Sep 2, 2008 Calorimetry
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Items for followup from Aug 18 meeting
- George: report on trip to Edmonton
- Estimates of pedestal width (electronic noise, etc.) for FM PMTs. The dark rate should be negligigle in this case.
- Resolution studies with up-to-date geometry (Blake) ONGOING
- Resolution studies with different segmentation for the outer section. - LOWER PRIORITY
- Add F100 rad hard glass to simulation. - Matt will do this
- Decision on Bcal sampling fraction needed by Sep. - Work by Stamatis (on vacation) will be summarized upon his return.
Documents to Review
- Please place documents here for review in advance of meeting
- Paul Smith's Fiber Pulser
Note: This meeting will be dedicated to reviewing calibration issues. Other reports will be included as time permits.
- Review of Calibration Issues
- Athens update report: GlueX-doc-1092
- Any other business
Attending: Athens: Christina, George, Pavlos; UofR: Zisis, George, Kathryn, Blake; JLab: Elton, Beni, Tim, Fernando; IU: Matt, Mijahlo, Claire Tareert; FIU: Werner.
- Claire Tarbert is a new research associate at IU. Welcome!
Review of Calibration System
- Athens update report: GlueX-doc-1092
- Christina went over the posted presentation
- First the laser option was presented
- APD used to monitor the absolute light from the laser, but noise pick up from the laser was a problem. Elton indicated that a full shield was necessary to shield the laser. Method for shielding similar laser can be found on the bottom of page 3 of Hall B CLAS-NOTE 91-002.
- Second, the LED option was presented.
- 2x1 cm2 boards with the LED and pulsing electronics have been made; 35 boards produced.
- The idea is to place the boards near each pmt to be calibrated, e.g. on the light guide of the SiPMs. George: could be placed on the tapered length of the guide.
- Fernando asked about the temperature dependence: it has not yet been measured.
- Control board (for about 30 LEDs) has been constructed and would be placed about 2-3 m away from the LED.
- Each channel requires three cables (voltage, trigger signal and ground). The trigger signal is a TTL pulse.
- Question about masking individual channels for firing? This would check (optical) cross talk between channels.
- The calibration system needs to have its requirements clearly defined. Each subsystem (Fcal, Bcal, Start counter) reviewed its requirements, but further refinement is necessary.
- Elton prepared the following table to clarify the requirements. We need to complete it to provide adequate feedback to Athens:
Calibration Specifications Table
|Light uniformity channel-to-channel||≤ 15%|
|Dynamic range of input (number of photoelectrons)||typically 100||100 up to 800|
|Requirement on absolute light input||none (PRIMEX might have)||150 pe on module|
|Variation in arrival times of cal pulses||~3 ns||≤ 2 ns||~3ns||~3ns|
|Time stability gain and timing (one channel)||≤ 10% in 6 months|
|Temperature stability (likely cause of time stability)||1o causes 3% gain change|
|Location of calibration input||From front to monitor rad damage||light guide tapered side|
|Geometrical constraints||Approximately 90% of front 4x4 cm2 area available||packing of WC and LGs, LED fitting, cable routing|
- Comment: Time (and temperature) stability most important.
- Comment: Option of delivering a range of light intensities important (e.g. using various filter settings).
- Comment from Werner: The flexibility in the use of the LED would be very useful for the start counter. Christina: Still need to test stability.
- Questions to Matt: What uniformity could one expect from the plexiglass input system? How many fibers were used to pulse the plexiglass, i.e. how often were they spaced?
- Comment: Matt drew attention to an LED pulser by Paul Smith which might be a useful reference.
- Fiber Test Stand at JLAB (Beni)
- Test setup now operational . Attenuation length and light output completed for Kuraray and recent Bicron Fibers. More measurements under way.
- Fiber Tests at Regina (Kathryn)
- Light output reported for Kuraray and Bicron fibers. Measurements of attenuation lengths will be summarized and included along with light output measurements.
- Preliminary conclusion is that Kuraray fibers have higher light output and longer attenuation length, but results still need to be digested.
- George noted that a couple of Quantacon pmts would simplify and give confidence to the calibration procedures.