© 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