A. Hatayama

Keio University · Faculty of Science and Technology

Understanding of key physics and engineering parameters is one of the most important issues to conduct fundamental design studies of future fusion reactors. Also, sensitivity analyses of performance by parameter surveys need to be done for optimizing a reactor. This research aims at a qualitative analysis to identify directions of design parameter...

In order to extract intense ion beams with good beam optics from hydrogen negative ion sources, it is important to control the shape of the plasma meniscus (i.e. beam emission surface). Recently, it is suggested experimentally that the degradation of beam optics in the RF negative ion sources may be due to the fluctuation of the distance d eff betw...

Collisional-radiative models are commonly used to analyse atomic and molecular processes in low temperature plasmas by determining the distribution functions of excited states as functions of various plasma parameters. This paper outlines the improvements to a zero-dimensional collisional-radiative model, developed at Keio University, for purposes...

In general, a quality of negative ion beam optics is determined by the shape of the plasma meniscus, which is an ion emitting surface. In this study, the key parameters to control the plasma meniscus and relevant physical structure in the electronegative plasma including the surface produced H ⁻ ions is investigated by using PIC-MCC simulation. The...

To extract intense ion beams with good beam optics from ion sources, controlling the distance deff between the plasma meniscus (i.e., beam emission surface) and the beam extraction grid is important. This study conducts a novel investigation into the dependence of the effective distance deff on the amount of surface H- production SH-. For this purp...

The emitting surface of ion beam (plasma meniscus) in the vicinity of the extraction aperture is theoritically investigated. In the present study, the electron, H+ ion, and volume produced H- ion are contained in the electronefative plasma. By solving the one-dimensional Poisson equation, the analytical formula is obtained from the balance between...

Sequences of hydrogen (H) and deuterium (D) experiments have been done by NIFS research and development negative ion source (RNIS) for the deuterium NBI development. In the experiments, the co-extracted electron current with the negative ions and the electron density in the plasma generation region in the D experiment have been around three times h...

It is reported from the measurement of a negative ion beamlet emittance that the characteristic three-Gaussian components are observed in the emittance diagram. The negative ion trajectories are calculated using 3D PIC-MCC simulation in order to clarify the origin of this complicated phase space structure and underlying physical mechanism. The char...

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...

This paper numerically investigates the impact of neutral gas puffing on the divertor power exhaust and particle control in GAMMA 10/PDX applying the plasma fluid code LINDA and the kinetic neutral code KMNC. The LINDA code is applied to GAMMA 10/PDX plasmas for understanding the physics of detachment and energy loss processes. The LINDA code is co...

Distribution of electric potential near the wall in the volume produced negative ion source with the magnetic field increasing toward the wall such as the cusp magnetic field is investigated analytically. The plasma-sheath equation that gives the electric potential in the plasma region and the sheath region near the wall is derived analytically and...

QUEST (Q-shu university experiment with steady state spherical tokamak) is a midsize spherical tokamak capable of steady-state operation, comprising all-metal plasma-facing walls and a hot wall (HW) to address issues pertaining to fuel particle balance. The HW was installed summer 2014. Quantitative analysis pertaining to the HW at 373K is carried...

In this research, we investigate the effect of magnetic flux tube expansion on the divertor plasma parameters by using the fluid code "LINDA". A comparison between the cylindrical flux tube (without the magnetic flux expansion) and the expansion magnetic flux tube has been undertaken. The aim of the study is to understand the impact of magnetic fie...

Eulerian-Lagrangian (EL-LG) scheme is a numerical scheme that tracks pseudo particles in Eulerian cells. It is widely used in the computational fluid dynamics, however, numerical errors associated with a particle source term has not yet been investigated much. Hence this study focuses on numerical errors of EL-LG caused by particle sources. The pur...

The transition phenomenon of detached plasma during additional heating effects has been studied by applying a short pulse (25ms) of Electron Cyclotron Heating (ECH) at the east plug-cell of the tandem mirror device GAMMA 10/PDX. In this paper, the plasma parameters on the target plate of the D-module are studied for understanding the impact of tran...

