Accelerator Handbook

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=== Accelerator Start-Up - Chopping and Bunching ===

Last modified 2009 April 15, 16:10

** Starting and Tuning Pulsed and Bunched Beam **

   - Start up source and described in the [[playground:sputter|Sputter Source]] or [[playground:alpha|Duoplasmatron Source]] instructions.
   - With the low energy cup in, tune for maximum current using the inflection magnet, two einzel lenses, and the steerers 2X, and 2Y.  
   - Set auxiliary width at maximum.
   - Turn on oscillator -- beam current will drop.  
   - Turn 2Y down -- look for peak in pulsed beam (its easier to find the correct peak if the auxiliary width is large).    You should normally expect to find the peak somewhere around 4.0  if you start from  5.0 .    If you reduce 2Y (after a D.C. tune-up) , the first peak you see is the correct one.
   - Adjust 2X for maximum current for the maximum current.   You usually need to adjust both 2Y and 2X together to find the maximum.
   - Change  to f/2. Adjust the chopper phasing for maximum current.  The beam current should drop by a factor of 2 if you are on the proper peak.   For best current tune both the 2X and chopper phasing.
   - Return to f/1
   - Adjust chopper phase for maximum beam current.
   - Turn "chopper power" on.
   - Turn buncher on.
   - Bring amplifier plate to 1 kV for for deuteron or protons, 0.2-0.4 kV for He-3 and He-4, and 0.5-0.75 kV for Li-7.
   - Adjust buncher phase for maximum current.
   - Adjust buncher tuning for peak output current by cranking the tuning knob.
   - Get high energy end of the accelerator going.
   - Adjust low energy steerers to maximize the beam.  Try to run the steerers as low as possible and avoid doglegs.
   - Adjust the "GRIDDED VOLTAGE TUBE LENS" to maximize the current.   Note that this has a slow response time.
   - Get beam through the analyzing magnet following steps in the Machine Setup steps 11-13 above.
   - Make sure proper doors are closed, and target cooling, etc. are on and take the beam into the target area.
   - Adjust H.E. steering, quads, tweaking magnet, etc. to maximize beam current.
   - Adjust auxiliary width for beam current; this will affect both beam current and timing and will need to be set when the final timing is set.  
   - Examine beam pick-off repetition rate;  if you have adjusted the chopper and buncher properly it should read 500,000 at f/1.
   - If you are using a gold foil: 
      - put the cup in, then 
      - put gold foil in, then 
      - take out cup.  
      - Look at TAC output.  
      - Adjust chopper phase, buncher phase and amplifier plate to obtain best time tune.
      - put the cup in,
      - take out gold foil
      - take cup out.  
   - Run time-tuned beam to target
   - Make final adjustments as necessary using detector timing if needed
Accelerator Handbook

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