Nuclear charge radii, a quantity crucial in many nuclear physics studies, can be extracted from H- and Li-like electronic transitions, even in heavy ions, when combined with atomic theory * **. The latter has progressed to permit such calculations from transitions in Na-like ions *** ****. Charge breeding to Na-like charge state eases experimental requirements. To this end, at TRIUMF's Ion Trap for Atomic and Nuclear science (TITAN) facility, we are developing a high-efficiency, flat-field grazing incidence extreme-ultraviolet (EUV) spectrometer, for the measurement of absolute nuclear charge radii of short-lived nuclides. It will be installed to the Electron Beam Ion Trap (EBIT), which is capable of electron beam energies up to 66 keV. The spectrometer is designed to optimize transmission efficiency in the EUV regime. The ray-tracing simulations done in Shadow3 ***** will be presented. The first measurement candidates are 211Fr and a suitable spin-0 isotope of Ra, which are relevant for atomic parity violation (APV) experiments and searches for time-reversal violating permanent electric dipole moments (EDM).

Highly charged ions (HCI) have many favorable properties*. In particular, they are well-suited for high accuracy optical atomic clocks. However, up to recently HCI were not accessible for such type of instruments. In this talk, I will briefly review how we overcame all previous obstacles by demonstrating Coulomb crystallization of HCI**, the implementation of quantum logic spectroscopy***, and ground-state cooling of weakly-coupled motional modes****. With these prerequisites we realized the first optical atomic clock based on an HCI by stabilizing an ultrastable clock laser to the ground-state fine-structure transition in Ar13+ at 441 nm. By comparing this optical frequency to the one of the electric-octupole transition in 171Yb+, we realized a frequency ratio measurement with a fractional uncertainty of about 1x10-16, limited by statistics. We thereby improved the uncertainty of the absolute transition frequency of Ar13+ by about eight orders of magnitude. Furthermore, we compared the transition frequencies of 40Ar13+ and 36Ar13+ and improved the isotope shift uncertainty by nine orders of magnitude.

Electron Beam Ion Traps (EBIT) can be used to create highly charged ions (HCI) of almost any charged state by simply tuning the energy of the electron beam. Atomic spectroscopy with EBITs, therefore, offers a great platform to identify previously unmeasured transitions, understand atomic processes in laboratory and astrophysical plasmas, and explore the structure of unique electron configurations to benchmark modern atomic theories. An interesting case of the latter is the fine structure 3d9 2D3/2 - 2D5/2 transitions in Co-like ions with suppressed correlations and enhanced relativistic and quantum electrodynamics (QED) effects *, **. These transitions, also labeled as "Layzer quenched" transitions, can be used to accurately test current methods to compute Breit and QED effects. Here, we present direct measurements of the 3d9 2D3/2 - 2D5/2 fine structure of Co-like Yb, Re, Os, and Ir using the National Institute of Standards and Technology (NIST) EBIT facility. Comparisons with the existing theories ***, **** are made in an effort to understand the Briet interaction and the self-energy contribution to QED.

For the determination of nuclear charge radii different measurement techniques have been developed over time such as elastic electron scattering or muonic spectroscopy. Atomic spectroscopy has so far been limited to H and He or to the differential nuclear charge radii of short-lived isotopes accessed by collinear laser spectroscopy (CLS). In an all-optical approach we want to determine the absolute charge radii of further He-like ions by exciting them from the metastable 2 3S1 state, which has a lifetime of a few 10-100 ms, to the 2 3PJ states. This experimental value is to be compared with nonrelativistic QED calculations* that are currently being performed. The results will compliment and improve existing measurements of nuclear charge radii. The first high-precision collinear laser spectroscopy measurements of 12C4+ have been carried out at the Collinear Apparatus for Laser Spectroscopy and Applied Physics (COALA) at TU Darmstadt which has recently been upgraded with an electron beam ion source to produce the highly charged ions. This contribution will summarize the current status of the project and present first results which will serve to benchmark the QED calculations.

Hyperfine-structure is a small energy splitting in an atomic or molecular level system. This mainly originates from magnetic interaction between the nucleus and electrons, and its spectroscopic research provides rich information for studying nuclear properties and atomic structures. Highly charged ions (HCIs) are excellent targets for such spectroscopic research because the contracted electron cloud enhances the splitting energy of its hyperfine-structure and gives advantages to searching for fundamental physics. Additionally, recent proposals for a new type of atomic clock using heavy HCIs with many electrons enhance the importance of understanding the hyperfine-structures. However, there have been no established spectroscopic methods for observing the hyperfine-structures of such moderate charge state HCIs. In this talk, we present a recent experimental demonstration for hyperfine-structure-resolved laser spectroscopy of HCIs stored in a compact electron beam ion trap at the University of Electro-Communications.

