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Protein tyrosine phosphatases (PTPs) are an important class of enzymes that modulate essential cellular processes through protein dephosphorylation and are dysregulated in various disease states. There is demand for new compounds that target the active sites of these enzymes, for use as chemical tools to dissect their biological roles or as leads for the development of new therapeutics. In this study, we explore an array of electrophiles and fragment scaffolds to investigate the required chemical parameters for covalent inhibition of tyrosine phosphatases. Our analysis juxtaposes the intrinsic electrophilicity of these compounds with their potency against several classical PTPs, revealing chemotypes that inhibit tyrosine phosphatases while minimizing excessive, potentially non-specific reactivity. We also assess sequence divergence at key residues in PTPs to explain their differential susceptibility to covalent inhibition. We anticipate that our study will inspire new strategies to develop covalent probes and inhibitors for tyrosine phosphatases.

Protein tyrosine phosphatases (PTPs) are an important class of enzymes that modulate essential cellular processes through protein dephosphorylation and are dysregulated in various disease states. There is demand for new compounds that target the active sites of these enzymes, for use as chemical tools to dissect their biological roles or as leads for the development of new therapeutics. In this study, we explore an array of electrophiles and fragment scaffolds to investigate the required chemical parameters for covalent inhibition of tyrosine phosphatases. Our analysis juxtaposes the intrinsic electrophilicity of these compounds with their potency against several classical PTPs, revealing chemotypes that inhibit tyrosine phosphatases while minimizing excessive, potentially non-specific reactivity. We also assess sequence divergence at key residues in PTPs to explain their differential susceptibility to covalent inhibition. We anticipate that our study will inspire new strategies to develop covalent probes and inhibitors for tyrosine phosphatases.

A review of tungsten technology development in Korea is briefly given. According to the upgrade plan of Korea superconducting tokamak advanced research (KSTAR) tokamak associated with Korean fusion energy R&D program, graphite plasma-facing components will be replaced with tungsten-based ones to handle the high-peak heat load caused by an increase of heating power up to 26 MW. Brazing technique to bond tungsten was developed and tungsten blocks were manufactured. Blocks were installed at the central divertor in KSTAR and exposed to high heat flux. Under high heat flux and long-pulse discharge, tungsten blocks were severely damaged. Molten tungsten materials show movements towards the high field side, which is j×B direction. The COMSOL® modeling described the melting event quantitatively well. The failure of a water cooling system with a metal wall environment during a long-pulse plasma operation is very critical.

We open an avenue for discussing how we can pave the way for compliance with existing regulations is a far-reaching factor for settling nuclear fusion technology. Based on a model of the Korean Fusion Demonstration Reactor (K-DEMO) with a target fusion power of 2.2 GW, we assess the intrinsic safety determinants of internal energy sources, the expected radioactive waste, and the tritium management. Regarding these safety factors, we scrutinize the compatibility of the current legislative environment in Korea with K-DEMO and envisage foreseeable obstacles, such as licensing of the nuclear facilities and acceptability of the radioactive waste. Based on precedent licenses for the Korean Superconducting Tokamak Advanced Research (KSTAR) and lessons learned from the International Thermonuclear Experimental Reactor (ITER), we examine hazardous factors that would threaten regulatory compliance of K-DEMO. This approach can help shape a fusion-compatible framework for consolidating the necessary technical provisions and regulatory baselines reflecting social acceptance with a sense of safety. Fusion-compatible aspects in the regulatory environment are discussed, from fusion philosophy to subordinate administrative and technical guidelines, facility classification, and detailed methods guaranteeing integrity and safety. This paper will contribute to the timely settlement of fusion demonstration facilities and subsequent commercial plants.

