Ion Bunches Research Articles

The General Purpose Ion Buncher: A radiofrequency quadrupole cooler-buncher for DESIR at SPIRAL2

We report on the conception and first tests of the General Purpose Ion Buncher (GPIB), the radio-frequency beam-cooler and buncher that will supply the DESIR (Decay, Excitation and Storage of Radioactive Ions) experimental hall to be constructed to complement the SPIRAL1 and SPIRAL2 facilities in GANIL. Its goals are both to reduce the emittance and if necessary to bunch the radioactive ion beam from the GANIL production facilities to adapt it to the needs of the different experimental setups in the DESIR hall. The mechanical design is similar to the existing ISCOOL quadrupole at ISOLDE but the new radio-frequency system enables a much stronger radial confinement. The GPIB is developed at LP2i Bordeaux11LP2i Bordeaux was known as Centre d’Études Nucléaires de Bordeaux-Gradignan (CENBG) before the name was changed in 2022. in parallel with the PIPERADE double Penning trap and a beamline has been constructed there to characterize both. The cooling of a 30keV beam to an emittance of 3 π mm mrad and a transmission above 80% in continuous mode is demonstrated for currents up to a few nA. Some first results concerning the bunching mode are also shown though this mode is still under development.

Characteristics of laminar ion beams accelerated via a few-joule laser pulse

Laser-driven carbon ion beams from a carbon foil target via a 2.5-J laser pulse are investigated with three-dimensional particle-in-cell simulations. An ion bunch with a narrow energy range exhibits a thin shell shape with a certain diameter. The ion cloud has a layered structure of these ion bunches with different energies. The divergences of the ion bunch in the laser inclination direction and perpendicular to it are different in an oblique incidence laser. In addition, theoretical formulas for the radius of the generated ion beam and the energy spectrum are derived, and they are shown to be in good agreement with the simulation results.

Online charge measurement for petawatt laser-driven ion acceleration.

Laser-driven ion beams have gained considerable attention for their potential use in multidisciplinary research and technology. Preclinical studies into their radiobiological effectiveness have established the prospect of using laser-driven ion beams for radiotherapy. In particular, research into the beneficial effects of ultrahigh instantaneous dose rates is enabled by the high ion bunch charge and uniquely short bunch lengths present for laser-driven ion beams. Such studies require reliable, online dosimetry methods to monitor the bunch charge for every laser shot to ensure that the prescribed dose is accurately applied to the biological sample. In this paper, we present the first successful use of an Integrating Current Transformer (ICT) for laser-driven ion accelerators. This is a noninvasive diagnostic to measure the charge of the accelerated ion bunch. It enables online estimates of the applied dose in radiobiological experiments and facilitates ion beam tuning, in particular, optimization of the laser ion source, and alignment of the proton transport beamline. We present the ICT implementation and the correlation with other diagnostics, such as radiochromic films, a Thomson parabola spectrometer, and a scintillator.

N@C60 formation by laser-induced breakdown in nitrogen gas flow

Nitrogen-atom-endohedral C 60 (N@C 60 ) was generated by laser induced breakdown in gaseous N 2 occurring near the surface of a C 60 film. The yield was estimated to be 3 × 10 −8 –5 × 10 −7 with respect to the empty C 60 . The high-density ion bunch plays a crucial role in generating N@C 60 , in contrast to the case of continuous ion beam sources.

Ion Bunching in Square-Wave-Driven Mobility Capillary Electrophoresis-Mass Spectrometry.

The ion-bunching effect was typically produced for ion beams in the gas phase, such as in ion accelerators. In this work, ion bunching was generated for ions in a liquid channel, specifically in a mobility capillary electrophoresis-mass spectrometry (MCE-MS) setup. MCE was recently developed and coupled with MS for ion separation and the precise measurements of ion hydrodynamic radius and effective charge in solution. In conventional MCE, a DC high voltage is applied, which serves as the separation voltage. In this study, square waves were employed to replace this DC voltage, and the ion-bunching phenomenon was observed and characterized in both simulations and experiments. After applying a high voltage square wave, cations and anions would be bunched and concentrated at the positive and negative half cycle of the square wave, respectively. Accordingly, ion signal intensities detected by the following mass spectrometer could be increased by up to ∼50 folds for the aspartic acid anion. This square wave could also dissociate metal adduct cations from nucleic acid anions, which results in stronger nucleic acid ion intensities (up to ∼10 folds) with cleaner backgrounds.

Stabilized Radiation Pressure Acceleration and Neutron Generation in Ultrathin Deuterated Foils.

