Download University of LeicesterPLUMERef: PLM-PAY- LabTestPlan-018

University of Leicester
PLUME
Ref: PLM-PAY- LabTestPlan-018-1
Date: 02/10/2008
Payload Lab Set-up Test Plan
L. Evans
Date
Updated Reference Number
change
02/10/2008
PLM-PAY- LabTestPlan-018-1
first version issued
Plan to test the payload (a micro channel plate - MCP) in the lab using a radioactive source
(55Fe ). The MCP and source will be in a vacuum chamber and results will be read out using
the electronics chain (pre-amp and amplifier) connected to a multi-channel analyser (MCA).
1. Set up electronics chain:
Page 1 of 6
University of Leicester
PLUME
Ref: PLM-PAY- LabTestPlan-018-1
Date: 02/10/2008
Fig 1
Figure 1 shows the set up for initial testing of the electronics chain.
Set up the equipment as shown above, see “Equipment Configuration” document for
details. This set up allows the electronics chain components to be tested.
2. Use tail pulse generator to produce test signals:
The tail pulse generator is used to produce a voltage pulse which can be set to our
specifications, see “Equipment Configuration” document. This pulse is used to test
the electronics chain is working and suitable for the purpose. If a stable, consistent
signal is seen, similar to the one shown below in figure 2, then the set up is working
correctly.
Page 2 of 6
University of Leicester
PLUME
Ref: PLM-PAY- LabTestPlan-018-1
Date: 02/10/2008
Fig 2
Figure 2 shows a shaped voltage pulse. The pulse will decay exponentially and will
drop past zero showing a negative peak as there is no pole zero cancelation – the
MCA’s discriminator will ignore negative pulses, so this is not a problem.
3. Replace oscilloscope with MCA
The oscilloscope shows the shape of the peak but it cannot record peak heights.
Connecting an MCA allows the number of peaks of different heights to be logged and
the data saved for analysis and calibration.
Connect the MCA as describes in the “Equipment Configuration” document.
4. Test vacuum chamber
Before the vacuum chamber can be used for the experiment it must be checked to
ensure that a suitable pressure can be achieved by the pumping system and that
there are no substantial leaks.
For correct operation of the MCP a vacuum of around 5  10 6 mbar is required.
Page 3 of 6
University of Leicester
PLUME
Ref: PLM-PAY- LabTestPlan-018-1
Date: 02/10/2008
The vacuum system is leak checked using Helium. A small nozzle is used to spray
the Helium around any joints in the vacuum system. A mass spectrometer is
connected to the system which detects any Helium that leaks in through the joints
indicating a leak.
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Open the valve on the Helium tank
Place the nozzle into a small bottle of water a squeeze – this allows the flow
of Helium to be seen as it can thus be adjusted to the required flow rate
Leak checking must start form the top of the system as the Helium rise
Use the nozzle to spray Helium around a joint in the vacuum system
Wait a short time (say, 10 seconds) to see if there is a reaction on the mass
spectrometer
If no reaction then repeat procedure on the next joint down
If the mass spectrometer does register Helium then there is a leak around the
joint
It must then be decided if the leak is severe and must be fixed (eg. by
retightening the fixing) or if it is small and inconsequential
5. Fit source and detector to vacuum chamber
Once the vacuum system has been leak checked (see step 4) the source and MCP
for the experimental procedure can be fitted.
Exact details of these fittings are not known yet but will be added shortly (18/7/08)
6. Connect electronics to MCP for detector read-out
Once the detector body has been fitted to the vacuum system the electronics chain
set up earlier (see steps 1 and 3) must be connected to the electronics on the back
plate of the detector so signals from the MCP can be measured.
The MCP setup for the actual experiment is detailed in the equipment configurations
document.
Power up procedure:
Check vacuum level. It should be less than 5e-6 mbar
Page 4 of 6
University of Leicester
PLUME
Ref: PLM-PAY- LabTestPlan-018-1
Date: 02/10/2008
Our plate has a 40:1 aspect. We want a plate voltage of about 700V, and an
accelerating voltage of 300V towards the resistor anode. Use the multimeter to
ensure the plates have the correct voltages on them.
- Increase front voltage to 200V.
- Increase front voltage to 300V, set back voltage to 100V
- Increase front voltage to 400V, set back voltage to 200V
- Increase front voltage to 500V, set back voltage to 300V
- Check current ratings, calculate plate resistances.
Gradually increase front voltage to 1000V.
- Again, check current ratings for both sides of the plate. The resistance of the MCP
we're using should be around 34 Megaohms.
If the current readings from the multimeter are equal to zero even with high voltages
on the plates, then the electrical contact is bad and the detector body will need to be
reassembled. The rated resistance for our MCP is 34Megaohms.
After saving the signal pattern produced from the MCA and stopping the MCA
recording, the power down procedure consists of:
- Gradually decrease front voltage to 500V.
- Gradually decrease back voltage to 0V.
- Gradually decrease front voltage to 0V.
- Switch off all power supplies.
It’s important to follow these procedures exactly. Reverse biasing the MCPs or
raising the voltage levels too quickly can cause a spark fault inside the plate that will
effectively destroy it. If the plate goes bust, the whole detector will have to be
reassembled.
Power down procedures may have to be carried out at any time during the
experiment. The basic rule of thumb is: don’t let the potential difference across the
plate exceed 850V or drop below 100V.
Page 5 of 6
University of Leicester
PLUME
Ref: PLM-PAY- LabTestPlan-018-1
Date: 02/10/2008
7. See signals received by MCA
Refer to “calibrating the MCA” document for details about using the MCA and
recording data.
8. Analyse signals
The signals that we see will be saved to the MCA computer as ASCII data files and
will then be analysed to see how our detector is responding. This information can
then be used to make predictions about how a dust impact will affect the MCP and to
start designing a test plan for use in a dust accelerator.
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