Magnetic Ion Source Research Articles

Design of ASTERICS: A Superconducting 28 GHz ECR Ion Source Magnet for GANIL

In the framework of the NEWGAIN project, which aims to build a second injector with a mass to charge-state ratio A/q=7 for the SPIRAL2 linear accelerator at GANIL, CEA is developing in collaboration with LPSC and GANIL a new superconducting 28 GHz ECR Ion Source Magnet named ASTERICS. The magnetic design is based on an advanced concept of the VENUS ECR ion source operating at Berkeley and the FRIB source under commisionning at MSU. The ion source superconducting magnet consists of a sextupole inside three solenoids to confine the plasma and a shell-based support structure to apply a preload to the sextupole coils. The confinement coils will be made in Nb-Ti and will be operated at 4.2 K. The cryogenic environment will be ensured by liquid helium thermosiphon closed loop thanks to six in-situ cryocoolers. Specific HTS current leads are being designed to power the magnet. A cold integrated He buffer will also allow He almost-lossless quenches. The preliminary design choices of the ASTERICS superconducting magnet are presented here from the magnetic, mechanical and protection design to the cryogenic definition emphasizing the global approach used to obtain the final magnet configuration.

The magnetic field design of a solenoid for the cold-cathode Penning ion source of a miniature neutron tube

A high-yield and beam-stable neutron tube can be applied in many fields. It is of great significance to the optimal external magnetic field intensity of the cold-cathode Penning ion source (PIS) and precisely controls the movement of deuterium (D), tritium (T) ions and electrons in the source of the neutron tubes. A cold-cathode PIS is designed based on the solenoidal magnetic field to obtain better uniformity of the magnetic field and higher yield of the neutron tube. The degree of magnetic field uniformity among the magnetic block, double magnetic rings and solenoidal ion sources is compared using finite element simulation methods. Using drift diffusion approximation and a magnetic field coupling method, the plasma distribution of hydrogen and the relationship between plasma density and magnetic field intensity at 0.06 Pa pressure and a solenoid magnetic field are obtained. The results show that the solenoidal ion source has the most uniform magnetic field distribution. The optimum magnetic field strength of about 0.1 T is obtained in the ion source at an excitation voltage of 1 V. The maximum average number density of monatomic hydrogen ions (H+) is 1 × 108 m−3, and an ion-beam current of about 14.51 μA is formed under the −5000 V extraction field. The study of the solenoidal magnetic field contributes to the understanding of the particle dynamics within the PIS and provides a reference for the further improvement of the source performance of the neutron tube in the future.

The Magnetic Center Alignment Based on FECR Superconducting Ion-Source Magnet After Cryostat Installation

IMP (Institute of Modern Physics, Chinese Academy of Science) developed the FECR (Fourth Generation ECR Ion-Source) superconducting magnet, which is made up of a sextupole magnet and four solenoid magnets. These component magnets are required to be installed and aligned on the same mechanical axis. After loading the ion-source magnet into the cryostat, we set up an adjustment device to rectify the location. For the alignment of two types of coils, two separate measurement methods are used. The rotating coil is used to measure sextupole offset, while the rotating Hall sensor is used to measure solenoid offset. Both measurement probes are mechanically connected to the cryostat's warm bore. The position of the magnet constitution will be adjusted several times until the magnetic axis of the FECR magnet and the mechanical axis of the cryostat warm bore coincides to a satisfactory degree.

Main magnetic focus ion source: Device with high electron current density

We discuss recent experiments performed with an upgraded version of the main magnetic focus ion source (MaMFIS) at the Joint Institute for Nuclear Research in Dubna. The device operates in the range of electron beam energies extended up to 40 keV. The achieved electron current densities are of the order of 10 kA cm−2. This assessment is consistent both with the very short ionization time and with the utmost ionization degree of the produced highly charged ions. Due to its high efficiency, the MaMFIS technology is especially promising for ionization of short-lived radionuclides and heavy elements. A new scheme for charge breeding is proposed.

