.

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The first step of the DAQ preparation consists of several steps:

CAEN N1470 HV Power Supply - Voltage and Current Monitoring

Create, if not already existing, the .txt file that will be filled with the monitored Voltage and Current values of the Programmable HV Power Supply - CAEN N1470.

The directory where to save the raw data is located in:

• GE1/1 - IV gen. chamber: C:\Users\cmsgemhw\Documents\GIF++_Data\GE11_IV_generation_chamber/HV_Power_Supply_Voltage&Current_Monitoring
• GE1/1 - V gen. chamber: C:\Users\cmsgemhw\Documents\GIF++_Data\GE11_V_generation_chamber/HV_Power_Supply_Voltage&Current_Monitoring

The name of this .txt file should follow the template:

GE11_X_Z_CERN_gifpp_Voltage_Monitoring_YYYYMMDD.txt

where: X – stands for the generation of the chamber; Z - stands for the type of the detector: S (short) or L (long); YYYYMMDD – stands for the date of the file creation.

KEITHLEY 6487 pico-ammeters - Anode Current Monitoring

Create, if not already existing, the .txt file that will contain the Anode Current values coming from the Keithley 6487 pico-ammeter.

The directory where to save the raw data is located in:

• GE1/1 - IV gen. chamber: C:\Users\cmsgemhw\Documents\GIF++_Data\GE11_IV_generation_chamber/Keithley6487_Picoammeter_Anode_Current_Monitoring
• GE1/1 - V gen. chamber: C:\Users\cmsgemhw\Documents\GIF++_Data\GE11_V_generation_chamber/Keithley6487_Picoammeter_Anode_Current_Monitoring

The name of this .txt file should follow the template:

GE11_X_Z_CERN_gifpp_anode_current_monitoring_YYYYMMDD.txt

where: X – stands for the generation of the chamber; Z - stands for the type of the detector: S (short) or L (long); YYYYMMDD – stands for the date of the file creation.

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Once the files are successfully created, the LabView based software, used for the monitoring of the parameters listed above, should be turned ON.

CAEN N1470 HV Power Supply - Labview Control Software

Open the LabView control software of the CAEN N1470 HV Power Supply named "HV-Power-supply-MultiChannel.vi". Its location is:

C:\Users\cmsgemhw\Documents\CAEN_PSM_Labview\HV-Power-supply-MultiChannel.vi

On the software front panel (see the attached picture), set the "VISA resource name" to COM8. Then press the white arrow in the left hand side, upper corner in order to start the programm:

On the software front panel (see the attached picture), set the power supply settings as follows:

Current limit [uA]:	750	V-Set [V]:	3713.5
V-Max [V]:	3720	Trip Time [s]:	0
Ramp-Down [V/s]:	250	Ramp-Up [V/s]:	50

Then press "Write Config to Selected Ch.”, ensuring that the "Channel number" field is set to 0 (Advice: Please click the "Write Button" plenty of times)

In the "File name" field, set the absolute path of the data file that is intended for the storing of the Voltage and Current data, previously created in the section: CAEN N1470 HV Power Supply - Voltage and Current Monitoring and press the "Saving Data" button.

Once all of the steps have been successfully followed, please put the switch in ON position ( top part of the Front Panel ).

KEITHLEY 6487 pico-ammeters - Labview Control Software

Open the LabView control software of the Keithley 6487 pico-ammeter named "GIF_Kiethley6487_MultiRead.vi". Its location is:

C:\Users\cmsgemhw\Documents\Current DAQ\GIF_Kiethley6487_MultiRead.vi

On the software front panel (see the attached picture), set the "Waiting time(s)" to 300, "Accumulations" to 100 and "nplc" to 1. These values are usually preset ( default values ) and the user does not need to modify them.

