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.
- Many efforts are being focused on the glass-metal sealed.
- UVa will order a full scale two-pumping-chambers cell, fill it and test it. JP asked for another standard hybrid cell (3.5in pumping chamber diameter) for the JLab target lab.
- Wolfgang has been working on FEA of of temperature distribution on the target cell: Media:He3Target_Temp.pdf
* 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, ...
- Bill showed the laser system developed at UNH: 2.7kW narrowed laser (see his slides below).
* 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 sufficient.
- A detailed study of the gas dynamics was recently published: Dolph, Singh et al.
* Budget:
- Hall C should be able to start contributing to the A1n/d2n/pol3He target R&D in FY13.
- Slides:
- from Patricia: talking points: Media:Cpol3he_meeting_jan5_2012.pdf - 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
- 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: JLab need more lasers (at least 2 more) - Polarimetry cross calibration and optimization - kappa_0 measurement - Get a SUltra laser and test it.
