Space Charge Compensation Research Articles

Irradiation damage reduces alloy corrosion rate via oxide space charge compensation effects

Radiation effects in materials often compound and accelerate other detrimental phenomena such as embrittlement, oxidation and creep. However, irradiation can also decrease the oxidation rate, for instance with ZrNb alloys nuclear fuel cladding. In this study, we rationalize this observation on Zr-0.5Nb alloy by introducing a mechanism based on oxide space charge modification, resulting from irradiation enhanced Nb clustering. This mechanism is investigated using a multiscale approach: from the macroscale, to determine post-irradiation oxidation kinetics, to the atomic scale, using in-situ atom probe tomography sample oxidation, to observe elemental solute redistribution across the oxide/metal interface. The mechanism is further supported by high resolution transmission electron microscopy characterization and density functional theory calculations. A point defect model is proposed to account for oxide space charge effects and their changes under irradiation. This integrated, multiscale experimental and modeling approach challenges the current paradigm on irradiation effects and how they can potentially improve materials performance in extreme environments.

Status of the development of the electron lens for space charge compensation at GSI

At GSI a prototype electron lens for space charge (SC) compensation is currently being designed and main components as the RF-modulated electron gun are already under commissioning. The goal of this project is the (partial) compensation of SC forces within the ion beam by an overlapping electron beam. This may help to increase the intensity of primary beams, especially in the FAIR facility and potentially all large synchrotrons operated at the SC limit. For an effective SC compensation, the generated electron beam needs to follow the transverse and longitudinal beam profile of the ion bunch structure. The requirements are maximum currents of 10 A and grid modulation to cover a broad frequency range from 400 kHz to 1 MHz. The RF-modulated electron gun was designed and manufactured in the scope of the ARIES collaboration and is currently being tested at the E-Lens Lab of Goethe-University Frankfurt. A dedicated test bench was built for commissioning of the major e-lens components and diagnostics. In this contribution the overall set-up will be presented putting special emphasis on the beam dynamics and collector design as well as simulation results of the electron gun.

Tungsten Electron Emitter (TE2) with direct heated cathode by plasma stream

At Goethe-University, a novel concept of heating metallic cathodes is currently under investigation. In the scope of the ARIES collaboration WP16, an RF-modulated electron gun was developed and manufactured for application in electron lenses for space charge compensation. The goal of this project is to increase the intensity of primary beams, especially in low energy booster synchrotrons like the SIS18 and SIS100 at GSI/FAIR or the SPS at CERN. The gun was designed to produce electron currents of 10 A at extraction voltages of 30 kV. The tungsten electron emitter (TE2) and the grid electrode were designed and manufactured to be integrated in the extractor of the original volume type ion source. Significant effort was put into a robust and flexible design with highly reliable key components. The cathode is heated by a plasma stream generated in the plasma chamber of the source. Different heating options of the cathode are currently being studied. This contribution presents the working principles of the electron gun and first measurements results of cathode heating.

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.

Development of Combined-Function Multipole Permanent Magnet for High-Intensity Beam Transportation

Space charge compensation technology using higher-order multipole magnetic field components has been proposed to transport high-intensity charged particle beams. In order to realize this compensation technology in a limited beam line space, we devised a compact-size combined-function multipole permanent magnet. This magnet can produce two multipole components at the same location on the beam line. As a first step, we have designed a magnet to simultaneously generate a fixed-strength quadrupole and an adjustable-strength octupole component using permanent magnet materials. In this magnet model, the magnetic circuit consists of two groups of magnets. The first one is a group of trapezoidal magnets that occupy most of the space to generate a quadrupole magnetic field component with a magnitude of 30 T/m. The second one is an inner group of cylindrical magnets to generate an octupole component with a magnitude up to 17,000 T/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The intensity of the octupole component can be varied from 17,000 T/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to 0 T/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> by rotating these cylindrical magnets. This design was used to build a prototype model. In this model, the modulation mechanism was implemented to verify the feasibility of the modulation scheme for the octupole magnetic field strength.

Space charge compensation of positive ion beams used in magnetic fusion applications

A model is presented for space charge neutralisation of positive ion beams. The model is used for the particular case of the beams used for magnetic based fusion applications. The beams consist, after a gas neutraliser, of ions and atoms at different energies. Account is taken of the contribution of all beam components to ionization of the background gas. Consideration is also given to not only beam heating of the plasma generated by the beam, due to Coulomb collisions, but also to Coulomb heating by fast electrons produced in ionization by all beam particles and stripping of the neutral components. Two approximations are considered for the motion of the secondary ions out of the beam potential; a drift approximation and a freefall approximation. All the beam plasma parameters can be calculated. The model is applied to a typical extracted beam of deuterium ions of 120 kV, 60 A. It is found that these beams are very highly compensated and that beam plasma heating by the electrons produced is generally greater than that due to the beam ions.

