Electrostatic Storage Ring Research Articles

Spatial Resolution Test of a Beam Profile Monitoring System for the Double Electrostatic Ion Storage Ring

A beam profile monitoring system based on the imaging of low energy electrons created when the ion beam impinges on a metal plate was built to monitor the beam profile and to cover the wide range of beam intensities and energies for the DESIREE (Double ElectroStatic Ion Ring ExpEriment) beam line diagnostics. The spatial resolution of the system was tested with different beams of various energies and was found to be around 2 mm. A significant steering effect on the ion beam before hitting the metallic foil was observed at low energies.

Controllable electrostatic surface storage ring with opened optical access for cold polar molecules on a chip

In order to meet the demands for laser manipulations and detection of cold molecules, we propose an optically accessible and controllable electrostatic surface storage ring for cold polar molecules on a chip, which is one based on extension and application of the three-wire surface guiding scheme [J. Opt. Soc. Am. B25, 1214 (2008)]. To our knowledge, this is the first real surface storage ring scheme. The spatial distribution of the electrostatic fields generated by two insulator-embedded charged rings and a grounded conductor plate is numerically calculated. Relationships between the height of the trap center above the surface and the setup parameters are analyzed in detail. Using OH radical molecules as a tester, the range of molecular velocities that the storage ring can confine is investigated. The dynamical process of weak-field-seeking OH molecules of state |J,KM〉=|3/2,−9/4〉 being loaded into and confined in the storage ring is studied using Monte Carlo simulations. Dependencies of translational temperature of molecules and their trapping efficiency in the storage ring on parameters of the setup and the initial molecular beam are examined. By incorporating a bunching function into our scheme, the number of round trips a trapped molecular packet makes can be improved by almost three times before getting spread out to fill the whole storage ring, as confirmed by numerical simulations.

Evidences for isochronous behavior in electron and ion storage for a low energy electrostatic storage ring

The temporal width of a stored bunch of low energy (~30eV) electrons circulating in desk-top sized passive electrostatic storage ring has been observed to be unchanging with orbit number. The storage ring has been operated with a range of asymmetric voltages for both stored electron and ion bunches with a particular focus on controllably probing the edges of stable storage regions to explore variations in the temporal widths as a function of storage time. For electron storage an operating condition is identified in which the temporal width approaches a constant value after a period of increase – isochronous behavior. Measurements using stored ions indicate similar behavior can be achieved. Possible mechanisms for the observed behavior are discussed.

Photo excitation and laser detachment of C60− anions in a storage ring

We have studied the photo physics of C60(-) anions in the electrostatic storage ring ELISA with ions produced in a plasma source and cooled and bunched in a He filled ion trap. A previous study using delayed electron detachment as a signal of resonance-enhanced multiphoton electron detachment (REMPED) has been repeated both at room temperature and with the trap cooled to liquid nitrogen temperature. However, wavelength dependence of the overlap of the strongly focused laser beam with the ion beam introduces distortions of the absorption spectrum. We have therefore applied a new method, combining the IR light with a slightly delayed, powerful UV pulse (266 nm). After absorption of three UV photons, the ions decay by delayed (thermal) electron emission, and time spectra are recorded for varying wavelength. The fraction of ions heated by absorption of a single IR photon is then extracted from a principal component analysis of these spectra. In good agreement with the earlier REMPED experiment, an origin band for transitions between the two lowest electronic levels of the anion, with t1u and t1g symmetry, is observed at 9380 cm(-1), with strong sidebands from excitation of the two A(g) and eight H(g) vibrations. As before, a hot band is observed at about 9150 cm(-1) and assigned to a transition from an excited vibronic Jahn-Teller state. However, an earlier observed band at higher energy, interpreted as a transition from this excited state to an excited vibronic state in the t1g electronic level, is much weaker in the new measurements and could be an H(g) vibrational sideband. Also earlier studies of direct laser detachment from C60(-) in the storage ring ASTRID have been revisited, with ions cooled by liquid nitrogen in the ion trap. We confirm the previous measurement with a determination of the threshold for s-wave detachment at 2.664 ± 0.005 eV, slightly lower than a recent value of the electron binding, 2.683 ± 0.008 eV, obtained from the energy spectrum of photo electrons. The detachment yield is observed to increase sharply for photon energies above a threshold at 2.78 eV, maybe caused by either Feshbach resonances or a shape resonance due to the presence of a bound electron state in the continuum.

Ion beam characterization in the Mini-Ring and kinetic energy release measurement of unimolecular decay of anthracene cations

The Mini-Ring is a compact electrostatic ion storage ring designed for molecular relaxation dynamics studies. In order to accomplish an injection of the incoming ion beam, the electrode voltage settings appear to be quite critical to avoid large betatron oscillations. The beam injection was controlled by taking pictures of a test Ar+ ion beam with a digital camera. The amplitude of the betatron oscillation was measured by the impact position of neutral fragments exiting the ring on a position-sensitive detector. The broad spot observed for anthracene was attributed to the kinetic energy release resulting from the delayed unimolecular dissociation of anthracene by emission of a neutral C2H2.

