Development of a Cs-free negative hydrogen ion source system using multi-pulsed plasma sources.

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.

Assessment and modification of an ion source grid design in KSTAR neutral beam system.

A new 2 MW NB (Neutral Beam) ion source for supplying 3.5 MW NB heating for the KSTAR campaign was developed in 2012 and its grid was made from OFHC (Oxygen Free High Conductivity) copper with rectangular cooling channels. However, the plastic deformation such as a bulging in the plasma grid of the ion source was found during the overhaul period after the 2012 campaign. A thermal-hydraulic and a thermo-mechanical analysis using the conventional code, ANSYS, were carried out and the thermal fatigue life assessment was evaluated. It was found that the thermal fatigue life of the OFHC copper grid was about 335 cycles in case of 0.165 MW/m(2) heat flux and it gave too short fatigue life to be used as a KSTAR NB ion source grid. To overcome the limited fatigue life of the current design, the following methods were proposed in the present study: (1) changing the OHFC copper to CuCrZr, copper-alloy or (2) adopting a new design with a pure Mo metal grid and CuCrZr tubes. It is confirmed that the proposed methods meet the requirements by performing the same assessment.

Operating characteristics of a new ion source for KSTAR neutral beam injection system.

A new positive ion source for the Korea Superconducting Tokamak Advanced Research neutral beam injection (KSTAR NBI-1) system was designed, fabricated, and assembled in 2011. The characteristics of the arc discharge and beam extraction were investigated using hydrogen and helium gas to find the optimum operating parameters of the arc power, filament voltage, gas pressure, extracting voltage, accelerating voltage, and decelerating voltage at the neutral beam test stand at the Korea Atomic Energy Research Institute in 2012. Based on the optimum operating condition, the new ion source was then conditioned, and performance tests were primarily finished. The accelerator system with enlarged apertures can extract a maximum 65 A ion beam with a beam energy of 100 keV. The arc efficiency and optimum beam perveance, at which the beam divergence is at a minimum, are estimated to be 1.0 A/kW and 2.5 uP, respectively. The beam extraction tests show that the design goal of delivering a 2 MW deuterium neutral beam into the KSTAR Tokamak plasma is achievable.

Hydrogen sensing under ambient conditions using SnO2 nanowires: synergetic effect of Pd/Sn codeposition.

Semiconducting SnO2 nanowires deposited with Pd and Sn nanoparticles on their surface are shown to be a highly sensitive hydrogen sensor with fast response time at room temperature. Compared with the SnO2 nanowire deposited with Pd or Sn nanoparticles alone, the Pd/Sn-deposited SnO2 nanowire exhibits a significant improvement in the sensitivity and reversibility of sensing hydrogen gas in the air at room temperature. Our investigation indicates that two factors are responsible for the synergistic effect of Pd/Sn codeposition on SnO2 nanowires. One is that in the presence of Pd the oxidation of Sn nanoparticles on the surface of the SnO2 nanowire is incomplete leading only to suboxides SnOx (1 ≤ x < 2), and the other is that the surface of the Pd/Sn-deposited SnO2 nanowire is almost perfectly hydrophobic.

Perioperative respiratory adverse events in children with active upper respiratory tract infection who received general anesthesia through an orotracheal tube and inhalation agents.

BACKGROUND: Active upper respiratory tract infection (URI), orotracheal intubation and use of inhalation anesthetics are known risk factors for perioperative respiratory adverse events (RAE). This study investigated the risk factors of perioperative RAE in children with these risk factors. METHODS: The records of 159 children who underwent general anesthesia with an orotracheal tube and inhalation were reviewed. These patients also had at least one of the following URI symptoms on the day of surgery: clear or green nasal secretion, dry or moist cough, nasal congestion, or fever. RAE such as laryngospasm, bronchospasm, oxygen desaturation and sustained cough were collected before induction, during intubation, during extubation, after extubation and in the postanesthesia care unit. RESULTS: Forty-five patients had RAE. The patients with RAE were younger than those without RAE. There were more passive smokers and a greater number of intubation attempts in patients with RAE than in those without RAE. The type of surgery and type of inhalation agents were not different between patients with and without RAE. Passive smoking was the only independent risk factor for RAE. CONCLUSIONS: In children with an active URI using orotracheal tube and inhalation anesthetics, passive smoking is an important risk factor for RAE.

The myth of the equiangular triangle for identification of sacral hiatus in children disproved by ultrasonography.

BACKGROUND AND OBJECTIVES: A triangle formed by the sacral hiatus and posterior superior iliac spines (PSISs) has been known as equiangular and has been proposed as a way to help identify the sacral hiatus for a caudal block. In children, however, no feasibility study of this triangle has been performed. We compared the expected sacral hiatus obtained from the equiangular triangle method and the real sacral hiatus confirmed by ultrasound. METHODS: Eighty children (aged 0.5-72 months) were placed in the left lateral decubitus position in full hip flexion. The vertex of an equiangular triangle formed inferior to PSISs was considered as the expected sacral hiatus by classic bony landmarks. The real sacral hiatus was identified by ultrasound. The angle formed by the 2 lines connecting each PSIS and the real sacral hiatus (angle θ) was also measured. The distances between the midpoint of PSISs and expected sacral hiatus (distance E) and real sacral hiatus (distance R) were measured and compared. RESULTS: The angle θ was greater than 60 degrees in all children (79.3 [9.3] degrees) and negatively correlated with age younger than 1 year. Distance R (3.5 [1.1] cm) was significantly shorter than distance E (4.9 [1.2] cm) (P< 0.001). The distance R positively correlated with age, weight, height, and the distance between the PSISs. CONCLUSIONS: In children, using the equiangular triangle to identify the sacral hiatus may be inappropriate because the actual triangle formed by the sacral hiatus and PSISs is not equiangular.