Results from KSTAR powder injection experiments, in which tens of milligrams of boron nitride (BN) were dropped into low-power H-mode plasmas, show an improvement in wall conditions in subsequent discharges and, in some cases, a reduction or elimination of edge-localized modes (ELMs). Injected powder is distributed by the plasma flow and is deposited on the wall and, over the course of several discharges, was observed to gradually reduce recycling by 33%, and decrease both the ELM amplitude and frequency. This is the first demonstration of the use of BN for ELM mitigation. In all of these experiments, an Impurity Powder Dropper (IPD) was used to introduce precise, controllable amounts of the materials into ELMy H-mode KSTAR discharges. The plasma duration was between 10 s and 15 s, I p = 500 kA, B T = 1 . 8 T, P NBI = 1 . 6 MW, and P ECH = 0 . 6 MW. Plasma densities were between 2 and 3 × 1 0 19 m−3. In all cases, the pre-fill and startup gas-fueling was kept constant, suggesting that the decrease in baseline D α emission is in fact due to a reduction in recycling. The results presented herein highlight the viability of powder injection for intra-shot and between-shot wall conditioning.

In this study, we investigated thermal and microstructural properties of pure and dispersion strengthened tungsten fabricated by Spark Plasma Sintering (SPS) method in comparison to the tungsten materials produced by different commercial suppliers. We measured the thermal conductivity of the examined materials and compared them with chemical composition, density and microstructure of the samples. Thermal conductivity up to 900 ℃ was derived from thermal diffusivity and specific heat measurement and chemical composition was analyzed through glow discharge mass spectroscopy. Thermal conductivity values show a close correlation with content of compositional element. On the other hand, Vickers hardness shows correlation with the average grain size of the samples. The sample produced by different fabrication process shows different density and thermal conductivity. While TiC and Y2O3 added tungsten fabricated by SPS method shows improved stability in microstructure against recrystallization after exposure to high heat flux, the reduction of thermal conductivity is analyzed in comparison to the amount of contained additive elements.

The variation of plasma current and magnetic fields generated by superconducting magnet coils causes electromagnetic (EM) loads especially during the abrupt plasma current changes such as major disruption (MD) and the vertical displacement event (VDE) of plasma. The EM loads are one of the most important external loads for in-vessel components like blanket and divertor modules. The aim of this study is to estimate the EM loads on the K-DEMO divertor module under MD by using the commercial finite element software, ANSYS Mechanical/Emag. The superconducting magnet system of K-DEMO includes 16 toroidal field (TF) coils, 8 central solenoid (CS) coils, and 12 poloidal field (PF) coils. The magnetic field at the plasma center is about 7.4 T and the peak field is as high as ˜16 T. The conceptual model of the K-DEMO divertor module including outboard and inboard targets, dome, and the cassette body with connecting supports was developed. The 22.5° sector model applying symmetric boundary condition on cutting surfaces was employed to calculate EM loads efficiently. The reduced activation ferritic martensitic (RAFM) steel has been considered as the structural material of in-vessel components. Based on the current design concept of the K-DEMO, EM loads and eddy current are calculated.

The development of W/Cu/CuCrZr mock-ups by hot isostatic pressing (HIP) bonding technology is in progress for the application to tungsten divertor. In HIP process, physical vapor deposition (PVD) method was applied for interlayer coating of high purity nickel (Ni) and copper (Cu). Interlayer coatings were selected to enhance diffusion between tungsten (W) and oxygen free high conductivity copper (OFHC-Cu) interlayer during the HIP bonding process. The Ni and Cu were deposited by different thicknesses on tungsten surface with roughness of 6Z and 0.8Z. HIP technology is employed with two kinds of processing conditions: 60 MPa, 600 ℃ and 70 MPa, 700 ℃. The interlayer of samples are observed by FE-SEM and EDS and subjected to shear test and heat flux test. There is no significant difference in shear strength due to PVD coating thickness. But the shear strength of samples fabricated by 70 MPa and 700 ℃ HIP condition is higher than those fabricated by 60 MPa and 600 ℃ condition. Heat flux tests were performed to compare the thermal conductance through the bonded layer and thermal fatigue behavior of the samples as a preliminary test of bonding quality. All these results were analyzed systematically to find the optimum fabrication conditions in the HIP bonding of W/Cu/CuCrZr.

