Difference between revisions of "Barrel Calorimeter Shift"

Revision as of 13:35, 20 May 2014

BCAL The Barrel Calorimeter

The barrel calorimeter (BCAL) is a lead-scintillating fiber matrix readout with 3840 S12045 Hamamatsu multi-pixel photon counters (MPPCs). The MPPC light sensors operate a bias voltage less than 76 V. Liquid coolant is circulated through the readout assemblies to set and maintain the temperature of the sensors at their operating temperature between 5 and 25$^\circ$C.

BCAL Routine operation

During routine operation the user will need to monitor the environmental conditions, which may affect BCAL performance, as well as turn the system on and off. Control and monitoring of the system is accomplished using the Hall D graphical user interfaces (GUI) to EPICS \cite{epics}. A description of how to bring up the GUI screens can be found in Section\,\ref{sec:controls}. The two screens pertinent to the BCAL are shown in Fig.\,\ref{fig:BCAL_environmental_sensors} and Fig.\,\ref{fig:BCAL_voltages}. We briefly describe the use of these interfaces:

BCAL Checking the environment

The temperature and humidity measurements of the BCAL can be displayed using the GUI shown in Fig.\,\ref{fig:BCAL_environmental_sensors}. The controls and monitoring of environmental conditions is accomplished separately for the upstream and downstream readouts of the BCAL, which are connected to individual chillers and nitrogen gas flow lines. The coolant in the chiller (water for initial operations and later water and 20\% propylene glycol for operation at $5^\circ$C) is circulated through input and output manifolds which feed two readout assemblies in series. The temperature of the chiller will be set prior to operation to maintain a relatively constant temperature for the light sensors. The coolant flows through the cooling plate in each readout assembly, which is in thermal contact with the multi-pixel photon counters (MPPCs), and their temperature is recorded using RTDs attached to the plate. The temperatures are displayed in the figure and should normally read within about 1 degree of each other. The space enclosed by the readout electronics is monitored using four temperature and humidity sensors, which determine the dew point, on both the upstream and downstream. These measurements are displayed on the GUI to monitor the humidity level of the environment of the electronics. The space enclosed by the readout assembly is purged with dry nitrogen to avoid condensation, and the nitrogen flow rate is also indicated on the GUI. During routine operation, this GUI is for information only.

BCAL Voltage control

The low voltage (LV) and bias voltages for the MPPC sensors can be set using the GUI show in Fig.\,\ref{fig:BCAL_voltages}. The voltages for normal operation are recorded in files, which can be restored using the button in the top middle of the screen. The LV and bias settings must be restored separately. Once the voltages have been restored to the memory of the voltage supplies, the user may turn the voltages on by using the ``All U Bias" and ``All U LV" left buttons in the middle of the BCAL sketch. The voltages for the downstream side are controlled using the buttons on the right. The voltage read back and the current draw of each channel are histogramed and plotted at the bottom of the GUI. When all voltages are on at their set values, the display turns green. Changes to the voltage settings are only allowed by an expert, or under his/her guidance.

BCAL Interlocks

The voltages and the chiller are interlocked using the temperature and dew point measurements described in Section\,\ref{sec:bcal_environment}. If the temperature exceeds the preset value in the GUI, or the dew point comes within a predetermined window of the measured temperature, or the chiller goes off, the interlock will be set and it will disable the voltage supply crates and turn off the chiller. Changes to the interlock settings are only allowed by an expert, or under his/her guidance.

BCAL Expert personnel

The individuals responsible for checking that the BCAL is ready to take data and setting its operating parameters are shown in Table\,\ref{tab:bcal}. Problems with normal operation of the BCAL 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 signature added to the document residing in the Hall D Counting House.