To increase the accuracy of a particle, momentum, and energy source terms in the detached helium plasma simulation, rate coefficients with the collisional-radiative model were introduced into the fluid code LINear Divertor Analysis (LINDA). Obtained effective rate coefficients and related source terms were compared with those from the conventional...

We are developing a Lagrange (LG)-Monte-Carlo (MC) scheme for three-dimensional (3D) SOL/Divertor plasma fluid modeling. By using test particles, the scheme is suitable for handling 3D complex geometries. The semi-implicit treatment of the pressure gradient term enables us to improve the robustness of the coupling of the continuity and the momentum...

A multi-cusp DC arc-discharge hydrogen negative ion (H⁻) source has been developed for proton cyclotron, which is used for Boron Neutron Capture Therapy (BNCT). The purpose of this study is to understand the dependence of H− production on the operation parameters and optimize H− production in the source. In this paper, we focus on the effect of mag...

In future fusion reactors, tungsten (W) is currently regarded as one of the most feasible candidates for the plasma-facing components (PFCs). Once the W impurities sputtered from the PFCs penetrate into the core plasma, the large radiation cooling and fuel dilution, which leads to the deterioration of the core plasma performance, take place. To und...

Negative hydrogen (H−) ion sources have a wide range of applications. The general requirement for these H− ion sources is to produce intense H− ion beams with good beam optics. The purpose of this paper is to clarify the effects of the beam extraction voltage on the beam divergence angle by three-dimensional Particle-in-Cell (PIC) modeling. Pervean...

The purpose of this study is to make clear the effects of the plasma blob on the impurity transport in the Scrape-Off Layer (SOL) regions. By using the two-dimensional (2D) interchange turbulence model with plasma transport along magnetic field line, we have simulated the plasma blob formation and transport in the SOL regions. We have studied the e...

Molecular activated recombination (MAR) has been received attention as one of the most important processes to realize the detached state, specifically in the linear plasma device, GAMMA10/PDX. The impact of ELMs on the MAR reaction and the resultant detached state, however, have not fully been understood. We have developed a zero-dimensional model...

Plasma distributions near the extraction region in a hydrogen negative ion source are investigated analytically. Where surface produced hydrogen negative ions and volume produced hydrogen negative ions are considered in addition to electrons and hydrogen positive ions. The plasma-sheath equation is derived analytically and the distributions of the...

Linac4 is radio frequency (RF) driven type negative hydrogen H− ion source. In the RF system, it is required to match the impedance between the RF-system and plasma loading. In order to match the impedance, it is essential to analyze the plasma impedance. In this study, we analyze the dependence of power transfer on the input parameters (frequency,...

This research investigated fuel particle balance during long duration discharge in an all-metal plasma facing wall (PFW)through intensive QUEST execution. A simple wall model including the plasma-induced deposition layer that creates hydrogen (H)barriers, called the H barrier model, was established. A simple calculation, based on a combination of H...

The purpose of this study is to understand the Ar impurity transport process in the GAMMA 10/PDX. In the present study, the initial simulation using LINDA code and IMPGYRO code has been done to establish the basis of further understanding of the Ar impurity transport. The validity of the simulation model has been discussed by comparisons with those...

This paper investigates the impact of Krypton (Kr) seeding on plasma parameters in the D-module of GAMMA 10/PDX experimentally based on the calorimeter, Langmuir probe and high-speed camera measurements. The heat flux distribution along the V-shaped target plate reduces with the increasing Kr injection. The time behavior of ion flux shows that it d...

The transition of a detached to attached plasma experiment has been performed in GAMMA 10/PDX by applying an additional plasma heating pulse of electron cyclotron heating (ECH). In a plasma detachment experiment, a short pulse (25 ms) of ECH was applied at the east plug-cell to examine the effects of electron heating on the plasma parameters in the...

This research numerically investigates the behavior of plasma flow in GAMMA 10/PDX. The impact of impurity gases seeding into the divertor region on the plasma parameters and the energy loss processes has been investigated numerically by using the multi-fluid code “LINDA”. The neutral particles are injected into the bulk hydrogen plasma and the ups...

The transition of a detached to attached plasma experiment has been performed in GAMMA 10/PDX by applying an additional plasma heating pulse of electron cyclotron heating (ECH). In a plasma detachment experiment, a short pulse (25 ms) of ECH was applied at the east plug-cell to examine the effects of electron heating on the plasma parameters in the...