Negative hydrogen ion dynamics inside the plasma volume of a linear device: Estimates from particle-in-cell calculations

Negative hydrogen or deuterium ions are the precursor particles used to generate a high power beam of neutrals in order to heat the tokamak plasma core of magnetic fusion devices, inject current, and to some extent control instabilities. In the case of ITER, for instance, the negative ions are produced inside a high power large volume low-pressure tandem type magnetized ion source and extracted toward an electrostatic accelerator which accelerates them to 1 MeV before entering a neutralizer converting the ions into a neutral beam. This so-called neutral beam injector relies on the production of negative ions on the surface facing the plasma of the ion source extraction electrode. The latter is covered by a cesium layer in order to increase the negative ion yield. The use of cesium is currently an issue as it may diffuse outside of the source and induce secondary particle production or voltage breakdowns inside the accelerator vessel requiring a regular maintenance in a nuclear environment. In this work, we analyze numerically with a 2.5D particle-in-cell model the production rate and transport of negative ions in a linear device used as an ion source. The negative ions are generated via a dissociative attachment process with a hydrogen molecule in the volume of a magnetized cesium-free plasma. The linear device in the model has a large aspect ratio with a radius of 5 and a length of 100 cm and the magnetic field strength ranges from 100 to 400 G. We show that the shape and depth of the plasma potential profile may be controlled by biasing the end-plates which in turn strongly influence the residence time of the electrons and hence the negative ion yield. We observe the formation of large-scale rotating structures when the positive ions become magnetized with a rotation velocity in the kHz range.

Performance Test of a Duoplasmatron: Dipole- Magnet Scanning and Detection of Carbon Beam

A negative carbon-ion source has been designed and tested at the Dongguk University accelerator mass-spectrometer facility in Korea. The beam-extraction conditions in the ion-source test stand were determined experimentally. Negative carbon-ion beam transport using a dipole magnet for separation was also investigated. Negative carbon was extracted using a 2.5 standard cubic centimeters per minute (sccm) CO2 flow at a −30.0 kV high voltage applied to the plasma electrode. The applied arc current, ion-source magnet could adjust various conditions, and dipole magnet could produce fields up to 5000 G. The effects of various operating conditions and geometrical configurations on beam transport were evaluated in this study.

Generation of focusing ion beams by magnetized electron sheath acceleration

We present the first 3D fully kinetic simulations of laser driven sheath-based ion acceleration with a kilotesla-level applied magnetic field. The application of a strong magnetic field significantly and beneficially alters sheath based ion acceleration and creates two distinct stages in the acceleration process associated with the time-evolving magnetization of the hot electron sheath. The first stage delivers dramatically enhanced acceleration, and the second reverses the typical outward-directed topology of the sheath electric field into a focusing configuration. The net result is a focusing, magnetic field-directed ion source of multiple species with strongly enhanced energy and number. The predicted improvements in ion source characteristics are desirable for applications and suggest a route to experimentally confirm magnetization-related effects in the high energy density regime. We additionally perform a comparison between 2D and 3D simulation geometry, on which basis we predict the feasibility of observing magnetic field effects under experimentally relevant conditions.

Mechanical Study of a Superconducting 28-GHz Ion Source Magnet for FRIB

The superconducting electron cyclotron resonance (ECR) source magnet for the facility for rare isotope beams at Michigan State University was designed and built by the Superconducting Magnet Group at Lawrence Berkeley National Laboratory (LBNL) in 2017. The 28 GHz NbTi ion source magnet features a sextupole-in-solenoids configuration which is comparable to the VENUS ECR magnet operated at LBNL. However, the mechanical design of this magnet utilizes a shell-based support structure which allows fine adjustments to the sextupole preload and reversibility of the magnet assembly process. The magnet has been assembled and tested to operational currents at LBNL. This paper describes the mechanical analyses performed to estimate the sextupole's and solenoids' preloads. We will report on the 3-D finite element analysis during room temperature assembly, cool-down, and magnet excitation, and then describe the magnet preload operations. Finally, we will describe the performance of the support structure during the quench training.

Test Results for a Superconducting 28-GHz Ion Source Magnet for FRIB

The superconducting ECR source magnet for the Facility for Rare Isotope Beams at Michigan State University was designed and built by the Superconducting Magnet Group at Lawrence Berkeley National Laboratory (LBNL). The 28-GHz NbTi ion source magnet features a sextupole-in-solenoids configuration, which is comparable to the VENUS ECR magnet operated at LBNL. A shell-based support structure using bladders and keys has been incorporated into the design to allow for adjustments of the preload and reversibility of the magnet assembly process. The magnet has been assembled and successfully tested to operational currents at LBNL. This paper describes the basic design of the magnet and the passive quench protection system. The test results are also presented, including the quench behavior of the magnet, the training performance, and the magnetic measurement results.

