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Le Journal de Physique Colloques

THE UNIVERSITY OF IOWA APPARATUS FOR PRODUCTION OF STABILIZED ATOMIC HYDROGEN

R. W. H. Webeler, R. F. Ferrante, W. C. Stwalley

Published Jul 1, 1980• 1 citation
Publisher

Abstract

We have completed the detailed design and most of the construction of a low temperature apparatus for preparation of stabilized atomic hydrogen, based on a proposed production method described previously (J. Physique 39 (1978) C6-108). We will briefly describe the apparatus which includes a microwave source of atomic hydrogen, a dilution refrigerator capable of temperatures below 0.1 K, a 11 T superconducting magnet, and a dewar with access from the bottom for introduction of the atomic hydrogen.

DOI
10.1051/jphyscol:1980726

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We have completed the detailed design and most of the construction of a low temperature apparatus for preparation of stabilized atomic hydrogen, based on a proposed production method described previously (J. Physique 39 (1978) C6-108). We will briefly describe the apparatus which includes a microwave source of atomic hydrogen, a dilution refrigerator capable of temperatures below 0.1 K, a 11 T superconducting magnet, and a dewar with access from the bottom for introduction of the atomic hydrogen.
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.
Atomic hydrogen has been loaded into a 1-K deep magnetic trap through the use of a dilution refrigerator. Evaporative cooling has been used to cool the trapped hydrogen into the submillikelvin temperature regime. These techniques have produced a sample with density of 8 × 1013 cm-3 at a temperature of 100 μK. At this density a transition to a Bose-Einstein condensate is predicted to occur at a temperature of 30 μK. These results have been obtained with a magnetic trap that has been constructed to accommodate upcoming experiments based on laser spectroscopy of the 1S-2S two photon transition in the trapped hydrogen. A frequency doubled narrow linewidth cw dye laser system has been constructed to excite the 1S-2S transition. The excitation will be detected by the observation of electric field-induced Lyman-alpha fluorescence. The optical detection system should yield improved sample density and temperature diagnostic capabilities that will facilitate a closer approach to the quantum degenerate regime. Additionally the cold, confined hydrogen gas offers the possibility of improving the level of resolution of Doppler-free hydrogen 1S-2S laser spectroscopy by several orders of magnitude.
The possible application of the stable atomic hydrogen (H↓) in intense polarized atom or ion beam sources is discussed. The proposed scheme is based on flipping the electron spin of stored atoms by microwaves; this results in the magnetic acceleration and focusing of the flipped atoms. The main advantages of such beams are: accumulation and pulsing with time structure convenient for injection into synchrotrons via Linac injectors; high density due to the slow velocity and high initial density; and monochromaticity which allows atomic beam transport with focusing elements having no large chromatic errors. The possible problems and limitations in such an extraction scheme are: depolarization and slow spin diffusion due to spin exchange collisions in the dense gas phase, and loss of density due to recombination of the flipped atoms on the walls, before reaching the extraction aperture and accelerating field gradient.The results of the first tests of our apparatus are presented. The apparatus, based on a powerful dilution refrigerator, is described briefly.
We describe the design and performance of a large magnetic trap for storage and cooling of atomic hydrogen (H). The trap operates in the vacuum space of a dilution refrigerator at a temperature of 1.5 K. Aiming at a large volume of the trap, we implemented the octupole configuration of linear currents (Ioffe bars) for the radial confinement, combined with two axial pinch coils and a 3 T solenoid for the cryogenic H dissociator. The octupole magnet consists of eight race-track segments, which are compressed toward each other with magnetic forces. This provides a mechanically stable and robust construction with a possibility of replacement or repair of each segment. A maximum trap depth of 0.54 K (0.8 T) was reached, corresponding to an effective volume of 0.5 l for hydrogen gas at 50 mK. This is an order of magnitude larger than ever used for trapping atoms.