Linac4 is radio frequency (RF) driven type negative hydrogen H⁻ ion source. In the RF system, it is required to match the impedance between the RF-system and plasma loading. In order to match the impedance, it is essential to analyze the plasma impedance. In this study, we analyze the plasma impedance by using the Electro-Magnetic Particle in Cell...

Multi cusp DC arc-discharge hydrogen negative ion (H⁻) source has been developed for the proton cyclotron applications. The purpose of this study is to understand the dependence of the H⁻ production on the operation parameters and optimize the H⁻ production in the source. In this paper, we focus on the effect of magnetic filter field on the H⁻ volu...

A radio frequency (RF) driven type hydrogen (H⁻) source is used as an injector of Linac4. The power transfer efficiency between the RF generator and the ion source plasma is one of the important parameters that determines the extracted H⁻ beam current. In order to achieve efficient power transfer, it is required to match the impedance between the R...

In order to compare the simulation and the experiments of the extracted H⁻ beams in JT-60SA negative ion source, an analysis of H⁻ ion transport has been conducted. It has been shown that, under the present conditions, the calculated beam profile correlates well with the experiments, and the majority of the extracted H⁻ ions are produced at the sur...

In order to make the predictive simulation tools for the extracted beam current and emittance in the Linac4 H⁻ ion source, we have launched the development of the integrated model for the H⁻ ion beam formation and extraction process. More specifically, our 3D KEIO-Beam Formation and eXtraction (3D KEIO-BFX) is coupled with the NINJA, IBSIMU and TRA...

A Multi-cusp DC arc-discharge hydrogen negative ion (H⁻) source has been developed for proton cyclotron applications. The purpose of this study is to understand the dependency of the H⁻ surface production on the operation parameters and optimize the H⁻ surface production in the source. In this paper, spatial distribution of H atom production due to...

We have worked on the development of a particle-based numerical model of a hydrogen Radio Frequency (RF) Inductively Coupled Plasma (ICP). In the previous work, it has been shown that the model is able to simulate the E-to-H discharge mode transition, which is one of the distinct features of RF ICP. The purpose of the present study is to investigat...

The purpose of this study is to investigate the extraction mechanisms of the H⁻ ions in the Linac4 negative ion source by using an improved two-dimensional in real space and three-dimensional in velocity space Particle in Cell (2D3V-PIC) model. In this model, the following collision processes of the surface produced H⁻ (Hsp−) ions have been introdu...

The negative ion beam optics is studied quantitatively from the viewpoints of the heat loads due to the beam halo in the accelerator and the emittance of the negative ion beam by using the 3D3V PIC model combined with a Monte Carlo calculation, in which negative ion beam from plasma meniscus formation to the beam acceleration is modeled. As for the...

Metal plasma‐facing materials (PFMs) are expected to be candidates for future fusion power plants from the view point of tritium retention. The purpose of this study is to develop a model including a long timescale plasma interaction with metal PFMs. As a first step, we have developed a simple zero‐dimensional (0D) model, which consists of particle...

Effects of H− ion on distributions of electric potential and plasma density near the wall with the magnetic field decreasing toward the wall are investigated analytically. In the analysis, the magnetic field is assumed to be perpendicular to the wall, and the problem is treated as one-dimensional model. The plasma-sheath equation is derived analyti...

Aiming at reproducing plasma detachment states with a three‐dimensional fluid code, we are developing the Lagrange–Monte Carlo (LG‐MC) scheme. It integrates two schemes, namely a Lagrange scheme for the convective part and a Monte Carlo scheme for the diffusive part. One advantage of the scheme is the semi‐implicit treatment of the pressure gradien...

This paper describes the behavior of plasma parameters in the E-divertor region of GAMMA 10/PDX numerically by using the multi-fluid code (LINDA) during injection of hydrogen (H) and Argon (Ar). A remarkable reduction in the electron temperature (Te) has been recognized due to Ar injection. For only Ar 6.0 × 1017 m−3 injection, Te on the target pla...

