bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatially resolved study of spokes in reactive HiPIMS discharge
Authors: Šlapanská Marta , Kroker Michael , Klein Peter , Hnilica Jaroslav , Vašina Petr
Published: April 2022

Understanding mechanisms behind the formation and propagation of ionisation zones, so-called spokes, have been highly important since the first observations in high power impulse magnetron sputtering discharges. To this day, however, a complete description is still lacking. This contribution gives an insight into the spokes in reactive Ar–N2 atmosphere using titanium target. The aim of this study is to describe not only global parameters of spokes such as their shape, length and propagation velocity but also provide a description of parameters evolving over the spoke, such as floating potential and spectral emission. The measurements of the latter clearly showed which species emission is most prominent and how it changes with transition from non-reactive argon discharge towards the discharge driven in a pure nitrogen atmosphere. Implications on the gas dynamics and discharge transitions are discussed.
Investigating CO2 streamer inception in repetitive pulsed discharges
Authors: Mirpour S , Nijdam S
Published: April 2022

In this study, we investigate the responsible species and processes involved in repetitive pulsed streamer inception in CO2. We applied a 10 kV high-voltage (HV) pulse with a repetition frequency of 10 Hz and pulse width of 1 ms to a pin electrode which is placed 160 mm apart from the grounded plane electrode. We measured the inception times by a photo-multiplier tube (delay between the rising edge of the HV pulse and the rising edge of the photo-multiplier waveform) for 600 high voltage cycles. We observed one peak in the histogram of inception times with a median of 1.2 μs. To identify the source of this peak, we applied a negative or positive low-voltage (LV) pulse before the main HV pulse to manipulate the leftover space charges. Three different phenomena are observed: (1) drift, (2) neutralization, and (3) ionization in the LV pulse. At low LV amplitude and pulse width, the peak starts to drift toward the faster and slower inception times under a positive and negative LV pulse, respectively. However, under the same LV pulse configuration for positive and negative LV pulse, the observed shift in inception times is not the same. We present a hypothesis to explain this asymmetry based on the difference of the detachment processes between air and CO2.
One-loop amplitudes in the worldline formalism
Authors: Edwards James P , Mata C Moctezuma , Schubert Christian
Published: April 2022

We summarize recent progress in applying the worldline formalism to the analytic calculation of one-loop N-point amplitudes. This string-inspired approach is well-adapted to avoiding some of the calculational inefficiencies of the standard Feynman diagram approach, most notably by providing master formulas that sum over diagrams differing only by the position of external legs and/or internal propagators. We illustrate the mathematical challenge involved with the low-energy limit of the N-photon amplitudes in scalar and spinor QED, and then present an algorithm that, in principle, solves this problem for the much more difficult case of the N-point amplitudes at full momentum in ϕ
3 theory. The method is based on the algebra of inverse derivatives in the Hilbert space of periodic functions orthogonal to the constant ones, in which the Bernoulli numbers and polynomials play a central role.
Effects of hydrostatic pressure and temperature on refractive index changes in tuned quantum dots under magnetic field
Authors: Chang Ceng , Li Xuechao , Duan Yiming , Zhao Zhuang , Zhang Liangcheng
Published: April 2022

The effects of external magnetic field, hydrostatic pressure, temperature and radius of the quantum dots (QDs) on refractive index changes (RICs) of tuned QDs are studied in detail theoretically. In the framework of effective mass approximation, energy levels and wave functions are derived. Simultaneously, the nonlinear RICs are obtained by compact-density-matrix approach and iterative method. Then, the numerical simulations show that under various constraint factors, the resonant peak position of RICs moves to high energy or low energy, that is, blue shift or red shift, and the peak value of RICs will also alter with the change of parameters.
Impact of viscous dissipation on the conjugate heat transfer between the walls of a porous microchannel
Authors: Monsivais I G , Méndez F , Lizardi J J , Ramos E A
Published: April 2022

In this work, the finite element method was used to study numerically the viscous dissipation that occurs when a Newtonian fluid circulates through a porous microchannel that operates as a heat sink, in which a constant heat flux is applied from the outer walls of the porous microchannel into the fluid. Taking into account that this is a conjugate problem, where the temperature fields of both the porous medium and the wall are unknown, there are two well-known asymptotic limits in the literature that allow us to obtain the solution for this problem: the first one is the thermally thick wall limit

γ

/

β

w

2

=
1

, which has been widely studied previously by other authors; the second one is the thermally thin wall limit

