Ion Storage Ring Research Articles

Huizhou accelerator complex facility and its future development

This paper provides an overview of the frontier research fields and significant questions in nuclear physics regarding particle accelerators, and the status and future development trends for big-science facilities of particle accelerators are reviewed. Two Chinese government-approved “12th Five-Year” major science infrastructure facilities, the “High Intensity heavy-ion Accelerator Facility (HIAF)” and “China Initiative Accelerator Driven System (CiADS)”, are being constructed in Huizhou, Guangdong Province. Based on these two big-science projects (HIAF and CiADS), we proposed to establish a large-scale charged particle accelerator complex facility named the “Bright Electron and Ion research Facility (BEIF).” This facility will be dedicated to the research and development of nuclear physics and its interdisciplinary frontier fields. The research frontier fields of nuclear physics at the BEIF will include nuclear structure and astrophysics, nucleon structure, quark matter phase structure, and interdisciplinary fields between several significant frontiers of fundamental and nuclear physics, such as highly charged atomic physics and heavy ion-driven high energy density physics. BEIF will be a large-scale scientific complex facility comprising several superconducting ion LINAC accelerators, synchrotrons, storage rings, reactors, and various large experimental detectors and setups. BEIF will be built in three construction phases and will become one of the premier global large-scale particle accelerator complex facilities dedicated to the research of nuclear physics and technology.

Beam gap transient analysis and mitigations in high-current storage rings for an electron-ion collider

The U.S. electron ion collider will utilize high current electron and ion storage rings with many bunches and large rf systems. Because of the dissimilarity of the two rings, the rf transients created by gaps or variations in the current distributions will be very different in the two rings. These transients cause a shift in the synchronous phase of the beams as a function of rf bucket position, can impact the luminosity through shifts in longitudinal position of the IP, will affect the performance of the rf and LLRF control loops, and may require significant rf power overhead to control. A machine design that uses superconducting crab cavities will also have sensitivity to gap transients and synchronous phase variations along the bunch train with variations in crab cavity voltage seen by each bunch, since the high $Q$ of the crab cavities precludes modulating them to compensate for the time of arrival shifts caused by the gap transients in the main rf systems. All these effects make the problem of managing gap transients crucial to the operation of the EIC. This work presents methods to study the dynamics of the rf and LLRF systems for these heavily beam loaded facilities. An illustrative machine design example is presented and used to investigate the expected magnitudes of the rf gap transients, and exploration of various possible remedies to match the gap transients in the two dissimilar EIC rings. In addition to the study of the power required and gap transients, this work also estimates longitudinal coupled-bunch instabilities due to the baseline cavity fundamental impedance. The work is motivated to emphasize the importance of tools and methods to estimate these effects as part of the early design phase of the Electron-Ion Collider or any high current storage ring design.

Radiative cooling dynamics of isolated N2O+ ions in a cryogenic electrostatic ion storage ring

We study radiative cooling processes of ${\mathrm{N}}_{2}{\mathrm{O}}^{+}$ ions isolated in vacuum by taking advantage of the extended storage times possible with a cryogenic electrostatic ion storage ring. The temporal evolution of the internal state populations of the ${\mathrm{N}}_{2}{\mathrm{O}}^{+}$ ions after being stored in the ring was state-selectively measured by action spectroscopy via a predissociation process using a wavelength-tunable pulsed laser. The rotational level population remained unchanged up to about 200 s after ion storage, which is consistent with theoretical predictions and the small permanent dipole moment. On the other hand, we found that depletion of the vibrational excited states in the NN-O stretching mode proceeded within 5 s, while a noticeable increase of the ground-state population was not observed. This implies that the initial populations of the vibrational excited states are relatively small. We discuss such behavior in the context of the initial population distribution of ions extracted from the ion source with a simulation based on simple cascade modeling.

A 410 MHz resonant cavity pickup for heavy ion storage rings.

An improved design of a longitudinally sensitive resonant Schottky cavity pickup for the heavy ion storage rings of the Facility for Antiproton and Ion Research in Europe (FAIR) project is reported. The new detector has a higher measured Q value of ∼3000 and a higher simulated shunt impedance of 473.3 kΩ. It is possible to vary the sensitivity of the cavity with a motorized mechanism by inserting a dissipative blade during the operation based on experimental needs. Apart from a lower price tag, the new design features a more robust and production-friendly mechanical structure suitable for a series production in the future FAIR project. The manufactured cavity was built temporarily into the experimental storage ring and had delivered its first results using stored heavy ion beams. The structure, simulation results, and performance of this cavity are presented in this work.

