Measurement of level-specific dielectronic-recombination cross sections of heliumlike Fe XXV

Hypersatellite Kα Production in Trapped Ar Ions at KK Trielectronic Recombination Energies

We report measurements of hypersatellite radiation of argon ions in the electron energy region of 5200 eV to 7500 eV. Here, we observed a strong enhancement of this hypersatellite Kαh production. Trielectronic recombination (TR) is discussed as a possible channel for Kαh production leading to this enhancement where main TR resonances are expected to occur. Data analysis was mainly based on the extracted intensity ratio of hypersatellite Kαh to Kα lines (Kαh/Kα). In addition, the collisional excitation and the collisional ionisation of the K-shell ions were modeled as main background processes of the Kα X-ray production. The Kαh/Kα intensity ratio shows a significant rise around 6500 eV electron energy by a factor of about two above the background level. This observation is compared with calculations of the expected electron energies for the resonant Kαh emission due to the KK TR process. The observed rise as a function of the electron collision energy, which occurs in the vicinity of the predicted TR resonances, is significantly stronger and energetically much wider than the results of theoretical calculations for the TR process. However, the experimental evidence of this process is not definitive.

An electron beam ion trap and source for re-acceleration of rare-isotope ion beams at TRIUMF

Electron beam driven ionization can produce highly charged ions (HCIs) in a few well-defined charge states. Ideal conditions for this are maximally focused electron beams and an extremely clean vacuum environment. A cryogenic electron beam ion trap fulfills these prerequisites and delivers very pure HCI beams. The Canadian rare isotope facility with electron beam ion source-electron beam ion sources developed at the Max-Planck-Institut für Kernphysik (MPIK) reaches already for a 5 keV electron beam and a current of 1 A with a density in excess of 5000 A/cm² by means of a 6 T axial magnetic field. Within the trap, the beam quickly generates a dense HCI population, tightly confined by a space-charge potential of the order of 1 keV times the ionic charge state. Emitting HCI bunches of ≈10⁷ ions at up to 100 Hz repetition rate, the device will charge-breed rare-isotope beams with the mass-over-charge ratio required for re-acceleration at the Advanced Rare IsotopE Laboratory (ARIEL) facility at TRIUMF. We present here its design and results from commissioning runs at MPIK, including X-ray diagnostics of the electron beam and charge-breeding process, as well as ion injection and HCI-extraction measurements.

Strong higher-order resonant contributions to x-ray line polarization in hot plasmas

We studied angular distributions of x rays emitted in resonant recombination of highly charged iron and krypton ions, resolving dielectronic, trielectronic, and quadruelectronic channels. A tunable electron beam drove these processes, inducing x rays registered by two detectors mounted along and perpendicular to the beam axis. The measured emission asymmetries comprehensively benchmarked full-order atomic calculations. We conclude that accurate polarization diagnostics of hot plasmas can only be obtained under the premise of inclusion of higher-order processes that were neglected in earlier work.

High resolution flat crystal spectrometer for the Shanghai EBIT

We report on a high resolution flat crystal spectrometer designed for the Shanghai EBIT. Its energy range is from 0.5 to 10 keV. Three crystals can be installed in the vacuum chamber simultaneously, and its effective Bragg angle can be covered from 15 degrees to 75 degrees . A vacuum version charge-coupled device detector is used for detection of photons. An energy resolution under 1 eV was reached in measurements of the 4.5 keV Kalpha(1) line by using an x-ray generator with a titanium anode. The spectrometer was also tested to operate well on the Shanghai EBIT by observing the lines of tungsten at around 3.2 keV.

Measurement of the electron cyclotron energy component of the electron beam of an electron beam ion trap

The energy component associated with the cyclotron motion of the beam electrons in the Livermore EBIT-II electron beam ion trap was inferred from measurements of the linear polarization of the K-shell x-ray lines emitted from helium-like Mg(10+) ions. The average line polarization was found to be reduced by about 20% from its nominal value. From this it was inferred that the electron cyclotron motion accounted for 190+/-30 eV of the total electron beam energy. The measured value is in good agreement with the predictions of optical electron beam propagation. It does not agree with the estimates derived from other model assumptions, such as the rigid-rotator model, for determining the size of the energy stored in the electron motion perpendicular to the beam propagation direction.