Electron Cyclotron Resonance Ion Source Research Articles

Proton Injector for Compact Neutron Source DARIA Systems Optimization

This paper is devoted to magnetic trap and extraction system upgrade of ECR ion source GISMO to utilize it as a proton injector for linear accelerator of compact neutron source DARIA. An open permanent magnet (Nd–Fe–B) trap was designed. It was adjusted to place the extraction system inside a part of magnet with larger inner diameter. Then, the three-electrode extractor optimization was made. It was shown that the use of additional magnetic lens allows to produce the proton beam with a low divergence angle. The use of the magnetic trap and the extraction system as a part of the proton injector for DARIA project possibility was shown using computer modeling. The following steps of the proton injector creation are discussed.

Tailoring of microwave power density in an ECR ion source using an optimized ridge coupler

One of the interesting areas in the Electron Cyclotron Resonance Ion Source (ECR-IS) design which requires further exploration is the microwave power launching scheme and the power coupling optimization with the plasma chamber. The electron heating efficiency and thereby the plasma density highly depends on the electric field distribution inside the plasma chamber; therefore, it is important to optimize the coupling of microwave power to the plasma chamber, to maximize the electric fields in the plasma chamber for a given microwave power. For this, a single-step quarter wavelength ridge coupler design study has been carried out using CST MW Studio Suite along with the plasma chamber and ridge wave guide designs. The experimental measurements of electric and magnetic field profiles in the plasma chamber assembly with different coupling configurations have been done using an innovative bead pull technique and a magnetic field probe. The experimental results match well with the simulation results and the comparative studies of different coupling configurations reveal that the single step ridge coupler based scheme improves the electric field inside the plasma chamber to at least five times than the conventional ridge waveguide. To further improve the E-field amplitude in the plasma chamber by another 40%, a novel tuning scheme for the coupler has been introduced. Preliminary plasma studies have been carried out with the optimized coupler on a multicusp ECR plasma source and the plasma density measurements performed using a microwave cut-off probe. The plasma measurements show that even at low input microwave powers (∼300 W) the plasma density is comparable with standard ECR-IS. The present study thus, sheds light on the coupling configuration of microwave to plasma chamber with experimental measurements of cavity mode and fields in the cavity which will be useful for high intensity accelerator applications in understanding the plasma evolution, beam parameters and its dependence on different operating parameters.

Improvement of multi-harmonic buncher’s quality factor for RAON

The high-intensity rare-isotope accelerator RAON, a component of the Rare Isotope Science Project, was developed to accelerate heavy ions from elements ranging from proton to uranium. The injector line consists of an Electron Cyclotron Resonance Ion Source, a Low Energy Beam Transport line, a Radio Frequency Quadrupole (RFQ), and a Medium Energy Beam Transport line. To improve beam quality, a multi-harmonic buncher (MHB) was proposed for inclusion before the RFQ. The MHB is needed to efficiently utilize two beams with different mass-to-charge (A/q) ratios. The fundamental frequency of the MHB is half the frequency of the RFQ; as such, a harmonic synthesis is effectively bunching a beam. Electric field simulations of the MHB were conducted using the CST Microwave Studio (MWS). The electrodes were designed as cone- type electrodes so that the electric field can be concentrated between the electrodes through which the beam passes. The electric field was optimized to account for structural changes such as gap length between electrodes, resonator position and other design details. The model optimized in the simulation tool was engineered through the 3D Inventor program.

Sputter sample preparation for ion beam delivery of radium-223 at ATLAS.

A radium-223 ion beam was delivered to an experiment from the electron cyclotron resonance ion source, ECR2, at the Argonne Tandem Linac Accelerator System (ATLAS). The radium-223 material was in a nitrate salt form within a vial, prior to being converted to a usable sputter sample. The sputter sample was produced using a new sample preparation method, where the radium nitrate was dissolved into a solution and pipetted onto pressed aluminum powder. This sample was then allowed to dry, distributing the radium-223 material throughout the sputter sample. Ion source operation using the radium sputter sample is described with the operating parameters listed. The intensity and energy requirements for this ion beam were 1 × 106 particles/s and 1.07 GeV, respectively. Because the intensity is relatively low compared to most experiments at ATLAS, previously developed accelerator mass spectrometry methods were used Scott etal. [Rev. Sci. Instrum. 87, 02A732 (2016)] to avoid the need for tuning of the low-intensity beam of interest. Handling of the radium material, as well as loading and unloading of the sputter sample from ECR2, required collaboration with Health Physics. Procedures were used and dry runs were carried out before, during, and after the experiment to ensure the safety of the workers. The processes used and lessons learned are described within.

