Development and commissioning of a compact electron beam ion trap for highly charged ion studies

Abstract

The Center for High Energy Astrophysics (CHEA) in UNIST, Korea, in collaboration with the Max Planck Institute for Nuclear Physics (MPIK), built an electron beam ion trap (EBIT) to create and confine highly charged ions (HCIs) for the investigation of astrophysical phenomena. To maximize the movement of the EBIT towards and away from the accelerator beamlines, we used permanent magnets to reduce the size and maintenance costs. With the help of 72 permanent magnets, a magnetic field of 0.84 T at the trap center provided a trap capacity of around 107 charges. The tested electron beam current was up to 20 mA, with a normal operating current level of about 10 mA. The perveance at 10 mA was approximately 0.7 µA/V3/2. The desired vacuum level is 10−9 mbar, achieved through the use of a tandem structure of TMPs connected to a scroll pump. To test the proper functionality of the UNIST-EBIT, an in situ experiment was conducted. By sweep- ing the electron beam energy from 2.4 keV to 3.3 keV at an electron beam current of 10 mA, the silicon drift detector successfully measured the KLL lines of the HCI states of argon, confirming the presence of up to He-like argon ions. Thus, the UNIST-EBIT was successfully able to produce the desired charged state of atoms. To study astrophysical experiments using accelerator X-ray photon sources, two beamtimes were attended: one at BESSYII in Berlin and another at PETRAIII in Hamburg. These are third-generation synchrotron facilities, slightly different from the PAL-XFEL facility where the UNIST-EBIT experiment was conducted. Before measuring highly charged irons for astrophysics purposes, preliminary experi- ments were conducted to connect the EBIT with the PAL-XFEL hard X-ray beamline. During two days of R&D beamtime, highly charged argon ion spectroscopy was conducted by sweeping the photon en- ergy near 3.1 keV. Unlike third-generation synchrotron facilities, the 60 Hz pulsed operation enables the time coincidence method to reduce background noise. This experiment marks a milestone at PAL-XFEL in Korea as it involved the transportation and utilization of large external devices for the first time. In this thesis, design and development of the UNIST-EBIT and the initial operation of the compact EBIT at an XFEL facility was presented, demonstrating its X-ray fluorescence measurement capability.