[Zurück]

F. Aumayr, G. Kowarik, R. Bereczky, E. Gruber, F. Ladinig, D. Schrempf, P. Gunacker, C. Lemell, J. Burgdörfer, K. Tökési:
"The effect of conductivity on ion guiding through insulating capillaries";
Poster: 25th International Conference on Atomic Collisions in Solids (ICACS-25), Kyoto University, Kyoto/Japan,; 23.10.2012; in: "Book of Abstracts, ICACS-25", (2012), S. 90.

First experiments on guiding of highly charged ions 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]. 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. 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].