Time evolution of the internal energy distribution of singly charged anthracene in a storage ring

We have stored singly charged anthracene molecular ions C14H10+ in a compact electrostatic storage ring called the Miniring. The neutral yield curves due to dissociation of the ions induced by laser excitation at different storage times were analyzed and fitted with a t−α law. The evolution of the internal energy distribution of the stored molecular ion ensemble was obtained as a function of the storage time by using a simple model which related the experimental decay factor α to the high-energy edge of the modeled energy distribution.

Direct observation of internal energy distributions of ${\rm C}_5^-$C5−

Photon induced decay of C5(-) has been measured in an electrostatic storage ring. The time dependence of the photo-enhanced decay is close to a 1∕t decay which indicates a thermal process. The deviation from the expected power of -1 is quantitatively explained by the small heat capacity of the anion. Measurements of the photo-enhanced decay at different storage times and photon energies allow a determination of the radiative cooling rate and the energy distribution of the ions. The average energy content between 15 and 70 ms is found to vary as time to the power -0.72, and at 50 ms the ions contain an average excitation energy of 0.5 eV. The time dependent energy distribution is consistent with cooling by infrared photon emission if published oscillator strengths are reduced by a factor 2.5, in contrast to cooling of larger molecular carbon-based ions where electronic transitions cause a much stronger cooling.

Nonlinear and long-term beam dynamics in low energy storage rings

Electrostatic storage rings operate at very low energies in the keV range and have proven to be invaluable tools for atomic and molecular physics. Because of the mass independence of electric rigidity, these machines are able to store a wide range of different particles, from light ions to heavy singly charged biomolecules, opening up unique research opportunities. However, earlier measurements have shown strong limitations in maximum beam intensity, fast decay of the stored ion current, and reduced beam lifetime. The nature of these effects has not been fully understood and an improved understanding of the physical processes influencing beam motion and stability in such rings is needed. In this paper, a comprehensive study into nonlinear and long-term beam dynamics studies is presented on the examples of a number of existing and planned electrostatic storage rings using the BETACOOL, OPERA-3D, and MAD-X simulation software. A detailed investigation into ion kinetics, under consideration of effects from electron cooling and multiple scattering of the beam on a supersonic gas jet target, is carried out and yields a consistent explanation of the physical effects in a whole class of storage rings. The lifetime, equilibrium momentum spread, and equilibrium lateral spread during collisions with the target are estimated. In addition, the results from experiments at the Test Storage Ring, where a low-intensity beam of ${\mathrm{CF}}^{+}$ ions at $93\text{ }\text{ }\mathrm{keV}/\mathrm{u}$ has been shrunk to extremely small dimensions, are reproduced. Based on these simulations, the conditions for stable ring operation with an extremely low-emittance beam are presented. Finally, results from studies into the interaction of 3--30 keV ions with a gas jet target are summarized.

First storage of ion beams in the Double Electrostatic Ion-Ring Experiment: DESIREE

We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (C(n)(-), n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C2 (-) molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s ± 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10(-14) mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.

Laser-induced thermal detachment of hot, large molecular ions under multiphoton-absorption conditions

We observed the delayed electron detachment induced by multiphoton absorption of hot, zinc phthalocyanine negative ions (C${}_{32}$H${}_{16}$N${}_{8}$Zn${}^{\ensuremath{-}}$) stored in an electrostatic ion storage ring. To examine the critical parameters and conditions that characterize the delayed processes, we performed a theoretical model simulation employing inferred values for molecular properties and experimentally controlled values of excitation laser energy and fluence. The thermal detachment rate was estimated by applying the detailed balance theory, and the internal energy distribution of the ions after multiphoton absorption was calculated as a function of the ion temperature immediately before laser irradiation. Our model simulation well reproduces the experimental results, and demonstrates that the experimental configuration determines the range of the observed detachment rate, namely the detectable energy window of the stored ions. The parameter dependence of the estimated ion temperature on the molecular properties was also obtained.

Photodissociation of the monoanions of gas-phase chlorophyllsaandbin an electrostatic storage ring

The photodissociation of the monoanions of chlorophylls $a$ and $b$ in the gas phase were studied using an electrostatic storage ring. The number of neutral particles produced by the photoabsorption of the ions was measured as a function of time after irradiating the ions with a laser pulse with wavelengths in the region 410\ensuremath{-}660 nm. Fast and slow decay components were observed in the photodissociation spectra of the chlorophylls, and the lifetimes of these components increased with an increase in the wavelength of the irradiating laser pulse. It is shown that the slow decay component was due to one-photon excitation whereas the fast decay component was due to two-photon excitation. A statistical model was used to simulate the decay processes, and the simulated decay spectra were in good accordance with the experimentally determined ones. The activation energies of the decay processes of the two chlorophylls were derived using the model, and were found to be approximately 0.6 eV for both. The measured wavelength spectra were markedly different from the photoabsorption spectra of the chlorophylls in the solution phase for the $B$-band-to-$Q$-band ratio.

