Ion trap for nuclear clock created by Russian scientists
Who said that atomic clock is the most precise in the world? The humankind opens new horizons of time measuring, and there comes a new, extra-precise clock – a nuclear one. While the first one is connected with the electron transfer in atom shells into states with more or less high energy, work of nuclear clock, under which MEPhI employees are working, is based on the counting of time periods with the help of registration of isomeric transfer, regularly taking place in ions of Thorium-229. Besides, nuclear clock will work to a precision of one hundredth of a second in 13,8 billion years – that's an approximate time of our Universe's existence. For its creation an ion trap which will allow filter and catch ions of Thorium-229 from ion beams with wide energy range is extremely important.
The precise measurement of energy of nuclear isomeric transfer 229mTh – 229gTh will let work out an optical nuclear frequency standard with relative precision of ~10–20, which five orders exceeds existing "caesium fountain" type of frequency standard (10–15).
The frequency standard with relative precision of 10–20 is necessary for enhancement of precision of the Global Navigation Satellite System, raising of efficiency of distant detection of rare-earth elements, oil and gas. It will also help find dependence of transfer frequency on gravitational field, measure some fundamental constants (fine structure constant, gravitational constant) with high precision and check basics of general relativity theory and cosmology.
However, there are some restrictions because of thorium. For instance, it is a refractory metal with high boiling temperature and low vapor pressure so for ionization it uses methods with high energy which leads to the production of ions with large energy range. Moreover, 229Th is radioactive. To get necessary result, 229Th3+ should be used, because triple-charged ions have a better corresponding structure of levels for fluorescent diagnostics and laser cooling. Thorium ions are also more active, even using helium as collisional gas, thorium ions actively react to admixtures. That is why it was necessary to create a method of ion trapping in a vacuum which is effective in different energy ranges.
Employees of MEPhI Departments №10 and №78 have become one step closer to the creation of nuclear clock. They have worked out and tested a linear quadrupole ion trap for optical spectroscopy of nuclear and electronic transitions. The ion source construction is based on an ultrahigh-vacuum vaporizer in which an atom and ion cloud of different charge is created because of irradiating the object by an electron beam with energy up to 1 keV.
The linear ion trap consists of 5 consecutive quadrupole sections: an input quadrupole, a quadrupole mass filter, a quadrupole ion trap and an output quadrupole. A high-frequency stress component is the same in different sections but the breakdown voltage values are different which helps create a flexible instrument for ion assemblies forming and spectroscopy measuring.
The device makes filtration and ion trapping possible in the range of masses and energies of ion beams with a wide energy spectrum and ion localization in the area of ion beam impact. The suggested theory and device allow effectively produce thorium ions, up to triple-charged ones and trap them for further spectroscopy. It has been suggested to use the device in optical clock and quantum computer development.
Provided by National Research Nuclear University
