Laser Ion Source Research Articles

Control System for a Heavy Ion Laser Source at Synchrotron Complex ICCR

The article describes the control system for a laser source of heavy ions. The control system has a hierarchical multilevel architecture, determined by the hierarchical structure of the laser ion source, and is a part of the control systems of the linear heavy ion injector and the entire synchrotron complex. The article describes the basic requirements for the control system and the general principles of its construction, and the circuitry and software solutions selected in accordance with these requirements and principles, such as: organization of data exchange between individual nodes in the automated control system; determination of algorithms for working with individual devices and subsystems of the ion source, and with the ion source as a unified system; selection of types and structural schemes of controllers of individual subsystems. The hierarchical structure of the automated control system and control subsystems for all the main devices of the laser source are also described.

High-Precision Mass Measurements of Neutron Deficient Silver Isotopes Probe the Robustness of the N=50 Shell Closure.

High-precision mass measurements of exotic ^{95-97}Ag isotopes close to the N=Z line have been conducted with the JYFLTRAP double Penning trap mass spectrometer, with the silver ions produced using the recently commissioned inductively heated hot cavity catcher laser ion source at the Ion Guide Isotope Separator On-Line facility. The atomic mass of ^{95}Ag was directly determined for the first time. In addition, the atomic masses of β-decaying 2^{+} and 8^{+} states in ^{96}Ag have been identified and measured for the first time, and the precision of the ^{97}Ag mass has been improved. The newly measured masses, with a precision of ≈1 keV/c^{2}, have been used to investigate the N=50 neutron shell closure, confirming it to be robust. Empirical shell-gap and pairing energies determined with the new ground-state mass data are compared with the state-of-the-art abinitio calculations with various chiral effective field theory Hamiltonians. The precise determination of the excitation energy of the ^{96m}Ag isomer in particular serves as a benchmark for abinitio predictions of nuclear properties beyond the ground state, specifically for odd-odd nuclei situated in proximity to the proton dripline below ^{100}Sn. In addition, density functional theory calculations and configuration-interaction shell-model calculations are compared with the experimental results. All theoretical approaches face challenges to reproduce the trend of nuclear ground-state properties in the silver isotopic chain across the N=50 neutron shell and toward the proton dripline.

Charge radii of thallium isotopes near the N=126 shell closure

The changes in the mean-squared charge radius of Tlg209 (N=128) and Tlm207 (N=126) relative to Tl205 have been measured for the first time using the in-source laser resonance-ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the dominant background from isobaric francium isotopes and allows access to thallium nuclides with A⩾207. The characteristic kink in the charge radii at the N=126 neutron shell closure, as well as the odd-even effect similar to that in the adjacent bismuth, lead, and mercury isotopic chains, have been observed. The self-consistent theory of finite Fermi systems based on the energy density functional by Fayans reproduces the behavior of charge radii in these isotopic chains near N=126. The comparison with calculations in the framework of the relativistic mean field (RMF) approach is also presented. In the case of the Fayans functional it is a specific form of pairing interaction with the dependence on the density gradient that is essential to provide agreement with the experimental charge radii. In particular, the kink is reproduced without the inversion of g9/2 and i11/2 neutron single-particle states, which is a prerequisite to correctly describe the kink in the RMF models. Published by the American Physical Society 2024

Multilayer film coating for laser ion source target for increase of low charge state production

The use of Laser Ion Source for accelerator facilities has the advantage to tune the characteristic of the produced beams by changing the laser parameters using the same primary target. The advantageous and innovative opportunity to manipulate the characteristic of charge state distributions by the use of composed target, may open new possibilities for the ion sources. In this experiment we characterize and study the plasma produced by the laser ablation of coated targets at constant laser parameters. The performed investigation has the double purpose to have a better understanding of penetration depth of laser in composed materials and understand how to tune the charge states by adding coating films. The obtained results showed that for particular thickness of coating, the low charge states were produced with higher yield than in the case of pure material.

Performance of a liquid Ga target for Laser Ion Source

We experimentally proved the feasibility of a liquid-based target for Laser Ion Source (LIS) application. The target consists of melted metal gallium contained in a heated crucible. Ions current resulting from laser irradiation. Moreover, given the explosive ablation mechanism involved, each laser shot has been found to induce fluctuations in the surface level. It takes about 0.7 sec to recover the steady condition fully. Despite the maximum fluctuation being 2.7 mm (top-bottom maximum displacement), these fluctuations have shown no significant influence on total ion current and are independent of the temperature of the sample within the tested repetition rate. This study provides valuable insights into the potential of employing such a system for LIS.

