Resonance Ion Research Articles

Development and validation of the numerical model of Electron Cyclotron Resonance Ion Sources

Processes of the secondary electron emission (SEE) from the walls are included into the Numerical Advanced Model of Electron Cyclotron Resonance Ion Sources (NAM-ECRIS). It is found that SEE strongly influences electron confinement time and ion production. With the modified model, we observe reactions of the source to changes in a gas flow into the source and in an injected microwave power. The source performance with scaling the hexapole magnetic field is investigated. The calculated tendencies are close to the experimental observations.

Origin of Resonant Character in the Electron Impact Two-Body Neutral-Fragmentation of Methane.

The observation of peaks in the threshold region of two-body neutral fragmentation of methane molecule, i. e., CH4 →CH3 +H, by low energy electron (LEE) impact has been an enigma. The prevailing explanation that this resonant behavior is due to excitation energy transfer is unsatisfactory since this process is not expected to show peaks in the cross-sections unless there is the involvement of electron-molecule resonances. Our first-principles calculations now reveal that the observed peaks could be explained as due to the formation of negative ion resonances, which dominantly dissociate into two neutral fragments and a free-electron. This case of methane is a pointer to the possibility that such reactions contribute significantly to neutral radical production from molecules by LEE impact in comparison to dissociative electron attachment, and in general could play a significant role in electron-based chemical control.

Probing the Atomic Structure of Californium by Resonance Ionization Spectroscopy

The atomic structure of californium is probed by two-step resonance ionization spectroscopy. Using samples with a total amount of about 2×1010 Cf atoms (ca. 8.3 pg), ground-state transitions as well as transitions to high-lying Rydberg states and auto-ionizing states above the ionization potential are investigated and the lifetimes of various atomic levels are measured. These investigations lead to the identification of efficient ionization schemes, important for trace analysis and nuclear structure investigations. Most of the measurements are conducted on 250Cf. In addition, the isotope shift of the isotopic chain 249−252Cf is measured for one transition. The identification and analysis of Rydberg series enables the determination of the first ionization potential of californium to EIP=50,666.76(5)cm−1. This is about a factor of 20 more precise than the current literature value.

Sorbicillinoid Derivatives with the Radical Scavenging Activities from the Marine-Derived Fungus Acremonium chrysogenum C10.

Sorbicillinoids are a class of structurally diverse hexaketide metabolites with good biological activities. To explore new structural sorbicillinoids and their bioactivities, the marine-derived fungus Acremonium chrysogenum C10 was studied. Three new sorbicillinoid derivatives, acresorbicillinols A–C (1–3), along with five known ones, trichotetronine (4), trichodimerol (5), demethyltrichodimerol (6), trichopyrone (7) and oxosorbicillinol (8), were isolated. The structures of new sorbicillinoids were elucidated by analysis of nuclear magnetic resonance (NMR) and high-resolution electrospray ionization mass spectroscopy (HRESIMS). The absolute configurations of compounds 1–3 were determined by comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. Compound 3 exhibited a strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, with the IC50 value ranging from 11.53 ± 1.53 to 60.29 ± 6.28 μM in 24 h. Additionally, compounds 2 and 3 showed moderate activities against Staphylococcus aureus and Cryptococcus neoformans, with IC50 values of 86.93 ± 1.72 and 69.06 ± 10.50 μM, respectively. The boundary of sorbicillinoid biosynthetic gene cluster in A. chrysogenum was confirmed by transcriptional analysis, and the biosynthetic pathway of compounds 1–8 was also proposed. In summary, our results indicated that A. chrysogenum is an important reservoir of sorbicillinoid derivatives, and compound 3 has the potential for new natural agents in DPPH radical scavenging.

Dose Variations Using an X-Ray Cabinet to Establish in vitro Dose-Response Curves for Biological Dosimetry Assays.

