Accelerator Handbook

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===== NMR Setup =====

   - Depress POWER switch if not illuminated.
   - After a 1 minute warm up period a horizontal line should appear on the oscilloscope face.
   - You may have to adjust the VERTICAL POSITION control to find the horizontal line.
   - Set the HORIZONTAL SWEEP to 60.
   - Recycle the analyzing magnet if needed.  This is done using the RECYCLE button on the analyzing magnet control window.
   - Set the analyzing magnet power supply to a current slightly lower than the current predicted for this energy.
   - Set the TUNING VERNIER control to about mid range on its 10 turn control.  Rotate counterclockwise until stop then 5 turns clockwise.
   - Select a frequency about 1% less than the frequency desired for the beam energy.
   - In the light yellow (Tandem) window type the command "nmrgoto 1234.567" where 1234.567 is the frequency calculated in the previous step.
   - Follow the instructions given in the TANDEM window.  You may have to move the NMR TUNING RANGE switch to a new range.
   - If requested to do so, switch the NMR TUNING RANGE switch to the requested range, then hit ENTER.
   - The TANDEM window will inform you of how many steps needed to move approximately to the frequency you entered.
   - When the NMR advances this number of steps it will inform you of the frequency the NMR has moved to at this step position.
   - The NMR frequency is read directly on the accelerator console by the Agilent 53131A Universal Counter located directly above the NMR.  The counter that is read by the computer is on the left and is the standard counter to use for the NMR frequency.  The NMR may also be connected to the similar counter on the right to allow comparing the frequency readout.  The accuracy of the NMR is determined by the accuracy of the counter so if there is disagreement in the counter frequency it needs to be checked.  The counters should agree to 7 digits.  The counters have 2 inputs and the NMR is connected to inpt #1.  Press the "Freq & Ratio" button until "Frequency 1" is displayed to read the NMR frequency.
   - If the counter is not updating the frequency readout you need to press the "Run" button on the counter.  These counters go into remote mode when read by the computer and need to be manually placed on local mode by pressing the "Run" button.
   - If this frequency is not close enough to the desired frequency, repeat the nmrgoto command and it should get closer.  The NMR moves to the entered frequency by estimating the number of steps needed to advance from the current frequency and then moving that number of steps.  The closer you are to the desired frequency, the closer the end result will be.
   - Set the FIELD SWEEP control to the optimum position.  The optimum setting will be near 15 for the upper three ranges of the fluxmeter and near 5 for the lower three ranges.
   - set the VERTICAL GAIN control for approximately 1/16-inch of "grass" on the face of the oscilloscope.  
   - Now that the NMR is set to a frequency slightly lower than the desired frequency, we can begin slowly increasing the analyzer magnet control upward toward the current that will show a resonance on the NMR.  Typical resonance patterns and control positions can be seen in the {{HVEC_NMR.pdf|Original HVEC NMR Manual}} figure 1.  The resonance will enter the display from the right side and move across the CRT display from right to left.  When the resonance is found and centered on the CRT display, the magnet flux (frequency) can be read on the Agilent counter located above the NMR Fluxmeter.  Remember that because of magnet hysteresis and saturation effects, we can only increase the magnet current from this point on.  If we decrease the magnet current we will have to recycle the magnet and start over for an accurate NMR flux value.
   - The NMR Fluxmeter is a very sensitive instrument and you must proceed slowly when raising the analyzer magnet current or you can easily miss the resonance on the CRT.  When the Analyzing Magnet computer control window is in the "ExtraFine" range, magnet at about 50 Amps and the FIELD SWEEP set at 5 gauss (these parameters will modify the the sensitivity) the resonance pattern will move completely across the CRT screen with a mouse movement of about 1/8 inch.  Also, the same resonance movement will be obtained with about 20 clicks of the mouse button.  On this range, one mouse click = 1 step of the stepping motor driving the NMR oscillator.
   - Once the resonance is found on the CRT, slowly advance the magnet and NMR frequency by alternately increase the magnet a few clicks then raise the NMR frequency by issuing the command "up #steps" in the yellow tandem window, for example, in the analyzer current control window click the right mouse button until the resonance pattern moves to the left side of the CRT (about 10 clicks) then issue the command "up 10" in the yellow tandem computer window.  This should move the resonance back near the center of the CRT.  This process takes some practice but you will soon get used to the sensitivities of the magnet and NMR and you can slowly move the magnet current up until the desired NMR frequency is obtained.  Once you are close to the desired frequency, you cam move the resonance to the center of the CRT with the VERNIER control and then read the exact NMR frequency on the counter.
   - COMPUTER COMMANDS TO CONTROL THE NMR.  Enter the commands in the yellow terminal window with the DAQ> prompt.
   -- nmrgoto frequency (format 1234.567) ; move the NMR approximately to the entered frequency.
   -- up #steps ; move the NMR frequency up #steps.
   -- down #steps ; move the NMR frequency down #steps.
   -- findnmr ; predict the NMR frequency from the analyzing magnet current and move the NMR to that frequency.  Usually close enough to find resonance with the browse command.
   -- browse #steps ;  move the NMR down #steps/2 then slowly step up #steps, then down #steps, repeating until enter is pressed.  Watch the CRT and when the resonance is seen, press enter.  For example, "findnmr" , followed by "browse 400".  The arrows on the yellow terminal indicate steps up (>) and down(<), repeating #steps until the enter key is depressed.

 
* {{HVEC_NMR.pdf|Original HVEC NMR Manual. Main frequency adjustment control and tracking feature now obsolete.  See above new procedures.}}
 
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Accelerator Handbook

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