NMR Measurement

Basic Instrumentation for NMR system

• DS345 Function Generator (Field Sweep Control)
• HP3324A Function Generator (NMR RF)
• SR844 Lock-in Amplifier
• Wavetek80 Function Generator (Field Sweep Trigger)

NMR Fequency Sweep Procedure

 Never do sweep in position other than 3He and Pickup !!! 
 Never do sweep during target movement !!! 
 Never do sweep when temperature not stable !!! 
 Never do sweep during production !!! 

Before an NMR Frequency Sweep, check NMR RF coils, pickup coils and Lock-in trigger connections:

• The connectors for pickup coils are in the front side of the rack
  

  Connectors for Pickup Coils
  ;
• The connector for RF coil is in the back side of the rack
  

  Connector for RF Coil
  ;
• The connector for Lock-in trigger is in the back side of the top NMR lock-in amplifier and make sure it's connected to the cable labeled with Frequency Sweep;
• The pickup coil cable connected to Upstream is labeled as Target 2;
• The pickup coil cable connected to downstream is labeled as Target 3;
• For Vertical direction, use

  * Transverse pickup(Target 4) pickup coil for pumping chamber;
  * Longitudinal RF(Target 5) RF coil;

• For Longitudinal direction, use

  * Transverse pickup(Target 4) pickup coil for pumping chamber;
  * Vertical RF(Target 6) RF coil;

Make sure the EPICS Daemon is runing, it can be found in:

 C:\AyeD\VI\Spin Flip\EPICS Daemon.vi

Then open the program for NMR frequency sweep

Window for NMR Frequency Sweep

:

 C:\AyeD\VI\NMR\NMR_Fequency_v7.vi

do the following steps:

1. Run the program if it's not currently running;
2. Select Helium;
3. Press Load Default button;
4. Make sure that Holding Field is about 25 Gauss, Sweep range is 77 to 85 kHz;
5. Make sure that Save Data is pushed;
6. Set Number of Sweeps to 1;
7. Press Start button to start the sweep;
8. The program can be stopped anytime by hitting the Stop button, other wise it will automatically stop after desired sweeps finished;
9. Once all sweeps completed, a report screen with a screen shot will automatically popped out, please save the screen shot into the picture folder on desktop;
10. Do not EXIT the program because it's monitoring the oven temperature.
11. Post a Halog entry with the descriptions of

  * Field direction
  * Which RF coil
  * Which pumping chamber pickup coil
  * At what target position
  * Taking time
  * Target Polarization
  * the screen shot you just saved.

NMR Field Sweep Procedure

Before a NMR field Sweep, check NMR RF coils, pickup coils and Lock-in trigger connections:

• The connectors for pickup coils are in the front side of the rack
  

  Connectors for Pickup Coils
  ;
• The connector for RF coil is in the back side of the rack
  

  Connector for RF Coil
  ;
• The connector for Lock-in trigger is in the back side of the top NMR lock-in amplifier and make sure it's connected to the cable labeled with Field Sweep;
• The pickup coils connected to Upstream are labeled as Target 2;
• The pickup coils connected to downstream are labeled as Target 3;
• For Transverse direction, use

  * Vertical pickup(Target 1) pickup coil for pumping chamber;
  * Longitudinal RF(Target 5) RF coil;

• For Longitudinal direction, use

  * Transverse pickup(Target 4) pickup coil for pumping chamber;
  * Vertical RF(Target 6) RF coil;

• For Vertical direction, use

  * Transverse pickup(Target 4) pickup coil for pumping chamber;
  * Longitudinal RF(Target 5) RF coil;

• Optional for Transverse direction, use

  * Longitudinal pickup(Not connected) pickup coil
  * Vertical(Target 6) RF coil

Then open the program for NMR field sweep

Window for NMR Field Sweep

:

 C:\HappyValentine\VI\NMR\NMR_FieldSweep_v12.vi

do the following steps:

1. Run the program;
2. Select Helium;
3. Press Load Default button;
4. Make sure that Holding Field is about 25 Gauss, High Field is 32 Gauss and RF Frequency is 91 kHz;
5. Make sure that Save Data is pushed;
6. Make sure that Number of Sweeps is 1;
7. Press Start button to start the sweep;
8. Once it's done, a report screen (a webpage) will automatically popped out, please copy it's address;
9. Post a Halog entry with the descriptions of

  * Polarization direction
  * Which RF coil
  * Which pumping chamber pickup coil
  * At what target position
  * Polarization (Using the calibration constants from latest EPR measurement log)
  * the address of the report you just copied.

