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In arc discharge plasma, ion species ratio depends on plasma density and ion confinement time. To increase an atomic ion species ratio in an NBI (neutral beam injector) ion source, various ion sources have been designed with a higher ratio of plasma volume to effective ion loss area for increasing ion confinement time. In such designs, most NBI ion sources have a large arc chamber with strong cusp magnetic field. KSTAR NBI ion source also has a large arc chamber with a strong azimuthal line cusp configuration but its atomic ion (H+) beam fraction is small because its normal operation power levels of the arc discharges are comparatively lower than those of other NBI ion sources. In particular, the H2+ ion beam fraction is relatively large at about 40%. This means that there are many primary electrons in the beam extraction region. Through several Ele-orbit code simulations, it was found that some magnetic cusp configurations are effective in preventing primary electrons from nearing the plasma grid facing a plasma and having a high voltage potential. To reduce the molecular ion fraction in KSTAR NBI ion source and consequently increase its atomic ion fraction, experiments regarding the application of several new magnetic cusp configurations to the arc chamber were performed. Experimental results show that the new magnetic cusp configuration can increase the atomic ion fraction to approximately 80%, despite the low arc operation power at KSTAR NBI ion source.

The Korea Atomic Energy Research Institute has recently proposed and developed a novel cesium-free negative hydrogen/deuterium ion source system based on two pulsed plasma sources for fusion and particle accelerator applications. The main feature of this ion source system is the use of both magnetic filters and plasma pulsing (also called the temporal filter). The system operates with two alternate pulsing sequences related to the respective plasma sources, thereby switching the plasmas in the after-glow state in an alternating manner. This study investigates the temporal behavior of deuterium negative ions in the system in a qualitative way by conducting a time-resolved measurement of laser photodetachment current commensurate with the negative ion density. In preliminary experiments, the current in the initial after-glow state remains higher than in the active-glow state identical to a steady-state continuous wave plasma, and the ratio reaches a maximum of about three times. This indicates that the pulsing gives highly efficient negative ion volume formation. Furthermore, it is observed that the time duration when the current is maintained at high values can be prolonged (or modulated) with the alternate dual pulsing, which is not possible with conventional single pulsing. These results provide a clue that the multi-pulsed ion source system may offer a continuous supply of negative ions at high densities and consequently become an alternative to cesium seeded ion sources.

KAERI is presently developing a rectangular RF driven deuterium ion source for both neutron source and fusion applications. For a model-based design of a reliable impedance matching network for the ion source, we extend an equivalent circuit model of the ion source system by allowing effects of an isolation transformer and a Faraday shield on the system to be reflected in our previous model (Huh et al., 2017 Fusion Eng. Des. 121 337). In this paper we use the model to investigate the trends in external electrical characteristics of the ion source system (e.g., voltage and current across and through an RF antenna coil and the impedance matching network circuit components) with RF power of up to 50 kW. The model results provide criteria for the impedance matching network design and data for an assessment of the ion source performance.

A neutral beam (NB) ion source aimed to inject a 0.5-MW NB has been developed for Versatile Experiment Spherical Torus (VEST) plasma heating. Beam energy is generally limited to less than ∼20 keV to reduce particle orbit loss and beam shine-through. To meet this power demand, high-current ion beam extraction is important to achieve the required performance of the ion source. In this study, a 0.7-MW ion source was designed, fabricated, assembled, and optimized at the NB test stand in Korea Atomic Energy Research Institute (KAERI) considering the beam power losses in the beamline components. The ion source comprises a multicusped-bucket-type plasma generator and a multislot-triode-type ion accelerator with an extraction area of 12 cm × 46 cm. The characteristics of arc discharge and beam extraction were investigated using hydrogen gas to obtain the optimum operating parameters of the arc power, filament voltage, gas pressure, extraction voltage, and suppression voltage. The ion source was then conditioned and performance tests were primarily completed. Results of the experiments show that the ion source can extract sufficient ion beam power that is than 0.75 MW (50 A/15 keV) with 100-kW arc power. The arc efficiency and beam perveance were estimated to be 0.6 A/kW and 20–25 μP, respectively. Moreover, the design goal of delivering a 0.5-MW NB into the VEST plasma will be achievable based on the optimum operating conditions. This ion source has been installed in the VEST NB injection system at Seoul National University and its commissioning is ongoing.