γ

/

β

w

2

=
25

, where the longitudinal effects of heat conduction in the microchannel wall are considerably more important than the ones occurring in the transverse direction. Therefore, in this study, we analyze the competition between these effects and viscous dissipation, as well as the influence that both have on the temperature profiles of the fluid and the wall. The results show that for Br ≥ 0.1, a notable temperature increase occurs in the system, which offers interesting results that have not been reported in the literature yet, because from χ = 0.6 (Br = 0.1), there is a higher temperature in the center of the microchannel than in the vicinity of the wall; that is, the fluid temperature is higher at η = 0 with respect to the temperature value at η = 1. This situation becomes more evident as the Brinkman number increases; for example, for Br = 1, the temperature in the center of the microchannel increases up to 23% with respect to the fluid temperature at the wall. Finally, the decrease of the Darcy number does not have a considerable effect on the temperature profiles.
A theoretical investigation of nonlinear optical and electronic molecular parameters of hexabutyloxytryphenylene and halogenated hexabutyloxytryphenylene molecules using density functional theory (DFT) for nonlinear device applications
Authors: Pal Bhavna , Mishra Mirtunjai , Singh Devendra , Kumar Devesh
Published: April 2022

In this work, we discuss the molecular properties of hexabutyloxytryphenylene (HAT4) and halogenated HAT4 using density functional theory (DFT) with B3LYP method and Pople basis set (6-31G, 6-31G*, 6-31G**) for the generation of non-linear optical and electronic parameters. Using DFT method, the dependence of electro-optical parameters of halogenated HAT4 such as dipole moment, mean polarizability, anisotropy in polarizability and hyperpolarizability along with global parameters such as ionization potential, electron affinity, electronegativity, chemical hardness and electrophilicity index on the halogens in the core of the considered molecules has been studied in this work. Further, the frontier molecular orbital analysis for pure HAT4 and halogenated HAT4 molecules has been carried out. The proposed study helps us to analyse the effect of halogenation on the linear, non-linear as well as thermodynamical properties of HAT4 molecules such as HOMO-LUMO gap, thermal energy, entropy and specific heat capacity. The effect of halogenation also leads to understand the modification of nonlinear parameters of HAT4 for the interaction of nonlinear fields.
The cavity method for minority games between arbitrageurs on financial markets
Authors: Ritmeester Tim , Meyer-Ortmanns Hildegard
Published: April 2022

We use the cavity method from statistical physics for analyzing the transient and stationary dynamics of a minority game that is played by agents performing market arbitrage. On the level of linear response the method allows to include the reaction of the market to individual actions of the agents as well as the reaction of the agents to individual information items of the market. This way we derive a self-consistent solution to the minority game. In particular we analyze the impact of general nonlinear price functions on the amount of arbitrage if noise from external fluctuations is present. We identify the conditions under which arbitrage gets reduced due to the presence of noise. When the cavity method is extended to time dependent response of the market price to previous actions of the agents, the individual contributions of noise can be pursued over different time scales in the transient dynamics until a stationary state is reached and when the stationary state is reached. The contributions are from external fluctuations in price and information and from noise due to the choice of strategies. The dynamics explains the time evolution of scores of the agents’ strategies: it changes from initially a random walk to non-Markovian dynamics and bounded excursions on an intermediate time scale to effectively random switching in the choice between strategies on long time scales. In contrast to the Curie–Weiss level of a mean-field approach, the market response included by the cavity method captures the realistic feature that the agents can have a preference for a certain choice of strategies without getting stuck to a single choice. The breakdown of the method in the phase transition region indicates possible market mechanisms leading to critical volatility and a possible regime shift.
Exact results for interacting hard rigid rotors on a d-dimensional lattice
Authors: Saryal Sushant , Dhar Deepak
Published: April 2022

We study the entropy of a set of identical hard objects, of general shape, with each object pivoted on the vertices of a d-dimensional regular lattice of lattice spacing a, but can have arbitrary orientations. When the pivoting point is situated asymmetrically on the object, we show that there is a range of lattice spacings a, where in any orientation, a particle can overlap with at most one of its neighbors. In this range, the entropy of the system of particles can be expressed exactly in terms of the grand partition function of coverings of the base lattice by dimers at a finite negative activity. The exact entropy in this range is fully determined by the second virial coefficient. Calculation of the partition function is also shown to be reducible to that of the same model with discretized orientations. We determine the exact functional form of the probability distribution function of orientations at a site. This depends on the density of dimers for the given activity in the dimer problem, which we determine by summing the corresponding Mayer series numerically. These results are verified by numerical simulations.
The evolution of creep curves of high impact polystyrene and polyurethane specimens after aging
Authors: Arutyunyan A R
Published: April 2022

Specimens of high impact polystyrene and polyurethane were studied for creep at room temperature and constant tensile force without aging and after aging according to various programs. For polyurethane specimens after aging, an increase in creep time for a given deformation by 3 times compared to specimens without aging is observed. For high impact polystyrene in the creep experiments after aging, a decrease of deformation by 6.5 times and the time to fracture by more than 24 times, compared with specimens without aging is shown. To describe the obtained experimental creep curves for polyurethane and polystyrene specimens without aging and after aging, modified versions of linear elastic–viscous models of Maxwell and Voigt written in the effective time scale are used. A good agreement between the theoretical and experimental creep curves is observed.
Examples of exact solutions to boundary value problems of the theory of elasticity for a truncated wedge
Authors: Kovalenko M D , Menshova I V , Kerzhaev A P , Yu G
Published: April 2022