The longitudinal energy spread of ion beams extracted from an electron cyclotron resonance ion source

We present a study of factors affecting the energy spread of ion beams extracted from a Charge Breeder Electron Cyclotron Resonance Ion Source (CB-ECRIS). The comprehensive simulations, supported by experiments with a Retarding Field Analyser (RFA), reveal that the longitudinal and transverse energy spread of the extracted beams are strongly affected by the electrostatic focusing effects, namely the extraction geometry and plasma beam boundary, to the extent that the electrostatic effects dominate over the magnetic field induced rotation of the beam or the effect of plasma potential and ion temperature. The dominance of the electrostatic focusing effect over the magnetic field induced rotation complicates parametric studies of the transverse emittance as a function of the magnetic field strength, and comparison of emittance values obtained with different ion sources having different extraction designs. Our results demonstrate that the full ion beam energy spread, relevant for the downstream accelerator, can be measured with the RFA only when all ions are collected. On the contrary, studying the effect of plasma properties (plasma potential and ion temperature) on the longitudinal energy spread requires heavy collimation of the beam accepting only ions near the symmetry axis of the beam for which the electrostatic and magnetic effects are suppressed. As the extraction system of the CB-ECRIS is similar to a conventional ECRIS, the conclusions of the study can be generalised to apply for all high charge state ECR ion sources. Finally, we present the results of systematic plasma potential measurements of the Phoenix-type CB-ECRIS at LPSC, varying the source potential, the microwave power and the axial magnetic field srength. It was observed that the plasma potential increases with the extraction magnetic field and the microwave power.

Absolute measurement of the relativistic magnetic dipole transition in He-like sulfur

We have made an absolute, reference-free measurement of the $1s2s\phantom{\rule{0.28em}{0ex}}^{3}S_{1}\ensuremath{\rightarrow}1{s}^{2}\phantom{\rule{0.28em}{0ex}}^{1}S_{0}$ relativistic magnetic dipole transition in He-like sulfur. The highly charged sulfur ions were provided by an electron-cyclotron resonance ion source, and the x rays were analyzed with a high-precision double-crystal spectrometer. A transition energy of 2430.3685(97) eV was obtained and is compared to most advanced bound-state quantum electrodynamics calculations, providing an important test of two-electron QED effects and precision atomic structure methods in medium-$Z$ species. Thanks to the extremely narrow natural linewidth of this transition and to the large dispersion of the spectrometer at this energy, a complementary study is also performed to evaluate the impact of different silicon crystal atomic form-factor models in the transition-energy analysis. We find no significant dependence on the model used to determine the transition energy.

Ion source and low energy beam transport prototyping for a single-ended heavy ion ToF-ERDA facility

We present the status of the ion source and low energy beam transport prototyping activities for a heavy ion time-of-flight elastic recoil detection analysis (ToF-ERDA) equipment, designed to accelerate a flux of 1–10 particle nano-Ampere of 40Ar6-12+ ions to 3–6MeV energy for depth profiling of light elements. The prototype injector consists of a novel permanent magnet electron cyclotron resonance ion source CUBE-ECRIS with a minimum-B quadrupole field topology, and a 90° permanent magnet dipole with adjustable field strength for charge state selection. We report experimentally measured argon beam currents as a function of the applied microwave power and ion source potential to demonstrate the feasibility of the CUBE-ECRIS as an injector for a single-ended ToF-ERDA facility with the ion source and low energy beam transport on a 500kV platform without SF6 electrical insulation. Finally, we present the design and field measurement results of the dipole magnet prototype.

Design and Development of the 200-kW Beam Dump

The Chinese Accelerator Front end (CAFe) is a demo superconducting proton linac for an accelerator-driven subcritical system (ADS). It includes an electron-cyclotron resonance ion source, a low-energy transport line, a radio-frequency quadrupole, a medium-energy transport line, a superconducting section, a high-energy transport line, and a beam dump. The design energy and current are 20 MeV and 10 mA, with a beam power of 200 kW. The goal of the CAFe is to demonstrate the 10-mA ability of a full superconducting linac, especially in the low-energy region. In previous beam commissioning, the maximum beam power achieved was 34 kW, which was limited by the capacity of the beam dump. Thus, for the high-power beam commissioning of CAFe, a new 200-kW beam dump has been designed and developed. Based on the thermal analysis, a maximum power density of 200 W/cm2 is adopted for the dump. To avoid a high-level residual dose, the material of the dump is aluminum alloy (Al6063). The dump is a conical structure, with water flow in the interlayer. During beam commissioning, the dump withstood 200-kW proton beam power and collected a total charge of 2049 mAh.