Boronization procedure for Versatile Experiment Spherical Torus (VEST) is developed in order to reduce the oxygen impurity during the Ohmic plasma discharge. Carborane (C2B10H12) powder has been chosen for a safe operation. During the helium glow discharge, the sublimated carborane is diffused into the vacuum vessel, which results in thin boron-containing coatings on the vacuum vessel wall. After the boronization, qualitative changes in visible light intensities of oxygen and boron lines are observed indicating that the water concentration is reduced globally. The quality of discharges is greatly improved: a discharge with less radiative loss is achieved, which leads to a record shot of 0.1 MA plasma current and a nearly doubled pulse length.

Plasma-facing components have castellated structure for thermo-mechanical durability and integrity under high heat flux loads. However, fuel co-deposition in the grooves of the castellation may enh ...

Damage and melting of ITER-like tungsten castellated blocks – made of tungsten top layer, copper inter-layer, copper alloy base (CuCrZr) – exposed to long pulse H-mode plasmas were investigated. Since the blocks were not actively cooled, the temperature of blocks was increased rapidly up to melting point of tungsten during H-mode plasmas resulting in severe damage such as cracks and melting of tungsten layer. It is observed that the copper inter-layer located at 5 mm below the surface of the tungsten was also melted indicating that the temperature of the interface had reached the melting point of copper, at least 1200 °C. Melted tungsten material was moved towards j × B direction (high filed side). The melting event was reproduced by 3D transient modeling using COMSOL with 2 MW/m2 heat load and explains the observation quantitatively well. This indicates that failure of cooling system during a long pulse operation with metal walls, especially melting of copper inter-layer will be critical.

Typical H-mode plasmas in tokamaks are accompanied by Edge localized modes (ELMs). ELM crash leads to a transient, but much higher heat load on the divertor, for instance, heat flux deposited during typical type I ELM in JET is several ten MW/m2. ELMs have to be suppressed or mitigated to protect divertor structure, even that made of tungsten. In order to control ELMs in H-mode, Resonant Magnetic Perturbation (RMP) is often applied. For instance, KSTAR has successfully suppressed ELMs by applying n = 1 and 2 RMP. RMP bifurcates separatrix into several smaller segments resulting in reduction of local heat load on divertor due to the use of much wider areas. Nevertheless, erosion, deposition and recycling behavior in divertor region have been changed significantly by applying RMP. This paper reports the effect of RMP on erosion of divertor region in KSTAR compared with standard H-mode plasmas. In H-mode plasmas without RMP, toroidal slit samples are eroded with an erosion rate of 0.96 nm/s. In H-mode plasmas with n = 1 and n = 2 mixed RMP, toroidal slit samples are eroded with erosion rate of 1.40 nm/s and with n = 2 RMP, poloidal slit samples show significant erosion with erosion rate of 1.42 nm/s. Those results indicate that RMP could enhance local erosion significantly by a factor of 50%. Results from more detailed analysis will be reported in this paper.

Korea Superconducting Tokamak Advanced Research (KSTAR) program is strongly focused on solving the scientific and technological issues in steady-state high performance plasma operation in preparation for ITER operation as well as the design basis for DEMO. In this regards, KSTAR has made significant advances in developing long pulse and high performance plasma scenarios utilizing the advantage of the fully superconducting tokamak. Ten-year of KSTAR operation showed the outstanding progress in the plasma control extending the operation window of the plasma discharges achieving the H-mode up to 1 MA in plasma current, up to 72 s in flat top duration, and up to 2.16 in elongation. In addition to the long pulse discharge, high performance discharges with high betas (βN ~ 3) could be achieved in the broad range of edge safety factor (q95) without external error field correction. The unique features of the KSTAR device (magnetic accuracy with extremely low error fields, steady-state capable heating systems, in-vessel control coils, and advanced imaging and profile diagnostics) has been fully exploited to explore the unveiled physics as well as to exploring the systematic solution for suppression of edge localized mode (ELM) crash. Achieved examples are the record long pulse of H-mode operation without an ELM crash (~ 30 s up to date), and progress in the fundamental transport physics through systematic study using these unique capabilities. Based on the previous research results, intensive research will be followed to explore the advanced high beta operation (βN ~ 4) with fully suppressed harmful MHD instabilities aiming the integrated solution for DEMO. In this regards, an additional current drive systems and in-vessel structures will be upgraded.

