A New Three-Dimensional Code for Simulation of Ion Beam Extraction: Ion Optics Simulator

A new thee-dimensional code, ion optics simulator （IOS）, to simulate ion beam extraction is developed in visual C＋＋ language. The theoretical model, the flowchart of code, and the results of calculation as an example are presented.

Numerical Simulation of Ion Extraction Through Ion Thruster Optics

Based on the particle-in-cell （PIC） method, a two-dimensional numerical scheme was developed to investigate the ion beam extraction phenomena through the ion thruster optics. According to the calculated results, the plasma sheath upstream of the screen grid, the electric field in the calculation domain, and the ion and electron spatial distributions are obtained for different accelerator grid voltages. The results indicate that the accelerator grid voltage affects the plasma sheath upstream of the screen grid significantly. It is found that a moderate accelerator grid voltage results in an ion optical performance better than either a higher or lower voltage, from a point of ion extraction from the discharge chamber and erosion mitigation of the accelerator grid due to the direct ion impingement.

Estimate of Lifetime of Ion Thruster Optics Based on Particle Simulation

A three-dimensional particle simulation of ion thruster optics with charge-exchange collision was developed in this study. The simulation code was based on tracking ions using the particle-in-cell method, and the Monte Carlo technique was used to model the charge-exchange collision. Simulations were performed for a 20 cm ion thruster optics. The results were compared with the corresponding experimental data from a test of the ion thruster optics for a duration of 800 hours. The Depth-From-Focus （DFF） method was used to measure the erosion depth of the downstream surface of the accelerator grid. The predicted erosion depth of the accelerator grid was consistent reasonably with the corresponding experimental data. The simulation results showed that the accelerator grid would be burned through after 1333 hours.

Preliminary Results of Ion Beam Extraction Tests on EAST Neutral Beam Injector

The neutral beam injection （NBI） system is one of the most important auxiliary plasma heating and current driving methods for fusion device. A high power ion beam of 3 MW with 80 keV beam energy in 0.5 s beam duration and a long pulse ion beam of 4 s with 50 keV beam energy ion beam extraction were achieved on the EAST neutral beam injector on the teststand. The preliminary results show that the EAST-NBI system was developed successfully on schedule.

Gate/Geant4-based Monte Carlo simulation for calculation of dose distribution of 400 MeV/u carbon ion beam and fragments in water

The applications of carbon ion beam in tumor therapy have attracted more attention in recent years.Monte Carlo simulation is an important approach to obtain accurate radiotherapy parameters. In this work, a400 Me V/u carbon ion beam incident on water phantom was simulated with Gate/Geant4 tools. In methods, the authors set up a carbon ion beam source according to the experiment parameters of Haettner, defined the geometries and materials, set up the physics processes, and designed the means of information collection. In results,the authors obtained the longitudinal dose distribution, the lateral dose distribution, and the relative uncertainty of dose. The dose contributions of all kinds of fragments were calculated detailedly and compared with the Francis results. This work is helpful for people's understanding of the dose distributions produced by carbon ion beam and fragments in water. The simulation method is also significative for radiotherapy treatment planning of carbon ion beam, and it is easy to extend. For obtaining a special result, we may change the particle energy, particle type,target material, target geometry, physics process, detector,etc.

GATE simulation based feasibility studies of in-beam PET monitoring in ^(12)C beam cancer therapy

In comparison with conventional radiotherapy techniques,12C beam therapy has its significant advantage in cancer treatment because the radiation dose are mostly concentrated near the Bragg peak region and damage to normal tissues along the beam path is thus greatly reduced.In-beam PET provides a way to monitor dose distribution inside human body since several kinds of positron-emitting nuclei are produced through the interaction between 12C beam and body matters.In this work,we study the quantitative relationship between the spatial location of the Bragg peak and the spatial distribution of positrons produced by positron-emitting nuclei.Monte Carlo package GATE is used to simulate the interactions between the incident 12C beam of different energies(337.5,270.0 and 195.0 MeV/u) and various target matters(water,muscle and spine bone).Several data post-processing operations are performed on the simulated positron-emitting nuclei distribution data to mimic the impacts of positron generation and finite spatial resolution of a typical PET imaging system.Simulation results are compared to published experimental data for verification.In all the simulation cases,we find that 10C and 11C are two dominant positron-emitting nuclei,and there exists a significant correlation between the spatial distributions of deposited energy and positrons.Therefore,we conclude that it is possible to determine the location of Bragg peak with 1 mm accuracy using current PET imaging systems by detecting the falling edge of the positron distribution map in depth direction.