Commissioning Results of the New Compact ECR Ion Source for Electrostatic Storage Ring at KACST

A compact microwave ECR ion source with low operating power was tested and commissioned for the ion injector line in the multipurpose low-energy ELASR storage ring facility at King Abdulaziz City for Science and Technology (KACST) in Riyadh. The compact ECR ion source can deliver singly charged ions with an energy of up to 50 keV and a beam current of up to 50 μA or up to 500 µA with a larger extraction aperture. The plasma in the ECR chamber is driven by a simple transmitter antenna, making the overall size of the ion source only 6 cm in diameter, which is relatively small when compared with other ECR systems. Additionally, the source operates without a high-voltage platform, which significantly reduces the overall footprint and simplifies the system operation. In this paper, the mechanical design and modeling of the ECR ion source are introduced, and the layout of the first part of the beam line is presented along with the numerical simulation results. In addition, the experimental results obtained for the first generated ion beam and commissioning of the ECR ion source are introduced and discussed.

Kinetic whistler instability in a mirror-confined plasma of a continuous ECR ion source

Kinetic instabilities in a dense plasma of a continuous electron cyclotron resonance (ECR) discharge in a mirror magnetic trap at the Gasdynamic Ion Source for Multipurpose Operation (GISMO) setup are studied. We experimentally define unstable regimes and corresponding plasma parameters, where the excitation of electromagnetic emission is observed, accompanied by the precipitation of energetic electrons from the magnetic trap. A comprehensive experimental study of the precipitating electron energy distribution and plasma electromagnetic emission spectra, together with theoretical estimates of the cyclotron instability increment proves that under the experimental conditions, the observed instability is related to the excitation of whistler-mode waves, which are a driver of losses of energetic electrons from the magnetic trap. The results of this study are important for the further development of the GISMO electron cyclotron resonance ion source facility and for the improvement of its parameters as an ion source. Also, this research on plasma kinetic instabilities is of fundamental interest and provides experimental tools to simultaneously study plasma electromagnetic activity and corresponding changes in a resonant electron energy distribution.

Iodine electron cyclotron resonance plasma source for electric propulsion

With the rapid development of commercial space in recent years, the low-power and low-cost propulsion systems are needed more and more urgently. Compared with conventional chemical propulsion, electric propulsion has a higher specific impulse. Compared with the conventional xenon propellant, iodine propellant that does not require high pressure storage, is cheap and close to the relative atomic mass and ionization energy of xenon. Electron cyclotron resonance source has the advantages of no internal electrode, low pressure ionization, high plasma density and compact structure, which is suitable for low power electric propulsion. Therefore, the study of low power iodine propellant electron cyclotron resonance plasma source is of great significance. In this study, a set of corrosion-resistant feed system with balanced and stable output of iodine vapor is designed. Then the iodine-corrosion-resistant electron cyclotron resonance thruster is designed completely. A corrosion-resistant coaxial cavity structure is used to feed the microwave to the thruster, and the channel magnetic field is changed into a cusped field to generate more electron cyclotron resonance (ECR) layers. Finally, the combined ignition experiment is successfully conducted, showing the first plasma source using electron cyclotron resonance to ionize iodine propellant that can be used for electric propulsion in the world. The analyses of experiments, static magnetic field, microwave electric field distribution show that the unstable plasma plume scintillation at low power and low flow is caused by the conversion between ordinary wave electron plasmon resonance heating mode and extraordinary wave electron cyclotron resonance heating mode. The decrease of ionization rate at a high flow rate is caused by electron loss, wall loss and electronegativity of iodine propellant. Based on this principle, an improvement scheme is proposed. The plasma source has no obvious damage after discharge, which indicates that it has the potential of long life. This work preliminarily proves that the low power electron cyclotron resonance electric propulsion scheme of low power iodine propellant is feasible.

Overview of Numerical Simulations for Calculating In-Plasma β-Decay Rates in the Framework of PANDORA Project

β-decay rates are essential inputs in stellar nucleosynthesis models to explain observed nuclear abundances. While current models continue to use terrestrial values, experiments in storage rings indicate strong divergence between decay rates of neutral and ionised atoms [1], necessitating renewed investigations into stellar decay rates. The PANDORA project aims at measuring lifetimes of specific radio-isotopes trapped in an ECR plasma (which mimics astrophysical environments to some extent) and compare them with theoretical predictions [2], consequently verifying the models and allowing decay rate estimation for any isotope in the stellar interior. We present here a simulation scheme to characterise the space-resolved charge state and level population distribution of buffer and radio-isotope ions in ECR ion sources in order to calculate in-plasma decay rates. The algorithm is based on a Particle-in-Cell Monte Carlo (PIC-MC) routine that simultaneously models charge transport with collision-radiative processes. Preliminary results from the simulation are also shown, along with important takeaways for code-optimisation.