The paper presents examples of exact solutions to boundary value problems of the theory of elasticity for a truncated wedge. The straight sides of the wedge are free, and normal stresses are given on its circular “end” (the tangential stresses are considered equal to zero). The solutions are sought in the form of expansions in Papkovich–Fadle eigenfunctions. The coefficients of the expansions are determined in a simple explicit form.
Investigation of mechanical properties and fracture surface of cylindrical specimens of Al 6101 alloy under static tension
Authors: Magomedova D K , Churakova A A , Gunderov D V
Published: April 2022

The data on the study of mechanical properties of cylindrical specimens of Al alloy 6101 in different states under static tension at room temperature are presented. The specimens were tested after natural aging, artificial aging, and ECAP. The surface of fractures of these specimens was also investigated using an electron microscope, and a chemical analysis of elements on the surface of fractures was carried out. Basing on the performed study, it can be concluded that alloy 6101 shows the highest strength (ultimate tensile strength 350 MPa) after ECAP treatment in UFG state. It was confirmed due to the chemical analysis that destruction pores in this material originate on particles of secondary phases based on impurity iron.
Stress analysis of composites with interfacial bridged cracks and damaged zones
Authors: Perelmuter M
Published: April 2022

Stress analysis of composite structures with bridged cracks and damaged zones is performed with the direct boundary integral equations method in axisymmetric formulation. It is assumed that: a) the crack faces interact in some zones behind of the cracks edges (bridged zones); b) these zones width can be comparable to the whole crack size; c) adjacent parts of the structure can be connected by mechanical ligaments (including interfaces ahead of cracks fronts) and the relative displacements of these parts can occur under the loading (these zones consider as damaged zones). The boundary element software to solve axisymmetric problems of elasticity with interfacial bridged cracks and damaged zones was developed. The results for different properties of composite materials and bonds are presented. Applications the bridged crack approach to modeling of cracks self-healing is remarked.
The role of intermediate structures in the combustion of high-energy condensed systems
Authors: Babuk V A , Budnyi N L , Nizyaev A A , Naryzhnyi S Yu , Kuklin D I
Published: April 2022

During the combustion of high-energy condensed systems, the formation of an intermediate structure - a skeleton layer, is possible, which has a significant effect on the combustion process. An experimental study was carried out to determine the nature of the effect of the curing of the binder on forming this structure. The article shows the specific role of the used hardener, polyethylene polyamine, presents the solutions for simulating the phenomena in the surface layer in the presence and absence of a skeleton layer, as well as shows the possibility of predicting the characteristics of the combustion process.
The influence of gasifier operating parameters on syngas composition of coal-fired power plant with CO2 capture
Authors: Sedacheva O V , Nesterova G A , Abaimov N A , Ryzhkov A F
Published: April 2022

This work investigated the influence of the operating parameters of the gasifier (pressure, temperature of the syngas at the outlet of the gasifier and the O2/CO2 ratio in the blast) on the composition of the syngas in relation to the Allam cycles and oxy-fuel IGCC. Thermodynamic modeling of the operation of Shell (Allam cycle) and MHI (oxy-fuel IGCC cycle) gasifiers by the entropy maximization method was carried out. For the Shell gasifier, a significant increase in methane concentration with an increase in pressure to 40 MPa has been revealed; it indicates the need to make changes to the syngas gas cleaning system. The optimal temperature at the outlet of the gasifier (1100°C) has been found for the MHI gasifier. At this temperature, there were high values of CO and H2, and, hence, the heating value of syngas. For both gasifiers, the most theoretically reasonable ratio of O2/CO2 in blast was 0.3, at which CO reached almost maximum values and decreased its growth rate.
Pyrolysis of boron-containing compositions upon exposure to radiant energy
Authors: Basalaev S A , Kuznetsov V T , Rashkovskiy S A
Published: April 2022

The article describes a method and a design of the experimental setup for determining the mass rate of pyrolysis of boron-containing compositions upon exposure to radiant energy and presents experimental data on the mass rate of pyrolysis of binary mixtures consisting of aluminum dodecaboride and polybutadiene binder SKDM-80 depending on the mass fraction of aluminum dodecaboride in the content and heat flux density. It is noted that the ratio of the mass rate of pyrolysis to the mass fraction of the binder in the sample for a given heat flux density depends weakly on the AlB12 content in the sample. This fact indicates that the presence of AlB12 in the mixture affects the sample heating intensity and the binder destruction rate and that AlB12 is carried away under the impact of outflowing gaseous products of the binder pyrolysis.
Improvement of Velocity Distribution Function Measurement of Hydrogen Atoms in ion Source Discharges
Authors: Tokai T , Bito K , Shimabukuro Y , Wada M
Published: April 2022

