Quintuplet Lens Configuration
The novel lens
configuration uses a separated quadrupole quintuplet, with a coupling
of +A+A-A-A+B. The drift spaces between the first 3 quadrupoles (S12
= 0.45 m, S23 = 0.6 m) have been used to reduce spherical
aberration, especially the cross-terms, increase demagnification,
reduce lens excitation, and approach equal demagnification in the
X and Y planes. This configuration has a demagnification of 70-90
in X and Y (depending on dift lengths) despite a short overall system
length of 4.7 m, low total spherical aberration for this demagnification,
and has all its significant aberration contributions concentrated
into x|thetan terms.
The theoretical performance of this new configuration [1-3], suggests
that sub-micron beam spot-sizes at 100 pA beam current can be achieved,
at the low brightness of the CSIRO tandem accelerator (~1 pA.µm-2.mrad-2.MeV-1).
A spot-size of 1.3 µm has been obtained at a beam current suitable
for trace element work (0.5 nA). As the acceptance of the system
is increased, and the beam current grows to ~20 nA, the modelling
suggests a slow rate of spot-size growth with a spot size of ~3
µm possible at these high currents. This is observed in practice
with the spot-size growing to 1.8 µm at 10 nA, despite the
low brightness, ideal for mineralogical work.
quadrupole quintuplet lens systems are being manufactured by, and are available through,
 C.G. Ryan and D.N. Jamieson, "A high performance quadrupole quintuplet lens system for the
CSIRO-GEMOC Nuclear Microprobe", Nucl. Instr. Meth. B158 (1999) 18-23.
 C.G. Ryan, D.N. Jamieson, W.L. Griffin, G. Cripps and R. Szymanski, "The New
CSIRO-GEMOC Nuclear Microprobe: First Results, Performance and Recent Applications",
Nucl. Instr. Meth. B181 (2001) 12-19.
 C.G. Ryan, D.N. Jamieson, W.L. Griffin, S.H. Sie, G. Cripps and G.F. Suter, "The new CSIRO-GEMOC
Nuclear Microprobe: A new highly integrated design for geoscience applications", proc.
10th Australian Conf. on Nuclear Techniques of Analysis, Canberra, ISSN 1329-8437 (1997) NTA/VSA8.