A newly developed ECR ion source with wide dynamic range of beam current

A newly developed ECR ion source with wide dynamic range of beam current

First results of a new quadrupole minimum-B permanent magnet electron cyclotron resonance ion source

The first experimental results of a novel permanent magnet electron cyclotron resonance ion source (ECRIS) with a minimum-B quadrupole magnetic field topology are presented. Bremsstrahlung measurements indicate that the electrons can reach energies of 150–200 keV. Ion charge states up to Ar11+ and Kr15+ were detected in the charge state distributions of the extracted beams. Measurements in pulsed operation mode reveal an afterglow peak, which implies that high charge state ions are confined electrostatically similar to a conventional ECRIS. The potential applications and future development of the ion source are discussed.

The capture of injected 1+ ions in charge breeder electron cyclotron resonance ion source plasma

The capture process of the 1+ ions in charge breeder electron cyclotron resonance ion sources has been attributed to cumulative small-angle scattering of the incident ions in ion–ion collisions with the buffer gas ions. The model results in controversy between the plasma potential and ion temperature values derived from simulations, and those found in the experiments. We demonstrate that the 1+ ion capture process is dominated by the slowing down of the incident ions by the ambipolar plasma potential, which has previously been assigned with a secondary importance. In this revised view, supported by experimental data, the 1+ capture does not depend on the mass of the injected and plasma ion species, or the ion temperature, which resolves the disagreement between modelling and experiments.

An extraction system design with a strongly inhomogeneous electric field for a JYFL electron cyclotron resonance ion source

A new ECR ion source extraction system has been designed. The design is based on the extraction conditions of the JYFL 14 GHz ECRIS, and its performance is compared to the existing extractor via numerical modeling. The aim is to improve the formation and quality of high-intensity ion beams. The plasma and the puller electrodes shape were changed. The plasma electrode has a narrow tip extruding toward the puller. It causes the electric field to increase near the plasma meniscus and subsequent higher ion velocity growth rate, which leads to the beam space charge reduction at fixed current and acceleration voltage. The extractor was developed with the ion optical code IBSimu. The initial beam parameters were taken from the experimental data. The calculations showed that the new extraction system allows to increase the total extracted current without compromising the beam quality. The new design allows the beam formation optimization for lower extraction voltages overcoming the present space charge limit.

Optimization of an Ecr Ion Source Beam Extraction and Formation System

Optimization of an Ecr Ion Source Beam Extraction and Formation System

LEBT Development for High-Current Multicharged Ion Injector Based on SC ECR Ion Source

LEBT Development for High-Current Multicharged Ion Injector Based on SC ECR Ion Source

Simulation as a Tool for Understanding Experimental Observations—Ion Beam Extraction from an ECRIS

A model for the simulation of ion beam extraction from an electron-cyclotron resonance ion source is proposed. It is based on the simple fact that charged particles follow magnetic field lines. Therefore, magnetic field lines are used to generate initial conditions for ray-tracing. This model reproduces in simulation experimentally obtained results. The importance of correlations in phase-space caused by the magnetic field is shown in the simulation. This model also describes the physics of space-charge and its compensation in the extracted (fast) ion beam by low-energy electrons. Simulation provides the possibility to test theoretical assumptions, as well as to optimize technical designs.

Diagnostics of highly charged plasmas with multicomponent 1+ ion injection.

We establish multicomponent 1+ injection into a charge breeder electron cyclotron resonance ion source and an associated computational procedure as a noninvasive probe of the electron density n_{e}, average electron energy 〈E_{e}〉, and the characteristic times of ionization, charge exchange, and ion confinement of stochastically heated, highly charged plasma. Multicomponent injection allows refining the n_{e}, 〈E_{e}〉 ranges, reducing experimental uncertainty. Na/K injection is presented as a demonstration. The 〈E_{e}〉 and n_{e} of a hydrogen discharge are found to be 600_{-300}^{+600}eV and 8_{-3}^{+8}×10^{11}cm^{-3}, respectively. The ionization, charge exchange, and confinement times of high charge state alkali ions are on the order of 1 ms-10 ms.