Generation and isolation of highly charged ions with low ionization thresholds
Date
2021
Authors
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Publisher
University of Delaware
Abstract
Electron beam ion traps (EBITs) have provided access to a wide range of highly charged ions(HCIs) for various applications. The recent use of high-field permanent magnets—e.g., neodymium iron boron (NdFeB)—has made it possible to construct small EBITs and other traps like Penning traps. Potential applications include creating certain low ionization threshold HCIs, such as Pr9+ and Nd10+,proposed by theoretical researchers as interesting candidates for the development of next-generation atomic clocks, quantum information processing, or the search for variation in the fine-structure constant. Highly-stripped heavy ions have been studied in an electron beam ion trap with a strong magnetic field(≈ 3 T) generally produced by superconducting magnets. However, many interesting charge states with low ionization thresholds are not generated efficiently in a conventional EBIT because of the difficulty with achieving a low energy electron beam with a high current. An EBIT with a lower magnetic field and a more compact geometry is better suited for abundantly producing the above-mentioned ions as well as other ions with relatively low ionization thresholds (e.g., 50 eV to 900 eV). A room-temperature miniature electron beam ion trap (mini-EBIT) using a pair of NdFeB magnets has been built as a source of ions with ionization thresholds less than 900 eV. A mini-EBIT also offers a simpler setup and an easy operation. To recapture and isolate ions of interest produced in the mini-EBIT, we discuss the design and construction of a NdFeB permanent magnet Penning trap with a peak magnetic field of ≈ 0.755 T along with the ion transport beamline. No other permanent magnet Penning trap of a similar size is known to provide a magnetic field as high as 0.755 T. This permanent magnet Penning trap employs six radially magnetized annular ring magnets to generate a trapping volume of ≈ 230 mm3 with a magnetic field inhomogeneity of less than 1%. The apparatus (both the mini-EBIT and the Penning trap) is designed to be portable to facilitate its use in various experiments. Highly charged ion experiments using the EBIT facility at the National Institute of Standards and Technology provided useful insights in the design and optimization of the devices.
Description
Keywords
Electron beam ion trap, Highly charged ions, Low energy EBIT operations, Mini-EBIT or compact EBIT, Paul trap, Penning trap