Background: Atherosclerosis is a major global health concern. Targeting macrophages is hypothesized as an alternative treatment for atherosclerosis. Methods: We synthesized alginate-based cisplatin-loaded nanogels (TANgel) as a pH-responsive drug-releasing theranostic nanoplatform for macrophage cells. Carboxylic acid groups of alginic acid were modified with iminodiacetic acid (IDA) to enhance chelation of platinum ions. The near infrared (NIR) fluorophore ATTO655 was conjugated to the modified alginic acid. Cisplatin was used as an antiproliferation drug and as a crosslinking agent between alginate molecules to form TANgel. Release behavior of cisplatin from TANgel was analyzed under different pH conditions. Cellular uptake and therapeutic efficacy of TANgel were tested in the macrophage cell line J774A.1 and normal human cell lines such as HDMVECn. Results: The nanogel had a narrow size distribution of approximately 100 nm. The nanogel showed highly pH-responsive drug release behavior. All incorporated cisplatin was released at pH 5 within 48 h, while less than 15% was released at pH 7.4. The nanogel was preferentially taken up by J774A.1 cells compared to normal human cells, enabling selective NIR fluorescence imaging and chemotherapy of macrophage cells. In addition, the nanogel formulation lowered the therapeutic concentration of the drug with and without low dose radiation therapy (RT) compared to the free drug form. Conclusions: This nanogel system may have potential utility for selective NIR fluorescence imaging and combined chemo/radio therapy of proliferating macrophage cells in atherosclerotic regions, allowing for reduction of systemic toxicity.

이 연구의 목적은 교생실습을 통한 예비체육교사의 반성적 문제해결과정을 알아보는 것에 목적이 있다. 이 연구는 셀프연구방법을 사용하였고, 연구참여자는 유목적 표집 중 결정적 사례 표집법에 의해 선정되었다. 이 연구사례는 교생실습강좌의 현장과제로 실시된 예비체육교사의 반성일지이며, 자료는 반성일지 보고서를 주 자료로 사용하였고 연구자의 심층면담 일지를 추가 자료로 수집하였다. 수집된 자료는 NVivo 11을 사용하여 수용적 문제인식-반성적 원인분석-인과적 단초발견-실천적 해결노력-창의적 문제해결의 단계로 범주화하였다. 예비체육교사의 반성적 문제해결과정에서 나타난 결과는 다음과 같다. 첫째, 체육교사로 성장하기 위해 맥락적 문제의식을 갖는 태도가 필요하다. 둘째, 문제해결과정에서 경험하는 좌절을 극복하고 재시도를 하는 노력을 통해 자긍심을 가져야 한다. 셋째, 지도교사의 영향력이 크므로 선정과정의 기준과 적절성이 요구된다. 넷째, 교사지식의 적정한 수준과 현장 적용 가능성에 대한 사전 준비가 필요하다. 따라서 예비체육교사의 반성적 실천 태도는 계획과 피드백을 통하여 촉진과 증진될 수 있다.

This paper presents a shutdown dose rate (SDR) calculation to estimate a newly developed preliminary concept of the equatorial port model for the Korean fusion demonstration reactor (K-DEMO). The equatorial port model was designed to provide effective radiation shielding abilities adopting the port shielding block and labyrinth structure, which was integrated into the modified K-DEMO neutronic analysis model by the Monte Carlo automatic modeling system. A rigorous two-step method was applied to couple transport (MCNP) and activation (FISPACT) codes according to three steps of calculation procedures. The results of neutron flux and decay gamma transport calculation for the equatorial port area have been indicated in this paper. The SDR calculation result near the equatorial port area reveals that a dose level in the equatorial port interspace was below $100~\mu $ Sv/h after 12 days of the shutdown. Shielding blocks and two labyrinth structures prove that they effectively attenuate neutrons on the current concept of the equatorial port model.

