National Fusion Research Institute Research Articles

A Framework for International Collaboration on ITER Using Large-Scale Data Transfer to Enable Near-Real-Time Analysis

The global nature of the ITER project along with its projected approximately petabyte-per-day data generation presents not only a unique challenge but also an opportunity for the fusion community to rethink, optimize, and enhance our scientific discovery process. Recognizing this, collaborative research with computational scientists was undertaken over the past several years to create a framework for large-scale data movement across wide-area networks to enable global near-real-time analysis of fusion data. This would broaden the available computational resources for analysis/simulation and increase the number of researchers actively participating in experiments. An official demonstration of this framework for fast, large data transfer and real-time analysis was carried out between the KSTAR tokamak in Daejeon, Korea, and Princeton Plasma Physics Laboratory (PPPL) in Princeton, New Jersey. Streaming large data transfer, with near-real-time movie creation and analysis of the KSTAR electron cyclotron emission imaging data, was performed using the Adaptable Input Output (I/O) System (ADIOS) framework, and comparisons were made at PPPL with simulation results from the XGC1 code. These demonstrations were made possible utilizing an optimized network configuration at PPPL, which achieved over 8.8 Gbps (88% utilization) in throughput tests from the National Fusion Research Institute to PPPL. This demonstration showed the feasibility for large-scale data analysis of KSTAR data and provides a nascent framework to enable use of globally distributed computational and personnel resources in pursuit of scientific knowledge from the ITER experiment.

Experimental results of multiple shattered pellet injection systems in KSTAR

Shattered pellet injection (SPI) is the technology chosen for the ITER Disruption Mitigation System and is explored at several fusion research devices, like DIII-D and JET and J-TEXT. The ITER disruption mitigation strategy relies on multiple injections to achieve RE (runaway electron) avoidance with optimum TQ (thermal quench), CQ (current quench) durations to adequately reduce wall loads. To demonstrate the feasibility of the multiple injection and to extrapolate to ITER, experiments with two identical injectors toroidally opposite to each other are needed urgently. KSTAR (Korea Superconducting Tokamak Advanced Research) can be a unique testbed to study the plasma disruption mitigation for ITER. KSTAR has installed two identical injectors in 180 degrees of toroidal opposite positions in 2019. For this system, ORNL (Oak Ridge National Laboratory) provided the two injectors, the shatter tubes, and auxiliary systems. NFRI (National Fusion Research Institute) provided the infrastructure of a vacuum pumping system, control & data acquisition system, and installed additional diagnostic systems for SPI in collaboration with the ITER Organization. This paper describes the engineering achievements during installation on KSTAR and the initial results of single and multiple SPI experiments in the 2019 campaign.

Deployment of multiple shattered pellet injection systems in KSTAR

Abstract Shattered pellet injection is of the most attractive way to mitigate the plasma disruption in fusion research facilities up to now. DIII-D has already utilized it and achieved very positive results. ITER has decided to adopt this technology for the DMS (disruption mitigation system) for PFPO-1 (Pre-Fusion Power Operation phase 1). The validation between simulation code and experiment, and continuous engineering development need to be carried out to meet the DMS’s requirement and reliability. KSTAR (Korea Superconducting Tokamak Advanced Research) is a possible candidate to test the urgent issues of plasma disruption for ITER. KSTAR can install two injectors in toroidal opposite positions. For this work, ORNL (Oak Ridge National Laboratory) will provide the two injectors, the shatter tubes and auxiliary systems. NFRI (National Fusion Research Institute) is preparing the infrastructure of a pumping system, control and data acquisition system, and arranging the location of diagnostic and the heating systems. This presentation describes the basic requirements and the engineering challenges to be solved for successful deployment and operation of multiple SPI injectors in 2019.

Design evaluation of hardwired F-LIC module for ITER AC/DC converters by FMEDA method

The Fast Local Interlock Controllers (F-LIC) are important components for the fast protection of ITER AC/DC converters and super conducting coils in the event of quench or converter faults. When the quench signal or converter fault is detected over the threshold set-point, it triggers fast bypass switch, gate block switch, Make Switch and/or Protective Make Switch (MS-PMS) and Circuit Breaker (CB) trip for the protection. To meet the requirements of the ITER local interlock system, the F-LIC design should assure that its safety integrity is attained by evaluation of the Safety Integrity Level (SIL), as per IEC 61508. The design and evaluation of the F-LIC of ITER AC/DC converters have been studied and developed in Korea Domestic Agency (KO-DA) of the National Fusion Research Institute (NFRI) and Dawonsys Corp. In this paper, the hardwired F-LIC design is introduced and the SIL analysis of the F-LIC module has been performed to meet the requirements of IEC 61508. The Failure Mode, Effect, and Diagnostic Analysis (FMEDA) technique is used for the evaluation method.

