Central Drift Chamber Shift
The Central Drift Chamber
The Central Drift Chamber (CDC) is a straw tube chamber. It has 28 layers(rings) of straws each 150cm long. It is operated with an Argon CO2 gas mixture of 50% each by mol. The nominal high voltage (HV) is +2110V and the pre-amplifier cards require low voltage (LV) drawing 0.47A of current. The gas supply is monitored and controlled by the Gas System GUI while the HV and LV are monitored and controlled by the HV GUI.
The HV GUI controls and monitors the HV and LV of the CDC. In figure 1 you see an example of the GUI with one channel off. There are three representations of the CDC status in terms of individual HV channels (left) in groups of sectors (middle) and in groups of rings(right). The color code is as follows; if the channel is off it is red as well as the sector it belongs to and the ring it belongs to. The buttons in the three CDC representations have menus to select different functions like turning on or off all channels belonging to this sector. You can also select to display a list of HV channels grouped by sector, ring or whole detector showing all parameters for the HV channels. There are two graphs for the HV and two graphs for the LV showing the voltage setting for each channel as well as the current it draws. This is a very useful visual indicator to check whether any channel is deviating from its operating parameters. During routine operation all channels should be green this will result in all three representations to be green.
Note that like all HV/LV systems the following conventions is used for the buttons. The color indicates what state a channel is in (on=green, off=red) while the text indicates the action the button will perform when pressed (off = turn channel off, on = turn channel on). This means if a channel is on the button will be green while the text will read off.
The shift worker will use the GUI to turn on and off all HV and LV as well as monitor its proper settings. If any channel is red and can not be reset with turning on/off its HV and/or LV by the shift crew the detector expert on call has to be contacted.
Turning on for the first time
The detector HV and LV should be turned off when beam is established for the first time or after long periods of shutdown. Once clean beam is in the hall the detector should be turned on starting with the outer most ring. At this point you can turn on the LV for all channels. Observe the currents while the HV is ramping to the nominal values. If the ramp up was successful and the current draw on the HV channels does not cause any trips proceed to the next ring inwards. Continue this procedure till you reach the inner most ring.
The low voltage that powers the preamplifiers is interlocked with the air blower cooling the preamplifiers.
The individuals responsible for checking that the CDC is ready to take data and setting its operating parameters are shown in following table. Problems with normal operation of the CDC should be referred to those individuals and any changes to their settings must be approved by them. Additional experts may be trained by the system owner and their name and date added to this table.
|Name||Extension||Date of qualification|
|FDC/CDC on call expert||383-1185||June 4, 2014|
|Benedikt Zihlmann||269-5310||June 4, 2014|