EGAS41 - Swansea University

41 st EGAS CP 138 Gdańsk 2009
Manipulation of ion bunches with time-dependent field
N. Debernardi ∗ , M.P. Reijnders, G. Taban, S.B. van der Geer, P.H.A. Mutsaers,
E.J.D. Vredenbregt, O.J. Luiten
Department of Applied Physics, Eindhoven University of Technology,
P.O Box 513, 5600 MB Eindhoven, The Netherlands
∗ Corresponding author: N.Debernardi@tue.nl
At present, the smallest spot size which can be achieved with state-of-art focused ion
beam (FIB) technology is mainly limited by the chromatic aberration associated with
the energy spread of the liquid-metal ion (LMI) source. We have already shown [1] that
a new concept, the ultra-cold ion source, which is based on near-threshold ionization of
laser cooled atoms, can provide lower energy spread than LMI sources [2].
In our experiment, rubidium atoms are confined in a magneto optical trap (MOT)
built directly inside an accelerator structure [3]. A spherical portion of the cloud is
ionized at the intersection of two laser beams and then accelerated by a pulsed electric
field. The ultra low temperature of the source permits collimated bunches to be created
at low energy, which allows using time dependent fields. These can be used to study space
charge effects and also to lower the energy spread. The duration of the electric field pulse
is tuned in order to cancel the negative lens effect due to the geometry of the accelerator
structure. Even more, with the same principle, one can reverse the effect and create a
focusing lens.
References
[1] S.B. van der Geer et al., J. Appl. Phys. 102, 094312 (2007)
[2] M.P. Reijnders et al., Phys. Rev. Lett. 102, 034802 (2009)
[3] G. Taban et al., PRSTAB 11, 050102 (2008)
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