Premature relativistic transparency of ultrathin, laser-irradiated targets is recognized as an obstacle to achieving a stable radiation pressure acceleration in the "light sail" (LS) mode. Experimental data, corroborated by 2D PIC simulations, show that a few-nm thick overcoat surface layer of high Z material significantly improves ion bunching at high energies during the acceleration. This is diagnosed by simultaneous ion and neutron spectroscopy following irradiation of deuterated plastic targets. In particular, copious and directional neutron production (significantly larger than for other in-target schemes) arises, under optimal parameters, as a signature of plasma layer integrity during the acceleration.

Photoelectron imaging of size-selected metal cluster anions in a quasi-continuous mode.

We present a novel high-repetition-rate photoelectron imaging (PEI) apparatus for exploring electronic structures of metal cluster anions. A continuous beam of mass-selected metal cluster anions, generated by a magnetron-sputtering cluster-ion source coupled with a quadrupole mass filter, is chopped into sub-megahertz ion bunches using a high-voltage pulser. The quasi-continuous anion beam is introduced into a PEI spectrometer, where the anions are photodetached using a 404nm (3.07eV) continuous-wave laser diode. As a demonstration, we acquire photoelectron images for size-selected Ag cluster anions, AgN - (N = 3, 7, 14), and show that each image can be obtained in a short accumulation time (50s) with a kinetic energy resolution (ΔE/E) of 4% at E = 1.77eV. The quasi-continuous PEI technique enables high-count-rate, space-charge-free acquisition of photoelectron spectra and angular distributions not only from size-selected metal cluster anions but also from anions prepared by other continuous ion sources, such as electrospray ionization.

Image charge detection of ion bunches using a segmented, cryogenic detector

The response of a dedicated image charge detector to a single passage of small ion bunches was studied. This detector was designed and built in our labs aiming for a maximized signal-to-noise ratio (SNR) with the motivation to enable single ion detection for deterministic ion implantation, a key technique for solid state based quantum technologies, in the future. It is shown how segmentation of the detector with the appropriate combination of the individual segment signal channels significantly increases the SNR. Additionally, the detector is cryogenically cooled to temperatures down to 163 K, further enhancing the SNR. The detection sensitivity of this detector prototype was measured to be 80 elementary charges for SNR=2, detecting 4 keV Xe+ ion bunches. At this SNR, the false-positive error rate is expected to be 0.1%. Comparing the measured sensitivity with a theoretical estimation yielding 22 elementary charges for SNR=2, the presented results lead the way to further optimizations of the detector components and the signal analysis techniques, necessary to realize single ion detection.

Selective determination of collectively accelerated 12C ion bunches by neutron time-of-flight spectrometry

In this work, we investigated the possibility of selectively detecting carbon ion bunches collectively accelerated in a Luce diode by a time-of-flight spectrometry of neutrons from the threshold reaction 2H(12C,n)13N induced in Ca(OD)2 layers deposited on Mo substrates by ‘staining’ lime freshly prepared by quenching CaO in heavy water. Oxygen and calcium isotopes do not produce any interference with the analytical reaction on the carbon and proton bunches. This spectrometry confirms that 12C ions and protons are collectively accelerated at the same speed, and 12C ions are captured in this acceleration all the way from the anode to the target, regardless of the conditions of the near-anode plasma.

Emittance growth caused by phase modulation in bunched electron beam cooling

The demand for electron coolers operating at much higher energies than previously achieved necessitates the use of radio-frequency (RF) fields for electron acceleration resulting in the bunched electron beams. Differences in the time structure of ion and electron bunches and variations in their relative timing significantly affect the cooling process. Experiments on ion beam cooling with a short electron bunch have been carried out in the CSRm storage ring at IMP (Lanzhou). Longitudinal painting by the electron bunch phase modulation is found leading to a significant ion beam loss. We show that the space charge field variations of the bunched electron beam play a major role in the ion beam emittance growth while cooling. In this paper, we study the dependency of the ion beam emittance growth on the electron beam parameters and present results of numerical simulation which support experimental observations.

Stacked-ring ion guide for cooling and bunching rare isotopes

In modern rare isotope facilities, ion cooling and bunching lies at the heart of the ion transfer along a low-energy beam line that consists of several differential pumping stages. We present a conceptual design of an ion guide as an alternative to the conventional linear Radio-Frequency Quadrupole (RFQ) for cooling and bunching rare isotopes. The ion guide is composed of stacked ring electrodes of varying apertures, to which a confining RF potential following a rectangular waveform is applied. The thicknesses of the rings and the gaps in between are varied accordingly to maximize the confining volume and to reduce ion losses. Ion transport within the ion guide is facilitated by a lower-frequency wave traveling on top of the higher-frequency confining field. The former is induced by locally adjusting the duty cycle of the rectangular waveform of the confining potential. Design parameters are first calculated by analytical studies and then optimized by ion trajectory simulations with SIMION®. The results show that the ion guide enables high ion transmission and produces well focused ion bunches. It will be used in the NEXT project—an experimental study of atomic masses of Neutron-rich EXotic nuclei produced in multi-nucleon Transfer reactions.