The optimization of 2.45 GHz microwave coupling in an electron cyclotron resonance (ECR) ion source is investigated through experiments and full wave simulation studies. The axial magnetic field profile and an impedance transformer are the two major factors affecting the optimum power coupling. Experimental observations have shown that the beam current density increases when the two ECR zones are located in the plasma chamber and when the first ECR zone is close to the RF entrance. A coupling study with various magnetic field profiles finds that the gap distance between the RF window and first ECR zone and the effective ECR zone width determines the coupling efficiency. Optimum power coupling is obtained under the condition of an appropriately slight gap distance comparable to the half width of the effective ECR zone. The extracted beam current density increases when the second ECR zone becomes closer to the plasma grid. With the optimized axial magnetic field profile, impedance transformers are designed in consideration of reflection coefficient with respect to the plasma density. The performance of the impedance transformers is experimentally evaluated in terms of the efficiency (mA/W) with the findings consistent with the results of a simulation. The highest beam current density (∼165 mA/cm2) in these experiments is achieved with the optimized axial magnetic profile and the impedance transformer.

A short-pulse and high power supply system is developed for the pulse arc ion source of the neutral beam injector (NBI) of the Versatile Experiment Spherical Torus (VEST). The NBI system, with the maximum ion beam power of 20 keV, 0.8 MW and pulse length of 10 ms, was designed for the auxiliary plasma heating and current drive source. However, the beam injection energy needs to be lower than 20 keV under the initial target plasma parameters of VEST due to the beam-plasma coupling efficiency. For this reason, modulation of the beam energy in pulse duration is important to increase efficiency of the VEST NBI system. To satisfy these requirements, a pulse power system based on Marx generator is developed by utilizing high-energy capacitors and a solid-state switching system for the ion beam extraction and arc power supply. In addition, a battery-based power supply system is developed for the filament heating power supply which is highly cost-effective. In this paper, circuit structure and features of the power supply system of the ion source for the VEST NBI is described and the results of the discharges test are presented.

Within the framework for the development of a radio frequency driven positive ion source for fusion applications, KAERI is currently constructing a new high power large area radio frequency ion source. An impedance matching circuit maximizing the power transfer to a plasma in the ion source, while taking into account the technical feasibility, is preliminarily designed at a conceptual level. In order to estimate the plasma load impedance and design parameters, an integrated model composed of the hydrogen plasma global model, the two-dimensional electromagnetic model, the relative plasma dielectric constant calculation module, and the impedance matching circuit module is developed for the ion source with a rectangular tube geometry. By employing this design model, the design parameters dependent on RF input powers of up to 50 kW are investigated and the preliminary design is assessed.

This study evaluated the effectiveness of antioxidant (AO) on retarding aging of asphalt mixture using the large molecular size (LMS) of gel-permeation chromatogram (GPC) technique. A polymer stabilizer (designated as KL) and a hydrated lime (HL) were used for preparing dense-graded asphalt (DGA) mixes to examine the effect of the AOs on age retardation. The asphalt mixtures prepared with and without AO were aged artificially in two stages; the short-term aging (SA) for one hour at 160 °C and the long-term aging (LA) for one week at 76 °C. The LMS values were used in the statistical test for estimation of age retardation effect of the AOs and for predicting absolute viscosity. It was found that the KL and HL were effective for inducing reduction of aging significantly at α = 0.05 after SA and LA. Therefore, it was found that the LMS, which was obtained by GPC test, was a dependable variable that can be used for evaluation of age retardation. It was also observed that the KL and HL did apparently have an effect of reducing the AV, predicted by LMS, after SA and LA.

