Accelerator Start-Up - Chopping and Bunching

Starting and Tuning Pulsed and Bunched Beam

  1. Start up source and described in the Sputter Source or Duoplasmatron Source instructions.
  2. With the low energy cup in, tune for maximum current using the proper tuning devices for the given source.
  3. Set auxiliary width at maximum.
  4. Turn on oscillator – beam current will drop.
  5. Turn 2Y down – look for peak in pulsed beam (its easier to find the correct peak if the auxiliary width is large). When you see 10% rise in LE current, adjust chopper phase for maximum LE current then continue dropping 2Y until first maximum is seen in LE current. 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. If you continue to reduce 2Y you will see the retrace peak. You should return to the first peak if you locate the second (lower 2Y) peak.
  6. Adjust 2X for maximum current for the maximum current. You usually need to adjust both 2Y and 2X together to find the maximum.
  7. 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.
  8. Return to f/1
  9. Adjust chopper phase for maximum beam current.
  10. Turn “chopper power” on.
  11. Turn buncher on.
  12. 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.
  13. Adjust buncher phase for maximum current.
  14. Adjust buncher tuning for peak output current by cranking the tuning knob.
  15. Proceed to the high energy cup and tune beam.
  16. Adjust low energy steerers to maximize the beam. Try to run the steerers as low as possible and avoid doglegs.
  17. Adjust the “GRIDDED VOLTAGE TUBE LENS” to maximize the current. Note that this has a slow response time.
  18. Send the beam on thru the Pick Off you intend to use.
  19. Adjust H.E. steering, quads, tweaking magnet, etc. to maximize beam current.
  20. 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.
  21. Examine beam pick-off repetition rate; if you have adjusted the chopper and buncher properly it should read the proper frequency for the f/n you are using. See the repetition rate list.
  22. Send the time-tuned beam to target
  23. Make final adjustments as necessary using detector timing if needed

Original HVEC Pulsing and Bunching instruction manual.

Instructional diagram about chopper operation

Instructional diagram about buncher operation

Instructional diagram about beam pickoff operation