The efficiency of negative hydrogen (H-) ion surface production in an ion source should be highly dependent upon the velocity distribution function of neutral atomic hydrogen (H0) striking the plasm grid (PG). A system composed of forming an atom beam, rotating beam chopper, ionizer and pulse count unit has been constructed to measure H0 velocity distribution functions. The background noise due to stagnation of hydrogen gas in the region between the beam formation skimmer and the ion source PG was improved by inserting a flow reflection structure. The short life time of the secondary electron emission detector (SEM) was prolonged by properly setting the hydrogen ion trajectories from the ionizer to the the first dynode of the SEM. The system is running stably to record the velocity distribution function but statistical noise synchronized to the trigger pulse of the chopper must be removed before the measurment of change in H0 velocity distribution functions dependin upon the type of discharge.
Measurement of ionization, charge exchange and ion confinement times in charge breeder ECR ion sources with short pulse 1+ injection of metal ions
Authors: Luntinen M , Angot J , Tarvainen O , Toivanen V , Thuillier T , Koivisto H
Published: April 2022

The Consecutive Transients (CT) method is used for estimating the characteristic times of ionization, charge exchange and confinement within the plasma of a Charge Breeder Electron Cyclotron Resonance Ion Source (CB-ECRIS). The method reveals differences in the characteristic times between different source configurations, with K9+ charge breeding efficiencies of 8.9 % and 20.4 %, and allows qualitative explanation of the improved breeding efficiency. The increase in K9+ efficiency is accompanied by a decrease in ionization time for low charge states, a decrease of charge exchange time for high charge states, and an overall decrease of the ion confinement time, which increases non-linearly with the charge state. The charge exchange time exhibits a minimum near charge state K8+, indicating low neutral density near the plasma core. The CT-method yields a distribution of possible ne and (Ee) corresponding to the spatial distribution of different charge state ions. The results hint at a non-uniform plasma electron density and energy distribution as well as a nested-layer distribution for the ion populations — hot and dense plasma with high charge state ions near the plasma core.
CERN hadron sources: status and innovation overview
Authors: Wenander F
Published: April 2022

The CERN accelerator complex is served by several different types of hadron sources, producing both high- and low-intensity negative H- beams, highly charged positive stable ions, but also transforming low-charge radioactive ions to higher charges before post-acceleration. Apart from the operational sources, research and development is carried out at dedicated test stands for H- production and pre-acceleration, ECRIS oven experiments and general EBIS development. In this paper, we will report on the performance and the latest development related to the sources. Efforts to enhance the theoretical understanding of the source physics will be briefly reviewed.
Status and prospects of the 60 GHz SEISM ion source
Authors: Andre Thomas , Angot Julien , Baylac Maud , Dumont Pierre Olivier , Lamy Thierry , Sole Patrick , Thuillier Thomas , Debray Francois , Izotov Ivan , Skalyga Vadim
Published: April 2022

SEISM is a unique ECR ion source operating at a frequency of 60 GHz. The prototype is based on a simple magnetic geometry, the cusp, allowing the use of polyhelix coils (developed with LNCMI, Grenoble) to generate the closed ECR surface at 2.14T. The plasma is sustained by a high intensity HF pulse (up to 300kW). Previous experiments at LNCMI have successfully demonstrated the establishment of the nominal magnetic field and the extraction of ion beams with a current density up to 1 A cm-2. The presence of afterglow peaks was also observed, proving the existence of ion confinement in a CUSP ECR source. An experimental campaign is carried out in 2021 using a new transport line designed to improve the transmission of the beam to the new detectors. Short and long-term research plans are presented to transform this high current density into a high intensity ion beam that can be used for accelerators of the future.
Caesium Balance of the ISIS H Penning Ion Source
Authors: Tarvainen O , Faircloth D , Lawrie S , Sarmento T , Abel R , Macgregor J , Cahill C , Stanley T , Whitehead M , Wood T
Published: April 2022

We have developed a model predicting the equilibrium caesium coverage work function of the cathode (in eV) and the expected H- beam current (in arb. units) of the ISIS Penning ion source. The model is based on semi-empirical expressions for the cathode work function, negative ion surface ionization yield, and caesium adsorption and desorption rates. We compare the model predictions to experimental data with 760 μs discharge and 250 μs beam pulses. It is concluded that the ISIS Penning ion source operates near the optimum cathode work function in a wide range of caesium pressures and cathode temperatures. The model implies that long pulse operation of the source requires elevated Cs oven temperature and improved cathode cooling.
Plasma commissioning in a high power external RF-coil volume-type H- ion source
Authors: Lawrie S , Abel R , Faircloth D , Sarmento T , Speed J , Tarvainen O
Published: April 2022

