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Canadian Journal of Physics

A new trap loading mechanism for hydrogenThis paper was presented at the International Conference on Precision Physics of Simple Atomic Systems, held at University of Windsor, Windsor, Ontario, Canada on 21–26 July 2008.

P. Crivelli, Claudio Lenz Cesar, Ricardo Lewis Lambo

Published Jul 1, 2009• 5 citations
Publisher

Abstract

In this paper, we report on our recent advances on a new trap loading mechanism for neutral atoms. The idea is based on our recently published results for chromium spectroscopy of atoms released from a solid neon matrix at cryogenic temperatures. The proposed trap loading mechanism consists of magnetically capturing the low-energy fraction of paramagnetic atoms being released from the matrix, while the host Ne atoms stick to the walls. Two different designs are described: one with a superconducting magnet producing a trap depth of 3 T and another with a superconducting dynamically switched magnet that generates a trap depth of about 1 T. Some preliminary results are presented.

DOI
10.1139/p09-007

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In this paper, we report on our recent advances on a new trap loading mechanism for neutral atoms. The idea is based on our recently published results for chromium spectroscopy of atoms released from a solid neon matrix at cryogenic temperatures. The proposed trap loading mechanism consists of magnetically capturing the low-energy fraction of paramagnetic atoms being released from the matrix, while the host Ne atoms stick to the walls. Two different designs are described: one with a superconducting magnet producing a trap depth of 3 T and another with a superconducting dynamically switched magnet that generates a trap depth of about 1 T. Some preliminary results are presented.
We have studied the velocity distribution of chromium atoms released from a solid neon matrix at cryogenic temperatures via Doppler spectroscopy. The Ne matrix is grown by directing a small flux of gas onto a cold substrate, while Cr atoms are simultaneously implanted by laser ablation, with the resultant plume directed toward the growing matrix. The atoms are then released by a heat pulse. We have observed neutral Cr atoms at temperatures around 13K13\phantom{\rule{0.3em}{0ex}}\mathrm{K}13K with densities close to ${10}^{12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. The released atoms have a large initial drift velocity, explained by simple kinetic theory arguments, due to the light species' drag force. The scheme could be adapted to produce cryogenic beams of atoms, molecules, and possibly ions, for collisional studies and spectroscopy. However, our main motivation was the construction of a hydrogen trap, and here we discuss the prospects and problems of using this technique for this purpose.
Hydrogen is of critical importance in atomic and molecular physics and the development of a simple and efficient technique for trapping cold and ultracold hydrogen atoms would be a significant advance. In this study we simulate a recently proposed trap-loading mechanism for trapping hydrogen atoms released from a neon matrix. Accurate ab initio quantum calculations are reported of the neon-hydrogen interaction potential and the energy- and angular-dependent elastic scattering cross sections that control the energy transfer of initially cold atoms are obtained. They are then used to construct the Boltzmann kinetic equation, describing the energy relaxation process. Numerical solutions of the Boltzmann equation predict the time evolution of the hydrogen energy distribution function. Based on the simulations we discuss the prospects of the technique.
Ground-state 52Cr{}^{52}\mathrm{Cr}52Cr atoms have been magnetically trapped using buffer-gas loading. The atoms are produced by laser ablation of solid 52Cr,{}^{52}\mathrm{Cr},52Cr, thermalized by collisions with a cryogenically cooled helium buffer gas, and trapped by an anti-Helmholtz quadrupole magnetic field. The atoms are detected by absorption spectroscopy on the ${a}^{7}{S}_{3}\ensuremath{\leftrightarrow}{z}^{7}{P}_{3}$ transition at 427.6 nm. Using this technique, approximately 1011{10}^{11}1011 atoms are loaded into the trap in a single ablation pulse. Loading has been demonstrated at temperatures from 0.3 to 1.4 K.
Abstract We present a design and performance tests of an intense source of cold hydrogen atoms for loading large magnetic traps. Our source is based on a cryogenic dissociator of molecular hydrogen at 0.6 K followed by a series of thermal accommodators at 0.5, 0.2 and 0.13 K with inner surfaces covered by a superfluid helium film. All components are thermally anchored to corresponding stages of a dilution refrigerator. The source provides a continuous flux of 7×10137\times 10^{13}7×1013 7 × 10 13 H atoms/s in a temperature range of 130–200 mK. We have successfully used the source for loading a large Ioffe–Pritchard magnetic trap recently built in our laboratory (Ahokas et al. in Rev Sci Instrum 93(2):023201, 2022). Calorimetric measurements of the atomic recombination heat allow reliable determination of the atomic flux and H gas density in the trap. We have tested the performance of the source and loading of H atoms into the trap at various configurations of the trapping field, reducing the magnetic barrier height to 75 %\%% % and 50 %\%% % of the nominal value of 0.8 T (0.54 K) as well as at the open configuration of the trap at its lower end, when the atoms are in contact with the trapping cell walls covered by a superfluid helium film. In the latter case, raising the trapping cell temperature to 200–250 mK, the low-field seeking atoms at densities exceeding 10 11^{11}11 11 cm−3\hbox {cm}^{-3}cm−3 cm - 3 can be stored for the time over 10 3^33 3 s, sufficiently long for experiments on precision spectroscopy of cold H gas. Graphic abstract
We present a design and performance tests of an intense source of cold hydrogen atoms for loading large magnetic traps. Our source is based on a cryogenic dissociator of molecular hydrogen at 0.6 K followed by a series of thermal accommodators at 0.5, 0.2 and 0.13 K with inner surfaces covered by a superfluid helium film. All components are thermally anchored to corresponding stages of a dilution refrigerator. The source provides a continuous flux of 7⋅\cdot⋅101310^{13}1013 H atoms/s in a temperature range of 130-200 mK. We have successfully used the source for loading a large Ioffe-Pritchard magnetic trap recently built in our laboratory [arXiv:2108.09123 or Rev. Sci. Instr. 93 (2), 023201 (2022)]. Calorimetric measurements of the atomic recombination heat allow reliable determination of the atomic flux and H gas density in the trap. We have tested the performance of the source and loading of H atoms into the trap at various configurations of the trapping field, reducing the magnetic barrier height to 75% and 50% of the nominal value of 0.8 T (0.54 K) as well as at the open configuration of the trap at its lower end, when the atoms are in contact with the trapping cell walls covered by a superfluid helium film. In the latter case, raising the trapping cell temperature to 200-250 mK, the low-field seeking atoms at densities exceeding 1011^{11}11 cm−3^{-3}−3 can be stored for the time over 1000 s, sufficiently long for experiments on precision spectroscopy of cold H gas.
Magnetic trapping of laser-cooled neutral atoms has been demonstrated at NBS and is progressing in other laboratories. Confinement of any object requires exchanging kinetic for potential energy, and for neutral atoms, this necessarily derives from shifts of internal energy levels. This is implemented through the force experienced by the atomic magnetic moment in a carefully designed, highly inhomogeneous field. Since magnetic fields of convenient strength can shift atomic energy levels by only a few gigahertz (temperature ≌ 0.1 K), neutral atom traps are very shallow and must be loaded with very cold atoms. We present some motivations for using magnetic traps and then discuss the constraints and optimal configurations of various arrangements. For example, no trap can be isotropic. Next we discuss both the classical and quantum mechanical motions of trapped atoms. These motions are important for at least two reasons: First, several schemes under study for further cooling depend on knowing the position and velocity of the atoms, as well as the vector field at each point along the orbit. Second, magnetic traps depend on the atomic moment remaining aligned with the field as the atom orbits in the trap, and this precludes rapid motion through a low-field region.