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T.p. gas. gas. 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. new. old. From the work of Roland Szymanski. - PowerPoint PPT Presentation
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© David N. Jamieson 1999
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
gas gas
T.p.
old new
From the work of Roland Szymanski
© David N. Jamieson 1999
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!
© David N. Jamieson 1999
Selected new quadrupole systems
1970 Russian quadrupletDx=Dy=30
1998 Leipzig separated quadruplet Dx=80 Dy=80
1998 CSIRO/MARC high excitation quintuplet Dx=67Dy=71
1980 Oxford high excitation triplet Dx=25 Dy=90
2000 Oxford separated triplet Dx=240Dy=50
2001 New systemDx=Dy=200?
© David N. Jamieson 1999
125 4 3
Strong demagnification in a long system
CSIRO quintuplet system Leipzig two stage system
Strong demagnification in a short system, 80 mm WD
Very intense beam spot into 1 m
© David N. Jamieson 1999
3 m at 20 nA
Resolution Versus Beam Current: CSIRO/MARC quintuplet system
1.3 m at 0.5 nA
Accelerator brightness =1.2 pA.m-2.mrad-2.MeV-1
12.7 m
1.2 m x 0.9 m at 0.1 nA
CSIRO-GEMOC Nuclear Microprobe
2.0 m at 10 nA
3100 pA/m2 !
1.8 m at 8 nA
12.7 m
From the work of Chris Ryan
© David N. Jamieson 1999
Future Developments
Conclusion: To break through the 1 micron wall
Install heavier magnetic shielding! But be sure to clean off DC fields (10 nT).
Don’t worry about chromatic and spherical aberration, they are not a severe as first though because of flux peaking (<0.1 m)
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 > 200)
Need more radical lens design to reduce working distance and increase fields (40 mm)
Apply the new system to some interesting problems! (< 0.1 m resolution)
MP2Bochum
Leipzig
Oxford tripletCSIRO 5
New Ox
© David N. Jamieson 1999
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
z
Pole tip
?
N
S N
S
Poletip
z
N
NS
S
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