In an electron beam ion trap highly charged ions (EBIT) can be produced and stored by compressing a mono-energetic electron beam to very high densities. The compression is carried out by strong magnetic fields usually produced by super conducting magnets reaching flux densities from 3 up to 8 T. To reduce size as well as costs and to ease final operation, we developed a room-temperature EBIT employing permanent magnets and reached magnetic field strength of 0.86 T.

The HC-EBITs can be used for spectroscopy of HCIs from the optical up to the x-ray regime. One application for example is the investigation of electron recombination processes with an accuracy never reached before using an EBIT. Furthermore, the produced HCIs can be extracted for experiments like Paul or Penning traps.

Forbidden optical transitions in highly charged ions (HCIs) are excellent candidates for novel optical frequency standards due to their low susceptibility to external influences. Some of those transitions can be used to stringently test the constancy of fundamental constants as they feature an enhanced sensitivity to a possible variation of the fine structure constant or the electron-proton mass ratio. Futhermore, quantum elctrodynamic effects as large as 1% of the transition energy and nuclear size effects of a few percent (e.g. in the hyperfine structure of heavy hydrogen-like ions) are found in such transitions.

For such high precision experiments HCIs need to be trapped and cooled. At the cryogenic Paul Trap experiment (CryPTEx), a broad range of HCIs can be trapped and sympathetically cooled by implanting them into a laser cooled (Be+) Coulomb crystal at mK temperatures, thereby reducing the HCI temperature from the megakelvin range down to 10 mK. In addition, long storage times are accomplished due to the extremely low background pressure <6x10^-14 mbar in the cryogenic environment of the trap at 6 K.

The next generation of CryPTEx focusses on extremely stable trapping conditions by isolating mechanical vibrations. Furthermore, a novel superconducting Paul trap resonator will enable precise localization and strong confinement of HCIs in low-noise trapping potentials.

To study highly charged ions in the extreme ultraviolet (XUV) with high precision, a coherent ultra-narrow light source in this spectral region is required.

For these reasons, we are developing an XUV frequency comb. High-harmonic generation (HHG) is used to transfer the coherence and stability of a near infrared frequency comb to the XUV. It is very challenging to reach the necessary high intensity levels for HHG, while operating at high repetition rates. Therefore, the comb laser pulses are first amplified in a chirped-pulse fiber amplification setup and then resonantly overlapped in a femtosecond enhancement cavity. To achieve high stability and low-noise performance, the cavity is placed on a rigid titanium structure with vibrational decoupling from the vacuum pumps. High-harmonics are generated in a target gas in the tight focus of the cavity.

The generated XUV light will be coupled out of the cavity and guided towards trapped HCI. By driving narrow transitions with individual comb lines, high-precision XUV spectroscopy of HCI will become possible for the first time