Radiative cooling of carbon cluster anions C2n+1\u2212 (n\xa0=\xa03\u20135)

Radiative cooling of carbon cluster anions C2n+1− (n = 3–5) is investigated using the cryogenic electrostatic ion storage ring DESIREE. Two different strategies are applied to infer infrared emission on slow (milliseconds to seconds) and ultraslow (seconds to minutes) timescales. Initial cooling of the ions over the millisecond timescale is probed indirectly by monitoring the decay in the yield of spontaneous neutralization by thermionic emission. The observed cooling rates are consistent with a statistical model of thermionic electron emission in competition with infrared photon emission due to vibrational de-excitation. Slower cooling over the seconds to minutes timescale associated with infrared emission from low-frequency vibrational modes is probed using time-dependent action spectroscopy. For C9− and C11−, cooling is evidenced by the time-evolution of the yield of photo-induced neutralization following resonant excitation of electronic transitions near the detachment threshold. The cross-section for resonant photo-excitation is at least two orders of magnitude greater than for direct photodetachment. In contrast, C7− lacks electronic transitions near the detachment threshold.Graphical abstract

Rotationally Resolved Excitation Spectra Measured by Slow Electron Detachment from Si2.

Laser-induced delayed electron detachment from Si2- stored in an electrostatic ion storage ring was observed on the 10 microsecond time scale. The excitation spectra for photon energies near threshold show well-resolved multipeak structures, which are attributed to rovibronic transitions to the electronic excited state. This structure appears only in the signal measured with the delay. The occurrence of delayed detachment on such a long time scale is unusual for diatomic molecules, suggesting that both the autodetachment and fluorescence are slow.

Structured ion beams produced by radiative recombination of twisted electrons

We present a theoretical investigation of the radiative recombination of twisted electrons into bound states of initially bare ions. Special emphasis is placed on the magnetic sublevel population of the residual hydrogenlike ions under the assumption that emitted photons remain unobserved. We show that this sublevel population strongly depends on the position of an ion within the incident electron wave front. To better understand this position dependence, detailed calculations are presented for the electron capture into $1{s}_{1/2}$ and $2{p}_{3/2}$ ionic states. The results of the calculations show that the structured beams of hydrogenlike ions can be produced in collisions with Bessel electrons at ion storage rings. Having multiple-ring intensity profiles and complex spin patterns, these structured beams can become a valuable tool for future ion collision studies.

Differential pumping unit for windowless coupling of laser beams to ultra high vacuum

Current laser technology enables table-top high flux XUV sources with photon energies from several tens to several hundreds of eV via high harmonic generation in noble gases. Here we present a compact versatile coupling unit to establish windowless, and thus lossless coupling of such light sources to ultra high vacuum (UHV). The particular coupling unit has been developed to couple a XUV laser source to a heavy ion storage ring. Three-stage differential pumping allows to reduce the input pressure of ~10−6 mbar down to the 10−12 mbar range at the output. The unit particularly reduces the partial pressure of argon, which is used to generate the XUV radiation, by 6 orders of magnitude. Measurements of the pressure distribution inside the different chambers agree well with theoretical simulations.In principle, this unit can also serve for other purposes, where a windowless vacuum coupling is needed, with a transition from High Vacuum (HV) levels to deep UHV, such as coupling to cryogenically cooled detectors, ion traps or to photoelectron emission spectroscopy experiments.

Opportunities for negative ions studies at the Frankfurt Low-energy Storage Ring (FLSR)

The room-temperature electrostatic heavy ion storage ring FLSR was originally designed to study the collision dynamics of atoms and molecules. Recently it has been equipped with a RF plasma ion source combined with a charge exchange cell to be able to perform studies with negative ions in the ring. In preliminary experiments beams of He−, O− and OH− could successfully be stored. The measured lifetime of the metastable He−–ion is in good agreement with previous results, showing that the lifetime measurement in this case is not limited by the storage time due to collisional detachment. In the case of O− and OH− storage times in the order of seconds have been achieved. In a next step laser beams will be introduced in the ring allowing photodetachment studies of vibrationally cold molecules.

Enhancement of electron–ion recombination rates at low energy range in the heavy ion storage ring CSRm**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0402300) and the National Natural Science Foundation of China (Grant Nos. U1932207, 11904371, and U1732133).