Poly(ethylene terephthalate) (PET) copolymers containing fluorenylidene bis(2-phenoxyethanol) (FBPE) were prepared. The glass transition temperature of copolymers increased continuously with the composition of FBPE. The glass transition temperature of PET/FBPE copolymer at loading of 15 mol% FBPE was 107 °C, which was 35 °C higher than that of PET. The melting temperature of PET/FBPE copolymers was decreased with the composition of FBPE, and it disappeared above 6 mol% of FBPE. The heat deflection temperature of copolymers increased from 60.7 °C for PET to 89.9 °C for the copolymer containing 15 mol% of FBPE. The values of optical transmittance of copolymers were 89-90 % at 550 nm, and no significant change was observed with the FBPE composition. The impact strength value of copolymer at loading of 10 mol% FBPE was 26 J/m, which was 20 J/m higher than that of PET.

Long-pulse operation has been initially and successfully demonstrated during a 100-s stable beam extraction in the neutral beam test stand (NBTS) system of the Korea Atomic Energy Research Institut...

A laser photodetachment (LPD) was applied to measure the absolute hydrogen negative ion (H−) density in an RF negative ion source. The ion source has been developed to study a Cs-free ion source utilizing a magnetic filter by permanent magnets to enhance the volume production of H− in the extraction region. Prior to a beam extraction experiment, the laser photodetachment was applied as an initial performance evaluation. The absolute H− densities were obtained by LPD with the variation of the RF power. The H− density reached 1.8 × 10 9 cm − 3 at an RF power of 5 kW. The comparison with the calculation of a particle balance model showed the discrepancy between the model and the LPD results. The LPD result showed the rapid increase in H− density with respect to the RF power compared to the model. By assuming the wall temperature increase and adjusting the recombination coefficient (γrec) of hydrogen (H) atoms on the walls, the discrepancy could be resolved. The recombination coefficient (γrec) plays an important role in determining the H− density in view of the fact that it can affect both the generation and the destruction processes of H−.

A large-area high-power radio-frequency (RF) driven ion source was developed for positive and negative neutral beam injectors at the Korea Atomic Energy Research Institute (KAERI). The RF ion source consists of a driver region, including a helical antenna and a discharge chamber, and an expansion region. RF power can be transferred at up to 10 kW with a fixed frequency of 2 MHz through an optimized RF matching system. An actively water-cooled Faraday shield is located inside the driver region of the ion source for the stable and steady-state operations of high-power RF discharge. Plasma ignition of the ion source is initiated by the injection of argon-gas without a starter-filament heating, and the argon-gas is then slowly exchanged by the injection of hydrogen-gas to produce pure hydrogen plasmas. The uniformities of the plasma parameter, such as a plasma density and an electron temperature, are measured at the lowest area of the driver region using two RF-compensated electrostatic probes along the direction of the short-and long-dimensions of the driver region. The plasma parameters will be compared with those obtained at the lowest area of the expansion bucket to analyze the plasma expansion properties from the driver region to the expansion region.

A 10 m s-pulsed NBI (Neutral Beam Injection) system for VEST (Versatile Experiment Spherical Torus) plasma heating is designed to provide a beam power of more than 0.6 MW with 20 keV H° neutrals. The VEST NBI injector is composed of 2 sets of 20 keV/25A magnetic cusp type bucket ion source, neutralizer ducts, residual ion dump, NB vessel with a cryopump, and rotating calorimeter. The position and size of these beamline components are roughly determined with geometric calculation of beam power transmission: the overall length of beamline is 1.8 m, spacing between ground grid and neutralizer of 1.0 m, and position of residual ion dump is 0.8 m downstream from the neutralizer exit. Optimizing the gas feed between ion source and neutralizer can leads to a neutralization efficiency of ∼76%. Finally, the beam power of maximum 0.6 MW can be delivered to the VEST plasma with a beam loss of 10%.

An efficient heating and current drive scheme in central or off-axis region is required to realize steady state operation of tokamak fusion reactor. And the fast wave in lower hybrid resonance range of frequency could be a candidate for such an efficient scheme in high density and high temperature plasmas. Its propagation and absorption characteristics including current drive and coupling efficiency are analyzed for Versatile Experiment Spherical Torus and it is shown that it is possible to drive current with considerable current drive efficiency in central region. The RF system for the fast wave experiment including klystron, transmission systems, inter-digital antenna, and RF diagnostics are given as well in this paper.