Hydrogen adsorption performance for large-scale cryogenic molecular sieve bed

Cryogenic hydrogen adsorption using molecular sieve beds is considered to be one of the main candidate processes for recovery of produced tritium from purge gas in breeding blankets and it has been chosen for separating hydrogen isotopes in Tritium Extraction System (TES) of Korean Helium Cooled Ceramic Reflector (HCCR) Test Blanket System (TBS). Various adsorbents and their performance have been studied for the cryogenic adsorption using small-scale experiments. However, large-scale experiments comparable to TBS-relevant scale are required to have sufficient confidence for component design and performance prediction of Cryogenic Molecular Sieve Bed (CMSB) for the TBS and beyond. To properly evaluate hydrogen adsorption performance of a large size CMSB, a series of experiments have been performed using PGLoop facility which is constructed and operated in the National Fusion Research Institute. The experimental conditions were set to include breeding-blankets-relevant parameters. As such, the effects of swamping ratio, total pressure, and flow rates on the performances of CMSB were studied in the range of hydrogen partial pressures from 100 to 700 Pa. While a slight reduction in hydrogen adsorption performance is observed in comparison to the small isotherm experiments, which can be attributed to scale-up effects, it shows that the experimental results agree reasonably well with existing literature data.

Initial operation results of NE213 scintillation detector for time-resolved measurements on triton burnup in KSTAR.

In time-resolved measurement for triton burnup in Korea Superconducting Tokamak Advanced Research (KSTAR) deuterium plasmas, an NE213 liquid scintillation detector was installed and operated during the 2017 KSTAR campaign. The detector is composed of an NE213 scintillator (50 mm in diameter and 10 mm in thickness) and a photomultiplier tube (PMT). The PMT anode signal was processed under a data acquisition system which contains a field programmable gate array circuit and pulse processing software that is capable of discriminating gamma-ray and neutron pulse signals. In order to determine an appropriate threshold level for the 14 MeV neutron signal resulting from triton burnup, the NE213 scintillation detector was calibrated by using d-d and d-t neutron generators at the National Fusion Research Institute and Intense 14 MeV Neutron Source Facility, OKTAVIAN, Osaka University, Japan. The detector was installed on KSTAR with a 10 mm thick soft-iron stray magnetic field shield and a radiation shield which consists of 100 mm thick lead blocks and 200 mm thick borated polyethylene blocks. A discrimination range for d-t neutron was determined based on test results from neutron generators and KSTAR. Data points selected from the discrimination range were consistent with the classical triton confinement characteristics. In conclusion, under condition of an input counting rate of 1.9 × 105 counts per second (CPS), the detector is able to measure triton burnup signals up to 500 CPS for various plasma parameters.

The Power Characteristic Results According to the Superconducting Magnet Coil Load Tests of the Motor Generator System

When the poloidal field (PF) magnet power supplies (MPSs) of 11 units are operated, maximum power of 200 MVA is required to achieve long pulse operation of Korea superconducting tokamak advanced research (KSTAR). Motor generator (MG) system was installed to resolve the power shortage because the available grid power is only 100 MVA at the National Fusion Research Institute site. MG system is composed of mechanical devices (stator, rotor, bearings, etc.), power control devices (variable voltage variable frequency and exciter), power facilities (transformers, switchboard, uninterruptible power system, filter, dynamic brake, etc.), utilities (cooling water pump, heat exchangers, cooling fans, oil circulation pump, mechanical brake, etc.), and control systems. MG system supplies power to the PF MPS of 11 units. And we configure the reactive power compensator (RPC) and harmonic filter (HF) system to stabilize the MG power system. After installing the MG system, individual tests and dummy coil tests were conducted to determine the safety and performance of MG system. And we completed the commissioning of the MG system by carrying out the superconducting magnet coil load tests for the 2014 KSTAR experiment. MG system was operated up to 150 MVA of PF MPS with the RPC and HF system. And the maximum operating duration was about 100 s. In this paper, we discuss about the power characteristic results of the MG system according to the superconducting magnet coil load tests.