Influence of extraction voltage on electron and ion behavior characteristics

The characteristics of the extracted ion current have a significant impact on the design and testing of ion source performance.In this paper,a 2D in space and 3D in velocity space particle in cell(2D3V PIC)method is utilized to simulate plasma motion and ion extraction characteristics under various initial plasma velocity distributions and extraction voltages in a Cartesian coordinate system.The plasma density is of the order of 10^(15)m^(-3)-10^(16)m^(-3)and the extraction voltage is of the order of 100 V-1000 V.The study investigates the impact of various extraction voltages on the velocity and density distributions of electrons and positive ions,and analyzes the influence of different initial plasma velocity distributions on the extraction current.The simulation results reveal that the main reason for the variation of extraction current is the spacecharge force formed by the relative aggregation of positive and negative net charges.This lays the foundation for a deeper understanding of extraction beam characteristics.

Fuel compression in the magnetized cylindrical implosion driven by a gold tube heated by heavy ion beams

A magnetized cylindrical target composed of a gold tube filled with deuterium-tritium fuel plasma at low density is studied numerically in the present paper.A shock wave is produced when a heavy ion beam heats the gold along the direction of the magnetic field.The density peak of the shock wave increases with the increase in time and it propagates in the-r direction in the cylindrical tube.It seems that this wave is the supermagnetosonic wave.It is found that the Mach number M is between 6.96 and 19.19.The density peak of the shock wave increases as the intensity of the heavy ion beam increases.Furthermore,the density peak of the shock wave increases as the external magnetic field increases.

Numerical Simulation of Characteristics of CEX Ions in Ion Thruster Optical System

Charge exchange （CEX） ions could inflict severe damages on the ion thruster optical system. This article is aimed at investigating the characteristics of the CEX ions and their influences upon the optical system by means of particle-incell（PIC） ion simulation and Monte Carlo collision（MCC） methods. The results from numerical simulation indicate that despite the fact that CEX ions appear in the entire beamlet region near the ion optical system, the ones that present themselves downstream of the accelerator grid have good reason for attracting more attention. As their trajectories are significantly affected by the local electric field, a great number of CEX ions are accelerated toward grids resulting in sputtering erosion. When the influences of the CEX ions are considered in the nulnerical simulation,there could hardly be observed augments in the screen grid current,but the accelerator grid current increases from zero to 1.4% of the beamlet current. It can be understood from the numerical simulation that the CEX ions formed in the region far downstream of the accelerator grid should be blamed for the erosion on the downstream surface of the accelerator grid.

Transient Behavior of Negative Hydrogen Ion Extraction from Plasma

For plasma source, the extraction of negative ions is quite different from that of positive ions. To understand the effect of extraction field on plasma, the time-dependent behavior of negative hydrogen ion extraction from a negative ion source has been studied by particle-in-cell simulation in the collisionless limit. The simulations have shown that, due to the difference in dynamics between electrons and ions, the imbalance of the numbers of charged particles occurs in the source, results in the broadening of plasma sheath and the great increase of plasma potential. The resultant high sheath field and the ambipolar electric field in plasma make the negatively charged particles congregate inside the sheath and move toward the extraction outlet. The emission area of negative ions is much smaller than that of the extraction aperture, which is in sharp contrast to the case of positive ion extraction.

Analysis of the characteristics of the plasma of an RF driven ion source for a neutral beam injector

A radio frequency(RF)driven ion source is a very important component of a neutral beam injector for large magnetic confinement fusion devices.In order to study the key technology and physics of an RF driven ion source for a neutral beam injector in China,an RF ion source test facility was developed at the Institute of Plasma Physics,Chinese Academy of Sciences.In this paper,a two-dimensional fluid model is used to simulate the fundamental physical characteristics of RF plasma discharge.Simulation results show the relationship of the characteristics of plasma(such as electron density and electron temperature)and RF power and gas pressure.In order to verify the effectiveness of the model,the characteristics of the plasma are investigated using a Langmuir probe.In this paper,experimental and simulation results are presented,and the possible reasons for the discrepancies between them are given.This paper can help us understand the characteristics of RF plasma discharge,and give a basis for further R&D for an RF ion source.