The default "GPIB address" need to be changed every time the "GIF_Kiethley6487_MultiRead.vi" is started. Set the "GPIB address" to GPIB0::XX::INSTR, where XX is the actual address of your pico-ammeter. The "GPIB address" fields shall be modified as follows ( More information can be found in the Keithley 6487 manual ):

Pico ammeter 1: GPIB0::15::INSTR	Pico ammeter 2: GPIB0::22::INSTR
Pico ammeter 3: GPIB0::18::INSTR	Pico ammeter 4: GPIB0::17::INSTR

In the "chemin du fichier" field, set the absolute path of the data file that is intended for the storing of the Anode Current data, previously created in the section: KEITHLEY 6487 pico-ammeters - Anode Current Monitoring:

Once all of the steps above are accomplished press the white arrow in the left hand side, upper corner in order to start the acquisition of the data. At this point please double check that the chamber did not TRIP and that the Anode Current plots are "reasonable". That's it – Log Out.

4.2 Maintaining the experiment

It is highly recommended to check at least twice a day the status of the chamber at the GIF++ facility in order to ensure that the chamber is operating without disturbances and did not TRIP.

CAEN N1470 HV Power Supply - Voltage and Current Monitoring

To check that the HV voltage and current are stable and there are no trips, open the LabView control software of the CAEN N1470 HV Power Supply named "HV-Power-supply-MultiChannel.vi". Its location is:

C:\Users\cmsgemhw\Documents\CAEN_PSM_Labview\HV-Power-supply-MultiChannel.vi

On the V_mon graph, ensure that the plotted value matches with the V_set value as shown.

Also ensure that there are no large variations in the V_mon or the I_mon from the plotted values on the graph.

Check that there are no trips in the power supply by checking the shown display. If the display is bright green, it means that there is a trip.

KEITHLEY 6487 pico-ammeters - Anode Current Monitoring

On the picure below ,the typical GIF_Kiethley6487_MultiRead.vi, output plots are shown with the indicated areas, corresponding to source ON and OFF time periods in the first raw. The second raw has a different shape because the picoammeters are currently not connected to the second chamber.

Gas Status

There are two ways of checking the gas status at the GIF++. The gas status can be checked either manually at the facility or remotely using "TeamViewer" application.

The first way is to manually check the input and output flow rates at the GIF++ facility. This is done once in a week. The input flow rate of the Ar/CO₂ - 70/30 (70/30) mixture should be above 5 L/hr and the output flow rate should be around 4L/hr. The input pressures of the gases should be around 1 bar.

The second way to check the gas status is to login to the "TeamViewer" application (request the team leader for access). This should be done once every day.

Go to the website webdcs.cern.ch and login to see the page as shown below (request the team leader for access).

Click on Plot Monitoring history to open the graph plotter. Open the plot for Pressure box 103 ( Ar/CO₂ - 70/30 mixture ) on parameter left (red) and Pressure box 106 ( Ar/CO₂/CF₄ mixture ) on parameter right (blue) to obtain a graph as shown in the figure.

Check that the pressure is constant with time. Note : The graph plots the gauge pressure with time and not the absolute pressure. The gauge pressure is the difference between the internal and the external pressures. So, the units is in mbar.

In case there is a decrease in the pressure, immediately switch off the detector to prevent any damage to it.

The gas mixture is supplied from an Ar/CO2 bottle. The bottle needs to be changed every 12 days. So please check with the team leader when the last time of bottle had been changed. Update the excel template GIF++ Gas Consumption in the location

C:\Users\cmsgemhw\Documents\Gas Status

Enter the date and time of evaluation and the date and time the gas bottle was replaced. The Autonomy of the bottle is the number of days the bottle has lasted.

4.3 Analysing the data

5) CMS Online - Elog

As the experiment is foreseen to be performed continuously for ~ 24 months, we'd like keep track of any modifications in order for better understanding of the situation and further analysis purposes etc. We kindly ask anyone who makes any modification to report them on the E-LOG.

6) External links

Gamma Irradiation Facility - Operation Page: GIF++ Operation Page

Gamma Irradiation Facility - Status of Source: GIF++ Status of Source

7) Contact

If you intend to perform any changes in the GEM setup, please contact Francesco Fallavollita and Marek Gruchala. Upon the internal agreement and in order to keep track of any modifications you are also obliged to report any activities you perform on the E-LOG.