We report our recent investigation on a passive mitigation strategy of the mirror deposition in magnetically confined fusion (MCF) devices, employing a newly designed duct system with baffles at KSTAR tokamak. Our mitigation strategy of the first mirror deposition is to suppress the deposition of impurity species onto the first mirror by confining inert gas such as helium in the duct with baffles located in front of the first mirror. To achieve this final goal, feasibility of this technique at a real tokamak was investigated with regard to the effect on the plasma condition in this paper. To assess the effect of the helium gas flow on the plasma condition, 5 sccm amount of helium gas was injected into the duct for about 70% of shots in the year 2016. This quantity of helium gas was found to be insignificant in terms of the effect on plasma performance. To estimate the deposition quantity on the sample during plasma operation in-situ, quartz crystal microbalances (QCMs) were also installed for thickness detection in real time at KSTAR. The net deposition rates of these samples at KSTAR were about 0.6–40 ng/h cm2 (2.7 × 10−3–0.18 nm/h (graphite)) depending on the kinds of operations such as plasma shots, glow discharge cleaning, and baking of the tokamak first wall. We found that the most detrimental condition with regard to the mirror deposition rate at KSTAR is the glow discharge wall cleaning (GDC) in the baking condition.

The laser-induced breakdown spectroscopy (LIBS) approach has been used to ex-situ measure the deuterium (D) retention and carbon (C) deposition on the surface of tungsten (W) castellated blocks adopted from the Korea Superconducting Tokamak Advanced Research (KSTAR). The well-resolved D∖H spectra with a high signal to noise ratio (S/N) up to 500 has been achieved.The lateral distributions of the deposited C and detained D on the three different shaped divertor blocks (Rounded, Chamfered, Double chamfered) were investigated. The depth of the deposited C layer was also measured as ∼200 nm to ∼650 nm based on the spectral line intensity using a self-defined function approach. It was found that the edge shape strongly affects the C and D distribution features, which are dependent on the particle and heat flux arriving on the related area. The features of C and D deposition and their distributions on the different shaped blocks provide valuable information for the theoretical model on plasma-wall interaction. This indicates that LIBS has a unique potential for the diagnosis of impurity deposition and fuel retention in KSTAR or related fusion devices.

We developed a hybrid probe comprised of an electrical probe and optical probe to investigate the properties of the far scrape-off layer (SOL) plasma and the blob in Korea Superconducting Tokamak Advanced Research (KSTAR). The hybrid probe is attached to a horizontal manipulator, and the radial profiles of plasma parameters such as electron temperature, ion flux, and the Dα signals are measured with time resolution (100 μs) by varying the radial position (0.15–0.4 m away from the last closed flux surface (LCFS)). In ELMy H-mode discharge, the blob radial velocity is obtained from the time delay between the start of the peak Dα signal and the peak electrical probe current and the corresponding radial position. The obtained blob radial velocity is in good agreement with the radial velocity of the filament obtained using the two radially separated electric probes at the far-SOL in the KSTAR. The profiles of the blob radial velocity for five discharges are obtained depending on the radial position in similar experimental parameters. The blob radial velocity is estimated as 44.1–250 m/s and 25.4–135 m/s at the radial position of 0.15 m (near the LCFS) and 0.4 m (near the outer wall), respectively. It is observed that the blobs are propagated to the outer wall with various radial velocities, and the radial velocity slows down as they get closer to the outer wall. The hybrid probe measurement found that the blob properties are about 2 to 10 times larger than the background plasma, and these show the same trend with the blob radial velocity. The hybrid probe is expected to contribute to the analysis and understanding of far-SOL plasma research in fusion reactors.