Space Charge Compensation Study of High Intensity Ion Beams

The space charge effect is one of the key factors affecting ion beam transport and ion beam quality, especially for low-energy high-intensity ion beams. It can be partially compensated by the secondary electrons produced from the ionization of residual gas molecules in the beam pipe, and we are interested in the accurate value of this compensation degree. In this paper, we use a Three-grid Energy Analyzer (TEA) to measure the secondary ion energy distribution of the beam, which corresponds to the compensated beam potential distribution. To have accurate evaluation of the compensation degree, it is essential to adopt a proper transverse distribution of the ion beam, other than using the Gaussian theorem for uniform beams. The results of a space charge compensation degree study for singly charged ion beams with a 2.45GHz microwave ion source and for multiply charged ion beams with a high charge state ECR ion source are presented.

Target erosion process during broad ion beam sputtering using 3D modeling of ion trajectories

Understanding the distribution of particles sputtered from a target requires an appreciation of how ions impinge on the target. In pursuit of this goal, a fully three-dimensional model of the ion trajectories in a broad ion beam, assuming full space charge compensation, Gaussian emission characteristics of the beamlets, and beamlet deflection, was constructed. The modeled ion trajectories were used to simulate target erosion, enabling a comparison between the modeled erosion and the experimental erosion. The focus was on Ar and Xe ion species at ion energies in the range of 1.4–1.9 keV and on target materials, Si, Ta, and SiO2. Conclusions were drawn on the erosion process, the potential radial inhomogeneity of the plasma in the discharge chamber of the ion source, and on the opening angle of the emission characteristics of the beamlets. For the investigated process and an applied target tilt angle of 55°, the model verified that material-specific and angle-dependent ion–solid interaction mechanisms at the atomic level played only a minor role in the target’s macroscopic surface modification in the context of the qualitative distribution of the erosion profile. In contrast, the applied sputtering geometry played a significant role.

Radio-frequency biasing of ion acceleration grids with different propellants

In order to ensure the space charge compensation of the plume, conventional ion thrusters need an additional neutralizer to release electrons. When a radio-frequency (RF) voltage is applied across the grid system instead of a direct-current voltage, the simultaneous extraction of ions and electrons is achieved, thereby a neutralizer is not required. In this paper, based on the non-uniform distribution of neutral gas density calculated using the angular coefficient method, the particle-in-cell Monte Carlo collision method is used to thoroughly investigate the spatial and temporal dynamics of particles and the grid system performance for different propellants (argon, krypton and xenon) in such an RF grid system. RPA and E × B probe are employed to measure the ion flux distribution functions (IFDFs) of RF ion thruster with RF biasing, which are used to compare with the simulations. The simulated linear relationship between the self-bias voltage and the RF voltage amplitude and the multi-peak behavior of IFDF under low RF frequency conditions are comparable with the experimental data. The simulated IFDFs compare well with the experiments with the deviation of energy peak position less than 7% and 10% from those by RPA and E × B probe respectively, indicating the effectiveness of the used model. Simulations show the RF grid system is able to realize the extraction of electrons for all three propellants, so as to achieve the plume neutralization without an external neutralizer through the spatial and temporal oscillations of the beams. Electrons pass through the grid twice (extracted from the upstream, and backflow from the downstream), bringing two peaks of electron current to the accelerator grid in one period. The thrust-RF voltage curves for all three propellants show obvious slope transition, when the perveance limit is reached. The low-energy ions in the plume are mainly generated by the electron impact ionization processes for Xe while by CEX collisions for Ar. A larger ion current density of Xe on the downstream surface of the accelerator grid, which may lead to possibly more serious erosions of grids, is found compared with those of Kr and Ar. This is mainly contributed by the larger density of electron impact ionization generated ions of Xe in the downstream because Xe propellant has a larger electron density and ionization cross-section.

