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
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!
1970 Russian quadruplet Dx=Dy=30 1980 Oxford high excitation triplet Dx=25 Dy=90 1998 Leipzig separated quadruplet Dx=80 Dy=80 Dx=67Dy=71 1998 CSIRO/MARC high excitation quintuplet Dx=240Dy=50 2000 Oxford separated triplet 2001 New system ? Dx=Dy=200 Selected new quadrupole systems
CSIRO quintuplet system Leipzig two stage system • Strong demagnification in a long system • Strong demagnification in a short system, 80 mm WD • Very intense beam spot into 1 mm 1 2 5 4 3
1.2 mm x 0.9 mm at 0.1 nA 1.8 mm at 8 nA 12.7 mm 12.7 mm 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
Leipzig New Ox Oxford triplet CSIRO 5 MP2 Bochum 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 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 > 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 mm resolution)
Poletip N S z N S 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 N S ? z S N