New ion source for KSTAR neutral beam injection system.

The neutral beam injection system (NBI-1) of the KSTAR tokamak can accommodate three ion sources; however, it is currently equipped with only one prototype ion source. In the 2010 and 2011 KSTAR campaigns, this ion source supplied deuterium neutral beam power of 0.7-1.6 MW to the KSTAR plasma with a beam energy of 70-100 keV. A new ion source will be prepared for the 2012 KSTAR campaign with a much advanced performance compared with the previous one. The newly designed ion source has a very large transparency (∼56%) without deteriorating the beam optics, which is designed to deliver a 2 MW injection power of deuterium beams at 100 keV. The plasma generator of the ion source is of a horizontally cusped bucket type, and the whole inner wall, except the cathode filaments and plasma grid side, functions as an anode. The accelerator assembly consists of four multi-circular aperture grids made of copper and four electrode flanges made of aluminum alloy. The electrodes are insulated using PEEK. The ion source will be completed and tested in 2011.

Numerical simulation for the accelerator of the KSTAR neutral beam ion source.

Recent experiments with a prototype long-pulse, high-current ion source being developed for the neutral beam injection system of the Korea Superconducting Tokamak Advanced Research have shown that the accelerator grid assembly needs a further upgrade to achieve the final goal of 120keV/65A for the deuterium ion beam. The accelerator upgrade concept was determined theoretically by simulations using the IGUN code. The simulation study was focused on finding parameter sets that raise the optimum perveance as large as possible and reduce the beam divergence as low as possible. From the simulation results, it was concluded that it is possible to achieve this goal by sliming the plasma grid (G1), shortening the second gap (G2-G3), and adjusting the G2 voltage ratio.

Korea Superconducting Tokamak Advanced Research vacuum and gas puffing system.

A piezoelectric valve, which has a flow rate of about 463 mbar l/s, has been installed to fuel the Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak. The valve flow rate is in situ calibrated by analyzing the pressure rise curve while fueling the vessel at a constant rate. The calibration method and results are presented. In addition to the flow rate, other vacuum system parameters, such as the pumping speed and the vessel volume, were experimentally obtained. Based on these measurements, a KSTAR vacuum system simulator was developed to calculate the valve drive signal to obtain a programmed pressure trace. An arbitrarily shaped pressure trace was successfully controlled in KSTAR with this hardware and software system.

Calculation of extracted ion beam particle distribution including within-extractor collisions from H-alpha Doppler shift measurements.

Prototype long pulse ion sources are being developed and tested toward the goal of a deuterium beam extraction of 120 keV/65 A. The latest prototype source consists of a magnetic bucket plasma generator and a four-grid copper accelerator system with multicircular apertures of 568 holes. To measure the angular divergence and the ion species of the ion beam, an optical multichannel analyzer (OMA) system for a Doppler-shifted H-alpha lights was set up at the end of a gas-cell neutralizer. But the OMA data are very difficult to analyze due to a large background level on the top of the three energy peaks (coming from H(+), H(2) (+), and H(3) (+)). These background spectra in the OMA signals seem to result from partially accelerated ion beams in the accelerator. Extracted ions could undergo a premature charge exchange as the accelerator column tends to have a high hydrogen partial pressure from the unused gas from the plasma generator, resulting in a continuous background of partially accelerated beam particles at the accelerator exit. This effect is calculated by accounting for all the possible atomic collision processes and numerically summing up three ion species across the accelerator column. The collection of all the atomic reaction cross sections and the numerical summing up will be presented. The result considerably depends on the background pressure and the ion beam species ratio (H(+), H(2) (+), and H(3) (+)). This effect constitutes more than 20% of the whole particle distribution. And the energy distribution of those suffering from collisions is broad and shows a broad maximum in the vicinity of the half and the third energy region.

Study on an azimuthal line cusp ion source for the KSTAR neutral beam injector.

In this study it is found that the cusp magnetic field configuration of an anode bucket influences the primary electron behavior. An electron orbit code (ELEORBIT code) showed that an azimuthal line cusp (cusp lines run azimuthally with respect to the beam extraction direction) provides a longer primary electron confinement time than an axial line cusp configuration. Experimentally higher plasma densities were obtained under the same arc power when the azimuthal cusp chamber was used. The newly designed azimuthal cusp bucket has been investigated in an effort to increase the plasma density in its plasma generator per arc power.

Long pulse beam extraction with a prototype ion source for the KSTAR neutral beam system.

Long pulse operational characteristics of the high current ion source for the KSTAR neutral beam system are described. The beam pulse length of 300 s was successfully operated at a beam power of 1.6 MW with a beam energy of 70 keV. Beam energy, beam current, beam divergence, arc power, and several other operational parameters were measured during a pulse to analyze the long pulse properties. The increase of the cooling water temperature of the accelerator grids and plasma generator components were measured by water flow calorimetric system using thermocouples. The temperature rises of the filament electrodes of the ion source and the G1 grids (plasma grids) of the accelerator turned out to be the critical factors of the long pulse operation in the current system.