Ti beam extraction from a laser plasma focused by a magnetic field of a solenoid

Laser ion sources (LISs) have the advantages of generating plasma from various solid targets and quickly switching the ion species by changing the target. Given these features, we aimed to develop a LIS for an ion implanter that requires a wide variety of ion species. The plasma generated by the LIS diffuses three-dimensionally with a wide angular distribution, such that only a small fraction of the generated ions reaching the extraction electrode aperture is extracted as a beam. With this procedure, the beam intensity is insufficient for the implanter LIS, which uses a laser with lower energy than the conventional LIS. To obtain a higher beam intensity by increasing the number of ions reaching the beam extraction electrode aperture, a plasma transport system with a linear solenoid magnet was installed immediately after the LIS chamber to focus the plasma by a magnetic field. In the Ti plasma focusing experiment using this system, the beam intensity increased up to 6.7 times compared to that of the case without a magnetic field. This result demonstrates that plasma focusing by a magnetic field is effective for increasing the beam intensity.

Performance of laser ion source LION operated at Brookhaven National Laboratory

LION is a laser ion source that has been in operation at Brookhaven National Laboratory (BNL) to provide heavy ions for NASA Space Radiation Laboratory (NSRL) and Relativistic Heavy Ion Collider (RHIC). It is the first laser ion source to supply stable ion beams for a long-term operation for users at a large accelerator facility in the world. LION is located at the upstream end of the heavy ion accelerator complex at BNL and supplies singly charged ion beams of various ion species. LION has been in operation since 2014 and is planned to be upgraded in 2024. This paper summarizes the operational performance achieved by LION.

Extraction of ion beam from laser ion source for direct plasma injection scheme

Laser ion sources are expected to be used in various applications of heavy ion beam technology. The plasma direct injection scheme (DPIS) is a method in which ion beams extracted from a laser ion source are directly injected into a radio frequency quadrupole (RFQ) linear accelerator. In this study, a new shape of the plasma electrode with a concave surface for the DPIS was proposed to inject a converging beam to a cavity of RFQ accelerator. This approach allows the use of a large-diameter extraction electrode, which is not limited by the aperture of the RFQ electrode rods. The DPIS, using the concave surface electrode, was employed to accelerate C6+ ion beams. The results indicated that both the beam current and the number of ions increased nearly twice with the proposed electrode shape compared to values obtained with the conventional electrode. This enhancement corresponded to the increased extraction area of the beam.

Simulation of laser-plasma focusing using taper solenoid

A laser ion source can produce ion beams of various elements, including high melting point metals. Owing to its ability to switch beams rapidly by loading multiple solid targets, we are developing a laser ion source to implement it in a 400 kV ion implanter, which requires a wide range of ion species. Although a laser ion source offers above advantages, most of the plasma is lost in an ion source due to the generation of the beam from a part of the diffused plasma with a broad angular distribution. To suppress this loss and enhance beam intensity, we employ a linear solenoid to increase the amount of plasma reaching the extraction electrode by suppressing the three-dimensional plasma diffusion. However, the linear solenoid cannot suppress the loss of plasma near the target as the plasma spreads three-dimensionally from the plasma generation point. Therefore, by placing a taper solenoid near the target, it is possible to suppress the diffusion of plasma immediately after its generation and to transport most of the generated plasma to the extraction electrode. In this paper, we present the results of plasma trajectory calculations using the particle-in-cell method by the plasma simulations involving taper solenoids.

Effect of solenoidal magnetic field on ion charge state distribution in laser ion source

Applying a solenoidal magnetic field to a laser produced plasma is a method to increase the ion beam current supplied from a laser ion source to applications. The purpose of this study is to investigate the effects of the solenoid magnetic field on the charge state distribution of the ion beam extracted from the laser ion source. A plasma generated by a Nd: YAG laser was injected into the solenoid lens with a length of 25 mm. The current waveforms of ion beams extracted from the laser produced plasmas were measured as a function of solenoidal field strength. In addition, the variation of beam current waveforms for each charge state ion was investigated. The results indicated that the charge state distribution in the plasma was kept after focusing by the solenoid magnetic field.

