Beam Extraction System Research Articles

Gas mixing and double frequency operation of the permanent magnet quadrupole minimum-B electron cyclotron resonance ion source CUBE-ECRIS

CUBE-ECRIS is a recently commissioned permanent magnet electron cyclotron resonance (ECR) ion source developed at the university of Jyväskylä accelerator laboratory. The special features of the new ion source design include an unconventional quadrupole minimum-B magnetic field structure and a slit beam extraction system necessitated by the line-shaped plasma loss fluxes. Gas mixing and double frequency operation are widely used methods to optimize high charge state ion production of conventional ECR ion sources. The work presented here demonstrates the applicability of these methods for boosting the high charge state beam currents of argon, krypton and xenon extracted from CUBE-ECRIS. Oxygen and helium were used as mixing gases and microwave frequencies between 10 and 11 GHz were used for single and double frequency operation. Gas mixing has a strong impact on the high charge state beam currents. For example, the highest observed charge state increased from 15+ to 19+ for krypton and from 16+ to 23+ for xenon with oxygen gas mixing. Double frequency operation provides an additional performance improvement, for example the currents of argon 9+ and 11+ beams, produced with gas mixing, increased 30% and 100% in double frequency operation at the same total power.

Enhanced beam extraction system at the U-120M cyclotron

Since its commissioning in 1977, the U-120M cyclotron was initially equipped with a single pair of harmonic coils aimed at optimizing beam quality at lower accelerating radii. In 2022, a significant upgrade introduced a second pair of harmonic coils, positioned at a radius of approximately 50 cm, aligning with the outermost beam orbit. This addition is essential for the efficient extraction of positively accelerated ions and serves as the basis for the newly developed extraction system, which, unlike the original fully electrostatic system, consists of electrostatic deflectors and magnetic channels. This paper describes the design and installation of new harmonic coils in the accelerator vacuum chamber and presents a new extraction system using precession and linear integer resonance methods. Basic properties of these two extraction methods are given and finally, an evaluation of their advantages and limitations concerning their possible use in the cyclotron and an estimation of the efficiency of the new extraction system is made.

A very low energy ion beam extraction system design of the GTS ECR ion source at GANIL

The GTS ion source, operated at 14.5GHz, provides multiply charged heavy ion beams for the ARIBE facility at GANIL. The facility variety is limited by the efficiency of the extraction especially in the few keV/q domain. In order to improve the ion source, the extraction system was upgraded numerically using IBSimu. The shape of the plasma and the puller electrodes was changed. It causes the increase of the electric field near the plasma meniscus and allows the use of lower extraction voltages at constant total ion beam current. The required beam parameters were taken from the experimental data. The opportunity of effective low energy beam formation (at a few keV/q or several hundreds eV/q beam energy) was studied. The high current and low energy ion beam production will provide new possibilities for ARIBE facility users.

Numerical Simulation of Beam-Extraction System and Grid Electrostatic Lens for I-4 Linear Accelerator

Numerical Simulation of Beam-Extraction System and Grid Electrostatic Lens for I-4 Linear Accelerator

Benchmarking of the NCrystal SANS Plugin for Nanodiamonds

Nanodiamonds have attracted attention in recent years for their exceptional albedo of slow neutrons. Several theoretical models have been proposed to compute the total elastic cross section. However, these models neglect the relatively complex internal structure and chemical composition of the diamond nanoparticles, relying often on the monodisperse structureless spheres approximation. In this work, we explore the possibility of adding the small-angle neutron scattering (SANS) process for nanodiamonds to NCrystal, a library that enables calculations for Monte Carlo simulations of neutrons in polycrystalline materials and powders. This approach aims to describe the scattering process also at neutron wavelengths below the diamond Bragg cutoff where simple models usually struggle. The extension relies on modeling the SANS process through the fitting of experimental data as well as theoretical inputs. The code can then be coupled with an existing simulation framework, such as McStas, and benchmarked in different setups. We tested the plugin for two properties of diamond powder nanoparticles: the backward reflection of very cold neutrons and the quasispecular reflections of cold neutrons. The validation of this simulation tool is intended to pave the way for the design of the beam extraction system for a future high-intensity cold neutron moderator at the European Spallation Source.

Optimization of an Ecr Ion Source Beam Extraction and Formation System

Optimization of an Ecr Ion Source Beam Extraction and Formation System

Simulation and optimization of a miniaturized ion source for a neutron tube

A miniaturized Penning ion source, capable of generating a milliampere ${\mathrm{H}}^{+}$ beam with low anode power supply and low gas consumption, was produced and tested for neutron tubes. For a better understanding and optimization of the Penning ion source, magnetic field, beam extraction system, and plasma simulations were conducted to research the optimization of the Penning ion source. The distance between the two cathodes is optimized based on the plasma simulations. Based on the optimization of the magnetic field, extraction system, and the distance of the cathodes, the extraction current of the Penning source had been increased from 1.21 to 1.72 mA, and the ${\mathrm{H}}^{+}$ ratio had been increased from 36% to 42.3%.

