Log entry time 02:16:03 on November 03, 2008

Entry number 246347

This entry is a followup to: 246333

During target preparation at 23:04 yesterday, the target apparent polarization dropped from 38%->31%. Related Logs are:

• 23:02 : NMR Pol = 38 %
• 23:04 : Laser Off; Rotate -> Longitudinal+ holding Field; Target -> Pickup Location
• 23:10 -> 23:13 : 3 Junk NMR by Jin Huang: Using Longi RF & No Field Sweep (sweep start stop field setting is same); No Field Sweep; Wrong Software Backgroud Substraction
• 23:14 : Pick up Position, Long Holding Field, Vert. RF NMR (by Jin Huang) : Pol = 31% (drop a lot!)
• 23:22 : Target -> BeO Position
• 23:15 : Since polarization is low and  Xin needs additional H2 run. Target is restored to transverse position to keep pumping.
• 23:31 : NMR Beo Position : Long RF : Trans Holding Field: Vert pick up coil (by Jin Huang): Pol = 35% (presuming cali constant is same for BeO & Empty Target)
• 23:58 : NMR Beo Position : Long RF : Trans Holding Field: Vert pick up coil (by Jin Huang): Pol = 38% (presuming cali constant is same for BeO & Empty Target)

The possible reason of dropping are:

Field Rotation from Trans+ -> Long + @ Empty Target Location 

It's possible, bug not confirmed.

It also has been observed on Oct 28 that, there is an apparent half Pol. loss on pumping chamber during field rotation-NMR combination:

1. NMR at Vertical Holding Field: http://www.jlab.org/~bbsoftw/TargetReports/GenericLog/NMRField_befiore_p ickup_28-10_17-24-17.html
2. Rotation to Long Holding Field
3. NMR at  Long Holding Field : http://www.jlab.org/~bbsoftw/TargetReports/GenericLog/NMRField_pickup_28 -10_17-31-51.html
4. Rotation back to Vertical Holding Field
5. Same NMR as step 1 : http://www.jlab.org/~bbsoftw/TargetReports/GenericLog/NMRField_after_pic kup_28-10_17-36-39.html

NMRs

If there is any problem with NMR, it should be large AFP loss, because:

1. For the first and second Junk NMR, the sweep rang is 24.982G->24.982G. So there shouldn't be much phisical affect on target
2. The thrid junk NMR and 4th NMR (correct one) should send exactly same RF& field sweep to target. The "junk point" is just that after taking data for the 3rd NMR, the way software processing data (background subtraction) is not correctly setted.
3. Both 3rd and 4th NMR show similar 31% low polarization.
4. The 4th NMR is using 1mV rather than 300mV as sensitivity of lockin amplifier. However, it has been tested that, as long as there is no overflow, the calibration constance should preserve.
5. the holding field is slightly different than that when taking beam
6. AFP loss at pickup coil is uncertain now. (tested to be ~1% on Transverse Pumping @ BeO location)

Calibration error

The calibration chain seems fine :

Vertical EPR -> NMR @ Optics Position, Vertical Holding Field, Long RF, Trans Pickup -> NMR @ PickUp Position, Long Holding Field, Vert RF, target chamber Pickup ->Vertical EPR

 The ending EPR shows to be consist within 10% relative error. The other chain is

Trans EPR -> NMR @ Empty Position, Trans Holding Field, Long RF, Vert Pickup 

It's suggested that next field rotation been taken slow