In biological dosimetry, dose-response curves are essential for reliable retrospective dose estimation of individual exposure in case of a radiation accident. Therefore, blood samples are irradiated in vitro and evaluated based on the applied assay. Accurate physical dosimetry of the irradiation performance is a critical part of the experimental procedure and is influenced by the experimental setup, especially when X-ray cabinets are used. The aim of this study was to investigate variations and pitfalls associated with the experimental setups used to establish calibration curves in biological dosimetry with X-ray cabinets. In this study, irradiation was performed with an X-ray source (195 kV, 10 mA, 0.5 mm Cu filter, dose rate 0.52 Gy/min, 1st and 2nd half-value layer = 1.01 and 1.76 mm Cu, respectively, average energy 86.9 keV). Blood collection tubes were irradiated with a dose of 1 Gy in vertical or horizontal orientation in the center of the beam area with or without usage of an additional fan heater. To evaluate the influence of the setups, physical dose measurements using thermoluminescence dosimeters, electron paramagnetic resonance dosimetry and ionization chamber as well as biological effects, quantified by dicentric chromosomes and micronuclei, were compared. This study revealed that the orientation of the sample tubes (vertical vs. horizontal) had a significant effect on the radiation dose with a variation of −41% up to +49% and contributed to a dose gradient of up to 870 mGy inside the vertical tubes due to the size of the sample tubes and the associated differences in the distance to the focal point of the tube. The number of dicentric chromosomes and micronuclei differed by ~30% between both orientations. An additional fan heater had no consistent impact. Therefore, dosimetric monitoring of experimental irradiation setups is mandatory prior to the establishment of calibration curves in biological dosimetry. Careful consideration of the experimental setup in collaboration with physicists is required to ensure traceability and reproducibility of irradiation conditions, to correlate the radiation dose and the number of aberrations correctly and to avoid systematical bias influencing the dose estimation in the frame of biological dosimetry.

Extraction of phytochemicals with health benefit from Peperomia pellucida (L.) Kunth through liquid-liquid partitioning

Peperomia pellucida (L.) Kunth has been traditionally used as food and medicine in both Eastern and Western countries. Owing to the vast variety of bioactive compounds, there is no definite extraction system or formula to efficiently extract the bioactive compounds with commercial value. This study aimed to evaluate the bioactive compounds in P. pellucida with liquid-liquid partitioning method and compare their anti-glycaemic, anti-inflammatory, antioxidant, and anti-glycation potential in different solvent fractions. The dried plant powder was macerated with methanol and successively partitioned with five solvents of different polarity. Five classes of bioactive compounds, four categories of biological activities and in vivo toxicity were evaluated with quantitative bioassays. This study found that the plant extraction yield varied with solvent polarity. The chloroform, ethyl acetate and n-butanol plant fractions were rich in phenolics, tannin, saponin and alkaloid despite their low extraction yields. Plant phenolics and saponin were positively correlated (p < 0.01) with antioxidant, anti-inflammatory and anti-glycation activities. The non-polar hexane fraction displayed high anti-inflammatory potential while ethyl acetate, aqueous and hexane fractions showed relatively strong anti-glycation effect. The anti-α-glucosidase and anti-α-amylase activities in all plant fractions except the non-toxic aqueous fraction were stronger than standard acarbose drug. Four main bioactive compounds, including the dillapiole, 2,4,5-trimethoxystyrene, 9-octadecenoic acid methyl ester and pheophorbide-a methyl ester have been characterized through nuclear magnetic resonance and electrospray ionization mass spectrometry. Principal component analysis confirmed that both solvent polarity and plant extraction yield contributed to 63% of biological activity variation in P. pellucida. This study has demonstrated that the liquid-liquid partitioning method could be optimized to extract bioactive compounds from P. pellucida with potent antioxidant, anti-diabetic, anti-inflammatory and anti-glycation activities.

Integrative simulation of a 2 cm electron cyclotron resonance ion source with full particle-in-cell method

A two-dimensional full particle-in-cell model is developed to simulate the operation process of a 2 cm electron cyclotron resonance ion thruster. The simulation regions include the discharge chamber, grid system, and plume, and the processes of neutral gas injection, plasma discharge, and ion beam extraction are simulated continuously. Neutrals are treated as particles and managed through an adaptive particle management algorithm. The collisions between charged and neutral particles are approached by the method of combining the Monte Carlo and directly simulation Monte Carlo collisions. The integrative simulation provides a global perspective to learn the gridded ion thruster, such as the Child-Langmuir sheath, acceleration grid erosion, plasma bridge, and so on. In this paper, the response of the plasma system to the accelerating voltage is analyzed, which is related to the bulk plasma, antenna floating voltage, and Child-Langmuir sheath. Besides, an ion density wave is observed in plume, which will increase the current of acceleration grid and cause ion backflow.

