Difference between revisions of "CDC HV scan instructions October 2021"
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| − | If the pressure has changed by 0.1 kPa or more since the start of the scan, stop the scan and start again from the previous measurement. | + | If the pressure has changed by 0.1 kPa or more since the start of the scan, stop the scan and start again from the previous measurement. If it changes again by 0.1 kPa, stop the scan and start again from the previous measurement. If it is changing by 0.05+ kPa between measurements, give up. We can try again after the empty target run. |
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You can skip the second measurement at 2125V if the pressure is within 0.02kPa of that for the first measurement. | You can skip the second measurement at 2125V if the pressure is within 0.02kPa of that for the first measurement. | ||
Revision as of 10:29, 8 October 2021
This should be done with stable beam and normal weather (not when a storm is rolling in). If the pressure is changing by 1 kPa/h or more, reschedule.
The most sensitive part of the scan is the first half, when the HV is highest and the CDC is on or close to its efficiency plateau. The atmospheric pressure can be monitored using the EPICS variable RESET:i:GasPanelBarPress1 Its units are kPa, the long-term mean is around 100kPa (due to a calibration offset).
Use the same beam current that will be used for the production runs with the CDC on. At present that is 200nA on the run plan doc.
Please collect 9M triggers at the following HV settings (in V) for ALL CDC, in the order given below.
In the logbook, please note the run number, HV and the pressure (listed in RCDB as cdc_gas_pressure) at the start of each run.
2125 2150 2140 2130 2125 2120 2110 2100 2090 2080
If the pressure has changed by 0.1 kPa or more since the start of the scan, stop the scan and start again from the previous measurement. If it changes again by 0.1 kPa, stop the scan and start again from the previous measurement. If it is changing by 0.05+ kPa between measurements, give up. We can try again after the empty target run.
You can skip the second measurement at 2125V if the pressure is within 0.02kPa of that for the first measurement.
If the beam is steady then the whole procedure should take a few hours at most. If there are any problems, please contact the CDC experts (Beni and Naomi. Beni will be easier to reach during the weekend.)
To set the HV:
Find the main action bar (vertical menu), click CDC voltages.
In the middle of the circle on the left, click ALL HV, then select from the dropdown menu "CDC: Set CDC HV parameters" Change voltage to what you want in the left column, hit return.
