Meetings

• January 5, 2012

Attendees: T. Averett (W&M), G. Cates (UVa), J-P. Chen (JLab), D. Gaskell (JLab), B. Hesman (UNH), W. Korsch (UK), Z-E. Meziani (Temple), B. Sawatzky (JLab), P. Solvignon (JLab), S. Wood (JLab), X. Zheng (UVa)

The meeting goal was to gather all the spokespeople of the Hall C A1n and d2n experiments for discussion on the polarized 3He target plans.

The general consensus was to use the same target system in Hall A and Hall C. Commissioning of the target system (A1n) would be likely in Hall A in 2015. In Hall C, the very preliminary schedule would put the start of A1n and d2n at the end of 2016.

Beam polarimetry:

   - Dave said there won't any problem to get a 2% systematics from the beam polarimetry but to get 1% he will need users contribution. However it doesn't seem that the two experiments need that level of precision after looking at the other sources of systematics. 

Coils:

   - The important aspect is that the holding field should be uniform in the pumping chamber.  With convection, the polarized gas in circulating so fast in the target chamber that a minimal holding field to limit the depolarization should be enough.
   - Zein-Eddine suggested two small solenoids, one for the pumping chamber and one for the target chamber. Multiple advantages can be seen if it would work: smaller system which will fit easily on the Hall A and Hall C platform, more room to access the target during the experiment and therefore work can be done faster (ALARA).
   - Concerns on the Hall C iron platform were expressed
   - Need an estimate of the fringe field from the SHMS. Paul Brindza said that it won't be a problem but it will be nice to have numbers/field map.
   - The UVa group is working on the holding field/coil design and will test the different ideas suggested during the meeting.

Target:

  - Todd reminded that it was seen in the past that too much laser power on the pumping chamber could damage permanently the target.
  - Gordon pointed out that a two-pumping-chambers-cell will allow to increase the gas volume to be polarized and the laser power.
  - Metallic target chamber should be OK with caps at each end.
  - 

Lasers:

  - Laser procurement is an big issue. The COMET production was discontinued.
  - Todd had contact with Laser Operations LLC. The system looks promising and cheap: here. Todd will order one to test and if all aspects are good more will be bought by JLab, ...

Polarimetry:

  - AFP will be used only for calibration: there will be significant polarization loss from this method with the new cell design.
  - Pulsed NMR is under development.
  - EPR can still be used.
  - With convection, the polarization gradient between the pumping chamber and the target chamber will be significantly reduced. So polarimetry in the pumping chamber should be enough.
  - A detailed study of the gas dynamics was recently published Dolph, Singh et al.

Task list:

   - Cell testing: polarization loss with different field gradients
   - Holding field design: look at the small field idea
   - Cell geometry optimization
   - Polarized gas dynamics
   - Max. polarization test: need more lasers (2 more)
   - Polarimetry cross calibration and optimization
   - kappa_0 measurement
   - Get a SUltra laser and test it.

Slides:

  - from Gordon: Conceptual design for the A1n targets: Media:a1n_impromptu_target_present.pdf
  - from bill: ex situ  3He polarizer system: Media:Xemed-polarizer.pdf