We measured electron-impact excitation and recombination rate coefficients at the Stockholm Electron Beam Ion Trap (S-EBIT) with Highly Charged Ions (HCI) such as Siq+ and Sq+ that are of astrophysical interest. The experimental method was a combination of photon detection from the trapped ions and subsequently extraction and time-of-flight analysis of these ions. This allows to obtain recombination rate coefficients separately for every charge state, and together with the photon spectra of these ions also the excitation rate coefficients. Particularly electron-impact excitation measurements are rare, although important for astrophysics, and their description are challenging for theory. Here we compare the experimental results* ** with calculations of recombination and excitation rates for Si10+-Si13+ and S12+-S15+ ions*** **** using relativistic distorted-wave approach*** ****. The direct and resonant excitation (EIE) cross sections associated with 1s nl core excitations are calculated for the ground states of Si10+-Si13+ and S12+-S15+ions3*** ****. The different recombination and excitation channels and differences between experiment and theory are discussed.

Spectral analysis of an EBIT plasma requires an understanding of the ionization balance. Simulations require accurate atomic data (excitation, ionization, and recombination cross sections) and known operating conditions (electron beam density and energy, and trapped ion temperature). For highly charged ions in an EBIT, charge exchange (CX) recombination is significant despite the relatively low density of neutral ions. Uncertainties of the CX cross sections combined with the limited knowledge of the experimental parameters (neutral density, relative ion velocity) constrain the models of spectral emission. To combine the unknown factors into one free parameter, we introduce a charge exchange factor that can be accurately determined experimentally using measured line intensity ratios and theoretical cross sections. Using measured Fe spectra at multiple electron beam energies (9.21 kV x 18 kV), the charge exchange factor was determined in a measurement at NIST. The factor was used in our collisional-radiative (CR) model* to produce simulated spectra and line intensity ratios. The agreement demonstrates the usefulness of this approach for spectral modeling.

Polarimetry of hard X-rays emitted through interactions between highly charged heavy ions and electrons is important. In particular, polarized hard X-rays emitted from high-Z ions are of significant importance in evaluating relativistic and quantum-electrodynamics interactions such as the Breit interaction. A new polarimetric method has been needed so far to achieve high sensitivity and accuracy for hard X-ray polarimetry. Recently, novel Compton polarimeters, called silicon (Si) / cadmium telluride (CdTe) Compton cameras, have proven powerful for observations of celestial X-ray and gamma-ray objects. We applied a Si/CdTe Compton camera for the polarimetry of hard X-rays from highly charged ions and evaluated its polarimetric performance. A series of experiments were conducted to measure the degree of polarization of X-rays emitted through radiative recombination of highly charged krypton ions. The uncertainty of the result is sufficiently small to probe effect of the Breit interaction on X-ray polarization.

Resonant photo-excitation provides a direct tool for investigating electronic transitions in atoms and ions. By combining EBITs and ultrabrilliant x-ray sources this kind of spectroscopy became also available for highly charged ions. Here we present the PolarX-EBIT, a compact permanent magnet EBIT* built by the Max-Planck-Institute for Nuclear Physics and University Jena specifically for operation at synchrotron radiation light source facilities. It employs a novel off-axis electron gun, allowing the photon beam to pass through the trap and be made available for downstream setups. Additionally, it features fast-switching power supplies for charge breeding and background reduction schemes, a time-of-flight ion extraction beamline and large area SDD detectors. Multiple successful experiments have been performed in the soft and hard x-ray regimes at the light sources BESSY II and PETRA III, measuring transition energies, oscillator strengths, natural line widths, photoionization and population balance**. Furthermore, narrow lines of He-like ions have also been used as a diagnostic tool for the spectral performance of the photon beamlines.

The development of electron beam ion sources/traps (EBIS/T) has advanced the study of highly charged ions (HCI). The original EBIT employed superconducting magnets to intensify the electron beam. In recent years, the use of rare-earth magnets, e.g. neodymium iron boron (NdFeB), has made it possible to construct small EBIS/T(s) and other ion traps* At NIST, a room-temperature miniature EBIT (mini-EBIT with a field of 0.29 T) using a pair of axial NdFeB rings was built as a source of ions with ionization thresholds up to 900 eV, offering a simpler setup and easy operation. Ease of construction should enable more applications. To recapture and isolate ions, we discuss the design and construction of a compact Penning trap** with a magnetic field of 0.755 T, in which three pairs of radial NdFeB rings are used to generate a trap volume of 230 mm^3 with good homogeneity. Based on the prototype mini-EBIT and the 0.755 T unitary Penning trap, another permanent magnet EBIT is being built at NIST to attain an axial field of about 0.676 T. Potential applications include the production of HCIs such as Pr X, Nd XI for HCI-based atomic clocks*** and the calibration of quantum sensors.