Difference between revisions of "Pair Spectrometer Shift"

Revision as of 14:51, 3 July 2014

The Pair Spectrometer

The pair spectrometer consists of the converter, the dipole magnet and two types of scintillator detectors: 290 high-granularity hodoscope and 16 low-granularity counters (PSC), which are used to detect e+e- pairs produced in the converter by a beam photon. The converter accommodates up to 3 thin foil targets and a wire, which will be used to study the profile of the photon beam. The magnet will be operated at 1.8 T field. Light from scintillators is detected by SiPMs and Hamamatsu H7415 assemblies for the hodoscope and PSC, respectively. The nominal operating voltage for PMTs is about 1.2 kV.

Checking PS settings

Before starting the run the shift should follow the run configuration requirements and perform the following actions:

• check that the magnetic field is switched on and the magnet current corresponds to the run configuration requirements. This can be done using a magnet Slow Control GUI. If the magnet is switched off
  • make sure that the photon beam is not present in the hall, otherwise call to MCC (999) and request switching the beam off.
  • switch on the magnet using the magnet Slow Control GUI. Press "ON' button on screen and wait until it becomes green. Switching the magnetic field on may take 10-15 minutes as the magnet degaussing procedure is involved. After the magnet is on make sure that the current reading corresponds to that from the run configuration requirements.

• check that the right converter is inserted in to the photon beam. This can be done using the Slow Control GUI. If the converter is not in the right position, the shift crew must call to MCC (7050) and request switching the beam off. The converter can be subsequently inserted by selecting the foil number on the GUI screen and clicking on "GO' button. Green color of the button indicates that the converter is on the right spot.

• Set high-voltages on the PSC using a Slow Control GUI. Press HV "ON" button on the GUI screen. If any of the bases fail to set their high voltage a non-expert will first retry clicking 'All HV'. If the problem persists the expert should be called.

• Set bias and low voltages for the PS hodoscope using a Slow Control GUI. Press HV "All LV" button and "All B'/"All A" buttons on the GUI screen.

Routine Operation

The shift crew should monitor the detector performance parameters such as:

• rates of the hodoscope and PS counters, and the spectrum of the photon beam. The monitoring should be performed using a Slow Control GUI. Any hot or dead channels have to be recorded in the log file. If the average counter rate significantly deviates (the range will be specified for each shift) from the expected rate, the run coordinator should be called.

• HV and voltage settings for the PCS and the hodoscope using the Slow Control GUI. In the case an alarm system detects the PMT current trip, the PMT high-voltage will be shutoff. The crew should set the voltage on the PMT using the GUI interface (see instructions below). If the problem persists the expert should be called.

• temperatures for the hodoscope SiPMs. The alarm will be generated if the SiPM temperature exceeds the critical value. If this happens the expert should be called.

Interlocks

Detector Expert On Call

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