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The electron capture (EC) decay of $^{163}$Ho to $^{163}$Dy is a promising candidate for the determination of the electron neutrino mass in the sub-eV range. For this purpose the ECHo collaboration [1] aims to perform a calorimetric measurement of the $^{163}$Dy$^{*}$ de-excitation spectrum. With its Penning-trap setup the \textsc{Pentatrap} [2] experiment performs a precision mass measurement of the mother and daughter nuclide with a relative mass-ratio uncertainty of $10^{-11}$, thus contributing an independent value of the energy available for the EC decay ($Q$-value). To achieve such a precision, highly charged ions are necessary which can be produced in electron beam ion traps (EBIT).
To cope with the strongly limited amount of $^{163}$Ho available, an efficient in-trap laser-induced loading technique into a Heidelberg compact EBIT [3] was developed for very rare atoms. Ions of various mass domains A=40 to A=209 have been successfully produced, in particular charge states of up to 45+ have been achieved for $^{165}$Ho using a sample size of only about $10^{12}$ atoms (about 0.27 ng). These small samples lasted for the production of more than 30000 HCI bunches, each containing thousands of Ho ions.
The EBIT was recently connected to the Pentatrap beam line and is currently being commissioned for the measurement of the mass ratio of $^{163}$Ho and $^{163}$Dy.
[1] Gastaldo, L. et al., Eur. Phys. J. Special Topics 226, 1623 (2017)
[2] Repp, J. et al., Appl. Phys. B 107, 983 (2012)
[3] Micke, P. et al., Rev. Sci. Instrum. 89, 063109 (2018)
