Time-of-Flight/Start-Counter/Target Meeting, December 11, 2009

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Location, Time

Friday, December 11, 2009
2:00 pm EDT
JLab: CEBAF Center, Room F326/7
ESNet: 8542553
EVO: direct meeting link
Conference Group: 800-377-8846, participant code: 77438230
Slides: talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2009-12 on the JLab CUE (you have to be a member of the "halld" group). This directory is accessible from the web at https://halldweb.jlab.org/talks/2009-12/ .


  1. Minutes from the last meeting
  2. Time-of-Flight Status: Sasha O.?
  3. Start Counter Status: Werner?
  4. Target Status: Aram?
  5. Action Items


JLab: Mark Ito (chair), Chris Keith, Sascha Somov, Simon Taylor, Tim Whitlatch, Beni Zihlmann


Sascha asked about whether we intend to use constant fraction or leading edge discriminators for the the TOF. Ben Raydo is working on a 16 channel leading-edge discriminator for Hall B and will build 5 for us as well. Richard Jones is planning to use leading-edge discriminators for both the microscope and the fixed array for the tagger because of the high rates in those counters.


Chris Keith reported on his thinking about a dedicated refrigerator for the target. He has identified a pulse tube refrigerator, made by Cryomech, that seems appropriate. It is a mechanical device; it has no cold moving parts and will therefore produce very little vibration. Maintenance is relatively easy; the maintenance cycle is 20,000 hours. It uses helium gas as the working substance and a room temperature compressor. There are two stages of cooling, 50 or 60 Watts to cool the radiation shield, tens of Watts of cooling of the target liquid at 20 K and 1.5 W at 4.5 K. It requires cooling water for the compressor and runs on 220 V 3-phase power. Hydrogen for the target cell would be circulated in a completely closed system; probably several liters will be needed. Chris mentioned that buying a spare compressor might be good idea.

The target group will take full responsibility for design and testing of the complete system, with the possible exception of the controls (see below). They will need engineering design authority from Hall D. Steve Christo will probably be consulted on the target cell fabrication. The control system is relatively small: about 10 thermometers, 5 pressure guages and a heater. If a PLC control system is chosen, the target group will not be able to help. If VME-based EPICS is chosen, they can take care of that.

Chris and his group probably cannot start thinking seriously about our target until Fall 2010. They have a frozen spin target experiment and Qweak coming up. He estimates that our project should take about 18 months. Tim noted that the schedule indicates that the target system should be done by July 2012, so this is a rough match. The total target group consists of three physicists, two engineers and three technicians.

Tim does not anticipate huge problems with mechanical support. The plan is to follow the scheme used in Hall B.

Chris and Tim thought it was premature to start regular dedicated target meetings. We will therefore continue to include target items in the agenda for this meeting.