Transient Hot-Wire Experimental System for Measuring the Effective Thermal Conductivity of a Ceramic Breeder Pebble Bed

Characterizing the thermo-physical properties of the ceramic breeder pebble bed is an integral step of developing breeder blankets for fusion energy applications. To that end, thermal conductivity is an important parameter to identify. In granular pebble bed materials, the thermal conductivity depends on the solid pebble material as well as any gas filling the interstitial void spaces, thus an effective thermal conductivity () of the bulk is used. A transient hot-wire apparatus is developed through a collaborative study between the Fusion Science and Technology Center at UCLA and the National Fusion Research Institute (NFRI) to measure the effective thermal conductivity of Korean-made Li2TiO3 pebble beds. In this study, current is pushed through a single strand of high purity platinum wire. The heat generated is conducted away by the surrounding pebble bed; the logarithmic change in temperature being used to calculate the rate of heat conductance. The apparatus is filled with roughly an atmosphere of helium and placed in a furnace to test the pebble bed under reactor relevant temperatures. Results and future improvements are presented.

Development of fast neutron pinhole camera using nuclear emulsion for neutron emission profile measurement in KSTAR.

We have developed a compact fast neutron camera based on a stack of nuclear emulsion plates and a pinhole collimator. The camera was installed at J-port of Korea superconducting tokamak advanced research at National Fusion Research Institute, Republic of Korea. Fast neutron images agreed better with calculated ones based on Monte Carlo neutron simulation using the uniform distribution of Deuterium-Deuterium (DD) neutron source in a torus of 40 cm radius.

Development of thermal-hydraulic analysis methodology for multiple modules of water-cooled breeder blanket in fusion DEMO reactor

According to the conceptual design of the fusion DEMO reactor proposed by the National Fusion Research Institute of Korea, the water-cooled breeding blanket system incorporates a total of 736 blanket modules. The heat flux and neutron wall loading to each blanket module vary along their poloidal direction, and hence, thermal analysis for at least one blanket sector is required to confirm that the temperature limitations of the materials are satisfied in all the blanket modules. The present paper proposes a methodology of thermal analysis for multiple modules of the blanket system using a nuclear reactor thermal-hydraulic analysis code, MARS-KS. In order to overcome the limitations of the code, caused by the restriction on the number of computational nodes, a supervisor program was devised, which handles each blanket module separately at first, and then corrects the flow rate, considering pressure drops that occur in each module. For a feasibility test of the proposed methodology, 46 blankets in a single sector were simulated; the calculation results of the parameters, such as mass flow, pressure drops, and temperature distribution in the multiple blanket modules showed that the multi-module analysis method can be used for efficient thermal-hydraulic analysis of the fusion DEMO reactor.

Demonstration of long-pulse acceleration of high power positive ion beam with JT-60 positive ion source in Japan–Korea joint experiment

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, 2MW 100s beam has been achieved for the first time. The achieved beam performance satisfies the JT-60SA requirement which is designed to be a 1.94MW ion beam power from an ion source corresponding to total neutral beam power of 20MW 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.

Plasma Electrochemistry: How to Control the Size and Size Distribution of Au Nanoparticles

Metal nanoparticles (NPs) have attracted a great deal of interest for their unique optical and catalytic properties. These novel materials are normally prepared in solution as colloids by chemically reducing metal salts in the presence of a stabilizer (i.e. surfactant). Recently, we have developed a green chemical approach based on plasma electrochemical reduction (PER). A novel microplasma source that plasmas formed at sub-millimeter spatial scale allows a non-thermal, atmospheric-pressure plasma to be stably formed at the surface of aqueous ionic electrolytes and thin polymeric films. This has enabled 1) charge transfer reactions at the plasma-liquid and plasma film interface [1] and 2) electrochemical applications of plasmas for novel materials synthesis [2-6]. However, although controlling the size and size distribution of nanoparticles is a primary requirement for their application potential in diversified area, still remained question is how to control the size and size distribution in plasma electrochemical approach. Here, we present plasma electrochemical approach to control the size and size distribution of Au nanoparticles. We initially prepared an aqueous solution including HAuCl4 and carried out PER (single-step process). In order to grow Au nanoparticles, we synthesized Au seed by PER. Afterwards, Au precursor was slowly added to grow Au seed (multi-step process). As the results, multi-step process successfully synthesized the size of Au nanoparticles at the range from ~60 nm to ~1 um To characterize the nanoparticle films, we have employed Ultraviolet-Visible absorbance spectroscopy, Nanoparticle size and Stability Analyzer, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Acknowledgment This work was supported by R&D Program of ‘Plasma Convergence & Fundamental Research’ through the National Fusion Research Institute of Korea (NFRI) funded by the Government funds.

