Speaker
Description
Today ion sources based on laser resonance ionization are well-established core techniques at the worldwide leading radioactive ion beam facilities such as CERN-ISOLDE or ISAC-TRIUMF. Ensuring both, highly efficient and element-selective ion beam production to the users, these devices in addition allow for direct laser spectroscopic investigations on exotic nuclei far off stability with lowest production yields. Further developments comprise preeminent suppression of isobaric contaminants by spatially separating the hot atomization cavity from a clean laser – atom interaction volume. This Laser Ion Source and Trap (LIST) design permits experimental access to nuclides such as neutron-rich Po, which were formerly inaccessible due to overwhelming contamination by easily surface ionized alkaline elements [1, 2].
Derived from operation experience and systematic studies, several changes have been implemented for the next generation of the LIST, intended to be run at ISOLDE in 2018. A dual repelling electrode design allows for simultaneous suppression of surface ionized contamination as well as electrons from the hot cavity, inhibiting electron impact induced ionization inside the LIST’s RFQ structure [3]. Also, based on atom beam divergence investigations, the overall length was decreased, potentially yielding additional space for a chemically selective quartz transfer line.
By matching the field-free drift length in the LIST to the hot cavity dimensions, a time-of-flight based operation mode can be established, creating very short ion bunches. This effect is enhanced by using a higher voltage gradient over the cavity via high resistance materials and/or pulsed heating with higher currents. A fast and robust high current switch is being developed to allow for both laser repetition rate synchronized heating and quick in-situ polarity switching to select between additional suppression and ion guiding operation.
A perpendicular laser irradiation mode has been developed to perform Doppler-free high resolution spectroscopy in the LIST. Experimental linewidths below 100 MHz FWHM allow for hyperfine structure investigations of isotopes with highly dense spectra, as well as isomer-pure ion beam production. In off-line experiments, valuable nuclear data from minuscule samples of 10 day half-life Ac-229 could be extracted.
The presentation will give an overview of the described developments and discuss future directions.
References
[1] D. Fink et al., NIMB 317 B, 417-421 (2013)
[2] D. Fink et al., PRX 5, 011018 (2015)
[3] R. Heinke et al., Hyperfine Interact 238:6 (2017)
[4] S. Rothe et al., NIMB 376, 86-90 (2016)