A high power, high duty cycle, negative hydrogen ion source is in development at ISIS. It will operate in pure volume-production mode and is driven by a 52-turn RF-coil mounted external to the plasma chamber. A solid-state amplifier with a maximum output of 100 kW in 50 Hz, 1 ms pulses delivers RF power to the coil via an impedance-matching network. The amplifier has a relatively wide bandwidth, able to deliver full power from 1.8-4.0 MHz. This flexibility allowed straightforward commissioning of the matching network into an inductively-coupled plasma. Striking of the pulsed plasma is facilitated by a compact microwave ignition gun, requiring only 10 W of power at 2.45 GHz to deliver 1 mA seed pulses of electrons. Experiments have shown that it is vital to encapsulate the RF-coil properly to mitigate high voltage sparking. In addition, the location of the coil relative to the ion source’s permanent magnets has a critical effect on the ease of plasma ignition. The result of commissioning work is that a full duty-factor (50 Hz, 800 ^s) plasma has been achieved at nominal operating power (30 kW) and detailed optical studies have begun.
Numerical analysis of isotope effect in NIFS negative ion source
Authors: Kato Ryo , Hoshino Kazuo , Nakano Haruhisa , Shibata Takanori , Miyamoto Kenji , Iwanaka Kengo , Hayashi Katsuya , Hatayama Akiyoshi
Published: April 2022

Result of hydrogen (H) and deuterium (D) experiments done by NIFS research and development negative ion source (RNIS) demonstrated that the co-extracted electron current with the negative ions and the electron density in the driver region in the D experiment have been around three times higher than that in the H experiment. To investigate mechanism of this difference, electron transport simulation using 3D kinetic particle tracking model KEIO-MARC code has been modified and applied to analysis of the isotope effect in the NIFS negative ion source. Simulation result suggests that impacts of isotope effects of sheath potential drop, coulomb collisions, and some reactions of ground state molecules and ions on the electron density is not large to explain the experimental result of the increase in the electron density in the plasma.
H- beam emittance analysis in a multicusp ion source
Authors: George A , Kalvas T , Melanson S , Dehnel M , Broderick N G R
Published: April 2022

Emittance of the ion beam extracted from an ion source is dependent on the initial focusing action at the plasma sheath. The properties of the plasma sheath is further dependent on the local electric fields and charge densities around the sheath. Experiments are conducted for creating different sets of conditions around the plasma sheath in an H- multicusp filament ion source and the resulting emittance of the extracted H- ion beam is measured. Variation of beam emittance under different plasma densities, electrode voltages and gas flows are analysed.
Simulation of Beam Formation in the CERN Negative Ion Source for the Linac4 Accelerator
Authors: Vnuchenko A. , Lettry J. , Mochalskyy S. , Wünderlich D. , Fantz U. , Revel A. , Minea T.
Published: April 2022

Linac4 is the negative hydrogen ion (H-) injector of the CERN accelerator complex. Modelling of the beam formation is essential for optimizing the current and emittance of the H- ion source. We exploited the 3D PIC-Monte Carlo ONIX (Orsay Negative Ion eXtraction) code for studying H- beam formation processes in caesiated negative ion sources. The various geometries of the IS03 prototypes have been implemented into ONIX. The code, designed for neutral injector multi-aperture sources for fusion has been adapted to match the single-aperture extraction region of the Linac4 H- source. A plasma electrode designed to ensure radial metallic boundary conditions was produced and tested. The simulation results of the beam formation region at low plasma density to validate the functionality of the modified ONIX version are presented.
Comparison of ion source plasma responses to extraction grid bias between hydrogen and deuterium operations in NIFS-RNIS
Authors: Nakano H , Masaki S , Rattanawongnara E , Tsumori K , Ikeda K , Hamajima T , Nagaoka K , Osakabe M
Published: April 2022

An isotope effect of negative ion motion in plasma near a plasma grid (PG), which is a plasma-beam boundary grid, has been investigated in a negative hydrogen-ion source with the surface production process of the negative ion on the PG surface. Negative deuterium-ion (D-) density was higher than negative hydrogen-ion (H-) density in the condition without extraction-grid bias (V
egb) and approached the H- density in the condition with V
egb. Thus, the D- density responded stronger than the H- density to the V
egb. The density of the negative hydrogen-ion isotopes and the density response to the V
egb have been organized into respective identical trends by momenta of isotopes emitting from the PG. The Larmor motion can be a dominant mechanism of the negative ion transport from the PG to the plasma.
On the effect of biased surfaces in the vicinity of the large extraction area of the ELISE test facility
Authors: Yordanov D , Wunderlich D , Wimmer C , Fantz U
Published: April 2022

The ion source at the ELISE test facility is an intermediate step towards the operation of the ITER NBI source and it demonstrated fulfillment of the ITER NBI requirements for accelerated negative current density in hydrogen. However, in deuterium operation the co-extracted electron current density (je) is higher and much more unstable and limits the source performance. In the standard setup of ELISE, je is reduced by a positive potential applied to the plasma grid (PG) with respect to the source body and the bias plate (BP). To further reduce and stabilize je in deuterium, an alternative scheme by biasing the BP is investigated. Measurements of the BP currents and of the extracted currents, combined with probe diagnostics in the vicinity of the PG for short-pulse in deuterium operation are presented. Biasing the BP, leads to a change in the distribution of the plasma potential in front of the extraction area, affecting the charged particle fluxes towards the BP and the PG and a strong reduction of je.
Techniques to widen the operational space of SPIDER Radio Frequency driven plasma source
Authors: Casagrande R , Dan M , Maistrello A
Published: April 2022