In this study, we investigated the material properties of tungsten mono-blocks undergone high heat flux test. The ITER-like tungsten mono-block specimens were fabricated by two kinds of joining methods. The tungsten-Cu interlayer joint was made by gas pressure casting and Cu interlayer-CuCrZr cooling tube were joined by hot radial pressing (HRP) or brazing method. To evaluate the integrity of the fabricated mono-blocks, high heat flux tests were done on the small mockups under cyclic heat load of 10 MW/m2 up to 5,000 cycles. We measured the microstructure, hardness, and surface state of the tungsten armors before and after the heat flux exposure experiment. The Vickers hardness profile measured from the surface down to the Cu interlayer showed a noticeable reduction around 200 μm ~ 500 μm depth after high heat flux test compared to that before the test depending on the bonding quality of mockup specimens. At depth beyond 800 μm, the Vickers hardness did not show any notable difference before and after the high heat flux test, which indicates the material property of tungsten is not so much affected in this region at the above heat flux condition. The microstructure and grain size distribution was measured and analyzed by SEM and EBSD. The correlation between the microstructure and hardness profile, and the impacts of the mockup performance under HHF test to the integrity of tungsten armors are analyzed.

Nanomaterials have revolutionized cancer imaging, diagnosis, and treatment. Multifunctional nanoparticles in particular have been designed for targeted cancer therapy by modulating their physicochemical properties to be delivered to the target and activated by internal and/or external stimuli. This review will focus on the fundamental “chemical” design considerations of stimuli-responsive nanosystems to achieve favorable tumor targeting beyond biological barriers and, furthermore, enhance targeted cancer therapy. In addition, we will summarize innovative smart nanosystems responsive to external stimuli (e.g., light, magnetic field, ultrasound, and electric field) and internal stimuli in the tumor microenvironment (e.g., pH, enzyme, redox potential, and oxidative stress).

Having a sub-ns response time and not requiring physical contacts to the measurement points, a voltage measurement system based on the Pockels electro-optic effect, referred to as a PE (Pockels effect)-based voltmeter, is widely used for pulsed high voltage devices such as accelerators and X-pinch systems. To correct for the misalignment of a Pockels cell and the transmittance ratio of a beam splitter, a polar-coordinate-based data analysis scheme has been proposed. This scheme also overcomes a limitation on the measurable range of a PE-based voltmeter without ambiguity and can measure the half-wave voltage of a Pockels cell. We present an improved polar-coordinate-based data analysis scheme using an ellipse fitting method, which can correct for misalignments of all the optics components of a PE-based voltmeter while keeping the advantages of the previous scheme. We show the results of the improved data analysis scheme for measuring a slowly modulated voltage up to approximately 5 kV in about 30 s and a pulsed high voltage up to 7 kV with a rise time of less than 20 ns.

The characteristics of the divertor particle and heat fluxes are investigated during ELM bursts in ELMy H-mode plasmas with the lower single null (LSN) configuration in Korea Superconducting Tokamak Advanced Research (KSTAR). The particle and heat fluxes are evaluated from the electric probe measurements at the divertor region. It is found that the peak amplitude of the divertor flux during an ELM burst obtained near the outer strike point (OSP) decreases up to about 20% as the ELM frequency increases by a factor of ∼6.5 due to the ELM mitigation and the plasma shaping, which is similar to the trend of the amplitude versus the frequency of the ELM observed in other tokamaks. The ELMs are mitigated by using several methods as magnetic perturbation (MP) field, supersonic molecular beam injection (SMBI) and electron cyclotron heating (ECH) at the edge region. In addition, the particle flux, evaluated at the far scrape-off layer (SOL) region, is less than 1% of the divertor particle flux. In this work, results from the experimental investigations of particle and heat fluxes during ELM bursts from the electric probe measurements at the divertor and far SOL regions are presented.

