Modify RF Ion Source

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Modify RF Ion Source

• Beam from ion source emerges with low energy
• Gas leakage from ion source canal fills low
  energy end of accelerator
• Gas scattering degrades ion source brightness
• Solution Add recirculating turbopump

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old
From the work of Roland Szymanski
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Modify Accelerator Column

• Remove corona needles and replace with resistors
• (Have now increased brightness by a factor of 10)
• So need to design a system optimised for a flux
  peaked beam
• High demagnification!

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Selected new quadrupole systems
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CSIRO quintuplet system Leipzig two stage
system

• Strong demagnification in a short system, 80 mm
  WD
• Very intense beam spot into 1 mm

• Strong demagnification in a long system

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Resolution Versus Beam Current CSIRO/MARC
quintuplet system
1.3 mm at 0.5 nA
3100 pA/mm2 !
2.0 mm at 10 nA
3 mm at 20 nA
Accelerator brightness 1.2 pA.mm-2.mrad-2.MeV-1
CSIRO-GEMOC Nuclear Microprobe
From the work of Chris Ryan
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Future Developments

• Conclusion To break through the 1 micron wall
• Install heavier magnetic shielding! But be sure
  to clean off DC fields (10 nT).
• Dont worry about chromatic and spherical
  aberration, they are not a severe as first though
  because of flux peaking (lt0.1 mm)
• Make brighter ion sources by small tweaks, even a
  factor of 10 is helpful (x1/3)
• Install an optimised system for a strongly flux
  peaked accelerator, this will have a large
  demagnification (of necessity a high excitation
  system) (M-1 gt 200)
• Need more radical lens design to reduce working
  distance and increase fields (40 mm)
• Apply the new system to some interesting
  problems! (lt 0.1 mm resolution)

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Spherical Aberration A closer look

• The TFF model also revealed the need for careful
  attention to the field overlap between adjacent
  lenses
• Must have a linear field gradient as a function
  of beam direction to minimise aberrations
• Need to shape pole ends to achieve this

Pole tip
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z
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