Simulation of beam extraction and space charge effect in an electromagnetic isotope separator

Space charge effect of intense ion beam has critical influence on separation efficiency in the electromagnetic isotope separator. In this paper, a ribbon beam extraction system with slit electrodes for an electromagnetic isotope separator was designed and studied. The extracted beam currents were varied from 10 to 40 mA and the corresponding extracted beam energies were 40 keV and 100 keV respectively. The simulated output beam density distributions were used in the subsequent multi species particle transmission simulation with the space charge effect included. The separated isotope beam spot distributions at the focal plane were simulated under different space charge compensation factors and thus the optimum operation gas pressures in vacuum box were roughly estimated. For the case of high intensity and high power isotope beam collection, an isotope collector with a deceleration electrode was proposed to mitigate the effect of high power beam bombardment and the resultant temperature rising on the collector surface.

Design and simulation of the high efficiency ion source for Damavand NBI heating system

Neutral beam injection (NBI) is known as one of the important methods of plasma auxiliary heating and current drive in fusion reactors. Optimization of the ion sources, as one of the main components of NBI systems, with high current and minimum divergence, can be very effective in order to reach more optimal dimensions of NBI systems. A high efficiency ion source designed using a helicon plasma source for neutral beam injection system (NBI) of Damavand Tokamak. The extraction system has the ability to extract a positive hydrogen ion beam with the current and voltage of 7A and 4.5 kV, respectively. In this paper, an ion source with optimized helicon plasma and optimized beam extraction system is developed using the COMSOL software. All parameters, including RF power, magnetic field, gas pressure, antenna length, and RF frequency, for the production of helicon plasma and ion beam extraction system with optimal geometry are investigated in the most effective way, in order to reduce the beam divergence and beam current increment. Finally, the helicon plasma with density of 4.12×1018m−3, electron temperature of 2.8eV and hydrogen beam extraction system consists of three Accel-Decel grid, each grid with 280 apertures of 3.5mm diameter, has been designed for neutral beam injection system of Damavand Tokamak. This ion production system has an extractor grid with very large transparency (60%) and the minimum single beamlet divergence of 27 mrad.

Optimization of transverse emittance for RF-driven negative hydrogen ion source developed at China Spallation Neutron Source.

The China Spallation Neutron Source project Phase-II aims to deliver 500 kW beam power to the spallation target. To meet the beam power requirement, an RF-driven negative hydrogen ion source with an external-antenna has been developed. In order to optimize the beam transmission through the radio frequency quadrupole and the downstream linac, the low energy beam transport line needs to be carefully studied and the transverse emittance is focused in this paper. With computational simulation and experimental verification, the emittance growth caused by nonlinear magnetic fields of the solenoid and the residual magnetic fields at the measuring position has been carefully analyzed. The measurement uncertainty of the double-slit scanner has also been quantitatively estimated. Using the same plasma-beam boundary setting, the beam extraction system is also optimized with particle tracking simulation in CST PARTICLE STUDIO.

Improvement of the Efficiency and Beam Quality of the TRIUMF Charge State Booster

An Electron Cyclotron Resonance Ion Source is used as the charge state booster (CSB) at the Isotope Separator and Accelerator facility (ISAC) of TRIUMF. Since its commissioning in 2010, the source has been used to charge breed radioactive ions ranging from potassium to erbium operating in single-frequency heating mode. Under this regime, the single charge state efficiency of the booster was measured up to 6 % for noble gases and the maximum charge state of Cesium that can be measured is 27+. The rf system of the source was recently upgraded to implement the two-frequency heating using a single waveguide. Preliminary operation of the booster in a two-frequency heating mode shifted the maximum charge state of Cesium that can be measured to 30+. Another point of improvement that is being addressed is the beam extraction system of the booster. A quadrupole scan technique using a thick lens approach has been developed to measure the emittance of the extracted beam and to analyze the quality of the extraction system. Overall, the system of the CSB is currently being optimized in preparation for the detailed determination of the effect of the two-frequency heating on the beam output.