FEBIAD ionization development via a web-app for multidimensional characterization

The ISAC-FEBIAD is an electron impact ion source typically used to ionize radioactive molecules or isotopes of elements beyond the reach of either surface or laser ion sources. The FEBIAD’s key tuning parameters are the cathode temperature defining the number of electrons created; the anode voltage establishing the electron energy; and the magnetic field controlling the electron density inside the anode volume. However, these parameters are typically scanned in a small and limited range when optimizing the source. Recent investigations have shown the need to explore the entire range of operational values accessible by the power supplies, not only due to the intrinsic variations from source to source but also to operate the source at optimal settings. To address this, a scanning algorithm has been implemented as a web interface thanks to the High-Level-Application (HLA) infrastructure available at TRIUMF. The ion beam intensity during both offline and online commissioning of the web app are presented here as contour plots. The optimal settings found for stable 20Ne are confirmed as the optimal settings for radioactive 18Ne. The main takeaway, however, is that the optimal ion source parameters differ between singly-charged, doubly-charged, and molecular species. This development demonstrate and facilitate the need for element and charge state-specific parameter optimization. Additionally, the results highlight the possibility of parameter optimization to enhance the ratio of the species of interest to co-ionized contamination.

Study on ion current density of different species in laser produced plasma in a solenoid magnet

A solenoid magnetic field along the expanding laser-produced plasma is an essential technique of the laser ion source. The solenoid field can increase ion beam current at beam extraction point by a factor of 2 to over 100 by confining moving laser produced plasma in transverse direction. This technique is used everywhere from development lab to operational machine for user operation. However, the motion of ions in laser produced plasma is not fully understood. In this study, we experimentally investigated the motion of ions in a solenoid magnet (inner diameter 102 mm, coil length 1980 mm) for Al, Fe, and Ta targets. Using the following three conditions: full solenoid bore, a φ51 mm collimator on the solenoid axis, and a thin-wall φ51 mm tube at the bottom of the solenoid, we found that extracting ions at off-axis position (20∼30 mm from the solenoid axis in this study) can enhance ion intensity by a factor of three or more. We continue to investigate ion motion in a solenoid field to develop better laser ion source design.

A Long-life Laser Ion Source Using a Reproducible Solidified Gas Target

A novel laser ion source using a reproducible cryogenic target has been developed for next-generation heavy-ion cancer therapy accelerators. A solid thin layer of butane formed on a cylindrical cold head cooled with liquid nitrogen is ablated by a frequency-doubled Nd:YAG laser to generate high-charged carbon ions. The properties and reproducibility of the carbon plasmas produced under various conditions are investigated.

Progress of the laser ion source upgrade (LION2) for RHIC and NSRL program at Brookhaven National Laboratory

At Brookhaven National Laboratory (BNL), the LION2 ion source is being constructed to replace an existing laser ion ablation ion source (LIS) at the EBIS facility, which provides heavy ion beams of multiple ion species for the operation of NASA Space Radiation Laboratory (NSRL) and Relativistic Heavy Ion Collider (RHIC). The LION1 ion source currently provides singly charged ions of Li, B, C, O, Al, Si, Ca, Ti, Fe, Cu, Zr, Nb, Ag, Tb, Ta, W, Au, Bi, and Th with a rapid-species-change capability. An electron beam ion source, Extended-EBIS captures, confines, and ionizes the ions to high charge state, suitable for injection and acceleration by an RFQ accelerator. Typically, single pulses of the LIS ion species for NSRL are changed sequentially during Galactic Cosmic Ray experiments, while multiple pulses of a given ion beam are provided quasi-simultaneously for RHIC. LION2 will have the same capability of the rapid-species-change with improved beam performance and reliability. LION2 is being constructed in a remote assembly location and is expected to finish in December 2023. The removal of LION1 and installation of LION2 is planned during the December 2023 or summer 2024 shutdown.

Generation of plasma from multiple targets by laser ion source for TIARA ion implanter

We investigated a laser ion source for use as an ion source for the ion implanter in Takasaki Ion Accelerators for Advanced Radiation Application to increase the number of ion species that can be produced and to enable rapid switching of ion species. Herein, we analyzed the charge state distribution of ions in a laser plasma generated through irradiation of graphite, titanium, copper, and tantalum targets with 30 mJ Nd:YAG laser to determine the particle number of low-charge ions per pulse at 1.1 m from the target. The particle number of singly charged ions could be increased by adjusting the laser power density. For carbon, titanium, and tantalum, the particle numbers were in the order of 1010 ions per pulse, whereas for copper, the particle numbers were in the order of 109, lower than for other target materials.