Advancing Radiation-Detected Resonance Ionization towards Heavier Elements and More Exotic Nuclides

RAdiation-Detected Resonance Ionization Spectroscopy (RADRIS) is a versatile method for highly sensitive laser spectroscopy studies of the heaviest actinides. Most of these nuclides need to be produced at accelerator facilities in fusion-evaporation reactions and are studied immediately after their production and separation from the primary beam due to their short half-lives and low production rates of only a few atoms per second or less. Only recently, the first laser spectroscopic investigation of nobelium (Z=102) was performed by applying the RADRIS technique in a buffer-gas-filled stopping cell at the GSI in Darmstadt, Germany. To expand this technique to other nobelium isotopes and for the search for atomic levels in the heaviest actinide element, lawrencium (Z=103), the sensitivity of the RADRIS setup needed to be further improved. Therefore, a new movable double-detector setup was developed, which enhances the overall efficiency by approximately 65% compared to the previously used single-detector setup. Further development work was performed to enable the study of longer-lived (t1/2&gt;1 h) and shorter-lived nuclides (t1/2&lt;1 s) with the RADRIS method. With a new rotatable multi-detector design, the long-lived isotope 254Fm (t1/2=3.2 h) becomes within reach for laser spectroscopy. Upcoming experiments will also tackle the short-lived isotope 251No (t1/2=0.8 s) by applying a newly implemented short RADRIS measurement cycle.

Observation of Collisional De-Excitation Phenomena in Plutonium

A program of research towards the high-resolution optical spectroscopy of actinide elements for the study of fundamental nuclear structure is currently ongoing at the IGISOL facility of the University of Jyväskylä. One aspect of this work is the development of a gas-cell-based actinide laser ion source using filament-based dispensers of long-lived actinide isotopes. We have observed prominent phenomena in the resonant laser ionization process specific to the gaseous environment of the gas cell. The development and investigation of a laser ionization scheme for plutonium atoms is reported, focusing on the effects arising from the collision-induced phenomena of plutonium atoms in helium gas. The gas-cell environment was observed to greatly reduce the sensitivity of an efficient plutonium ionization scheme developed in vacuum. This indicates competition between resonant laser excitation and collisional de-excitation by the gas atoms, which is likely being enhanced by the very high atomic level density within actinide elements.

Substitution-induced Nonplanarity of 3-Fluorothioanisole in the First Electronically Excited State.

Vibronic spectra of 3-fluorothioanisole (3FTA) in the first electronic excited state (S1) and the cationic ground state (D0) have been obtained by one-color resonant two-photon ionization (1C-R2PI) and mass-analyzed threshold ionization (MATI) spectroscopy. Spectroscopic measurements and theoretical calculations indicate that both cis- and trans-rotamers of the 3FTA molecule are stable and coexist in the S0 (the electronic ground state) and D0 states, and the cis-rotamer is shown to be slightly more stable than the trans-rotamer. In the S1 state, theoretical calculations predict a stable gauche-structure of 3FTA, manifested by the observation of strong activation of the vibrational modes involving the motion of the -SCH3 group in the low-frequency regions of the 1C-R2PI and MATI spectra. The electronic excitation energy from the S0 state to the S1 state (E1) and the adiabatic ionization energy (IE) are respectively determined to be 34 820 ± 3 and 65 468 ± 5 cm-1 for cis-3FTA, and those of the trans-rotamer are respectively determined to be 35 047 ± 3 and 65 644 ± 5 cm-1. The structural properties of the stable rotamers of 3FTA and their comparison with other F- and Cl-substituted thioanisole derivatives are discussed as well.

Simulation study of fast ion losses associated with the rotating n = 1 resonant magnetic perturbations in KSTAR

This paper describes a simulation framework for testing the fast ion loss mechanism associated with the experimentally observed beam ion losses when an externally applied toroidally rotating perturbed magnetic field is used to control edge localized modes in the KSTAR tokamak. The simulations reproduce the key qualitative features of neutral beam injection (NBI) ion detection by a fast ion loss detector. The NBI ion losses in the simulation mainly occur for passing particles due to orbit stochastization, which is caused by orbit resonance with the 3D field perturbations. The relative toroidal angle of NBI ion deposition to the orbit island determines the radial path of the particles between confinement or loss. The fast ion loss quantity depends on the toroidal angle rotation of the 3D field with respect to the beam deposition position. The averaged transport of toroidal canonical angular momentum reveals that linear and nonlinear resonance of the NBI ions within the 3D field are the main factors determining fast ion transport and loss.