Space charge compensation of positive ion beams used in magnetic fusion applications

Abstract A model is presented for space charge neutralisation of positive ion beams. The model is used for the particular case of the beams used for magnetic based fusion applications. The beams consist, after a gas neutraliser, of ions and atoms at different energies. Account is taken of the contribution of all beam components to ionization of the background gas. Consideration is also given to not only beam heating of the plasma generated by the beam, due to Coulomb collisions, but also to Coulomb heating by fast electrons produced in ionization by all beam particles and stripping of the neutral components. Two approximations are considered for the motion of the secondary ions out of the beam potential; a drift approximation and a freefall approximation. All the beam plasma parameters can be calculated. The model is applied to a typical extracted beam of deuterium ions of 120kV,60A. It is found that these beams are very highly compensated and that beam plasma heating by the electrons produced is generally greater than that due to the beam ions.

Design and Beam Dynamics of the Electron Lens for Space Charge Compensation in SIS18

Design and Beam Dynamics of the Electron Lens for Space Charge Compensation in SIS18

Status of the Electron Lens for Space Charge Compensation in SIS18

Status of the Electron Lens for Space Charge Compensation in SIS18

Space charge compensation in air by counterion flow in 3D printed electrode structure

Electrospray ionization is commonly employed in modern mass spectrometry experiments for applications ranging from proteomics to environmental science and for fundamental studies of the chemical reactivity of ions. Despite the ubiquity of electrospray ionization, the total ion currents achieved using the technique remain relatively poor. While there are significant losses within the atmospheric pressure interface of the mass spectrometer (MS), many ions are lost due to space charge repulsion before ions and charged microdroplets enter the instrument. Space charge effects also limit the extent to which multiplexing of electrosprays can be used to increase ion currents. In this work, a flow of oppositely charged ions produced by atmospheric pressure chemical ionization (APCI) is employed to mitigate space charge effects in an analyte ion beam produced by nanoelectrospray ionization (nESI) as it is passed through an atmospheric pressure ion guide outside of a mass spectrometer. A decrease in the nESI beam width together with an increase in peak intensity is observed using an ion charge coupled detector in the presence of a counterflow of ions of the opposite charge. This result indicates that focusing occurs in the ion guide. Measurements of the space charge compensated ion beam using an Agilent Ultivo triple quadrupole mass spectrometer are correlated with changes in ion focusing, indicating that space charge compensation occurring before the ion beam enters the mass spectrometer can increase detected ion currents.

Optimization and analysis of a low-energy injector for high-intensity proton beam

Nanjing University and local government are pushing ahead with a high-intensity proton linac project called Nanjing Proton Source (NPS). At the first stage, a low-energy injector including an ion source and a low-energy beam transport (LEBT) will be set up to provide 65 keV, 28 mA proton beam. A duoplasmatron source with triode electrodes and a two-solenoid magnetic focusing LEBT is our favorable choice. As we know, the most important role of the LEBT is to minimize the emittance growth and optimize the Twiss parameters into radio frequency quadrupole (RFQ). This paper clearly introduces the optimization procedure that sets effective solenoid fields as two free parameters to search for the minimum rms emittance and the best-matched Twiss parameters by plotting contour maps. The detailed LEBT layout and solenoids design are completed based on the optimization. The robustness and stability of the LEBT are also analyzed in the end. The beam phase-space distribution and beam qualities are discussed under a range of space charge compensation degrees and different initial beam distribution types. Besides, the LEBT is designed to eliminate the vast majority of beam contaminants by using two collimators.

Beam physics research with the IOTA electron lens

The electron lens in the Fermilab Integrable Optics Test Accelerator (IOTA) will enable new research in nonlinear integrable optics, space-charge compensation, electron cooling, and the stability of intense beams. This research addresses scientific questions on high-brightness beams and operational challenges of high-power accelerators for nuclear and particle physics. We review the roles that electron lenses play in this field and the physical principles behind their applications. The design criteria and specifications for the IOTA storage ring and electron lens are then discussed. We conclude with a description of the components of the apparatus.

Pulsed electron lenses for space charge compensation in the FAIR synchrotrons

The FAIR heavy-ion synchrotrons SIS18 and SIS100 as part of the new FAIR accelerator facility at GSI will be operated at the “space charge limit” for light and heavy-ion beams. In SIS100 beam loss due to space charge induced resonance crossing should not exceed a few percent during the 1 s injection plateau. In order to further increase the beam intensities beyond the FAIR reference parameters, a new concept of (partial) space charge compensation by pulsed electron lenses is considered. We describe the general space charge compensation concept together with detailed simulations results. A prototype lens for SIS18 is presently under development and will be used to validate the concept. This new approach, aiming for mitigating the most prominent intensity limitation, should be applicable to many of the existing large scale proton and heavy-ion synchrotrons world wide.