Design and tests of 500 kW RF windows for the ITER LHCD system

In the frame of a R&D effort conducted by CEA towards the design and the qualification of a 5GHz LHCD system for the ITER tokamak, two 5GHz 500kW/5s windows have been designed, manufactured and tested at high power in collaboration with the National Fusion Research Institute (NFRI). The window design rely on a symmetrical pill-box concept with a cylindrical beryllium oxide ceramic brazed on an actively water cooled copper skirt. The ceramic RF properties have been measured on a test sample to get realistic values for guiding the design. Low power measurements of the manufactured windows show return losses below −32dB and insertion losses between −0.01dB and −0.05dB, with an optimum frequency shifted toward lower frequencies. High power tests conducted at NFRI show unexpected total power loss for both windows. The ceramic temperature during RF pulses has been found to reach unexpected high temperature, preventing these windows to be used under CW conditions. A post-mortem RF analysis of samples taken from one window shows that the dielectric properties of the ceramic were not the ones measured on the manufacturer sample, which partly explain the differences with the reference modelling.

Upgrades of the Liquid Helium-Free Superconducting Magnet for the 18-GHz Electron Cyclotron Resonance Ion Source at NFRI

The superconducting magnet is successfully installed on the 18-GHz ECR ion source at the National Fusion Research Institute (NFRI). The ECR ion source will be used as a multi-application source of highly charged ions and their interaction with matter. The magnetic system compromises of four superconducting coils sets for the axial mirror field and a permanent hexapole magnet for the radial mirror field. The previous superconducting magnet with a single cryocooler (1.5 W at 4.2 K) had been designed to reach peak mirror fields of 2.2 T in the injection and 1.5 T in the extraction regions (You et al., Rev. Sci. Instrum. 85, 02A916, 2014). However, it has not been successful in reaching the designed value (125 A) of current excitations; magnet coils have been shown to repeatedly quenched around 50–60 A of current ratings. After a detailed analyses and inspection, we found several weak points to be the possible cause of quenching. In this presentation, we describe important upgrades and technical improvements that have been made, followed by the test results of cooling and coil excitations. The four superconducting coils were successfully cooled to less than 4 K and excited accordingly to the designed current densities of 125 A/mm2.

Safety studies on Korean fusion DEMO plant using integrated safety assessment methodology

The purpose of this paper is to suggest methodology that can investigate safety issues and provides a case study for Korean fusion DEMO plant (K-DEMO) as a part of R&D program through the National Fusion Research Institute of Korea. Even though nuclear regulation and licensing framework is well setup due to the operating and design experience of Pressurized Water Reactors (PWRs) since 1970s, the regulatory authority of South Korea has concerns on the challenge of facing new nuclear facilities including K-DEMO due to the differences in systems, materials, and inherent safety feature from conventional PWRs. Even though the follow-up of the ITER license process facilitates to deal with significant safety issues of fusion facilities, a licensee as well as a licenser should identify the gaps between ITER and DEMO in terms of safety issues. First we reviewed the methods of conducting safety analysis for unprecedented nuclear facilities such as Generation IV reactors, particularly very high temperature reactor (VHTR), which is called as integrated safety assessment methodology (ISAM). Second, the analysis for the conceptual design of K-DEMO on the basis of ISAM was conducted. The ISAM consists of five analytical tools to develop the safety requirements from licensee's viewpoint in interactive manner: qualitative safety features review (QSR), phenomena identification and ranking table (PIRT), objective provision tree (OPT), probabilistic safety assessment (PSA), and deterministic and phenomenological analysis (DPA). Considering the design phase of K-DEMO, the current study focused on the PIRT process with the fusion safety advisory group in South Korea.