Duoplasmatron beam characteristic in an ion source test stand for an accelerator mass spectrometer

A gaseous ion source has been designed at Dongguk University accelerator mass spectrometer facility, Korea. Radiocarbon dating is conducted at this facility with a mini carbon dating system and a prototype ion source has been developed for a gas injection system for high-level 14C samples, which can decrease the precision of sample measurements for carbon dating. To improve the efficiency of carbon counting of gas samples, a gaseous ion source called a duoplasmatron has been installed in the prototype ion source test stand with low cost, easy maintenance, and direct gas discharge. It is necessary to verify the operation characteristics of the duoplasmatron of the ion source test stand with the beam characteristics to measure the beam current with various ion source parameters. The effects of the arc current, ion source magnet field, and extraction voltage on the beam current are presented in this paper.

Universal main magnetic focus ion source for production of highly charged ions

A novel room-temperature compact ion source has been developed for the efficient production of atomic ions by means of an electron beam with energy Ee and current density je controllable within wide ranges (100eV ≲Ee≲60keV, 10A/cm2≲je≲20kA/cm2). In the first experiments, the X-ray emission of Ir64+ ions has been measured. Based on a combination of two different techniques, the device can operate both as conventional Electron Beam Ion Source/Trap and novel Main Magnetic Focus Ion Source. The tunable electron-optical system allows for realizing laminar and turbulent electron flows in a single experimental setup. The device is intended primarily for fundamental and applied research at standard university laboratories.

Universal main magnetic focus ion source: A new tool for laboratory research of astrophysics and Tokamak microplasma

A novel room-temperature ion source for the production of atomic ions in electron beam within wide ranges of electron energy and current density is developed. The device can operate both as conventional Electron Beam Ion Source/Trap (EBIS/T) and novel Main Magnetic Focus Ion Source. The ion source is suitable for generation of the low-, medium- and high-density microplasma in steady state, which can be employed for investigation of a wide range of physical problems in ordinary university laboratory, in particular, for microplasma simulations relevant to astrophysics and ITER reactor. For the electron beam characterized by the incident energy Ee = 10 keV, the current density je ∼ 20 kA/cm2 and the number density ne ∼ 2 × 1013 cm−3 were achieved experimentally. For Ee ∼ 60 keV, the value of electron number density ne ∼ 1014 cm−3 is feasible. The efficiency of the novel ion source for laboratory astrophysics significantly exceeds that of other existing warm and superconducting EBITs.

Singularity and Bohm criterion in hot positive ion species in the electronegative ion sources

The structure of the discharge for a magnetized electronegative ion source with two species of positive ions is investigated. The thermal motion of hot positive ions and the singularities involved with it are taken into account. By analytical solution of the neutral region, the location of the singular point and also the values of the plasma parameter such as electric potential and ion density at the singular point are obtained. A generalized Bohm criterion is recovered and discussed. In addition, for the non-neutral solution, the numerical method is used. In contrast with cold ion plasma, qualitative changes are observed. The parameter space region within which oscillations in the density and potential can be observed has been scanned and discussed. The space charge behavior in the vicinity of edge of the ion sources has also been discussed in detail.

Main magnetic focus ion source: Basic principles, theoretical predictions and experimental confirmations

It is proposed to produce highly charged ions in the local potential traps formed by the rippled electron beam in a focusing magnetic field. In this method, extremely high electron current densities can be attained on short length of the ion trap. The design of very compact ion sources of the new generation is presented. The computer simulations predict that for such ions as, for example, Ne8+ and Xe44+, the intensities of about 109 and 106 ions per second, respectively, can be obtained. The experiments with pilot example of the ion source confirm efficiency of the suggested method. The X-ray emission from Ir59+, Xe44+ and Ar16+ ions was detected. The control over depth of the local ion trap is shown to be feasible.

Main magnetic focus ion source with the radial extraction of ions

In the main magnetic focus ion source, atomic ions are produced in the local ion trap created by the rippled electron beam in focusing magnetic field. Here we present the novel modification of the room-temperature hand-size device, which allows the extraction of ions in the radial direction perpendicular to the electron beam across the magnetic field. The detected X-ray emission evidences the production of Ir44+ and Ar16+ ions. The ion source can operate as the ion trap for X-ray spectroscopy, as the ion source for the production of highly charged ions and also as the ion source of high brightness.