Some components in electric probe diagnostics (EPDs) are improved in order to investigate characteristics of edge plasmas in the upstream scrape-off-layer (SOL) region and to measure wall and divertor fluxes during L-mode and H-mode plasma discharges in the Korea Superconducting Tokamak Advanced Research (KSTAR). From the upgrades in the EPDs, the measured error of the elapsed distance for the evaluation of the SOL profiles can be reduced up to 1% and the ion saturation current of up to 1.0 A near an outer strike point (OSP) can be measured at the divertor region. In the SOL profile measurements during L-mode and inner wall limited plasma (BT = 2.0 T, Ip = 0.4 MA), the e-folding lengths in the main SOL region λTe and λne are evaluated as 3.5 cm and 2.1 cm, respectively. From particle flux measurement at the far SOL region during a diverted ELMy H-mode discharge (BT = 1.8 T, Ip = 0.65 MA), peaked heat flux toward to outboard wall during ELM bursts is estimated up to ∼20 k Wm−2, which may be less than 1% of the peaked divertor heat flux expected for the neutral beam (NB) heating power PNB of ∼2.66 MW and stored energy WTOT of ∼0.38 MJ. In addition, the movement of the OSP during a diverted H-mode plasma (BT = 2.4 T, Ip = 0.5 MA) can be detected from the divertor probe measurement and peaked heat flux near the OSP is estimated as few MW m−2 for PNB = 3.0 MW, WTOT = ∼0.25 MJ. In this work, the technical details of the EPDs including its upgrades and some experimental results from EPD measurements are presented.

To evaluate the capability of Fe Cr Al ferritic steels as tritium permeation barrier in fusion systems, the oxidation behavior together with the permeation behavior of a Fe Cr Al steel was investigated. Gas driven permeation experiments were performed. The permeability of the oxidized Fe Cr Al steel was obtained and a reduced activation ferritic/martensitic steel CLF-1 was used as a comparison. In order to characterize the oxide layer, SEM, XPS, TEM, HRTEM were used. Al 2 O 3 was detected in the oxide film by XPS, and HRTEM showed that Al 2 O 3 in the α phase was found. The formation of α-Al 2 O 3 layer at a relatively low temperature may result from the formation of Cr 2 O 3 nuclei.

The preliminary conceptual design of the Korean fusion demonstration reactor (K-DEMO) with a major radius of 6.8 m and the fusion power of 2200 MW has been studied since 2012. The overall configuration of the K-DEMO divetor system based on the ITER-like water-cooled tungsten technology is a double-null type symmetric divertor subdivided into 32 toroidal modules for the vertical maintenance. A detached divertor scenario with impurity seeding was considered as the primary approach for the power exhaust to reduce the peak heat flux lower than the engineering limit of 10 MW/m2. The power exhaust performance at the scrap off layer was estimated by using UEDGE-2D code, a two-dimensional fluid transport code for collisional edge plasma and neutral species like N, Ne, and Ar. Particle and heat flux on inboard and outboard divertor targets were calculated for the detached cased depending on parameters such as the impurity seeding rate, pumping rate, and the pedestal density. On the other hand, a magnetic solution like X-divertor, snowflake divertor, and super X-divertor to expand the plasma wet area was considered for K-DEMO since the detached divertor increasing a radiation fraction by impurity seeding might be able to be unstable. However, the extremely high current of poloidal coils was required more than the engineering limit, 20 MA, to form magnetic field lines for the alternative divertors. Based on the physical calculation of the edge plasma, engineering analyses were carried out to find out the thermal and structural reliability. The thermo-hydraulic analysis confirmed thermal stability, whether all comprising materials are operating within their allowable temperature windows when the case of the peak heat flux is set to 10 MW/m2 on the outboard divertor target. The response surface optimization method derived two optimal design candidates employing two kinds of heat sink materials, respectively: the reduced activation ferritic martensitic (RAFM) steel and CuCrZr alloy. The drawbacks and merits of the two materials were definite. The optimal design with applying RAFM steel was vulnerable to withstand thermal and mechanical loads since low thermal conductivity caused too thin thickness of the heat sink. On the other hand, the CuCrZr alloy has critical drawbacks in terms of activation and radioactive waste despite its high thermal conductivity. Meanwhile, preliminary electromagnetic (EM) analysis was carried out to estimate the EM loads caused by the abnormal behaviors of plasma since EM loads are one of the most critical external loads for designing a DEMO divertor.