Fusion Licensing and Safety Studies in Korea

Korean activities on fusion licensing and safety studies have been going through three phases. The first phase started with the licensing of the Korean Superconductor Tokamak Advanced Research (KSTAR) classified as a radiation-generating device on the basis of the existing nuclear regulations. To accommodate the specific characteristics of a tokamak device that is to use deuterium in fusion plasma physics studies, a set of instructions to examine the safety of KSTAR and to approve an operating permit were developed and issued by the regulatory body, Korean Institute of Nuclear Safety. The second phase is being investigated for the International Thermonuclear Experimental Reactor (ITER). To verify the design of the test blanket module that will be installed and tested in the ITER, safety studies were carried out using the experimental results and computational codes. To minimize occupational irradiation damages, a study on the tritium behaviors is being carried out as Korea will provide a part of the tritium systems of ITER. The last phase has initiated to recognize significant safety issues and to support future licensing process for a fusion DEMO plant. Relevant studies are being carried out in collaboration with the academies funded by the National Fusion Research Institute of Korea. These front-end studies include the conceptual analysis on the safety and radiological consequences, preliminary studies on the layout of research, and on the future regulatory requirements of the fusion DEMO plant. This paper summarizes these activities on fusion safety with the findings of the front-end studies to date. It also proposes a pathway for the novel licensing process of a fusion DEMO plant with the tokamak concept.

Completed installations and the individual commissioning of the KSTAR MG system

Peak power of 200MVA is required in order to achieve the goal within a long pulse scenario for the final operation of the Korean Superconducting Tokamak Advanced Research (KSTAR). The available grid power is only 100MVA at the National Fusion Research Institute (NFRI) site. Motor generator (MG) was considered as a method of resolving such problems. The design of the KSTAR MG system was completed in July 2010 and individual devices were produced by relevant manufacturers. The installation of individual devices was completed in December 2012. Specifically, the stator and rotor were assembled at the site due to their large size and weight. The bearings, variable voltage variable frequency (VVVF) and excitation systems were transported and installed on site after being manufactured externally.The building used for MG installation was built in 2011. With the building designed for ease of installation, an overhead crane was designed to allow access to the loading bay.In this paper, we discuss the installation of the MG system and the construction of the building suitable for installation of individual devices. In addition, performance on the test results of individual devices is also discussed.

Neutronics design on DD neutron spectrometer for KSTAR

Toward fusion plasma diagnostics using DD neutron emitted from deuterium plasma, we installed a DD neutron spectrometer in magnetic confinement fusion experimental device, the Korea Superconducting Tokamak for Advance Research (KSTAR) at the National Fusion Research Institute (NFRI), Korea. We developed a Monte-Carlo model of KSTAR for neutron transport calculation based on PHITS and considered a neutronics design of a shielding structure including a collimator for a prototype of a DD neutron spectrometer.

Development status of the 18 GHz superconducting electron cyclotron resonance ion source at National Fusion Research Institute

A new superconducting 18 GHz electron cyclotron resonance ion source is being developed at the National Fusion Research Institute in South Korea. This source will be dedicated for future application of highly charged ions in the area of matter interaction, diagnostic imaging, and probing. In this paper, we describe the status of the source development consisting of a double electrode biased disk, sputtering systems for metal ion production, diagnostic ports for the extraction region, a variable gap extraction-Einzel lens system, and a low energy beam transport system.

Recent progress on lower hybrid current drive and implications for ITER

The sustainment of steady-state plasmas in tokamaks requires efficient current drive systems. Lower hybrid current drive is currently the most efficient method to generate a continuous additional off-axis toroidal plasma current and to reduce the poloidal flux consumption during the plasma current ramp-up phase. The operation of the Tore Supra ITER-like lower hybrid (LH) launcher has demonstrated the capability to couple LH power at ITER-like power densities with very low reflected power during long pulses. In addition, the installation of eight 700 kW/CW klystrons at the LH transmitter has allowed increasing the total LH power in long-pulse scenarios. However, in order to achieve pure stationary LH-sustained plasmas, some R&D is needed to increase the reliability of all the systems and codes, from radio-frequency (RF) sources to plasma scenario prediction. The CEA/IRFM is addressing some of these issues by leading a R&D programme towards an ITER LH system and by the validation of an integrated LH modelling suite of codes. In 2011, the RF design of a mode converter was validated at a low power. A 500 kW/5 s RF window is currently under manufacture and will be tested at a high power in 2012 in collaboration with the National Fusion Research Institute. All of this work aims to reduce the operational risks associated with the ITER steady-state operations.