The Arc Regulation Characteristics of the High-Current Ion Source for the EAST Neutral Beam Injector

The arc regulation method is applied to the high-current ion source for high-power hydrogen ion beam extraction for the first time. The characteristics of the arc and beam, including the probe ion saturation current, the arc power and the beam current, are studied with feedback control. The results show that the arc regulation method can be successfully applied to ion beam extraction. This lays a sound foundation for the testing of a new ion source and the operation of a conditioned ion source for neutral beam injector devices.

The development of data acquisition and control system for extraction power supply of prototype RF ion source

A 16 kV/20 A power supply was developed for the extraction grid of prototype radio frequency（RF） ion source of neutral beam injector. To acquire the state signals of extraction grid power supply（EGPS） and control the operation of the EGPS, a data acquisition and control system has been developed. This system mainly consists of interlock protection circuit board, photoelectric conversion circuit, optical fibers, industrial compact peripheral component interconnect（CPCI） computer and host computer. The human machine interface of host computer delivers commands and data to program of the CPCI computer, as well as offers a convenient client for setting parameters and displaying EGPS status. The CPCI computer acquires the status of the power supply. The system can turn-off the EGPS quickly when the faults of EGPS occur. The system has been applied to the EGPS of prototype RF ion source. Test results show that the data acquisition and control system for the EGPS can meet the requirements of the operation of prototype RF ion source.

Effect of ion and electron beam irradiation on surface morphology and optical properties of PVA

Polyvinyl alcohol(PVA) is a well-known friendly polymer for paper-making, textiles, and a variety of coatings, biomedical applications such as artificial pancreas, synthetic vitreous body, wound dressing, artificial skin,and cardiovascular device. In this paper, ion/electron beam is employed to get insight into the irradiation effect on surface morphology and optical properties of PVA polymer. UV-Vis spectra are recorded to investigate the effect of induced defects on the optical band gap and the formed carbon clusters size. Scanning electron microscopy(SEM) is used to relate and investigate surface morphology and optical properties of the target polymer with different doses(15, 30 and 60 min). Also, PVA polymer is subjected to theoretical studies by using semi-empirical PM7 quantum chemical method.

Effects of the ion-beam voltage on the properties of the diamond-like carbon thin film prepared by ion-beam sputtering deposition

Diamond-like carbon （DLC） thin film is one of the most widely used optical thin films. The fraction of chemical bondings has a great influence on the properties of the DLC film. In this work, DLC thin films are prepared by ion-beam sputtering deposition in Ar and CH4 mixtures with graphite as the target. The influences of the ion-beam voltage on the surface morphology, chemical structure, mechanical and infrared optical properties of the DLC films are investigated by atomic force microscopy （AFM）, Raman spectroscopy, nanoindentation, and Fourier transform infrared （FTIR） spec- troscopy, respectively. The results show that the surface of the film is uniform and smooth. The film contains sp2 and sp3 hybridized carbon bondings. The film prepared by lower ion beam voltage has a higher sp3 bonding content. It is found that the hardness of DLC films increases with reducing ion-beam voltage, which can be attributed to an increase in the fraction of sp3 carbon bondings in the DLC film. The optical constants can be obtained by the whole infrared optical spectrum fitting with the transmittance spectrum. The refractive index increases with the decrease of the ion-beam voltage, while the extinction coefficient decreases.

Thermal analysis of EAST neutral beam injectors for long-pulse beam operation

Two sets of neutral beam injectors(NBI-1 and NBI-2) have been mounted on the EAST tokamak since 2014. NBI-1 and NBI-2 are co-direction and counter-direction, respectively. As with indepth physics and engineering study of EAST, the ability of long pulse beam injection should be required in the NBI system. For NBIs, the most important and difficult thing that should be overcome is heat removal capacity of heat loaded components for long-pulse beam extraction. In this article, the thermal state of the components of EAST NBI is investigated using water flow calorimetry and thermocouple temperatures. Results show that(1) operation parameters have an obvious influence on the heat deposited on the inner components of the beamline,(2) a suitable operation parameter can decrease the heat loading effectively and obtain longer beam pulse length, and(3) under the cooling water pressure of 0.25 MPa, the predicted maximum beam pulse length will be up to 260 s with 50 keV beam energy by a duty factor of 0.5. The results present that, in this regard, the EAST NBI-1 system has the ability of long-pulse beam injection.