SPIDER is the full-size prototype of the ion source of the ITER Neutral Beam Injectors, and is in operation since June 2018 as part of the ITER Neutral Beam Test Facility. The ion source is composed of 8 Radio Frequency drivers supplied by 4 RF oscillators, rated for operation at 1 MHz, for a total power of 800kW. This article presents a strategy for the selection of source biasing and of operating frequencies of the different RF generators to facilitate plasma initiation and to improve plasma stability. This operational strategy improved the plant reliability at high RF power in a broader range of operational conditions in SPIDER.
A 2D semi-analytical electromagnetic model for cylindrical ICP sources with Faraday shield
Authors: Chen P , Yang J , Zhou L , Zuo C , Li D , Chen D
Published: April 2022

Faraday shield(FS) is a metallic shield with slits through which electromagnetic energy is coupled into cylindrical ICP sources. Thus, the effect of FS on the RF field and power coupling is important. A 2D semi-analytical electromagnetic model considering both FS and plasma is proposed. The results compared to a 2D numerical model shows that the semi-analytical model is available in electromagnetic field calculations. It is found that both FS and plasma have no influence on the magnetic field outside them. FS strengthens the electric field around the slits and weakens the electric field around the middle of the stripes, and this effect is due to the gradient field generated by the electric charge accumulated on the FS surfaces. From the point of view of the pure 2D electromagnetic field, FS affects the electric field distribution in a small region, and it seems to not affect the total power coupling into plasma.
Study of the charged particle flow near the plasma grid in negative ion source
Authors: Masaki S. , Nakano H. , Rattanawongnara E. , Nagaoka K. , Ikeda K. , Fujiwara Y. , Osakabe M. , Wada M. , Tsumori K.
Published: April 2022

Flows of the charged particles in hydrogen (H) and deuterium (D) plasmas were measured with the single-tip directional Langmuir probe. The flow patterns of positive and negative ions have been constructed from the data by moving the probe near the plasma grid. The positive ion flow from driver to extraction regions showed the different velocity equivalent to the mass difference between H and D. The negative ion flow indicated the surface production of negative ions on the plasma grid, and changed the direction corresponding to the magnitude of the extraction electric field.
Recent developments and results of the LPSC PHOENIX type ECR charge breeder
Authors: Angot J , Baylac M , Luntinen M , Migliore M , Tarvainen O , Thuillier T
Published: April 2022

Four models of the PHOENIX ECR charge breeder have been manufactured for ISOL application. Two are currently under operation at TRIUMF (ISAC) and GANIL (SPIRAL 1) while the SPES one is being installed on the facility. The last model is set on the LPSC 1+N+ test bench where a R&D program is ongoing to improve its performances. The last modifications consisted in improving the beam line vacuum and the alignment. Commissioning experiments showed an improvement of the charge breeder performances for all the tested species. The global CB efficiency is close to 100% for Cs when correcting the measurements with the beam transmission. Na and K efficiencies have increased significantly to reach 18.7% for Na8+ and 22.7% for K9+. In parallel, the charge breeder plasma was studied injecting short pulses of 1+ ions and using a zero-dimension model to estimate the plasma parameters. These experiments have provided a better understanding of the performance improvement. The last developments of the LPSC Charge Breeder together with the experimental results are presented.
Improvement of the Efficiency and Beam Quality of the TRIUMF Charge State Booster
Authors: Adegun J , Ames F , Kester O
Published: April 2022

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.
High-voltage breakdown in the injection-extraction region of the CANREB EBIS: A possible mechanism
Authors: Charles Chris R.J. , Cavenaile Mathieu , Harford Paige , Ames Friedhelm , Schultz Brad , Kester Oliver
Published: April 2022

OmniTrak simulations were performed in the 40°K injection-extraction region near the collector trumpet of the CANREB EBIS to understand the nature of chronic electrical breakdowns of PEEK feedthroughs. These feedthroughs are designed to route high-voltage wires (up to +15 kV) from room temperature to each drift-tube at 4°K, while operating in the strong superconducting semi-Helmholtz field. The electric field strength |E| at the PEEK feedthroughs are ∼ 7 × 105 V/m within about 2-3 mm of the surroundings at ground potential. When simulating only bare wires (with no PEEK feedthroughs), |E| increases by about 1 order-of-magnitude to > 106 V/m in the same region. Assuming a 3 Tesla magnetic field, electrons starting with 0 eV near the PEEK feedthroughs undergo helical motions due to

E
→

×

B
→

-drift and demonstrate reflections from magnetic mirror effects. A combination of this helical motion, reflecting mirror trajectories, and attraction of electrons to exposed HV wires may be responsible for the ongoing HV breakdown of insulating feedthroughs in this region of the EBIS. Solving this problem requires complete ground-shielding of all HV wiring to eliminate |E| and should encapsulate all wires to prevent breakdown paths.
Non-destructive beam spatial profile measurement using a gas sheet monitor for a high-intensity ion beam
Authors: Yamada I , Wada M , Kamiya J , Kinsho M
Published: April 2022

