Difference between revisions of "DIRC Shift"

Revision as of 08:14, 28 January 2019

The DIRC

The DIRC is a plane of 4 independent boxes each containing 12 fused silica radiator bars with a size of 4.9 m x 35 mm x 17.25 mm, which are housed in an honeycomb shell with a thin aluminum skin. Each pair of bar boxes is optically coupled to a water-filled expansion volume, known as the Optical Box (OB). The Cherenkov photons from the radiators propagate through the water-filled OB and are detected by an array of Hamamatsu H12700 multi-anode photomultiplier tubes in each OB.

Checking the environment

DIRC Environment GUI

The important elements of the DIRC environment are the nitrogen purge of the bar boxes which are monitored by flow and pressure sensors in the GUI above. In addition, the optical box environment is monitored by a temperature and light sensor to ensure the environment in the dark box is appropriate for the electronics and PMTs. Finally a water leak sensor is located beneath the optical box which will disable the low and high voltage in the case of a water leak.

The H12700 multi-anode PMTs are operated inside a dark box attached to the optical box, which allows for maintenance of the system while the bases are powered off. An interlock on the low and high voltage to the electronics and PMTs protects the readout system from damage. A proximity sensor provides an interlock to shut off the LV and HV if the dark box is opened, exposing the PMTs to external light. A fan provides cooling to the electronics to prevent excessive temperatures inside the dark box, and an interlock will shut off the LV and HV if the fans are not operating or the temperature exceeds the safe value.

Voltage controls

DIRC Voltage GUI

Each DIRC electronics module (instrumenting three MAPMTs) is powered by the Wiener LV modules at 5V, separated into 9 groups for each optical box (North and South). To turn on the LV supplies for each modules push the "ON" button and verify the voltage read back matches the figure given here. The high voltage can be set individually for each DIRC electronics module as seen in the HV GUI. To turn on the HV supplies click the "South" box and select "Turn ON all HV South channels"

LED Pulser controls

DIRC LED Pulser GUI

The DIRC PMTs are monitored by an LED pulser which injects pulsed low intensity light inside the optical box. The GUI above shows the LED pulser GUI which can be controlled to set the pulser rate and LED bias magnitude. These parameters should not be changed unless you're directed to do so by an expert.

Expert personnel

The individuals responsible for checking that the DIRC is ready to take data and setting its operating parameters are shown in following table. Problems with normal operation of the DIRC 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.