Difference between revisions of "Hall-B Collimators and Flux"

From GlueXWiki
Jump to: navigation, search
Line 1: Line 1:
 
Teleconference - June 1st
 
Teleconference - June 1st
  
Elliott, David Lawrence and Zisis
+
Elliott, David Lawrence and Zisis discussed issues in connection to collimation and beam flux.  The consensus was that the tagger t-counters can be driven to around 1 MHz which would result in 8 KHz on the BCAL Module when using the 1.0 mm collimator.  Since this collimator will result in a beam spot of 6.7 mm in diameter, we probably do not need use an additional collimator immediately in front of the BCAL, although its use is not excluded and may be desired.  The use of such a collimator would have to be decided after simulating its effect.  As far as the DAQ rate it was agreed that this should be kept around 1 KHz to avoid deadtime and related problems.
  
===
+
Other interesting items that were discussed: BPM (David has received some responses and will chase this), data stream (the desire is to have digitized MC and cosmics data for David to pass through DANA), use of a He bag leading to BCAL module from CLAS, use of veto counter in front of module, and Coda tutorial by Elliott.
 +
 
 +
-----
  
 
Hi,
 
Hi,

Revision as of 19:11, 7 June 2006

Teleconference - June 1st

Elliott, David Lawrence and Zisis discussed issues in connection to collimation and beam flux. The consensus was that the tagger t-counters can be driven to around 1 MHz which would result in 8 KHz on the BCAL Module when using the 1.0 mm collimator. Since this collimator will result in a beam spot of 6.7 mm in diameter, we probably do not need use an additional collimator immediately in front of the BCAL, although its use is not excluded and may be desired. The use of such a collimator would have to be decided after simulating its effect. As far as the DAQ rate it was agreed that this should be kept around 1 KHz to avoid deadtime and related problems.

Other interesting items that were discussed: BPM (David has received some responses and will chase this), data stream (the desire is to have digitized MC and cosmics data for David to pass through DANA), use of a He bag leading to BCAL module from CLAS, use of veto counter in front of module, and Coda tutorial by Elliott.


Hi,

as I mentioned before (and presented on the Coll.Meeting in November (cf. http://argus.phys.uregina.ca/cgi-bin/private/DocDB/ShowDocument?docid=555&version=1), the spot size in the alcove is always of the order of >=1.5cm for existing collimators. In order to get a tagging range of ~137-653 MeV (mentioned in Rafael's mail), the electron beam energy has to be ~685MeV (Hall-B tagging range: 21.1% to 95.2% at this E0). Incoherent brems. has a comparatively wide spread at this energy causing a reduction of the photon flux after collimation to only:

  • 6.4% for Eg=145MeV to 7.0% for Eg=650MeV for 2.6mm colli
  • 3.0% for Eg=145MeV to 3.3% for Eg=650MeV for 2.0mm colli
  • 0.8% for Eg=145MeV to 0.9% for Eg=650MeV for 1.0mm colli

The beam sizes after collimation are as follows:

  • colli.(0.0m) PRIMEX (3.6m) CLAS center (15.9m) alcove (33.0m)
  • 1.0mm diam. 0.7mm 3.2mm 6.7mm
  • 2.0mm diam. 1.4mm 6.5mm 13.5mm
  • 2.6mm diam. 2.4mm 9.0mm 18.7mm

If you want a beam spot smaller than 1cm (at decent rates), you might consider to put the BCAL module at the PRIMEX position upstream of CLAS. An object of size 400x12x23cm^3 fits there quite good (even enough space for rotating the module).

Greetings

Franz