The present status of kinetic modeling of particle dynamics in hydrogen negative ion (H⁻) source plasmas and their comparisons with experiments are reviewed and discussed with some new results. The main focus is placed on the following topics, which are important for the research and development of H⁻ sources for intense and high-quality H⁻ ion bea...

Detailed results of spectral measurements in the gas injection performed in GAMMA 10/PDX divertor simulation experiments are presented. From the comparison of the emission intensity at the end-cell and plug/barrier-cell, impurity behavior along the magnetic field line is discussed in GAMMA 10/PDX. The emission intensity of Ar II is decreased due to...

This paper studies the transport of hydrogen neutral particles towards the upstream region in the end cell of GAMMA 10/PDX by developing a neutral transport code. As a first step, a series of initial test calculations have been performed by injecting hydrogen molecules from the target plate with fixed plasma background. It has been shown that neutr...

The purpose of this study was to clarify the effects of a plasma blob on the impurity transport in the scrape‐off layer (SOL) and divertor region of fusion devices. As a first step, plasma blob formation and transport were simulated by a two‐dimensional interchange turbulence model. Its effects on impurity transport were studied by the impurity equ...

Recently, in Cs-seeded H⁻ ion sources for fusion applications, the experiments have shown that the surface produced H⁻ ions are mainly extracted from the bulk plasma region, that is, 1–2 cm inside from the beam aperture. The purpose of this paper is to clarify the extraction mechanism of the surface produced H⁻ ions from the bulk plasma region in C...

The discharge process of a radiofrequency (RF) inductively coupled plasma (ICP) has been modeled by an ElectroMagnetic Particle-in-Cell Monte Carlo Collision method (EM PIC-MCC). Although the simulation had been performed by our previous model to investigate the discharge mode transition of the RF ICP from a kinetic point of view, the model neglect...

This paper describes the recent progress in divertor simulation research using the GAMMA 10/PDX tandem mirror towards the development of divertors in fusion reactors. During a plasma flow generation experiment in the end cell of the GAMMA 10/PDX, ICRF heating in the anchor cell successfully extended the particle flux up to 3.3 × 10²³ m² s⁻¹. Superi...

We have developed an extended kinetic model for the thermal force on test impurity particles in plasmas. This model makes use of a combination of the plasma ion heat flux qGM derived from the generalized moment equations (E. Zawaideh et al., Phys. Fluids 1988, 31) and the numerical algorithm presented earlier (Y. Homma, A. Hatayama, J. Comput. Phys...

The linear divertor analysis with fluid model (LINDA) code has been developed in order to simulate plasma behavior in the end-cell of linear fusion device GAMMA 10/PDX. This paper presents the basic structure and simulated results of the LINDA code. The atomic processes of hydrogen and impurities have been included in the present model in order to...

We present a fully-implicit electromagnetic Particle-In-Cell Monte Carlo collision code, called NINJA, written for the simulation of inductively coupled plasmas. NINJA employs a kinetic enslaved Jacobian-Free Newton Krylov method to solve self-consistently the interaction between the electromagnetic field generated by the radio-frequency coil and t...

The power requirements of RF heated sources for negative hydrogen ions in fusion are substantial, which poses strong demands on the generators and components of the RF circuit. Consequently, an increase of the RF coupling efficiency would be highly beneficial. Fundamental investigations of the RF efficiency in inductively coupled hydrogen and deute...

A cesiated DC negative ion source has been developed for proton cyclotrons in medical applications. A continuous H⁻ beam of 23 mA was stably extracted at an arc power of 3 kW. The beam current gradually decreases with a constant arc power and without additional Cs injection and the decay rate was about 0.03 mA (0.14%) per hour. A feed-back control...

Linac4 cesiated surface H⁻ sources are routinely operated for the commissioning of the CERN’s Linac4 and on an ion source test stand. Stable current of 40-50 mA are achieved but the transmission through the LEBT of 80% was below expectations and triggered additional beam simulation and characterization. The H⁻ beam profile is not Gaussian and emitt...

A filament driven multi-cusp negative ion source has been developed for proton cyclotron applications. In this study, numerical analysis of the H⁻ volume production in the negative ion source has been conducted by the KEIO-MARC code and zero dimensional rate equations. The code calculate the Electron Energy Distribution Function (EEDF) in multi-cus...