Optical Excitation of Ultra‐Relativistic Partially Stripped Ions

AbstractThe Gamma Factory (GF) initiative aims at the construction of a unique experimental tool exploiting resonant interaction of light with ultra‐relativistic partially stripped ions (PSI) stored in circular accelerators at CERN. Resonant excitation of high‐energy electronic transitions in the ions is achieved through Doppler‐boosting (by twice the Lorentz factor; from hundred to several thousand times) of light energy. In order to efficiently excite the ions, and hence generate intense beams of scattered/fluorescent photons, a detailed knowledge of the ions' electronic energy structure and the dynamics of optical excitation is required. Spectroscopic properties of PSI selected for the GF operation, as well as their optical excitation schemes, are investigated. Two regimes of the ion–light interaction are identified, leading to different dynamics of the excitation. The efficiency of the ion–light interaction, as well as the number of photons emitted from a single ion bunch, are estimated, both analytically and numerically, for three ions considered for the GF, that is, Li‐like Pb79 + , Li‐like Ca17 + , and H‐like Pb81 + .

First Offline Results from the S3 Low-Energy Branch

We present the first results obtained from the S3 Low-Energy Branch, the gas cell setup at SPIRAL2-GANIL, which will be installed behind the S3 spectrometer for atomic and nuclear spectroscopy studies of exotic nuclei. The installation is currently being commissioned offline, with the aim to establish optimum conditions for the operation of the radio frequency quadrupole ion guides, mass separation and ion bunching, providing high-efficiency and low-energy spatial spread for the isotopes of interest. Transmission and mass-resolving power measurements are presented for the different components of the S3-LEB setup. In addition, a single-longitudinal-mode, injection-locked, pumped pulsed-titanium–sapphire laser system has been recently implemented and is used for the first proof-of-principle measurements in an offline laser laboratory. Laser spectroscopy measurements of erbium, which is the commissioning case of the S3 spectrometer, are presented using the 4f126s23H6→4f12(3H)6s6p optical transition.

Simulations of a digital ion filter and a digital ion trap for heavy biomolecules

Ion trajectories have been simulated for an assembly of a linear quadrupole ion-filter and a linear Paul trap with additional pin electrodes for MS SPIDOC, a project in preparation for the study of biomolecules by single-particle imaging with X-ray pulses. The ion-optical components are based on digital RF guiding and trapping fields. In order to carefully handle biomolecules over a wide mass-over-charge range, the module presented consists of separate components for filtering and accumulation/trapping in order to select the ions of interest and to convert the beam from a continuous ion source to ion bunches, respectively, as required for the experiments downstream. The present analysis focuses on the transmission efficiency and mass resolving power of the filter, as well as the buffer-gas-pressure-dependent ion capture and thermalization in the trap for the example of a mass-to-charge ratio equivalent to hemoglobin 15+ ions. The resulting optimized ion bunch delivered by the assembly is characterized.

Geant4 Monte Carlo simulation study of the secondary radiation fields at the laser-driven ion source LION

At the Center for Advanced Laser Applications (CALA), Garching, Germany, the LION (Laser-driven ION Acceleration) experiment is being commissioned, aiming at the production of laser-driven bunches of protons and light ions with multi-MeV energies and repetition frequency up to 1 Hz. A Geant4 Monte Carlo-based study of the secondary neutron and photon fields expected during LION’s different commissioning phases is presented. Goal of this study is the characterization of the secondary radiation environment present inside and outside the LION cave. Three different primary proton spectra, taken from experimental results reported in the literature and representative of three different future stages of the LION’s commissioning path are used. Together with protons, also electrons are emitted through laser-target interaction and are also responsible for the production of secondary radiation. For the electron component of the three source terms, a simplified exponential model is used. Moreover, in order to reduce the simulation complexity, a two-components simplified geometrical model of proton and electron sources is proposed. It has been found that the radiation environment inside the experimental cave is either dominated by photons or neutrons depending on the position in the room and the source term used. The higher the intensity of the source, the higher the neutron contribution to the total dose for all scored positions. Maximum neutron and photon ambient dose equivalent values normalized to 109 simulated incident primaries were calculated at the exit of the vacuum chamber, where values of about 85 nSv (109 primaries)−1 and 1.0 μSv (109 primaries)−1 were found.

