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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. 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. Page 6 of 6