The K-DEMO superconducting tokamak is being studied for the realization of the fusion plant since 2012. The preliminary design of the conductor of each magnet introduced in 2015 and the design are being updated for solving engineering issues. In the previous study, the K-DEMO CS(Central Solenoid) conductor was modified to reduce the number of the cooling channel. A central cooling spiral was applied to the CS conductor to minimize the pressure drop in a long cooling path and the shape of conductor was changed to square. This design change should guarantee to provide sufficient cooling conditions to reach the full flattop current under a wide range of conditions especially, the selected for the plasma ramp-up sequence development of CS coils. In this study, the updated CS conductor and coil design are presented. A CFX simulation carried out to check the pressure drop condition and a thermo-hydraulic analysis is performed.

The experimentally observed in/out detachment asymmetry in KSTAR L-mode plasmas with deuterium (D) fueling and carbon walls has been investigated with the SOLPS-ITER code to understand its mechanism and identify important atomic processes in the divertor region. The simulations show that the geometrical combination of a vertical, inner target with a short poloidal connection from the X-point to the target and a much longer outer divertor leg on an inclined target lead to neutral accumulation towards the outer target, driving the outer target detachment at lower upstream density than is required for the inner target. This is consistent with available Langmuir probe measurements at both target plates, although the inner target profile is poorly resolved in these plasmas and further experiments with corroborating diagnostics are required to confirm this finding. The pressure and power loss factors defined in the two-point model (Stangeby 2018 Plasma Phys. Control. Fusion 60 4; Kotov and Reiter 2009 Plasma Phys. Control. Fusion 51 115002; Stangeby and Sang 2017 Nucl. Fusion 57 056007; Moulton et al 2017 Plasma Phys. Control. Fusion 59 6) of the divertor scrape-off layer (SOL) and the sources contributing to the loss factors are calculated through post-processing of the SOLPS-ITER results. The momentum losses are mainly driven by plasma-neutral interaction and the power losses by plasma-neutral interaction and carbon radiation. The presence of carbon impurities in the simulation enhances the pressure and power dissipation compared to the pure D case. Carbon radiation is a strong power loss channel which cools the plasma, but its effect on the pressure balance is indirect. Reduction of the electron temperature indirectly increases the momentum loss and increasing the volumetric reaction rates which are responsible for the loss of momentum. As a result, the addition of carbon saturates the momentum and power losses in the flux tube at lower upstream densities, reducing the roll-over threshold of the upstream density. The relative strengths of the various mechanisms contributing to momentum and power loss depend on the radial distance of the SOL flux tubes from the separatrix (near/far SOL) and the target (inner/outer target). This is related to the strong D2 molecule accumulation near the outer strike point, which makes the deuterium gas density at the outer target 2-10 times higher than that at the inner target. A large portion of the recycled neutral particles from both targets reach and accumulate in the outer SOL, which is predominantly attributed to the target inclination and gap structure between the central and outboard divertors and hence to the impact of geometry. The accumulated neutrals enhance the reactions involving D2, which causes momentum and power loss.

Efforts have been made to obtain vacuum condition that is essential for the plasma experiments. Under certain situations, for example, the vacuum vessel should be vented to repair in-vessel components such as diagnostic shutter, exchange of window for diagnostic equipment, and PFC damaged by high energy plasma. For the quick restart of the campaign, a recovery process was established to make the vacuum condition acceptable for the plasma experiment. In this paper, we present the recovery process of wall condition in KSTAR after temporal machine-vent for repair. It is found that an acceptable vacuum condition has been achieved only by plasma based wall conditioning techniques such as baking, GDC, and boronization. This study was that the proper recovering method of the vacuum condition should be developed according to the severity of the accident.