A non-destructive beam spatial profile monitor system using a gas sheet has been developed. The 4 mm thick gas sheet of over 40 mm width enables increase of the local gas pressure high enough to record a two-dimensional beam profile. A CCD camera coupled to an image intensifier detects photons produced by beam-gas interaction with the signal intensity that makes the time evolution study of the beam possible. We demonstrated that the J-PARC 3MeV, 60 mA H- beam profile which is measured with intensity error of 8.4-12% and spatial resolution of 1 mm changed depending on the controls of the acceleration cavity in the beam pules of 50 μs.
Extraction and low energy beam transport models used for the IFMIF/EVEDA RFQ commissioning
Authors: Bellan L. , Akagi T. , Bolzon B. , Cara P. , Carin Y. , Cavenago M. , Chauvin N. , Comunian M. , Dzitko H. , Fagotti E. , Grespan F. , Kondo K. , Moya I. , Pisent A. , Podadera I. , Scantamburlo F. , Sugimoto M.
Published: April 2022

The Linear IFMIF Prototype Accelerator (LIPAc) is a high intensity D+ linear accelerator; demonstrator of the International Fusion Material Irradiation Facility (IFMIF). In summer 2019 the IFMIF/EVEDA Radio Frequency Quadrupole (RFQ) accelerated its nominal 125 mA deuteron (D+) beam current up to 5 MeV, with 90% transmission for pulses of 1 ms at 1 Hz. This success was possible thanks to an intense previous campaign of modelization and measurements in order to characterize the RFQ input beam, which is affected by the ECR ion source extraction and the low energy beam transport. The simulation models used with the measurement benchmarks are here presented.
Mass distributions of ions extracted from target cavity confined plasmas produced by nanosecond laser pulses
Authors: Hernandez J E , Wada M
Published: April 2022

Ion and electron current signals produced from a solid graphite target under 1064 nm nanosecond laser pulse irradiation were investigated. A cavity is formed by laser incidence at the center of the target surface at 10 Hz repetition rate while being rotated along its axis. Ion mass distributions were recorded via a time-of-flight spectrum coupled with a detector assembly attached along the propagation axis. Peak shifts towards slower times were observed for increasing number of pulses. The effect of magnetic detection on the ion current signals is investigated, and showed significant peak shifts for 20 GW/cm
2 laser power density.
Effects of axial magnetic field in a magnetic multipole line cusp ion source
Authors: Rawat Bharat Singh , Sharma S K , Choksi B , Bharathi P , Sridhar B , Gupta L N , Thakkar D , Parmar S L , Prahlad V , Baruah U K
Published: April 2022

Experiments have been performed to study the effects of axial magnetic field on plasma and ion beam parameters in a magnetic multipole line cusp ion source. Studies performed on ring cusp and Kaufmann type ion sources suggest that the axial component of magnetic field may help in improving the ion extraction current at a low discharge power. The line cusps ion sources have been used since long to produced uniform beams, however, they lack axial component of the magnetic field. These ion sources generally suffer from low efficiency possibly due the absence of axial magnetic field. In this work, an additional magnetic coil is added at various axial positions between the back-plate and the plasma grid of the multipole line cusp ion source. We have investigated the effects of axial magnetic field on the discharge efficiency and source parameters like beam current and uniformity in the multipole line cusp ion source. The beam profiles are obtained using an eleven-channel faraday cup array to estimate the effects of the axial magnetic field on beam uniformity and divergence. Initial studies suggest a reduction of beam divergence with increasing axial magnetic field. A significant rise in the beam current and the discharge current is also observed when the axial magnetic field is increased. Particle trajectory simulation using the CST-Studio suite is utilised in understanding the role of confinement of primary electrons behind the improved performance of the ion source.
Studies of bremsstrahlung and characteristic X-Ray lines using the VENUS ECR
Authors: Benitez Janilee , Todd Damon , Xie Daniel
Published: April 2022

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 Tscan 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.
Design and simulations for a Penning Ion Trap Source for the CHIP-TRAP Mass Spectrometer
Authors: Horana Gamage M. , Bhandari R. , Gamage N. D. , Keblbeck D. , Redshaw M.
Published: April 2022

At Central Michigan University (CMU) we have been developing the CMU High Precision Penning Trap (CHIP-TRAP) mass spectrometer for precise mass measurements on stable and long-lived radioactive isotopes. As part of this apparatus, we have designed a Penning Ion Trap (PIT) source to produce singly-charged, low intensity (∼100s to 1000s of ions in ∼1 μs duration) ion pulses from gaseous samples. The PIT source is similar to a PIG type source, composed of an electric field superimposed on a magnetic field. The electric field is produced by a cylindrical Penning trap structure consisting of two end caps and a center ring with a trap volume of about 0.8 cm3. The trap structure is housed inside a permanent neodymium ring magnet bore. Gas is inserted into the trapping region and ionized by an ∼1 μA electron beam from a thermal emitter. Ions are extracted from the PIT source by lowering the voltage on one of the end caps. They are then accelerated into the beam line. In this paper, we report on the design of the PIT source and simulations to investigate and characterize the expected beam properties.
Duoplasmatron type molecular carbon ion source
Authors: Wada M , Aki H , Miyamoto N
Published: April 2022