Main magnetic focus ion source, state-of-the-art technology for production of highly charged ions

SynopsisAn extremely efficient method for the production of highly charged ions has been realized. The method is based on the control of a local ion trap created by the rippled electron beam in a focusing magnetic field. Highly charged ions such as, for example, neon-like iridium can be prepared in the room-temperature hand-size device. This offers wide opportunities for laboratory studies of a variety of physical problems.

Design of a Superconducting 28 GHz Ion Source Magnet for FRIB Using a Shell-Based Support Structure

The Superconducting Magnet Program at the Lawrence Berkeley National Laboratory (LBNL) is completing the design of a 28 GHz NbTi ion source magnet for the Facility for Rare Isotope Beams (FRIB). The design parameters are based on the parameters of the ECR ion source VENUS in operation at LBNL since 2002 featuring a sextupole-in-solenoids configuration. Whereas most of the magnet components (such as conductor, magnetic design, protection scheme) remain very similar to the VENUS magnet components, the support structure of the FRIB ion source uses a different concept. A shell-based support structure using bladders and keys is implemented in the design allowing fine tuning of the sextupole preload and reversibility of the magnet assembly process. As part of the design work, conductor insulation scheme, coil fabrication processes and assembly procedures are also explored to optimize performance. We present the main features of the design emphasizing the integrated design approach used at LBNL to achieve this result.

Application of evaporative cooling technology in super-high power density magnet

Evaporative cooling technology utilizes phase-change heat transfer mode to achieve the cooling for heating equipment. The heat transfer capacity of evaporative cooling technology is far more than air or water cooling technology. The Electron Cyclotron Resonance ion source magnet is a typical super-high power density magnet, and the evaporative cooling technology is an ideal cooling method for the coils of magnet. In this paper we show the structure and process of coils and the special design of flow channels of coolant for an experiment magnet model. Additionally, the heat transfer circulation is presented and analyzed. By the finite element method, the flow channels are optimized to rationally allocate coolant and to reduce the temperature of coils. For the experiment model, the current density of copper wire of coils is 19 A/mm(2), and the coil-windows current density is larger than 12 A/mm(2). The max temperature of coils is below 80 °C, and the total heat is about 200 kW.

High-efficiency cross-beam magnetic electron-impact source for improved miniature Mattauch-Herzog mass spectrometer performance

We describe a newly designed cross-beam magnetic electron-impact ion source (CBM-EI). We demonstrate its superiority in comparison with a conventional source (CB-EI) when used with a commercial miniature sector-field-type, non-scanning mass spectrometer featuring Mattauch-Herzog geometry (MH-MS) and a permanent sector-field magnet. This paper clearly shows the value of the CBM-EI for enhancing MH-MS sensitivity. Unlike secondary electron-multiplier type detectors, the pixelated detector (IonCCD™) used in the commercial MH-MS has no gain. The MH-MS/IonCCD system is therefore challenged to compete with time-of-flight and quadrupole MS systems due to their higher ion transmissions and detector gains. Using the new CBM-EI, we demonstrate an instrument sensitivity increase of 20-fold to 100-fold relative to the CB-EI-equipped instrument. This remarkable signal increase by the simple addition of the magnet assembly arises from the magnet-induced gyromotion of the thermionic electrons, which vastly increases the effective path length of the electrons through the ionization region, and the collimated nature of the electron flux, which optimizes the ion transmission through the 100-μm object slit of the MH-MS. Some or all of the realized sensitivity increase may be exchanged for an increase in resolution and/or mass range through the use of a narrower object slit, or for a reduction in ion-source pressure to limit quenching. The CBM-EI should facilitate development of a differentially pumped ion source to extend the lifetime of the filament, especially in otherwise intractable applications associated with oxidizing and corrosive samples.

Upgrade of the extraction system of permanent magnet electron cyclotron resonance ion source

A set of new ion extraction electrodes have been designed for the permanent magnetic electron cyclotron resonance ion source at Peking University to improve beam quality and transmission. PBGUNS has been used to optimize the extraction electrodes and simulate the beam behavior at the extraction region. The experiments showed that with the new system, the beam half divergence angle can be less than 40 mrad and the normalized rms emittance is about 0.13pi mm mrad when the extracted current is 100 mA at 50 keV in pulse mode. The voltage of the suppression electrode has great effect on beam divergence. The effect of the microwave power and gas flow is also studied.