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@PHDTHESIS{Horst:348998,
      author       = {Horst, Max Henrik},
      title        = {{L}aser {S}pectroscopy of ²⁰⁸{B}i⁸²⁺ and
                      {C}ommissioning of the {HITRAP} {C}ooling {T}rap},
      school       = {TU Darmstadt},
      type         = {Dissertation},
      address      = {Darmstadt},
      publisher    = {ULB Darmstadt},
      reportid     = {GSI-2024-00459},
      pages        = {127},
      year         = {2023},
      note         = {Dissertation, TU Darmstadt, 2023},
      abstract     = {Today, quantum electrodynamics (QED) is considered the most
                      precisely tested theory in physics. The most precise tests
                      have been performed mainly on comparatively simple systems
                      such as the free electron. However, since QED should also be
                      valid in the most extreme electric and magnetic fields,
                      according to today’s understanding, tests must be
                      performed in this regime as well. Heavy and highly charged
                      ions are suitable for this purpose, because the remaining
                      electrons near the nucleus are exposed to these extreme
                      fields. Since such ions do not occur naturally on earth,
                      they must be produced artificially. This requires high
                      energies and, especially for the heaviest elements, large
                      accelerator facilities, such as the GSI Helmholtzzentrum
                      für Schwerionenforschung in Darmstadt, Germany. In this
                      work, laser spectroscopy of artificially produced
                      ²⁰⁸Bi⁸²⁺ at relativistic energies was performed at
                      the storage ring ESR of GSI. This is the first time that
                      in-flight produced ions have been successfully studied by
                      laser spectroscopy in a storage ring. The main challenge is
                      the small amount of ions, which leads to low signal count
                      rates in the detectors. In part due to the data analysis
                      performed in this work, the measured background has been
                      reduced to a point where the energy difference of the
                      hyperfine splitting can be extracted. The obtained result is
                      ²⁰⁸∆E⁽¹ˢ⁾ = 5598.97(1)(8) meV and represents an
                      important milestone for the test of QED in the strongest
                      magnetic fields. The accuracy of laser spectroscopy in
                      storage rings like the ESR is limited by the velocity
                      distribution of the ions. To improve the accuracy by several
                      orders of magnitude, ion traps can be used. However, it is
                      not possible to directly capture ions produced at
                      relativistic energies in an ion trap. Therefore, in the
                      second part of this work, the Cooling Trap of the HITRAP
                      facility was commissioned. The task of the HITRAP facility
                      is to decelerate the highly charged ions, to cool them and
                      to transport them further to the subsequent experiments. The
                      Cooling Trap is the final step of the deceleration process
                      and is responsible for the sympathetic cooling of the ions
                      by electrons. In this work, the Cooling Trap was
                      commissioned with highly charged ions and electrons from
                      local sources. Moreover, for the first time, ions and
                      electrons were simultaneously stored in the Cooling Trap.
                      This finally led to the first demonstration of cooling
                      effects of electrons on highly charged ions in a Penning
                      trap.},
      cin          = {ATP / DEC},
      cid          = {I:(DE-Ds200)ATP-20051214OR020 /
                      I:(DE-Ds200)DEC-20121002OR240},
      pnm          = {631 - Matter – Dynamics, Mechanisms and Control
                      (POF4-631)},
      pid          = {G:(DE-HGF)POF4-631},
      experiment   = {$EXP:(DE-Ds200)no_experiment-20200803$},
      typ          = {PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:tuda-tuprints-263672},
      doi          = {10.26083/TUPRINTS-00026367},
      url          = {https://repository.gsi.de/record/348998},
}