CERN ’s new particle accelerator Linac4 is part of the upgrade of the LHC accelerator chain. Linac4 is required to deliver 160 MeV H⁻ beam to improve the beam brightness and luminosity in the Large Hadron Collider (LHC). The Linac4 H⁻ source must deliver 40-50 mA, 45 keV H⁻ beam in the RFQ acceptance. Since the RF power coupled to the H⁻ source pla...

The energy relaxation processes of the surface produced H⁻ ions due to the Coulomb collision and the charge exchange collision is verified by using 3D3V-PIC (three dimensions in real space and three dimensions in velocity space particle in cell) simulation. Under the present simulation condition (ne = 1.0 × 10¹⁸ m⁻³, TH+ = 0.25 eV, TH- = 1.5 eV (th...

In order to understand the H⁻ extraction mechanism and investigate the effect of the extraction voltage applied by the puller-electrode on the H⁻ extraction in the Linac4 negative ion source, we are developing a 2D3V-PIC (two dimensions in the real space and three dimensions in the velocity space, Particle in Cell) model with volume produced H⁻ ion...

This paper presents a Particle-In-Cell Monte Carlo Collision simulation of the Radio-Frequency (RF) plasma heating in the Linac4 H⁻ ion source at CERN. The model self-consistently takes into account the electromagnetic field generated by the RF coil, the external static magnetic fields and the resulting plasma response, including a kinetic descript...

In order to improve the uniformity of the negative ion production, the KEIO-MARC code has been applied to the QST’s JT60SA negative ion source in three different magnetic configurations (i) MC-PGMF (Multi-Cusp and PG Magnetic Filter), (ii) TNT-MF (TeNT Magnetic Filter) and (iii) MTNT-MF (Modified TeNT Magnetic Filter). From the results, we have con...

The development of the kinetic particle model for the extraction region in negative hydrogen ion sources is indispensable and helpful to clarify the H⁻ beam extraction physics. Recently, various 3D kinetic particle codes have been developed to study the extraction mechanism. Direct comparison between each other has not yet been done. Therefore, we...

In order to obtain a better understanding of tungsten (W) transport processes, we are developing the Monte-Carlo W transport code IMPGYRO. The code has the following characteristics which are important for calculating W transport: (1) the exact Larmor motion of W ions is computed so that the effects of drifts are automatically taken into account; (...

This research investigates the effect of Argon (Ar) and Neon (Ne) injection on the plasma parameters in the end-cell of GAMMA 10/PDX numerically by using a multi-fluid code. Reduction in the temperature of the electrons and ions is observed according to the increment of impurity injection. The electron density and the particle flux show tendency of...

Erosion reduction of tungsten (W) divertor target is one of the most important research subjects for the DEMO fusion reactor design, because the divertor target has to sustain large fluence of incident particles, composed mainly of fuel ions and seeded impurities, during year-long operation period. Rate of net erosion and deposition on outer divert...

h i g h l i g h t s • This research investigates the effect of Argon (Ar) and Neon (Ne) injection on the plasma parameters in the end-cell of GAMMA 10/PDX numerically by using a multi-fluid code. • Temperature reduction in the electrons and ions during Ar injection is higher than those of the Ne injection. • Particularly in the electron temperature...

The effect of neutral Ar injection on the plasma parameters is investigated numerically by using a multi-fluid code in this research. Reduction of electron and ion temperature has been observed according to the increment in injected neutral Ar density. The heat flux on the target plate has been also reduced with the increasing of injected neutral A...

Inductively coupled plasmas (ICP) are well known to exhibit two modes of operation: a low density capacitive E-mode and a high density inductive H-mode. In this study we investigate the E-H transition in a cylindrical ICP, and show the effect of an external magnetic cusp field on the transition dynamics. The plasma is simulated by an electro-magnet...

Understanding of impurity transport in tokamaks is an important issue in order to reduce the impurity contamination in fusion core plasmas. Recently, a new kinetic numerical scheme of impurity classical/neoclassical transport has been developed. This numerical scheme makes it possible to include classical self-diffusion (CL SD), classical inward pi...

