Electron transport in macroscopic borosilicate capillaries with bending angles of 90° and 360°

Abstract

In this work, we present observations about the transport of 15.2 keV electrons with a beam current of 21 μA through macroscopic dielectric capillaries. These capillaries are made of borosilicate glass with an inner diameter of about 6 mm, and samples with a bending angle of 90° and 360° were investigated. The electron gun was adjusted, and the beam injected into the capillary had a current of 21 μA and a divergence half angle of about 0.75°. A retarding field analyzer (RFA) was installed at the outlet of the capillary to collect the transported current and to investigate the particle energy of exiting electrons (Fig. 1). The transport of electrons to the outlet occurred nearly instantaneous in both capillaries, and the RFA at the outlet detected a current of around 20 μA for both capillary samples resulting in a transmission coefficient of over 95%. Energy measurements showed that the particle energy at the outlet is only at several electron volts, which reveals that electrons lost almost all of their incident energy while traveling through the capillary. A large amount of exiting particles are most likely secondary electrons emitted from the capillary sample. The fact that transmission coefficients for both samples are similarly high, and that the particles can still be transported through the 360° capillary although most of their energy is already lost at 90°, results in many questions that shall be investigated in further studies. The capillaries showed a blueish glow during electron transmission due to cathodoluminescence effects.