Can positrons be guided by insulating capillaries?

Guiding of positrons and electrons by macroscopic insulating capillaries is studied both experimentally and via static 2D modeling of positron trajectories. Using sub-femtoamp beams, the transmitted intensities through a macroscopic tapered borosilicate glass capillary are measured as a function of capillary tilt angle and time. In agreement with previous guiding experiments, a portion of the entering beams are found to emerge in the same direction of the capillary axis and the transmitted intensities are found to decrease with increasing capillary tilt angle. But, a comparison with transmitted photon data implies that these features may result from purely geometric reasons. Our simulations imply that even sub-femtoamp beam intensities are sufficient to form charge patches and produce guiding within a short time and that too high intensities may lead to defocusing effects in tapered capillaries. But measurements of the transmitted positron and electron beams as a function of charge entering the capillary could not definitely confirm or reject guiding as no major increases in the transmitted intensity were observed. Thus, guiding of low-intensity positron beams is still in question. (C) 2011 Elsevier B.V. All rights reserved.