Time-of-Flight System Shift
The Time-of-Flight (TOF) consists of 92 scintillator counters arranged in two planes. The upstream plane has counters running horizontally and the downstream plane has them running vertically. Most have dimensions of 2.54x6.00x252 cm with exceptions noted below. The 46 counters in each plane consist of 42 counters with a PMT on each end, with 4 counters only read-out from one end (due to the beam hole in the center of the plane). Single-ended counters are of roughly half the length of the standard counters. In addition, the four double-ended counters nearest the beamline (two on each side) are of half-width (3 cm rather than 6 cm), to reduce counting rate.
The downstream counters have ends labeled "top" and "bottom" while the upstream counters have ends labeled "north" and "south". The PMTs themselves are numbered from 1 to 44 going from top to bottom or north to south.
The Time-of-Flight is located just upstream of the FCAL and downstream of the FDC. It is mounted on the forward carriage.
All PMTs in the system are the same: Hamamatsu H10534MOD. There are 176 PMTs altogether.
There are no devices providing environmental information (such as temperature) associated specifically with the TOF.
Shift crews should be monitoring the following:
- high-voltage status
- statistical information from raw data ("monitoring histograms")
In general, most important properties of individual HV channels will be monitored automatically by the EPICS alarm system and shift crews need to respond to alarms as they arise. To facilitate this, each shift should check that the TOF HV is up and running.
The conditions that may cause EPICS alarms are:
- tripped voltage
- read-back voltage out-of-range
- supply current out-of-range
- EPICS communication lost
In responding to alarms shift crews should check the guidance for the alarms as provided by the alarm handler.
Turning High Voltage On
- verify that no work on TOF is under way in the hall
- start the scaler monitoring program as described below; while the HV is coming up, keep an eye on the rates; if a rate for a channel exceed 20kHz with beam off, immediately turn off HV for this channel; with beam on, no rate should exceed 1 MHz
- under hdops account, run 'css' program
- in the pull-down menu, select TOF desktop
- TOF HV control in expert mode ('TOF_voltages.opi') should open
- click on 'Save/Restore' and select 'TOF: Restore HV parameter setpoints'
- the file list should open; select the latest file with 'TOF_HV==All@OptimalHV==' name and click 'restore'
- click on 'North-South' field and select 'Turn ON ALL North HV Channels'
- click again and select 'Turn ON ALL South HV Channels'
- now click on 'Top-Bottom' field and select 'Turn ON ALL Top HV Channels'
- click again and select 'Turn ON ALL Bottom HV Channel'
- in less than a minute, all channels should reach their setpoints
- verify that all individual channel buttons are green; if any buttons are red click again on them to turn that channel on; if the button remains red after 20 seconds, contact the experts
- if any button is yellow, make a note in the logbook
- use the 2 histograms at the bottom to check that currents for all channels are in the 250-350 range
- quit 'css' if you have started it.
Monitoring Scaler Rates
- login to ROCTOF3: 'ssh hdtofops@roctof3'
- run scaler program: '/home/hdtofops/scaler/ao/jledScaler -n -t 5'
- discriminator scaler rates will be printed on the screen for all 176 channels
- typical rate with the beam completely off is in the 200-500 Hz range
- if any of the rates exceed 10kHz with beam off, notify TOF experts; if the rate exceed 20kHz, turn HV off for this channel and notify TOF experts about possible light leak.
Each run produces a set of monitoring histograms that should be compared to nominal histograms and scanned for anomalies. The histograms include:
- occupancy, channel-by-channel
- end-to-end coincidence rates (where appropriate)
- geometrical distribution of plane-to-plane matches
- timing distributions
The TOF calibration trigger should be running at about 0.1 percent of the total triggers during normal running. If this is not the case contact the trigger or TOF expert.
The individuals responsible for checking that the TOF is ready to take data and setting its operating parameters are shown in following table. Problems with normal operation of the TOF 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|
|Mark Ito||269-5295||June 12, 2014|