In order to understand the effect of impurity injection into divertor plasma, a multi-fluid code was developed and applied to the region from west plug/barrier-cell to end cell in GAMMA 10/PDX. In this research, Ar is applied as impurity neutrals. To investigate the effect of impurity injection on plasma parameters, interactions between Ar impurity...

Monte Carlo method is thought to be effective to solve fluid plasma equations for SOL/divertor plasmas, especially for three dimensional simulation. In the Monte Carlo algorithm based on a Lagrangian scheme, how to treat the Monte Carlo test particles at the calculation boundaries is not always trivial. In this paper, 1D diffusion equation with sou...

The initial simulation study of the neoclassical perpendicular self-diffusion transport in the SOL/Divertor regions for a realistic tokamak geometry with the IMPGYRO code has been performed in this paper. One of the most unique features of the IMPGYRO code is calculating exact Larmor orbit of the test particle instead of assuming guiding center app...

In the divertor region, the plasma contains deuterium (D) ion and tritium (T) ion in an open magnetic field. The effect of D ion and T ion on the electric potential near the wall in plasma with magnetic field decreasing toward a wall is investigated analytically. The distribution of the electric potential is obtained by plasma-sheath equation, wher...

Radio Frequency (RF) Inductively Coupled Plasmas (ICPs) are widely known for their two discharge modes, i.e., H-mode and E-mode, where the dynamics of the plasmas are completely different from each other. We have performed a kinetic simulation of a hydrogen plasma discharge in order to clarify the discharge mechanism and the E-to-H transition of th...

In order to enhance the H− surface production in hydrogen negative ion sources, it is important to increase the density of the H atoms dissociated from H2 molecule and the resultant atomic flux towards the surface of the plasma grid. In this paper, the effect of the Electron Energy Distribution Function (EEDF) on the dissociation of H2 in Linac4 H−...

A filament driven multi-cusp negative hydrogen ion source has been developed for proton cyclotrons. In order to increase the H⁻ beam current, the dependences of H⁻ beam current on various design/operating parameters has been studied experimentally and numerically. In this paper, the effects of arc-discharge voltage and current on H⁻ production via...

A new kinetic model for neoclassical impurity particle transport simulation has been developed. Our model is able to simulate the following two effects, which have been theoretically predicted, but neglected in most of the existing kinetic impurity transport simulations in the SOL (scrape-off layer)/Divertor plasmas of tokamak; (1) the neoclassical...

To improve the H− ion beam optics, it is necessary to understand the energy relaxation process of surface produced H− ions in the extraction region of Cs seeded H− ion sources. Coulomb collisions of charged particles have been introduced to the 2D3V-PIC (two dimension in real space and three dimension in velocity space particle-in-cell) model for t...

The physical mechanism of the formation of the negative ion beam halo and the heat loads of the multi-stage acceleration grids are investigated with the 3D PIC (particle in cell) simulation. The following physical mechanism of the beam halo formation is verified: The beam core and the halo consist of the negative ions extracted from the center and...

A numerical model of plasma transport and electromagnetic field in the J-PARC (Japan Proton Accelerator Research Complex) radio frequency ion source has been developed to understand the relation between antenna coil heat loadings and plasma production/transport processes. From the calculation, the local plasma density increase is observed in the re...

To understand the Electron Energy Distribution Function (EEDF) in the Radio Frequency Inductively Coupled Plasmas (RF-ICPs) in hydrogen negative ion sources, the detailed analysis of the EEDFs using numerical simulation and the theoretical approach based on Boltzmann equation has been performed. It is shown that the EEDF of RF-ICPs consists of two...

Recently, a filament driven multi-cusp negative ion source has been developed for proton cyclotrons in medical applications. In this study, numerical modeling of the filament arc-discharge source plasma has been done with kinetic modeling of electrons in the ion source plasmas by the multi-cusp arc-discharge code and zero dimensional rate equations...

A filament driven multi-cusp negative ion source has been developed for proton cyclotrons in medical applications. In Cs-free operation, continuous H- beam of 10 mA and D- beam of 3.3 mA were obtained stably at an arc-discharge power of 3 kW and 2.4 kW, respectively. In Cs-seeded operation, H- beam current reached 22 mA at a lower arc power of 2.6...

CERN's 160 MeV H- linear accelerator (Linac4) is a key c