The SPES Laser Ion Source: Time Structure and Laser Enhancement Measurements with Sm+ beam

A two-step resonance photo-ionization scheme has been used to ionize samarium atoms in the SPES tantalum hot-cavity ion source. The effect of the ion load on the ion beam time structure and the laser enhancement of the ion yield has been studied at different ion source temperatures. Generally, the introduction of more positive ions (ion load) affects negatively the overall confinement of the laser ions inside the volume of the ion source. Possible enhancement of the laser ion confinement through the introduction of neutrals is observed as well. The ion load is also observed to affect the confinement in the transfer line much more than in the hot cavity. Measurement of the time structure with inverted polarity of the cavity DC heating supply confirmed the significance of the longitudinal potential for ion extraction. The laser enhancements of the ion yield are found to be sensitive to the ion load at low operating temperature of the ion source i.e. 1800°C, whereas at 2050°C and 2200°C, they are relatively stable till an ion load value of 1.2 µA.

Magnetic moments of thallium isotopes in the vicinity of magic N = 126

The magnetic dipole moments (μ) of 209Tlg (N=128) and 207Tlm (N=126) have been measured for the first time using the in-source laser resonance-ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the usually overwhelming background of the isobaric francium isotopes and allows access to heavy thallium isotopes with A⩾207. The self-consistent theory of finite Fermi systems based on the energy density functional by Fayans et al. well describes the N dependence of μ for 1/2+ thallium ground states, as well as μ for the 11/2− isomeric states in europium, gold and thallium isotopes. The inclusion of particle-vibration coupling leads to a better agreement between the theory and experiment for μ(Tlg, Iπ=1/2+). It is shown that beyond mean-field contributions to μ cannot be neglected at least for thallium isotopes with Iπ=1/2+.

CERN-MEDICIS: Operational indicators to support the production of new medical radionuclides by mass-separation

CERN-MEDICIS is an isotope mass separation facility dedicated to biomedical research located in a type A work sector, receiving on average 50% of the 1.4 GeV protons delivered by the Proton Synchrotron Booster (PSB). It was commissioned with Radioactive Ion Beams (RIB’s) in 2017. MEDICIS has operated for the past 5 years in batch mode, with targets irradiated in a station located at the HRS beam dump, and with external sources provided by MEDICIS cyclotrons and nuclear reactors partners, notably during the Long Shutdown (LS2). Additional features of the facility include the MELISSA laser ion source, radiochemistry on implanted radionuclides and an online gamma-ray spectroscopy implantation monitoring. In 2022, we introduced Key Performance Indicators (KPI’s) to monitor the operation of the facility for collected efficiencies, the optimisation of the radiological risks and evaluate impact of possible modifications of the station, paralleling for instance LHC’s integrated luminosity. Defined KPI’s cover aspects in the operation cycle, e.g. planning in CERN schedule, target irradiations, duration of the process, radiological risk mitigation, facility up-time, developments and maintenance. MEDICIS KPI’s can help distinguish which of the operation and infrastructure life cycle requires immediate intervention, developments or consolidation. Those are related to the irradiation stations and irradiation possibilities, the beamlines (parallel collections), target and ion sources (reliability), robot handling and infrastructure, or the separation process itself.

Design and Simulation of a Liquid-Microjet Time-of-Flight Mass Spectrometer with a Femtosecond Laser Ionization Source

Design and Simulation of a Liquid-Microjet Time-of-Flight Mass Spectrometer with a Femtosecond Laser Ionization Source

Characterization of the field ionization extension for the laser ion source and trap: Measurement of the ionization potential of ytterbium

We report on the development and application of the Field Ionization Laser Ion Source and Trap (FI-LIST) at the RISIKO mass separator at Mainz University. The FI-LIST is an adaptation of the well-established LIST unit developed at Mainz and successfully adapted to CERN-ISOLDE. It is specifically designed for field ionization of highly excited atoms in a homogeneous electric field. To assess the performance of the device for future use on radioactive species of e.g. actinides, we conducted ionization potential (IP) measurements on ytterbium, for which the IP is precisely known. The IP value was derived by applying the saddle-point model with a relative precision of 3⋅10−6 and in very good agreement with the literature value.