Loading of mass spectrometry ion trap with Th ions by laser ablation for nuclear frequency standard application

Abstract

We describe an original multisectional quadrupole ion trap aimed to realize nuclear frequency standard based on the unique isomer transition in thorium nucleus. It is shown that the system effectively operates on Th, Th and Th ions produced by laser ablation of metallic thorium-232 target. Laser intensity used for ablation is about 6 GW/cm. Via applying a bias potential to every control voltage including the RF one, we are able not only to manipulate ions within the energy range as wide as 1-500 eV but to specially adjust trap potentials in order to work mainly with ions that belong to energy distribution maximum and therefore to effectively enhance the number of trapped ions. Measurement of energy distributions of Th, Th, Th ions obtained by laser ablation allows us to define optimal potential values for trapping process. Observed number of ions inside trap in dependence on trapping time is found to obey an unusually slow - logarithmic decay law that needs more careful study.

Investigation by simulation of the RF carpets for the transport of ions at atmospheric pressures

“…This approach was discussed in course of development of setup for nuclear transition investigation of 229Th 3 +. 24,25 In this case 229Th3+ ions are produced in the a decay of 233U. 26 An employment of RF carpet system leads to significantly increase the capture efficiency of formed 229 Th 3+ ions.…”

Ion generation and loading of a Penning trap using pulsed laser ablation

“…The need for ions is largely fulfilled by producing atoms from a resistively heated oven [5][6][7][8][9] and subsequently ionizing them using an electron or laser beam. To achieve the desired number of ions, an oven is typically operated for tens of seconds and at temperatures in excess of 500 K. Ions may also be loaded into a trap using a laser-cooled source of neutral atoms [10,11], or directly via laser ablation of a target surface [12][13][14][15][16][17].…”

Studies of thorium and ytterbium ion trap loading from laser ablation for gravity monitoring with nuclear clocks

“…Regardless of the nominally sub-threshold fluence level, we observed the ablation of thorium targets and the creation of singly and doubly ionized atoms similarly to [64] where authors reached 1.1 J/cm 2 with the same kind of laser for ablation. Successful trap loading 232 Th 3+ has been reported in [40] but with a more powerful laser source and fluence reaching 320 J/cm 2 , calculated from their 50 mJ pulse energy and 100 µm laser spot size. A metallic thorium-232 target was used.…”

“…In addition, the 229 Th nucleus is expected to be an excellent system for the search for time variation of fundamental constants [34][35][36]. To this date, a few groups worldwide have demonstrated thorium trapping in ion traps [37][38][39][40][41][42][43][44]. The nuclear clock is not the only stimulating application of thorium ion traps.…”