A 1.5D fluid—Monte Carlo model of a hydrogen helicon plasma

Helicon plasma sources operating with hydrogen or deuterium might be attractive for fusion applications due to their higher power efficiency compared to inductive radiofrequency plasma sources. In recent years, the resonant antenna ion device (RAID) has been investigating the physics of helicon plasmas and the possibility of employing them to produce negative ions for heating neutral beam injectors (HNBs). Herein, we present a fluid Monte Carlo (MC) model that describes plasma species transport in a typical helicon hydrogen plasma discharge. This work is motivated by an interest in better understanding the basic physics of helicon plasma devices operating in hydrogen and, in particular, the volume production of negative ions. This model is based on the synergy between two separate self-consistent approaches: a plasma fluid model that calculates ion transport and an MC model that determines the neutral and rovibrational density profiles of . By introducing the electron density and the temperature profiles measured by Langmuir probes as model constraints, the densities of ion species (, , , ) are computed in a 1.5D (dimensional) geometry. The estimate of the negative ion density profile represents a useful benchmark that is comparable with dedicated diagnostics, such as cavity ring-down spectroscopy and Langmuir probe laser photodetachment. Neutral gas particles (atoms and molecules) are calculated assuming a fixed plasma background. This gas–plasma decoupling is necessary due to the different timescales of plasma (microseconds) and gas kinetics (milliseconds).

Superconducting Linac Booster for Super-Heavy Element Experiments at RIKEN Radioactive Isotope Beam Factory

The Rikagaku Kenkyūjo (RIKEN) heavy-ion linac was upgraded by introducing a new super-conducting linac-booster to advance the super-heavy elements synthesis program beyond nihonium at the RIKEN Radioactive Isotope Beam Factory (RIBF). The total acceleration voltage was upgraded from 25 MV with 12 room temperature drift-tube-linacs (DTLs) to 39 MV by introducing a superconducting linac booster, SRILAC. The upgrade of the beam intensity is realized by a newly constructed superconducting electron-cyclotron resonance ion source (SC-ECRIS). The construction of SRILAC and the SC-ECRIS started in FY2017. After the hardware installation and commissioning, the first beam acceleration test was successfully conducted at the end of FY2019, and user beam service was started in FY2020. This article provides an overview of the upgrade and its present performance.

Low Z gas mixing effects of Ar and Xe multicharged ions in electron cyclotron resonance ion source

An electron cyclotron resonance (ECR) ion source (ECRIS) has wide applications such as cancer therapy and material synthesis. We have constructed a single ECRIS capable of producing various ions with low to high mass/charge ratio, and have been conducting various experiments. We focus on the efficient production of multicharged ions and aim to increase the yield of multicharged ions by new effects of electromagnetic waves in ECRIS. We investigated the possibility of selective heating to low Z ions under low Z gas mixing. Therefore, as a preliminary step of these experiments, the low Z gas mixing effect with rare gases are investigated. The optimum mixing ratio of the main gas Ar and the low Z gas He was investigated by varying the mixing ratio. The Ar multicharged ion beam current, impurity fraction and plasma parameters were measured. As a result, it was confirmed that the Ar multicharged ion yield was sufficient reproducibly increased by mixing He gas into Ar plasma. In addition, this from the measured plasma parameters is not an effect of the plasma parameters, but maybe a cooling effect.

A few ECRIS developments at LBNL

In addition to the ongoing investigation of bremsstrahlung radiation produced by energetic electrons in the superconducting Electron Cyclotron Resonance (ECR) ion source VENUS, the LBNL ion source group has pursued several other research topics since 2015 to explore potential advancements of ECR ion sources. Three of these activities are investigations into the benefits of non-cylindrical plasma chambers, the development of new high-temperature ovens that will efficiently produce the intense, metallic ion beams necessary for super heavy element production at the 88-Inch Cyclotron facility, and the finalization of the conceptual and engineering design of the superconducting NbTi magnet structure for the 4th generation, 45 GHz ECR ion source MARS-D. This article summarizes and briefly discusses the highlights of these ECRIS developments.

Development and status of the FRIB 28 GHz SC ECRIS

T o meet a beam power requirement of 400 kW for heavy ions, a high intensity 28 GHz superconducting Electron Cyclotron Resonance (ECR) ion source is under development at the Facility for Rare Isotope Beams (FRIB) in collaboration with Lawrence Berkeley National Laboratory (LBNL). The magnet was built and tested at LBNL and integrated into the ion source cryostat on the FRIB high voltage platform. Magnet cooldown to 4.2K was completed successfully in December of 2020. The static heat load at 4.2K has been measured to be around 1.2 W, in good agreement with the design value. The heat load is managed through 2 Gifford-McMahon/Joule-Thomson (GM-JT) cryocoolers that have been in operation for several months. Magnet energization is scheduled in November of 2021. Warm components preparation and assembly test are ongoing in parallel. The ion source commissioning with 18 GHz Klystron shall start in December of 2021. Details of the ion source development, status, and commissioning plan will be presented in the paper.