Recombination of Ar14+, Ar15+, Ca16+, and Ni19+ ions with electrons has been investigated at low energy range based on the merged-beam method at the main cooler storage ring CSRm in the Institute of Modern Physics, Lanzhou, China. For each ion, the absolute recombination rate coefficients have been measured with electron–ion collision energies from 0 meV to 1000 meV which include the radiative recombination (RR) and also dielectronic recombination (DR) processes. In order to interpret the measured results, RR cross sections were obtained from a modified version of the semi-classical Bethe and Salpeter formula for hydrogenic ions. DR cross sections were calculated by a relativistic configuration interaction method using the flexible atomic code (FAC) and AUTOSTRUCTURE code in this energy range. The calculated RR + DR rate coefficients show a good agreement with the measured value at the collision energy above 100 meV. However, large discrepancies have been found at low energy range especially below 10 meV, and the experimental results show a strong enhancement relative to the theoretical RR rate coefficients. For the electron–ion collision energy below 1 meV, it was found that the experimentally observed recombination rates are higher than the theoretically predicted and fitted rates by a factor of 1.5 to 3.9. The strong dependence of RR rate coefficient enhancement on the charge state of the ions has been found with the scaling rule of q3.0, reproducing the low-energy recombination enhancement effects found in other previous experiments.

Photodetachment of negative ion beams for the ion-neutral merged-beam experiments at RICE

SynopsisGeneration of neutral atomic beam is under development for the ion-neutral merged-beam experiment at the RIKEN Cryogenic Electrostatic ion storage ring (RICE). The beam is produced by a photodetachment of a negative ion beam using a high power laser diode array with a wavelength of 808 nm. In order to increase the detachment efficiency, we have developed an optical cavity built with a planar mirror. In this presentation we will present the current status of the neutral atom beam source.

Color tuning of chlorophyll a and b pigments revealed from gas-phase spectroscopy

Chlorophyll (Chl) pigments are responsible for vital mechanisms in photosynthetic proteins: light harvesting, energy transfer and charge separation. A complex interplay between the Chl molecule and its microenvironment determines its transition energy. Interactions such as excitonic coupling with one or more pigments (Chls or carotenoids), axial ligation to the magnesium center, or electrostatic interactions between Chl and nearby amino-acid residues all influence the photophysical properties. Here we use time-resolved photodissociation action spectroscopy to determine transition energies of Chla/b complexes in vacuo to directly compare the impact of a negatively charged axial ligand (formate) to that of exciton coupling between two Chls. Experiments carried out at the electrostatic ion storage ring ELISA allow dissociation to be sampled on hundreds of milliseconds time scale. Absorption-band maxima of Chla-formate complexes are found at 433 ± 4 nm/2.86 ± 0.03 eV (Soret band) and in the region 654-675 nm/1.84-1.90 eV (Q band) and those of Chla dimers tagged by a quaternary ammonium ion at 419 ± 5 nm/2.96 ± 0.04 eV (Soret band) and 647 nm/1.92 eV (Q band). The axial ligand strongly affects the Chla transition energies causing redshifts of 0.21 eV of the Soret band and 0.04-0.1 eV of the Q band compared to Chla tagged by a quaternary ammonium. Slightly smaller shifts were found in case of Chlb. The redshifts are approximately twice that induced by excitonic coupling between two Chlas, also tagged by a quaternary ammonium ion. Axial ligation brings the absorption by isolated Chls very close to that of photosynthetic proteins.

Spontaneous decay of small carbon cluster dianions (n=7-11)

SynopsisWe have studied the stabilities of small carbon dianion clusters, (n = 7 – 11) in the cryogenic electrostatic ion storage ring, DESIREE. We observe spontaneous electron emission for tens of milliseconds, where dianions containing an even number of carbons decay slower in comparison to their neighbouring cluster sizes. For all the systems considered here, we find that there is a component which is stable at least on the time scales of hundreds of milliseconds.

Application of nature-inspired optimization algorithms and machine learning for heavy-ion synchrotrons

The application of machine learning and nature-inspired optimization methods, like for example genetic algorithms (GA) and particle swarm optimization (PSO) can be found in various scientific/technical areas. In recent years, these approaches are finding application in accelerator physics to a greater extent. In this paper, nature-inspired optimization as well as the machine learning will be shortly introduced and their application to the accelerator facility at GSI/FAIR will be presented. For the heavy-ion synchrotron SIS18 at GSI, the multi-objective GA/PSO optimization resulted in a significant improvement of multi-turn injection performance and subsequent transmission for intense beams. An automated injection optimization with genetic algorithms at the CRYRING@ESR ion storage ring has been performed. The usage of machine learning for a beam diagnostic application, where reconstruction of space-charge distorted beam profiles from ionization profile monitors is performed, will also be shown. First results and the experience gained will be presented.