NMR Frequency/Field Sweep Cross Calibration Procedure

Pre-check List

1. Lasers are OFF.
2. Holding field is stable.
3. Oven/Cell temperature is stable.
4. All cable connections are good. Special attention to: Pumping chamber pickup coil/Lock-in Trigger.
5. No data taking.
6. No beam.
7. Automatic spin flip is Paused.
8. Target is in He3 position.

NMR Frequency Sweep

Use the code

C:\HappyValentine\VI\NMR\NMR_FrequencySweep_v6.vi

1. Make sure that the NMR pumping chamber lock-in has trigger from Frequency Sweep.
2. Make sure that correct pumping chamber pickup coil and RF coils are connected.
3. Load the settings for automatic spin flip.
4. Make sure to save data.
5. Do Frequency Sweep.
6. Make a snapshot and exit.

Target move/Field Rotation

Use the code

C:\HappyValentine\VI\Field Rotation\3D_Rotation_v4.vi

1. Move target to pickup coil position.
2. Rotate the field to Longitudinal + with 25 Gauss Magnitude.

NMR Field Sweep

Use the code

C:\HappyValentine\VI\NMR\NMR_FieldSweep_v12.vi

1. Make sure that the NMR pumping chamber lock-in has trigger from Field Sweep.
2. Make sure that correct pumping chamber pickup coil and RF coils are connected.
3. Load default settings.
4. Make sure to save data.
5. Do Field Sweep.
6. Make a snapshot and exit.

Target move/Field Rotation

1. Rotate the field back to original direction.
2. Move target back to He3 position.

NMR Frequency Sweep

1. Do the NMR Frequency sweep one more time.
2. Make a snapshot and exit.

Back to Production (Optional)

1. Redo the setup of the automatic spin flip.
2. Continue automatic spin flip.
3. Ask for beam and take production.

Submit a Report

1. Fit out the amplitudes of 4 NMR frequency sweeps from pumping chamber pickup coils and 4 NMR field sweeps from target chamber pickup coils.
2. Post a Halog with all the numbers and all snapshots collected.

Principle

The target used in the upcoming GEn experiment, E02-013, in Hall A is the polarized 3He target. The 3He nuclei are polarized by the spin-exchange mechanism via optically polarized rubidium. (The detailed process of Rb polarization is discussed elsewhere.) There are two methods currently employed to determine the polarization of the helium viz. NMR (Nuclear Magnetic Resonance) and EPR (Electron Paramagnetic Resonance). Here, we shall talk about Frequency Sweep (FS) NMR polarimetry.

The basic principle of NMR relies on sweeping either the magnetic field, or the RF through resonance. In the case of frequency sweep NMR we sweep the RF while holding the magnetic field (H0)1 constant. The expression is symmetric with respect to these two parameters.

The way NMR was performed so far is as follows (field sweep NMR):

• Set the RF at 91kHz. (This gives the resonance at H0 ~ 28G for 3He (~ 21.5 G for water). These quantities are related through the formula: ω = γ H1 where γ is the gyromagnetic ratio (3.24 kHz/G for 3He; 4.26 kHz/G for water), and H1 is the RF field.)
• Sweep the holding field H0 from 25G to 32G (18G to 25G for water) and back; so we sweep through resonance twice (up and down sweeps).
• Plot the data and fit the resonance peak with the square-root of a Lorentzian; extract the peak heights which correspond to the polarization of the substance (after proper calibration of course).

See here [PDF] for a treatise on FS NMR. It follows Abragam in the initial stages. The AFP condition is derived.

For the RF sweep, we keep the holding field H0 constant at 28G (21.36G) and sweep the RF from 87kHz to 95kHz and back. The sweep rate is pretty much determined by the AFP condition, and we found that 4KHz/s works really well (in terms of polarization loss).

This method was tested at University of Kentucky by Dr. Wolfgang Korsch (my advisor) and at The College of William and Mary by Dr. Todd Averett.

Procedure

 Field Sweep for 3He cell

1)  Open the NMR_fieldSweep_v?.vi (current version is v11)
2)  Click the run button on the left top of the window (under the menu bar of the window you just opened).
3)  On the right side of the window, make sure the option button is on the "Helium" position.
4)  Click "Load Default" button to load the default values of the parameters.
5)  In most cases, you do not need to change any default setting EXCEPT the phase in the "Lock-in Settings" part.
    To determine the phase, you can follow the steps below. You can also jump to the next step and come back later.

