Experiments and simulations of 4.5-keV Ar 7 + − ion guiding through a conical glass macrocapillary

Experimental and theoretical studies are performed to investigate guiding of 4.5-keV Ar7+ ions through a conical macrocapillary. The tilt angle of the capillary axis relative to the incident beam is varied within 0 degrees-2 degrees. The experiments are performed using a glass capillary whose bulk conductivity could be varied by changing its temperature from 24 degrees C-110 degrees C. At lower temperatures a minimum in the transmitted ion intensity is observed in the forward direction. After strongly increasing the electrical conductivity of the capillary by increasing its temperature to 110 degrees C, the transmission profile becomes geometrical without a forward minimum. The experimental data are compared with theoretical results, which are based on simulations previously developed for nanocapillaries and a straight macrocapillary. Both the surface and bulk conductivities are implemented in the calculations, providing clear evidence that the bulk conductivity is dominant. The major experimental features are reproduced by the simulations, providing evidence for the mechanisms producing the forward minimum.