[Zurück]

G. Kowarik, R. Bereczky, E. Gruber, F. Ladinig, D. Schrempf, P. Gunacker, C. Lemell, J. Burgdörfer, K. Tökési, F. Aumayr:
"The effect of conductivity on ion guiding through straight insulating macro - capillaries";
Poster: 16th International Conference on the Physics of Highly Charged Ions (HCI 2012), Heidelberg/Germany; 03.09.2012; in: "Book of Abstracts, 16th International Conference on the Physics of Highly Charged Ions (HCI 2012)", (2012), S. 136.

First experiments on guiding of highly charged ions (HCI) through straight insulator nano-capillaries
showed a remarkable effect: after an initial charge up phase, the ion beam could be steered by tilting
the capillary axis while remaining in the initial charge state indicating that the transmitted ions never
touched the inner walls [1]. Subsequent experiments confirmed this guiding effect also for
macroscopic glass capillaries, both straight [2, 3] and tapered ones [4] while microscopic simulations
revealed that a self-organized charge up of the capillary walls due to preceding HCI impacts leads to
an electric guiding field, which steers the incoming projectile ions along the capillary axes [5]. Ion
guiding ensues as soon as a dynamical equilibrium of charge-up by the ion beam and charge
relaxation by bulk or surface conductivity is established. These simulations showed that a stable
transmission regime required a delicate balance between incident ion flux and charge relaxation via
surface and bulk conduction, conditions, which were obviously met in almost all cases studied
experimentally so far. In this contribution we show that a key control parameter for guiding is the
small residual electric conductivity of the highly insulating capillary material whose dependence of
temperature !(T) is nearly exponential.
We use a single straight macroscopic glass capillary (inner diameter: 160 "m; length: 11.4 mm)
made of Borosilicate (Duran) for which the guiding effect has been previously established [2]. The
current experimental set-up allows for a controlled and uniform temperature variation of the glass
capillary between -30°C and +90°C [6]. Within such a moderate variation of the temperature the
conductivity changes by almost five orders of magnitude. Our experiments [7] show that increasing
the temperature of a glass capillary and therefore its conductivity leads to a reduction of guiding and,
eventually, to a complete disappearance of the guiding effect. This strong temperature dependence
can be employed to stabilize guiding against Coulomb blocking due to a high incident ion flux [8].