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playground:alphatross

NEC Alphatross RF Source Instructions

START UP

In the Vault

  1. LE Extension vacuum must be good as evidenced by Ion Gauge controller with orange displays on magnet.
  2. Source vacuum must be good as evidenced by Ion Gauge controller with blue displays in 19“ rack.
  3. Unground alpha source and hang shepherd's hook on concrete wall conduits, close gate.
  4. Go around and unground sputter source, hang shepherd's hook on gate, and close gate.

In the Control Room

  1. Source camera must have a view of the faraday screen on the blue box of the source head.
    1. To gain control of the source camera: On the joystick unit press “2” then “CAM” to specify the camera.
    2. Use the joystick and “TELE” or “WIDE” to create a view of interest.
  2. If not already present, launch the Alphatross software (Version 6.0) on the source computer.
  3. In prompt succession press the “on” buttons for: Water Cooling, Source Power, and He4 Gas.
    1. These actions start a 60 second timer on the RF supply and set initial conditions on the Magnet and Mass Flow Controller.
    2. After 60 seconds the RF power starts, gives a reading on the meter above the faraday screen, and hopefully the plasma will ignite giving an intense white glow. It is bright enough to illuminate the faraday screen if not looking directly at it in the mirror.
  4. Plasma or not, raise the Magnet to 4 A, maybe the plasma will ignite.
    1. Monitor the Ion Gauge pressure, it should remain less than 4 x 10-6 Torr while setting the Probe. It should settle to around 2 x 10-6 or less when done.
    2. Raise the Probe Voltage to 3 KV as a start, this might be enough to get the plasma going. Monitor the Probe Current, maintain 3 mA +/- 1 mA, and continue raising the Probe Voltage, 0.5 KV every couple minutes, until it reaches 6 KV. Plasma should ignite somewhere in this process.
    3. If there is still no plasma try raising the Mass Flow setting to as much as 0.5 SCCM to inspire ignition and then return to 0.35 SCCM.
    4. This is a pause point for source clean up, can run like this for days, should reduce probe current over time
  5. Set the Oven Voltage to 80 V. Wait until the Oven Temperature is at least 160 C, 10 - 20 minutes.
  6. Set the Extractor Voltage to 5.5 KV and the Bias Voltage to a value that gives the desired injection energy. Injection Energy is displayed in the upper window, it is the sum of Probe, Extractor, and Bias. Beam yield seems to increase with injection energy above 30 KeV. Suggest trying 41 or 53 KeV settings if pulsing.
    1. You may now be able to look at negative beam in the source faraday cup (#7 on the FC meter). Its not clear if this is a useful endeavor.
    2. Beam yield will increase as Mass Flow is reduced, expect optimum yield at around 0.25 SCCM.
    3. Optimize negative beam yield by tuning Focus Voltage, and Mass Flow. Adjust Bis Voltage accordingly if an exact injection energy is required for P&B. Expect little or no Focus Voltage.
  7. Use software buttons to take out faraday cup and open gate valve.
  8. Set Lens A to 10 KV and use the inflection magnet to pass beam on to the LE faraday cup. Tune Lens A, Focus, and magnet for optimum conditions. The BPM may be useful too. The source Einzel Lens seems to have no useful effect.
  9. You may need to re-tune with Focus Voltage and Mass Flow setting.
  10. Oven Voltage of 80 V should give a temperature of ~181C and 500 nA. 87.5 V is giving ~189 V and 900 nA.
  11. The maximum Oven Temperature is around 190 C, seems to be around 91 Volts. At this point Rb begins to escape the chamber and the beam becomes twitchy. If the beam is unstable briefly reduce the Oven Voltage until stabile beam and return Oven Voltage to a slightly lesser value.

SHUT DOWN

  1. Click the software button “Automatic Shutdown”
  2. Confirm you wish to quit be answering “y”
  3. Walk away.
  4. Do not open the source gates until the process is finished
    1. This process puts in the cup, closes the gate valve, and shuts down the source as things cool to proper levels.
    2. The automated process can be stopped by clicking the “Automatic Shutdown” again.
playground/alphatross.txt · Last modified: 2020/10/19 14:24 by jacobs