Testing of the Ti foil with TiN coating as an exit window of a pulsed electron accelerator

Increasing the efficiency of electron beam extraction from a vacuum diode is an urgent problem for the practical use of accelerators. In the general case, the given problem is reduced to decreasing the mass thickness (g/cm2) of the exit window membrane while ensuring sufficient mechanical properties. The paper presents the results of testing an exit window 85 mm in diameter with a 25 μm Ti membrane and a 0.8 μm TiN coating. When tested, the coated membrane exhibited mechanical characteristics comparable to those of a 60 μm Ti membrane, which deteriorated upon repeated pumpings of the accelerator chamber volume due to the appearance of cracks in the coating. The energy loss of the electron beam in the exit window of the accelerator was decreased by 18%, as compared to the Ti 60 μm membrane. The use of a 25 μm Ti membrane with a 0.8 μm TiN coating provided 16 J per pulse energy output of more than 104 pulses of the electron beam (50–275 keV) with a repetition rate of 1–10 pulses per second. The obtained results will be used to further improve the electron beam extraction systems in the field of high-pressure applications.

Experiments on intense ion beam formation with an inhomogeneous electric field

The high efficiency of a new ion beam extraction system with a strongly inhomogeneous electric field has been experimentally demonstrated. Previously, this approach was proposed and analysed numerically by the authors. The experiment was carried out using a pulsed high-current electron-cyclotron resonance (ECR) ion source SMIS 37 with high frequency (37.5 GHz) and high power (100 kW) microwave plasma heating. The accelerating field strength is increased (when compared to a flat or a quasi-pierced geometry) in the plasma meniscus region due to its inhomogeneity. It allows for the increase of the ion acceleration rate and for expansion of the available range of current densities with effective ion beam formation. The experiment demonstrated the main advantages of this approach, such as: a significant decrease in the optimal accelerating voltage for certain values of current density; a possibility of ion beam formation with previously inaccessible current densities; a significant decrease in the ion flux to the puller in non-optimal modes of ion beam formation. Proton beams with a current density of up to 1.1 A cm−2 were obtained for the first time with an ECR ion source.

Simulation of Penning ion source with optimized beam extraction system for tagged neutron tube

The magnetic field structure of the Penning ion source has been optimized with the use of permanent magnets. The ion source has been designed for small sealed tagged neutron tube. By using CST Studio Suite, the magnetic field profile inside the ion source was simulated and a variety of magnetic system was designed to improve the magnetic field uniformity of the Penning ion source and to increase the neutron yield. And the simulation results were compared with the experimental data to verify the correctness of the model. A new type of ion focusing system was devised by using the characteristics of conducting magnetic and consolidating magnetic of different metallic materials. There is more uniform magnetic field distribution and less material for the structure of 6-ring magnets placed outer anode than the structure of cylindrical magnet below the cathode. Stainless steel is selected as the material of the new extraction system after comparing the magnetic relative permeability of several materials. The new system has obvious focusing effect on the ion beam. It is also easy to obtain a small beam spot with 1 mm radius suitable for the tagged neutron tube and the extraction electrode voltage gets lower than original voltage. The results can provide reference for the improvement of the tagged neutron tube.

Plasma lens-based beam extraction and removal system for plasma wakefield acceleration experiments

Plasma Wakefield Acceleration represents one of the most promising techniques able to overcome the limits of conventional RF technology and make possible the development of compact accelerators. With respect to the laser-driven schemes, the beam-driven scenario is not limited by diffraction and dephasing issues, thus it allows to achieve larger acceleration lengths. One of the most prominent drawback, conversely, occurs at the end of the acceleration process and consists of removing the depleted high-charge driver while preserving the main features (emittance and peak current) of the accelerated witness bunch. Here we present a theoretical study demonstrating the possibility to reach these goals by using an innovative system consisting of an array of beam collimators and discharge-capillaries operating as active-plasma lenses. Such a system allows to extract and transport the accelerated and highly divergent witness bunch and, at the same time, provides for the removal of the driver. The study is completed by a set of numerical simulations conducted for different beam configurations. The physics of the interaction of particles with collimator is also investigated.

Optimization Study of the IBR-2 Reactor

The article considers the neutronics aspect of the IBR-2 reactor optimization: whether it is possible in theory to create an IBR-2-type reactor with a neutron flux in beams above the existing 0.5 × 1013 n/(cm2 s). The calculations have shown that the thermal neutron flux theoretically can be increased to (2.0−2.5) × 1013 n/(cm2 s), but only with a complete change in the reactor design: reducing the core volume, replacing the fuel type with a denser one, and changing the beam extraction system from radial to tangential. The technical implementation of these requirements is currently a challenge.

Atom beam emersion from hot cavity laser ion sources

Ion sources exploiting laser resonance ionization offer efficient and element-selective radioactive ion beam production at the leading isotope separation on-line facilities worldwide. Most commonly, laser resonance ionization takes place inside a resistively heated atomizer tube directly coupled to the production target, where the element of interest is evaporated and provided as atomic vapor. While naturally the majority of atoms is ionized inside this hot cavity, a fraction of the neutrals effuses towards the high voltage beam extraction system of the subsequent mass separator.We report on several systematic investigations on this phenomenon regarding its significance and implications on the operation of resonance ionization laser ion sources. Experiments suggest a less sharply directed atom cone than expected from theoretical model, up to a lateral opening angle of 45°. Inside the tubular volume defined by the laser beam diameter around the central axis behind the source exit, more than 90% of potentially ionizable atoms are found within the first 2 cm. Geometrical constraints for the construction of devices based on ionization in the effusing atom beam directly downstream of the hot cavity are derived, and causes for cross-mass beam contamination are identified. Counter measures using laser repetition rate synchronized beam gating by fast electrostatic beam deflection to overcome these problems are presented.