Fast Radiative Cooling of Anthracene Observed in a Compact Electrostatic Storage Ring

Fast radiative cooling of anthracene was observed in a compact electrostatic storage ring by probing the evolution of the internal energy distribution of a stored (C(14)H(10))(+) molecular ensemble via laser excitation. We have measured the mean radiative decay rate to be about 120 to 250 s(-1) for internal energies in the range from 6.6 to 6.8 eV. Such a high decay rate is 2 orders of magnitude larger than the infrared emission cooling rate expected for vibrational transitions. It is attributed to fluorescence from thermally excited electrons. This fast cooling mechanism may have important implications in astrophysics concerning the lifetime and the critical size of polycyclic aromatic hydrocarbons in interstellar conditions.

Design of a novel electrostatic ion storage ring at KACST

A new electrostatic storage ring for beams at energies up to 30keV·q is currently under development at the National Centre for Mathematics and Physics (NCMP), King Abdulaziz City for Science and Technology (KACST). The ring design is based on the existing electrostatic storage rings, but stretches significantly beyond them in that it shall form the core of a unique flexible experimental facility at KACST. The lattice of this ring has been designed in a way that enables the use of state-of-the-art experimental methods to study electron–ion, laser-ion, and ion-neutral beams interactions. The lattice design also allows for a future upgrade of the ring to a double storage ring structure that would enable ion–ion beam interactions to be performed. In this paper, we present the design of this ring with a focus on beam dynamics calculations for the 7° single-bend racetrack layout. The study is principally based on the SIMION8 program. We complemented this study further by using purpose-written routine and MAD-X simulation code. An in-depth investigation into beam stability under consideration of non-linear field components in the electrostatic optical elements, is presented. Finally, different working points and stability regions are discussed.

Photodissociation of cold fluorescein monoanion studied using an electrostatic storage ring

Photodissociation of fluorescein monoanions was studied by using an electrostatic storage ring. The ions are stored in an ion trap and the storage ring before laser irradiation. Photodissociation neutral spectra of the relaxed ions as a function of time consist of components with short and long lifetimes. By comparing their wavelength spectra with those in the liquid phase, it is concluded that the spectra originate from different tautomers of fluorescein monoanions. Moreover, via storage in the storage ring, one of them disappears due to interconversion.

Laser spectroscopy of the methylene blue cation in an electrostatic ion storage ring

We have performed a spectroscopic study of the methylene blue cation (MB+) stored in an electrostatic ion storage ring in Tokyo Metropolitan University. Isolated MB+ ions were extracted from an electrospray ionization source and introduced into the storage ring. An excitation spectrum of isolated MB+ was obtained from the intensity of delayed fragmentation observed for about 1 ms after laser irradiation in the visible range.

Identification of isochronous operating mode for passive electrostatic storage ring

Slightly offsetting lens voltages of an electrostatic storage ring from known voltages of maximum recycling yield results in approximate isochronous behaviour. Identification of this operating mode using area maps of regions of recycling and comparisons of peak width evolution in spectra will be discussed along with presentation of new experimental data for previously presented electron recycling spectrometer (ERS).

The Double ElectroStatic Ion-Ring ExpEriment, DESIREE

We describe the status of the DESIREE facility, which is an electrostatic ion-storage device consisting of two storage rings with a common section, where ion beams of opposite charges stored in the two rings are merged. The electrostatic storage rings are mounted in a single common vacuum vessel, which is isolated inside an outer vacuum chamber and cooled by means of four cryogenerators. This unique system will allow for studies of interaction among ions of opposite charges at well controlled conditions both in terms of internal degrees of freedom and relative velocity. An advanced ion-beam production system for intense pulses of cold complex molecular ions is also presented.

A multiple-orbit time-of-flight mass spectrometer based on a low energy electrostatic storage ring

The results are presented for an electrostatic storage ring, consisting of two hemispherical deflector analyzers (HDA) connected by two separate sets of cylindrical lenses, used as a time-of-flight mass spectrometer. Based on the results of charged particle simulations and formal matrix model, the Ion Storage Ring is capable of operating with multiple stable orbits, for both single and multiply charged ions simultaneously.

First experiments using a table-top electrostatic ion storage ring, the Mini-Ring

We report experiments using a small electrostatic ion storage ring. We demonstrate its capability to measure the lifetime of metastable anions and cations up to hundred of milliseconds produced in the ECR source. First experiments using LASER heating are also presented.

Stable operating conditions for a passive desktop sized electrostatic storage ring

A passive desktop sized electrostatic storage ring has been demonstrated to store charged particles. The storage of charged particles within the ring has been investigated as a function of the potentials applied to the electrostatic lenses. The aim of this investigation was to examine predicted operating potentials for long term storage and to explore the types of orbits produced.