Progress in space charge compensation using electron columns

Space charge compensation allows for increased beam current in linacs and RFQs. A novel application of space charge compensation, the electron column, offers the opportunity to realize more intense beams for high energy physics in circular accelerators. The concept relies on ionization of residual gas by the primary beam, with electromagnetic fields used to confine and shape the space charge neutralizing plasma. Prior experimental efforts and simulation studies are reviewed. They indicate that electron columns could be successfully deployed in accelerator rings. The experimental demonstration of an electron column is underway at the Integrable Optics Test Accelerator at Fermilab. The experiment, instrumentation, and physics program are discussed.

Self-consistent PIC simulations of ultimate space charge compensation with electron lenses

Further progress of fundamental particle physics requires high intensity and high brightness of accelerated proton and ion beams. This goal is essential for the FAIR hadron beams at GSI, for the neutrino production at the facilities such as Fermilab and JPARC, and for the Large Hadron Collider luminosity at CERN. One of the most formidable obstacles toward that goal is the beam's own space charge, whose forces cause beam emittance growth, losses and lifetime degradation. Typically, such effects become intolerable when the space charge tune-shift parameter Δ QSC exceeds ∼ - (0.25–0.5). To reduce these detrimental effects, it was suggested to use electron lenses to compensate the space charge forces. This paper reports on detailed particle-in-cell space charge and electron lens compensation simulations for extremely intense proton bunches whose space charge tune-shift parameter exceeds -1.0. Different scenarios were evaluated based on reduction in the emittance growth and particle loss at a 4σ aperture. We investigate phenomena and issues related to the focusing lattice errors, importance of the transverse and longitudinal matching of the electron beam profiles to the proton ones, and vary the strength and the number of the electron lenses distributed around a circular machine to optimize the reduction of harmful space charge effects.

McMillan electron lens in a system with space charge

Space charge (SC) forces of a circulating beam in a ring have both linear (defocusing) and nonlinear components, due to a nonuniform beam distribution. The linear component of SC forces produces a betatron tune shift, which is the largest for a zero-amplitude particle, while the nonlinear component produces an amplitude-dependent betatron tune spread. These SC effects are responsible for several undesirable phenomena in accelerators: emittance growth, particle losses, beam halo, etc. In this paper, we investigate the possibility to mitigate the distributed SC forces by a thin McMillan lens, providing an axially-symmetric kick, which is qualitatively opposite to the accumulated effect of beam's own SC. Experimentally, the proposed concept can be tested in Fermilab's IOTA ring. A thin McMillan lens can be implemented by a short (70) insertion of an electron beam with a specifically chosen density distribution in transverse directions. In this article, to test if McMillan lenses can reduce the tune spread induced by SC, we make several simulations with a 6-D particle tracking code, Synergia. We choose such beam and lattice parameters that the SC tune spread is roughly 0.5 and the emittance growth due to the half-integer resonance is clearly observed without the SC compensation. Then, we focus on reducing the emittance growth by adjusting the bare betatron tunes using the ring quadrupoles, and reducing the tune spread by the McMillan lenses. The results of reducing a large tune spread (≈ 0.5), reported here, are not perfect, but substantial. There is still room for further investigation. The simulations performed so far indicate that McMillan lenses can cope with an SC tune spread of ≈ 0.1 per lens.

Design of a compact, cryogen-free superconducting solenoid for the electron lens of the Fermilab Integrable Optics Test Accelerator (IOTA)

The proposed electron lens for Fermilab's Integrable Optics Test Accelerator (IOTA) will broaden its capabilities by enabling new research in nonlinear integrable optics, space-charge compensation, proton beam cooling, and more. The electron lens is based on a 5–10 keV, 1–2 A electron beam, shaped using a 0.7 m long, 0.8 T solenoidal magnetic field. A cryogen-free superconducting solenoid has been designed to provide this solenoidal field, taking into consideration the constraints on space, utilities, and infrastructure in the IOTA experimental hall. The solenoid is made of copper stabilized niobium-titanium conductor, conduction-cooled using 4 K closed-cycle cryocoolers. This paper describes the overall design of the solenoid encompassing its mechanical construction, current leads optimization, cryogenic thermal modeling that provides estimates of cooldown time and static/dynamic heat loads, and quench analysis.