Taper angle dependence of the dynamical transmission of several-hundred-keV protons through PC conical capillary
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THE EUROPEAN PHYSICAL JOURNAL D
Regular Article
Taper angle dependence of the dynamical transmission of several-hundred-keV protons through PC conical capillary Ai-Xiang Yang,a , Chao-Yang Zhu, Zheng Qu, Dian-Wei Zhou, Xi-Long Han, Xi-Meng Chen, and Jian-Xiong Shao School of Nuclear Science and Technology, Lanzhou University, Lanzhou 73000, P.R. China Received 13 January 2020 / Received in final form 29 July 2020 / Accepted 31 July 2020 Published online 22 September 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. The dynamical transmission of intermediate-energy protons through a polycarbonate (PC) conical capillary with taper angle from 0.48◦ to 2◦ are simulated. The results show that for small taper angle of 0.48◦ , the transmission of 100 keV protons is dominated by the deposited-charge-assisted specular reflection. This reflection effect decreases with the increase of the taper angle. When the taper angle is increased to 2◦ , the transmission of the protons is mainly influenced by small angle scattering, which is consistent with the experimental data. The asymptotic transmission rate decreases with the increase of the capillary taper angle. These results suggest that the deposited-charge-assisted specular reflection is significant in focusing several-hundred-keV protons.
1 Introduction In last decade, tapered glass capillaries with micro or sub-micro order outlet diameters attract much attention as ion beam focusing lens. Such micro- and nano-beams are widely applied in physics [1], chemistry [2], biology [3], and materials science [4]. Previous studies have reported the focusing effect with respect to keV [1,5,6] and MeV [7,8] ions. It is well accepted that slow highly charged ions are guided electrostatically due to the charging up of the inner wall, and the density enhancement coefficient was as high as ∼7–10 [1,6]. In addition, the calculated results indicated that for small exit diameters of the capillary the flux density is expected to be enhanced [5]. In contrast to the case of slow highly charged ions, the small angle scattering plays a significant role in focusing of MeV ions [9]. The transmitted beam has suffered slight energy loss and its intensity decreases with the increase of the capillary taper angle [10]. For several-hundred keV ions, in 2005, Vokhmyanina [11] experimentally explored the transmission process of 200–500 keV protons through a conical capillary. It was found that the density enhancement coefficient was ∼5 at 200 keV, and decreased as ∼E−1 . Last year, our group [12] presented a simulation of 100–500 keV protons being transmitted through a conical capillary, found that the deposited-charge-assisted specular reflection greatly enhances the transmission rate and causes the transmission rate to exhibit an energy dependence proportional to E −1 . The taper angle of the aforementioned conical capillary is about 0.2◦ . In 2015, an experiment of 200 keV H+ 2 transmitted through PC conical multi-capillaries (the
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