An ion source capable of producing molecular ions delivers a beam of impurity dopant for shallow ion implantation of semiconductor device fabrication. Production and transport of low energy molecular ions is indispensable for tabulating fundamental data on plasma-wall interactions that should be used to design a future nuclear fusion reactor. An ion source plasma can produce molecular ions of solid materials by sputtering, while low temperature plasma efficiently transports produced molecular ions to the source extraction hole. A duoplasmatron ion source with the carbon plasma electrode has successfully produced poly-atomic carbon ions up to C6
+. The intermediate electrode has six holes to guide cathode plasma to the carbon anode performing as the plasma electrode. A 1 mm diameter extraction hole is opened at the center of the carbon plasma electrode, where is no direct exposure to the plasma from the cathode region. The ion source maintains a stable discharge with both H2 and Ar as discharge support gas, but works better at lower pressure with Ar. A hydrogen plasma produced molecular ions of hydrocarbons with the mass separated current of C3H5
+ with the intensity comparable to other ion species including atomic, diatomic and triatomic hydrogen ions.
Laser ion source for semiconductor applications
Authors: Kulevoy T V , Losev A A , Alekseev P N , Satov Yu A , Shumshurov A V , Lagov P B , Letovaltseva M E , Zinoviev S A
Published: April 2022

Carbon implantation can be effectively used for axial minority charge carriers’ lifetime control in various silicon bulk and epitaxial planar structures. When carbon is implanted, more stable recombination centres are formed and silicon is not doped with additional impurities, as for example, when irradiated with protons or helium ions. Economically, such a process competes with alternative methods, and is more efficient for obtaining small lifetimes (several nanoseconds). I-3 ion injector with laser-plasma ion source at Institute for theoretical and experimental physics (ITEP) is used as ion implanter in semiconductors. The ion source uses pulsed CO2 laser setup with radiation-flux density of 1011 W/cm2 at target surface. The ion source produces beams of various ions from solid targets. The generated ion beam is accelerated in the two gap RF resonator at voltage of up to 2 MV per gap. Resulting beam energy is up to 4 MV per charge. Parameters of carbon ion beam generated and used for semiconductor samples irradiation during experiments for axial minority charge carriers lifetime control in various silicon bulk and epitaxial planar structures are presented.
Suppression of damages on cathodes in the negative hydrogen ion source for the stable NBI system
Authors: Shimabukuro Y , Hiratsuka J , Ichikawa M , Murayama M , Saquilayan G , Kisaki M , Kojima A , Tobari H , Kashiwagi M
Published: April 2022

A protection system of ion source components from local abnormal discharge has been developed with ITER-class filament-driven negative ion source for high power and stable long-term operation. Protection from unpredictable discharge is a common issue for filament and RF-driven ion sources. To understand how fast should be cut off the discharge, threshold energy not to cause critical damage on the filament was investigated. The experimental exploration concluded that the energy less than 1.87 J or fast cut-off faster than 343 μs is the threshold for the robust protection of the filaments. A developed system successfully detected and cut off the discharge at 100 μs under noisy environments with the high current power supply. Moreover, the detection system is remotely adjustable. Such versatile protection system can contribute to any abnormal discharges in high current system including various ion sources, gyrotron, and high voltage components.
Development of ECR ion source with high-temperature superconducting REBCO coils
Authors: Chong T H , Fukuda M , Yorita T , Kanda H , Yasuda Y , Koay H W , Morita Y , Takeda K , Hara T , Hisamatsu M , Zhao H , Ishiyama A , Noguchi S , Ueda H , Fukui S , Matsubara Y , Mikami Y , Takahashi N , Yoshida J , Hirayama T , Nagaya S , Watanabe T
Published: April 2022

A new High-Temperature Superconducting ECR (HTS-ECR) ion source is under development in Research Center for Nuclear Physics (RCNP), Osaka University. This ion source will be used for production of high intensity proton, deuteron and He ion beams. The HTS-ECR magnets are composed of three solenoid coils and a set of sextupole coils made of REBCO tapes, a high-temperature superconductor. The HTS-ECR ion source is designed to operate at frequency of 2.45 GHz and 10 GHz. Performance test of the HTS coils had been carried out at 31 K and 77 K. This HTS coil technology will be applied to development of a meter-size HTS coil system of a high intensity compact AVF cyclotron. This paper introduces the basic design of the HTS-ECR ion source. The performance test results showed that REBCO solenoids remain superconducting state with a current up to 400 A. Simulation results of the magnetic field and electromagnetic field distributions in a plasma chamber fulfilled the requirements of electron cyclotron resonance conditions at 2.45 GHz and 10 GHz. Simulation result of mirror ratios and electromagnetic field amplitudes are also presented in this paper.