A small-scale test stand of a negative NBI source composed of a prototype negative ion source, an RF generator, and an HV power supply for negative ion beam extraction has been established. The magnetic filter and a beam extraction grid system with electron deflection magnets were designed for the prototype negative ion source. The BL value of the magnetic filter is 1.6 mTm and almost all electrons are deflected onto the surface of the extraction grid. The first negative ion beam extraction experiments have been carried out. When the extraction voltage is 5.6 kV, the negative ion current density is 0.6 mA/cm2 at 5 kW RF power. The e/H− ratio is about 2–3 and it decreased below 1 when the electrical potential of the plasma bucket is grounded.

A large-scale hydrogen arc plasma source was developed at the Korea Atomic Energy Research Institute for a high power pulsed NBI system of VEST which is a compact spherical tokamak at Seoul national university. One of the research target of VEST is to study innovative tokamak operating scenarios. For this purpose, high current density and uniform large-scale pulse plasma source is required to satisfy the target ion beam power efficiently. Therefore, optimizing the plasma parameters of the ion source such as the electron density, temperature, and plasma uniformity is conducted by changing the operating conditions of the plasma source. Furthermore, ion species of the hydrogen plasma source are analyzed using a particle balance model to increase the monatomic fraction which is another essential parameter for increasing the ion beam current density. Conclusively, efficient operating conditions are presented from the results of the optimized plasma parameters and the extractable ion beam current is calculated.

This article presents the Cartesian position control of a quadrotor system in the indoor environment. Prior to applying the position control to a quadrotor system, the quadrotor is localized to measure the status of the quadrotor system under the vision system. Due to the expensive cost of motion-capturing sensors, a single camera is used to detect the heading angle and the position by using the color of markers on the top of the quadrotor system. Since a single camera cannot detect the distance from the object, compensation methods for the position and height are presented. Localization for the height can be done by using local information on the basis of the regular rectangular shape of the tiles on the floor. Control performances of the hovering, heading angle and trajectory are evaluated by empirical studies.

The long-pulse acceleration of the high-power positive ion beam has been demonstrated with the JT-60 positive ion source in the joint experiment among Japan Atomic Energy Agency (JAEA), Korea Atomic Energy Research Institute (KAERI) and National Fusion Research Institute (NFRI) under the collaboration program for the development of plasma heating and current drive systems. In this joint experiment, the increase of the heat load and the breakdowns induced by the degradation of the beam optics due to the gas accumulation was one of the critical issues for the long-pulse acceleration. As a result of development of the long-pulse operation techniques of the ion source and facilities of the neutral beam test stand in KAERI, 2 MW 100 s beam has been achieved for the first time. The achieved beam performance satisfies the JT-60SA requirement which is designed to be a 1.94 MW ion beam power from an ion source corresponding to total neutral beam power of 20 MW with 24 ion sources. Therefore, it was found that the JT-60 positive ion sources were applicable in the JT-60SA neutral beam injectors. Moreover, because this ion source is planned to be a backup ion source for KSTAR, the operational region and characteristic has been clarified to apply to the KSTAR neutral beam injector.

An efficient current drive scheme in central or off-axis region is required for the steady state operation of tokamak fusion reactors. The current drive by using the fast wave in frequency range higher than two times lower hybrid resonance (w>2wlh) could be such a scheme in high density, high temperature reactor-grade tokamak plasmas. First, it has relatively higher parallel electric field to the magnetic field favorable to the current generation, compared to fast waves in other frequency range. Second, it can deeply penetrate into high density plasmas compared to the slow wave in the same frequency range. Third, parasitic coupling to the slow wave can contribute also to the current drive avoiding parametric instability, thermal mode conversion and ion heating occured in the frequency range w

Minimizing power loss of a neutral beam imposes modification of the accelerator of the ion source for further improvement of the beam optics. The beam optics can be improved by focusing beamlets. The injection efficiencies by the steering of ion beamlets are investigated numerically to find the optimum modification of the accelerator design of the NBI-1B ion source. The beam power loss was reduced by aperture displacement of three edge beamlets arrays considering power loadings on the beamline components. Successful testing and operation of the ion source at 60 keV/84% of injection efficiency led to the possibility of enhancing the system capability to a 2.4 MW power level at 100 keV/1.9 μP.