Enhanced abundance of primordial HeH+

Astrochemistry Though only recently detected in space, the helium hydride ion (HeH+) is thought to be the first molecule ever to have formed in the early Universe. Novotný et al. report state-specific rate coefficients for the dissociative reaction of HeH+ with electrons, obtained using a cryogenic ion storage ring combined with a merged electron beam (see the Perspective by Bovino and Galli). They detect substantial rotational dependence and a decrease of the rates for the lowest states of HeH+, far below the values listed in astrochemistry databases and those previously applied in early-Universe models. These results suggest high abundance of this important primordial molecule at redshifts of first star and galaxy formation. Science , this issue p. [676][1]; see also p. [639][2] [1]: /lookup/doi/10.1126/science.aax5921 [2]: /lookup/doi/10.1126/science.aay5825

Dissociative recombination of H3+and D5+

Compared with earlier years, the dissociative recombination of [Formula: see text] has not been very actively studied in recent years. New results from afterglow experiments are quoted and compared with results from ion storage rings and theory. New results for [Formula: see text] are discussed. This article also contains some historical remarks on hydrogen and its importance for the advancement of physics and chemistry. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.

Experiments with low energy ion beam transport into toroidal magnetic fields

Abstract The stellarator-type storage ring for accumulation of multi-Ampere proton, and other intense ion beams with energies in the range of 100 A k e V to 1 A M e V is designed at Goethe university, Frankfurt am Main. The first proposal for beam confinement with high transversal momentum acceptance was presented in EPAC2006. This ring is typically suited for experiments in plasma physics and nuclear astrophysics. The accumulator ring with a closed longitudinal magnetic field is foreseen with a flux density up to 6 − 8 T . For demonstration, experiments were carried out with two toroidal segments operated at room temperature. The beam transport experiments in toroidal magnetic fields were first described in EPAC2008 within the framework of a proposed low energy ion storage ring. The test setup aims at developing a ring injection system with two beam lines representing the main beam line and the injection line. The primary beam line for the experiments was installed and successfully commissioned in 2009. A special diagnostics probe for “in situ” ion beam detection was installed. This modular technique allows online diagnostics of the ion beam along the beam path. In this paper, we present new results on beam transport experiments, with single segment and coupled configuration. The measurements are shown to be in agreement with the numerical model.

Quantum-state-selective electron recombination studies suggest enhanced abundance of primordial HeH.

The epoch of first star formation in the early Universe was dominated by simple atomic and molecular species consisting mainly of two elements: hydrogen and helium. Gaining insight into this constitutive era requires a thorough understanding of molecular reactivity under primordial conditions. We used a cryogenic ion storage ring combined with a merged electron beam to measure state-specific rate coefficients of dissociative recombination, a process by which electrons destroy molecular ions. We found a pronounced decrease of the electron recombination rates for the lowest rotational states of the helium hydride ion (HeH+), compared with previous measurements at room temperature. The reduced destruction of cold HeH+ translates into an enhanced abundance of this primordial molecule at redshifts of first star and galaxy formation.

Construction of a table-top ion storage ring and its application to cross section measurements

A table-top electrostatic ion storage ring was constructed, and an argon ion (Arn+, n = 1, 2) beam was successfully stored. As an application of the storage ring, the electron capture cross section for a neutral Ar target was measured.

Position sensitive resonant Schottky cavities for heavy ion storage rings

Resonant Schottky pick-up cavities are sensitive beam monitors. They are indispensable for the beam diagnostics in storage rings. Apart from their applications in the measurements of beam parameters, they can be used in nondestructive in-ring decay studies of radioactive ion beams. In addition, position sensitive Schottky pick-up cavities enhance precision in the isochronous mass measurement technique.The goal of this work is to construct and test such a position sensitive cavity (e.g. Schottky detector) based on previous theoretical calculations and simulations. These cavities will allow measurement of position using the monopole mode using a non-circular(elliptic) geometry. This information can be further analyzed to increase the performance in isochronous mass spectrometry. A brief description of the detector system from elliptical and cylindrical cavities is described in this work.