      What you need to do is try a random number in the range from 0 to 180 and do a sweep first. Then from the
      height of the peaks in "Lock-in X Channel" and "Lock-in Y Channel" you get get some idea that
      what the phase should be. Change it and do another sweep. Check the result and make sure all signals go
      into X chennel and there is almost nothing in Y channel compared with X channel. You can try several
      times til you get satisfied signal.

6)  Make sure the "Wait Time" is 20 minutes.
7)  If you have set the phase right, select enable the "Save Data" option button. If you haven't, disable it.
8)  Click "Start" button. Then you start the field sweep.

 Frequency Sweep

Constants

• Gyromagnetic ratio for He3 = -32.434 MHz/T or 3.2KHz/G.
• NMR Resoncance Freq @ 25.000G = 81.085 kHz

polarization quick check by NMR 3He signal

Transverse

Halog # 246567. For condition:

• He3 Cell Position
• Trans Holding Field
• Long RF
• Vert Pickup
• Lock-In Phase = 98.5 Degree

Pol. = 2.13 %/mV x (X Channel Average Sweep Up/Down)

Vertical

Halog # 246037. For condition:

• Reference Cell Position
• Vertical Field
• Long RF
• Trans Pickup
• Lock-In Phase = 0 Degree

Pol. = 1.48 %/mV x (NMR X Channel)

Longitudinal

Halog # 246271. For Condition:

• PickUp Position
• Long Holding Field
• Vert RF
• Target Chamber Trans pickup Coil
• LockIn Phase = 0

Pol = 0.122%/mV * (UpStream NMR + DownStream NMR)

Old Constants

according to our EPR calibration on Nov 01, one can have a quick estimation of target polarization by the amplitude of 3He NMR signal

P_longitudinal(%) = 2.3675 * (signal got from pumping chamber, in mV)
P_vertical(%) = 1.48 * (signal got from pumping chamber, in mV)

Internal Temperature Test Procedure

The internal temperature test is required to know the internal temperature of our cell and its probably one of the most important quantities as far as the course of our "polarization measurement accuracy is concerned. Its pretty simple and is as follows.OK ! before that lets make sure couple of things. First the NMR field sweep VI should be open and UP there. Next thing is to make sure you know how to bring the LASER ON/OFF gui and more importantly to know how to TURN the lasers ON and OFF. So go to the hacuser@hacsbc2 and enter the password ( its on the wall near the white board which is no longer white now).GO to the Hall_A_Tools and type NewTools and hit ENTER.Click on the little icon ( EOS menu) that is already popped up and then click on the HLA MAIN. The menu will pop up and click on the POLARIZED he-3 target control. Then click on the MAIN LASER CONTROL. Click on 1,3,4,5 and 6 lasers.If you want to play around , I can show you after the experiment, not now. But just bring up all the 5 lasers to the screen. Now you are more or less set. Go back to the Polarized He-3 control main menu and click on the RTD Readback. There you will see two stripcharts. The left one contains the RTD readbacks from the two RTDs on the pumping chamber and the right one contains all the five RTDs that are on the target cell.the Lets do the following ::::

1. Keep the lasers ON.
2. Move target to 3He position.
3. For now, use Longitudinal RF and Vertical pickup coil for transverse pumping.
4. Take a look into the NMR VI and make sure everything is "perfect". ( again its assumed that you know the "NMR")
5. Make the wait time 25 min or 30 min between the sweeps and make the sweep number =5 or more.
6. Take one NMR measurement ( Here its assumed that you know the checklist for the NMR or basically you know how to do NMR.)
7. (Optional) Just before the NMR or during the NMR sweep , record down all the temperatures to 10^(-1) level. Note the oven temperature too.
8. Turn the Lasers OFF.
9. Wait for the next NMR to begin i.e. 25 min. Meanwhile, watch the temp. charts.. The pumping chamber RTDs should be decreasing. ( A nominal decrement is from 255 C to 215C "usually")
10. (Optional) When its time to have the next NMR , get ready to record the RTDs
11. (Optional) Record the RTD temps during or just before the sweep.
12. SO TILL NOW WE HAVE 2 SETS . ONE with lasers ON and ONE with lasers OFF.
13. Now turn the lasers ON and do the same from step 4 to step 11.
14. When you are done, make sure that the Lasers are ON and halog the numbers accordingly with the NMR signal height.

( During the wait time period of 25 min, you can actually analyze the NMR data by looking into the datafile stored in Data directory. You can see the path in the VI. Then you can use spinup.C to fit the peak and just record the number. If you have problems or these writings seem ridiculous , just ask any target expert and complain that the guy who wrote this is a crap)