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arXiv:1501.05915 · New Journal of Physics

A compact design for a magnetic synchrotron to store beams of hydrogen atoms

Aernout P. P. van der Poel, Katrin Dulitz, T. P. Softley, Hendrick L. Bethlem

Published May 12, 2015• 12 citations
arXivHTMLPDF

Abstract

We present a design for an atomic synchrotron consisting of 40 hybrid magnetic hexapole lenses arranged in a circle. We show that for realistic parameters, hydrogen atoms with a velocity up to 600 m s −1 can be stored in a 1 m diameter ring, which implies that the atoms can be injected in the ring directly from a pulsed supersonic beam source. This ring can be used to study collisions between stored hydrogen atoms and supersonic beams of many different atoms and molecules. The advantage of using a synchrotron is two-fold: (i) the collision partners move in the same direction as the stored atoms, resulting in a small relative velocity and thus a low collision energy, and (ii) by storing atoms for many round-trips, the sensitivity to collisions is enhanced by a factor of 100–1000. In the proposed ring, the cross-sections for collisions between hydrogen, the most abundant atom in the universe, with any atom or molecule that can be put in a beam, including He, H 2 , CO, ammonia and OH can be measured at energies below 100 K. We discuss the possibility of using optical transitions to load hydrogen atoms into the ring without influencing the atoms that are already stored. In this way it will be possible to reach high densities of stored hydrogen atoms.

DOI
10.1088/1367-2630/17/5/055012

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We present a design for an atomic synchrotron consisting of 40 hybrid magnetic hexapole lenses arranged in a circle. We show that for realistic parameters, hydrogen atoms with a velocity up to 600 m s −1 can be stored in a 1 m diameter ring, which implies that the atoms can be injected in the ring directly from a pulsed supersonic beam source. This ring can be used to study collisions between stored hydrogen atoms and supersonic beams of many different atoms and molecules. The advantage of using a synchrotron is two-fold: (i) the collision partners move in the same direction as the stored atoms, resulting in a small relative velocity and thus a low collision energy, and (ii) by storing atoms for many round-trips, the sensitivity to collisions is enhanced by a factor of 100–1000. In the proposed ring, the cross-sections for collisions between hydrogen, the most abundant atom in the universe, with any atom or molecule that can be put in a beam, including He, H 2 , CO, ammonia and OH can be measured at energies below 100 K. We discuss the possibility of using optical transitions to load hydrogen atoms into the ring without influencing the atoms that are already stored. In this way it will be possible to reach high densities of stored hydrogen atoms.
Abstract Molecular synchrotrons offer a promising platform for molecular beam collision studies with enhanced collision sensitivity. However, existing synchrotron designs suffer from constraints in velocity range, particle mass, and molecular flux. Here, we propose a novel magnetic synchrotron consisting of 1048 coils arranged in a nearly perfect circular ring, which generates a series of deep (~2.2 T), moving three-dimensional traps. Its key advantages are as follows: I) It enables direct loading of supersonic light species (400 m/s for NH) from a pulsed valve, thereby circumventing the flux limitations of upstream decelerators and significantly increasing the number of captured molecules. II) It is capable of confining heavy paramagnetic molecules (e.g., YO) at the modest injection velocities (tens of meters per second) typical of buffer-gas cooling. III) The high symmetry of the structure eliminates stop-bands, allowing paramagnetic molecules to be confined over a continuously tunable velocity range and achieving a long storage lifetime (~1.5 s for NH). This synchrotron design overcomes major limitations of previous devices and opens new possibilities for high-sensitivity collision studies and quantum-state-resolved chemistry. Moreover, by straightening the ring, the structure can function as a Zeeman decelerator, which is predicted to surpass recent deceleration schemes (Y. Ji et al., Phys. Rev. A 108, 043115, 2023) in efficiency by several times for both light and heavy molecules.
Using calculations and mathematical modeling, we demonstrate the feasibility of constructing a synchrotron storage ring for neutral polar molecules. The lattice is a racetrack type 3.6 m in circumference consisting of two of 180-degree arcs, six bunchers, and two long straight sections. Each straight section contains two triplet focusing lenses and space for beam injection and experiments. The design also includes a matched injector and a linear decelerator. Up to 60 bunches can be loaded and simultaneously stored in the ring. The molecules are injected at 90 m/s but the velocity of the circulating beam can be decelerated to 60 m/s after injection. The modeling uses deuterated ammonia molecules in a weak-field seeking state. Beam that survives 400 turns (15 s), has horizontal and vertical acceptances of 35 mm-mr and 70 mm-mr respectively, and an energy acceptance of plus or minus 2%.
We present a synchrotron for polar molecules consisting of 40 straight hexapoles arranged in a circle with a 50 cm diameter. The mechanical design and alignment procedure as well as the trigger scheme used to switch the voltages applied to the hexapoles are described in detail. The stability of the synchrotron is demonstrated by measurements in which multiple packets are stored for over 13 s, during which they have completed over 1000 round trips and traveled a distance of over one mile. Furthermore, we demonstrate the simultaneous trapping of 26 packets; 13 revolving clock-wise and 13 counter clock-wise, that are injected into the synchrotron by two Stark decelerator beamlines. We discuss the opportunities for using the synchrotron as a low-energy collider.
Using calculations and mathematical modeling, we demonstrate the feasibility of constructing a synchrotron storage ring for neutral polar molecules. The lattice is a racetrack type 3.6 m in circumference consisting of two 180° arcs, six bunchers, and two long straight sections. Each straight section contains two triplet focusing lenses and space for beam injection and experiments. The design also includes a matched injector and a linear decelerator. Up to 60 bunches can be loaded and simultaneously stored in the ring. The molecules are injected at 90 m/s but the velocity of the circulating beam can be decelerated to 60 m/s after injection. The modeling uses deuterated ammonia (14N2H3) molecules in a weak-field seeking state. A beam that survives 400 turns (15 s), has horizontal and vertical acceptances of 35 and 70 mm mrad, respectively, and an energy acceptance of ±2%.
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.
A molecular synchrotron offers unique possibilities to study molecular collisions at low energies. For such a study, it is imperative that the velocity of the stored molecules can be tuned over a wide range. Bunching elements, used to provide the necessary longitudinal focusing forces in a synchrotron, introduce instabilities for certain velocities of the stored molecules. Here we present an experimental study of these motional resonances and show how they can be avoided. A packet of ND3\mathrm{N}{\mathrm{D}}_{3}ND3​ molecules is stably confined in the synchrotron as its injection velocity is continuously scanned from 60m∕s60\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}60m∕s $({E}_{\mathrm{kin}}=3.0\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1})\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}87.5\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}$ $({E}_{\mathrm{kin}}=6.4\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1})$.