Cutoff limitation of left-hand polarization wave and candidates for further enhanced producing multicharged ions on ECRIS

Based on experimentally obtained plasma parameters in an electron cyclotron resonance (ECR) ion source (ECRIS) and theoretical considerations, it is turned out the essential factor that is currently presumed to define the increase in multicharged ion current in ECRIS is not simply the density limit of ordinary wave and right-hand cutoffs, but is also higher density one of left-hand cutoff. There are two response guidelines that can be considered to make it possible to overcome limitations, except for the conventional simply increasing the frequency and the magnetic field strength. One is advanced high-frequency resonance, i.e., upper-hybrid resonance (UHR), which is conversion from electromagnetic to electrostatic wave essentially without cutoff. The others are due to the introduction of lower frequency waves than ECR’s one, which has no density limit in a more essential sense. The latter is the introduction of lower-hybrid resonance (LHR) or ion cyclotron resonance (ICR). We will describe experimentally obtained plasma parameters, and will discuss these candidate applications.

Redefining plasma chambers for ECR Ion Sources: the IRIS structure

One possible way to optimize microwave coupling and plasma confinement in Electron Cyclotron Resonance (ECR) Ion Sources is a revolutionary design strategy of plasma chambers, breaking the cylindrical symmetry. This contribution reports about the design and numerical validation of an innovative resonant cavity playing as plasma chamber of ECR ion sources. The new chamber, named IRIS (Innovative Resonators for Ion Sources), was argued starting from the 3D structure of the plasma and, therefore, fashioned to the twisting magnetic structure. The microwave launching scheme was radically changed as well, consisting of side-coupled slotted-waveguides with diffractive apertures smoothly matching the overall structure of the camera. This approach also enables a profound optimization of cooling systems and overall spaces in general (for gas feedings, oven systems, sputtering, etc.). Here we report on the conceptual study, electromagnetic design and PIC simulations of the electron heating in the novel resonant cavity, comparing results with those for standard (cylindrical) chamber, and also considering the impact of microwave feeding led by single aperture rectangular waveguides vs. waveguide-slotted antennas. Manufacture strategy, based on additive manufacturing techniques, will also be discussed.

Studies of bremsstrahlung and characteristic X-Ray lines using the VENUS ECR

Though known for their production of high currents of highly-charged ion beams, advanced electron cyclotron resonance (ECR) ion sources like VENUS at Lawrence Berkeley National Laboratory (LBNL) also generate significant numbers of x-rays. The LBNL ECR ion source group has spent many years studying the x-rays emitted from VENUS in order to gain a better understanding of the ECR plasma. Based on the emitted bremsstrahlung continuum, a spectral temperature Ts can be calculated which is a relative indication of the temperature of the plasma electrons. We will present correlations between Ts with respect to parameters such as magnetic fields. In addition to the bremsstrahlung continuum, the plasma ions emit characteristic x-rays. We will show that additional information can be gained by investigating spectral line shifts. A summary of this recent research using VENUS will be presented and discussed.

Concept design of new compact electron cyclotron resonance ion source with permanent magnets for multi-ion radiotherapy

The multi-ion radiotherapy with dose distribution and Liner Energy Transfer optimization is being studied at QST. Helium, carbon, oxygen and neon ions are considered as ion species for multi-ion therapy. A basic experiment using these ion beams has been carried out at the HIMAC. For heavy-ion radiotherapy facility, it is desirable to operate with only one ECR ion source with permanent magnets from the viewpoint of cost and maintenance. We considered the operating method with only one ion source for multi-ion radiotherapy. Ionization gases were helium, methane, oxygen, and neon to produce He2+, C4+, O6+ and Ne7+ ions. Requirement values of beam current were 940 μA correspond to He2+, 290 μA to C4+, 330 μA to O6+, and 245 μA to Ne7+, respectively. This value was obtained from the number of particles required for the cancer treatment and the transmission efficiency of the accelerator in the HIMAC. We performed some beam tests for design of a new compact ion source with the existing 18 GHz ECR ion source (NIRS-HEC). From the results of the beam tests, we estimate the mirror magnetic field of NIRS-HEC by using POISSON/SUPERFISH code. Then, the structure of the permanent magnets for new ECR ion source is determined so that they reproduce the values of the upstream mirror peak (Binj), B minimum (Bmin) and the downstream mirror peak (Bext) at the NIRS-HEC. The magnetic field of Binj, Bmin and Bext at NIRS-HEC were 1.14 T, 0.475 T and 0.9 T, respectively.