A new tungsten wire calorimeter for the negative ion source testbed BATMAN Upgrade

Within the framework of the ion source development for the ITER and DEMO Neutral Beam Injection (NBI) systems, IPP Garching has recently upgraded the radiofrequency-driven negative ion source testbed BATMAN. One of the requirements for the ITER NBI system is to produce a beam power density homogeneity above 90% over its large beam size extracted from an ion source of 1 × 2 m2. The beam uniformity is going to be investigated, on a smaller scale, in BATMAN Upgrade with the new ITER-like beam optics. The testbed is equipped with several beam diagnostic tools to measure beam power, uniformity and divergence. A new tungsten wire calorimeter (TWC) has recently been developed to characterize the beam quantitatively and with an improved spatial and temporal resolution. The TWC consists of an array of thin tungsten wires with a diameter of 0.3 mm, placed in the beam path. The wires are heated by the beam up to 3000 °C and emit visible light, which is observed by an optical camera. While the existing TWC provides a qualitative impression of beam power characteristics and is placed at a distance of almost 2 m from the beam extraction system, the new TWC is positioned only 19 cm downstream from the extraction system and allows observation of the single beamlets for the first time in this testbed. In order to determine the correlation between the pixel intensity measured by the camera and the power density impinging on the wires, one wire is equipped with an ohmic heating system which allows heating up the wire with a known power, thus enabling calibration of the diagnostic tool.In this paper the design, including FEM simulations of the wire thermal behavior, manufacturing and installation of the new TWC inside the BATMAN Upgrade testbed are described and the first, very promising, observations of beamlet intensities are presented.

Development of a variable-energy, high-intensity, pulsed-mode ion source for low-energy nuclear astrophysics studies.

The primary challenge in directly measuring nuclear reaction rates near stellar energies is their small cross sections. The signal-to-background ratio in these complex experiments can be significantly improved by employing high-current (mA-range) beams and novel detection techniques. Therefore, the electron cyclotron resonance ion source at the Laboratory for Experimental Nuclear Astrophysics underwent a complete upgrade of its acceleration column and microwave system to obtain high-intensity, pulsed proton beams. The new column uses a compression design with O-ring seals for vacuum integrity. Its voltage gradient between electrode sections is produced by the parallel resistance of channels of chilled, deionized water. It also incorporates alternating, transverse magnetic fields for electron suppression and an axially adjustable beam extraction system. Following this upgrade, the operational bremsstrahlung radiation levels and high-voltage stability of the source were vastly improved, over 3.5 mA of target beam current was achieved, and an order-of-magnitude increase in normalized brightness was measured. Beam optics calculations, structural design, and further performance results for this source are presented.

H[formula omitted] extraction systems for CERN’s Linac4 H[formula omitted] ion source

Linac4 is a 160MeV linear H− accelerator at CERN. It is an essential part of the beam luminosity upgrade of the Large Hadron Collider (LHC) and will be the primary injector into the chain of circular accelerators. It aims at increasing the beam brightness by a factor of 2, when compared to the currently used 50MeV linear proton accelerator, Linac2.Linac4’s ion source is a cesiated RF-plasma H− ion source. Several beam extraction systems were designed for H− beams of 45keV energy, 50 mA intensity and an electron to H− ratio smaller than 5. The goal was to extract a beam with an rms-emittance of 0.25πmmmrad.One of the main challenges in designing an H− extraction system is dumping of the co-extracted electrons. Separating the electrons from the negative ions as early as possible reduces space-charge induced emittance-growth. However, a strong magnetic field close to the extraction might cause unnecessary strong deflection in a region of low beam energy. For this purpose a novel magnetic configuration was designed using a magnetic shield between the magnetic fields of the source and the electron dump, which conserves the filter field strength to keep the electron to H− ratio low and effectively dumps the co-extracted electrons. Magnetic configuration and beam trajectories were calculated using the TOSCA Opera 3D code and IBSimu, respectively. Three extraction systems will be discussed in terms of electron dumping efficiency, emittance and transport through the extraction system and LEBT to the RFQ and compared to the simulations.An improved emittance conservation through the extraction system and LEBT is predicted and further design improvements are proposed. Measurements show that the novel electron dump successfully traps the co-extracted electrons.