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Chinese Physics B

Design of a magnetic synchrotron for atoms and paramagnetic molecules

Wenli Li, Yabing Ji, Shanwu Wang, Xiaolei Zhang, Zhenghai Yang, Tao Yang, Shunyong Hou, Jianping Yin

Published May 29, 2026• 0 citations
Publisher

Abstract

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.

DOI
10.1088/1674-1056/ae74c0

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arXiv:1011.0418•New Journal of Physics•Oct 24, 2011•51 citations
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.
Limited by the construction demands, the state-of-the-art molecular synchrotrons consist of only 40 segments that hardly make a good circle. Imperfections in the circular structure will lead to the appearance of unstable velocity regions (i.e. stopbands), where molecules of certain forward velocity will be lost from the structure. In this paper, we propose a stopband-free molecular synchrotron. It contains 1570 ring electrodes, which nearly make a perfect circle, capable of confining both light and heavy polar molecules in the low-field-seeking states. Molecular packets can be conveniently manipulated with this synchrotron by various means, like acceleration, deceleration or even trapping. Trajectory calculations are carried out using a pulsed (88)SrF molecular beam with a forward velocity of 50 m/s. The results show that the molecular beam can make more than 500 round trips inside the synchrotron with a 1/e lifetime of 6.2 s. The synchrotron can find potential applications in low-energy collision and reaction experiments or in the field of precision measurements, such as the searches for electric dipole moment of elementary particles.
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.
Taming a broader range of molecular species with large density has been a long-standing goal in molecular science. Heavy molecules with masses greater than 100 amu are of particular interest for precision measurements. However, decelerating a fast-moving beam of such heavy molecules to rest remains challenging for Zeeman deceleration. Moreover, the traditional approach of pulsed Zeeman decelerator suffers from serious molecular loss during deceleration, significantly limiting its potential applications. Herein, we present a proposal of ring-shaped traveling wave Zeeman decelerator (RTWZD) featured with true three-dimensional smoothly moving magnetic potential wells that effectively solve the above intractable problems. With the RTWZD approach, not only can the density of the molecule be greatly increased but also the range of molecular species for Zeeman deceleration can be extended from light to heavy. The performances of the RTWZD are characterized by theoretical analysis and numerical simulations, utilizing a group of atoms and molecules such as 7Li,16O2,88Sr19F^{7}\mathrm{Li}, ^{16}\mathrm{O}_{2}, ^{88}\mathrm{Sr}^{19}\mathrm{F}7Li,16O2​,88Sr19F, and 174Yb19F^{174}\mathrm{Yb}^{19}\mathrm{F}174Yb19F as testers. Notably, losses encountered in the traditional Zeeman decelerator can be avoided, yielding more than two orders of magnitude improvement in molecular density. These characteristics of the RTWZD make it an ideal toolbox to produce cold and dense atomic/molecular samples, with promising prospects for cold collision, sympathetic cooling, and precision measurement.
Abstract Taming more species of molecules with large density is a long-standing goal in molecular science. Heavy molecule (> 100 amu) is of particular interest for precision measurements. However, decelerating a fast-moving beam of heavy molecules to rest remains challenging for Zeeman deceleration. Additionally, the traditional approach of pulsed Zeeman decelerator suffers from serious molecular loss during deceleration, significantly limiting its potential applications. Herein, we present a ring-shaped traveling wave Zeeman decelerator (RTWZD) featured with true three-dimensional smoothly-moving magnetic potential wells that directly solve the above intractable problems. With this approach, not only the density of the molecule can be greatly increased but also the range of molecular species for Zeeman deceleration can be extended from light to heavy. The performance of the RTWZD is characterized with both the theoretical analysis and the numerical calculation, where a group of atoms and molecules such as 7Li, 32O2, 88Sr19F and 174Yb19F are employed as testers. Losses in the traditional Zeeman decelerator can be avoided, yielding more than two orders of magnitude improvement in molecular density. These characteristics of the RTWZD make it an ideal toolbox to produce cold and dense atomic/molecular samples, enabling promising prospects for cold collision, sympathetic cooling, and precision measurement.
A novel traveling-wave Zeeman decelerator based on a double-helix coil geometry capable of decelerating paramagnetic molecules with high efficiency is presented. Moving magnetic traps are generated by applying time-dependent currents through the decelerator coils. Paramagnetic molecules in low-field-seeking Zeeman states are confined inside the moving traps which are decelerated to lower forward velocities. As a prototypical example, we demonstrate the deceleration of OH radicals from an initial velocity of 445 m s −1 down to various final velocities. The experimental results are analyzed and numerically reproduced with the help of trajectory simulations confirming the phase-space stability and efficiency of the deceleration of the molecules in the new device.
We present an experimental realization of a moving magnetic trap decelerator, where paramagnetic particles entrained in a cold supersonic beam are decelerated in a co-moving magnetic trap.Our method allows for an efficient slowing down of both paramagnetic atoms and molecules to near stopping velocities.We show that under realistic conditions we will be able to trap and decelerate a large fraction of the initial supersonic beam.We present our first results on deceleration in a moving magnetic trap by bringing metastable neon atoms to near rest.Our estimated phase space volume occupied by decelerated particles at a final velocity of 50 m s -1 shows an improvement of two orders of magnitude as compared to currently available deceleration techniques.Cold chemistry (at temperature of ∼1 K) is a fast developing field with many interesting theoretical predictions yet only a few experiments [1][2][3][4].It has been predicted that in the cold chemistry regime, reactions might proceed through resonance states [5] and both reaction rate and path could be controlled [6] via external magnetic or electrostatic fields.Low-temperature chemistry is not limited to artificially created conditions alone but occurs naturally at the low temperature of interstellar space [7] and the atmospheres of remote planets and moons [8].It is anticipated that cold chemistry will follow the enormous progress in molecular chemistry that was spurred by the advent of supersonic beams more than half a century ago [9].However, the progress in experimental cold chemistry is rather slow partly due to the absence of a general method of atomic and molecular cooling.Although the low-temperature environment created within a supersonic expansion has been used to observe many reactions [10], a direct 1 Author to whom any correspondence should be addressed.