Copper Ion Beam Irradiation-Induced Effects on Structural,Morphological and Optical Properties of Tin Dioxide Nanowires

The 0.8 Me V copper （ Cu） ion beam irradiation-induced effects on structural, morphological and optical properties of tin dioxide nanowires （Sn02 NWs） are investigated. The samples are irradiated at three different doses 5 × 10^12 ions/cm2, 1 ×10^13 ions/cm2 and 5 × 10^13 ions/em2 at room temperature. The XRD analysis shows that the tetragonal phase of Sn02 NWs remains stable after Cu ion irradiation, but with increasing irradiation dose level the crystal size increases due to ion beam induced coalescence of NWs. The FTIR spectra of pristine Sn02 NWs exhibit the chemical composition of SnO2 while the Cn-O bond is also observed in the FTIR spectra after Cu ion beam irradiation. The presence of Cu impurity in SnO2 is further confirmed by calculating the stopping range of Cu ions by using TRM/SRIM code. Optical properties of SnO2 NWs are studied before and after Cu ion irradiation. Band gap analysis reveMs that the band gap of irradiated samples is found to decrease compared with the pristine sample. Therefore, ion beam irradiation is a promising technology for nanoengineering and band gap tailoring.

Ion Source Optimisation for Proton Beam Quality of the Van De Graaff Accelerator at iThemba LABS for Ion Beam Analysis

The operating principles of the two duoplasmatron ion sources and the PIG source available for the Van de Graaff accelerator have been determined qualitatively, mainly by studying the extensive literature on ion sources. The main characteristics of the three sources have therefore been determined experimentally on an ion source test bench. Important parameters of the sources such as the pressure and temperature in different regions of the sources not measured, because of space limitations. However, in spite of these limitations in quantitative understanding of the sources, sufficient information to continue with the study of the beam transport through the Van de Graaff accelerator and its beamlines could be obtained from these measurements. With regard to beam intensity, lifetime and gas consumption the measurements showed that the hotcathode duoplasmatron is at present by far the most suitable source for the van de Graaff accelerator. The emittance of the ion source was measured with two slits, 90 mm apart, and a Faraday cup in the ion source test bench at an arc voltage of 83 V, an arc current of 1 Amp, a filament voltage of 24 V and an extraction voltage of 5 kV. The measured emittance for 90% of the beam intensity is 48π mm mrad. This figure will be used to calculate the beam transmission through the Van de Graaf accelerator. Different computer programs have been used for these calculations from the ion source through the terminal section, the accelerator and beam line up to the Nuclear Microprobe (NMP) for beam quality.

Progress of the RF negative hydrogen ion source for fusion at HUST

Huazhong University of Science and Technology has developed an experimental setup of a radio frequency(RF) driven negative hydrogen ion source,to investigate the physics of production and extraction of the H^(-)ions for neutral beam injection in nuclear fusion reactors.The main design parameters of the ion source are:RF power ≤40 kW;extraction voltage ≤10kV;accelerator voltage ≤20 kV.This paper gives an overview of the progress of the ion source with particular emphasis on some issues.The RF driver and source plasma are analyzed and optimized in terms of impedance matching,plasma characteristics and power coupling.In regard to the simulation analysis,a plasma model based on the particle-in-cell method and a beam trajectory model considering beam stripping loss are developed to investigate the plasma and negative ions transport inside the ion source.Furthermore,a collisional radiative model of H and H2is built for plasma optical diagnosis.

Hefei utility negative ions test equipment with RF source:commissioning and first results

In order to study the key technology and physics of RF driven negative ion source for neutral beam injector in China, the Hefei utility negative ions test equipment with RF source was developed at Institute of Plasma Physics, Chinese Academy of Sciences（ASIPP）. Its negative ion source can be equipped with single or double RF drivers. There is a plasma expansion chamber with depth of 19 mm and an enhanced filter field. A three electrodes negative ion accelerator was employed to extract and accelerate the negative ions, which are plasma grid,extraction grid and ground grid. And there are several diagnostic tools for the plasma and beam parameters measurement. The characteristics of plasma generation, negative ion production and extraction were studied on the test equipment. The negative ion beam was extracted from the RF driven negative ion source for the first time. The detailed structure and main results are presented in this article.