Influence of pulse frequency on discharge characteristics of micro-cathode arc thruster

The objective of this study is to investigate the effect of pulse frequency on the discharge characteristics of a micro-cathode arc thruster. We used an intensified charge-coupled device (ICCD) and high-resolution spectrometer to capture the plasma emission process of a micro-cathode arc thruster. The change in the valence ion ratio under different discharge frequencies of the thruster is studied with respect to the change in light intensity. The relationship between the pulse frequency and Ti + ion ratio, cathode emission plasma bunch velocity, and normalized thrust are studied. The spectral and electrical test results demonstrate that the proportion of high-energy ions emitted from the cathode increases with the increase in interpole discharge frequency, and the ion bunch velocity and normalized thrust of the thruster are both improved.

A photoionized pulsed low-energy ion beam source for quantum state-to-state crossed ion-molecule scattering.

Here, we report the designand test of a pulsed low-energy ion beam source for crossed ion-molecule scattering studies. The ions are produced by laser photoionization based methods and thus can be prepared in well-defined quantum states. By using the combination of a double Einzel lenses setup and a specially designed shielding tube, a well spatially confined ion bunch with tunable kinetic energies in the range of 1.0-5.0eV and typical spreads of ∼150meV (full width at half maximum) can be formed in the center of a velocity-map imaging (VMI) stack. By combining it with a recently constructed three-dimensional VMI system, the present apparatus is readily available for quantum state-to-state crossed ion-molecule scattering studies.

Fast ion bunch compression by barrier pulse control

We report a novel scheme for fast ion bunch compression by barrier pulse control in an induction synchrotron in which an effective acceleration voltage pulse with a pseudo-linear slope is generated by temporal handling of rectangular induction acceleration pulses. With beam handling, a head-to-tail momentum gradient is yielded to the beam in a desired manner and the beam is gradually compressed over 30 turns. In the proof-of-principle experiment, which used a 75 μA He1+ beam at 50 keV per nucleon, the root mean square bunch length was reduced to 0.44 μs by a factor of 3.5 in 30 turns with no appreciable beam loss due to the beam compression scheme. This scheme is useful for various beam applications including ion beam heating.

Energization of cold ions by electromagnetic ion cyclotron waves: Magnetospheric multiscale (MMS) observations

Electromagnetic ion cyclotron (EMIC) waves have been studied in this manuscript which are triggered by hot proton thermal anisotropy having energy ranging from 7 to 26 keV with a minimum resonant energy of 6.9 keV. However, an opposite effect can be observed for the hot protons for energy less than the minimum resonant energy. When the intensity of EMIC waves is large, the cold protons (ions) having low-energies can be energized by the EMIC waves. The possible reasons for this energization are the phase bunching of low energy ions with EMIC waves and the generation of electric fields at the relaxation time of substorm. As a consequence, these undetectable protons now become detectable, and the number density and temperature anisotropy of the protons also increase within the energy range from 1 to 100 eV. Accordingly, the helium ions are also energized by the EMIC waves.

Structural and Dynamic Insights into the Conduction of Lithium-Ionic-Liquid Mixtures in Nanoporous Metal-Organic Frameworks as Solid-State Electrolytes.

Metal-organic framework (MOF)-based separators in Li-ion batteries (LIBs) have the potential to improve the battery performance. The mobility and conduction of lithium and organic ionic liquids (ILs) in these materials acting as (quasi) solid-state electrolytes are crucial for the battery power output. Here, we investigate the mobility of a Li-based IL in MOF nanopores and unveil the details of the conduction mechanism by molecular dynamics (MD) simulations. A complex conductivity depending on the Li-IL loading and on the IL composition is observed. Most importantly, the presence of Li prevents the collapse of the conductivity at high IL loadings. The fully atomistic MD simulations including guest-guest and guest-host interactions elucidate the competing mechanisms: Li follows a Grotthuss-like conduction mechanism with large mobility. While at small pore fillings, the Li conduction is limited by the large distance between the anions facilitating the Grotthuss-like conduction; the conduction at high pore fillings is governed by field-induced concentration inhomogeneities. Because of the small MOF pore windows, which hinders the simultaneous passage of the large IL cations and anions in opposite directions, the IL shows field-induced MOF pore blocking and ion bunching. The regions of low anion concentration and high cation concentration represent barriers for Li, decreasing its mobility. In comparison to Li-free IL, the IL bunching effect is attenuated by the formation of charge-neutral Li-anion complexes, resulting in a tremendously increased conductivity at maximum pore filling. The exploitation of this mechanism may enhance the development of advanced batteries based on IL and nanoporous separators.