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An electron cyclotron heating (ECH) power absorption model was integrated with a plasma burn-through simulator, DYON, and the new version, DYON-EC, was validated against KSTAR ECH-assist start-up experiments. The absorbed ECH power was calculated with an analytic formula which is a function of the electron density and electron temperature and ECH hardware settings, namely, the injected power, wave frequency, harmonic number, mode fraction, and beam injection angles. Wave parameter changes by wall reflection was also included to simulate multiple reflections. The absorbed ECH power was self-consistently included in the electron energy balance equation. The simulation settings of the plasma-wall interaction model and the electromagnetic scenario including the eddy current model were optimized to reproduce the plasma parameter evolution and line emission data in a pure ohmic start-up discharge. The study revealed that assumption of double-path EC beam absorption is required to reproduce a KSTAR ECH-assisted start-up discharge. Using the same optimized settings, DYON-EC modelling successfully reproduced multiple KSTAR EC-assisted discharges in a large range of operation parameters. The good statistical reproduction of measured plasma parameter evolution confirms the validity of the DYON burn-through modelling with ECH.

We report a discovery of a fusion plasma regime suitable for commercial fusion reactor where the ion temperature was sustained above 100 million degree about 20 s for the first time. Nuclear fusion as a promising technology for replacing carbon-dependent energy sources has currently many issues to be resolved to enable its large-scale use as a sustainable energy source. State-of-the-art fusion reactors cannot yet achieve the high levels of fusion performance, high temperature, and absence of instabilities required for steady-state operation for a long period of time on the order of hundreds of seconds. This is a pressing challenge within the field, as the development of methods that would enable such capabilities is essential for the successful construction of commercial fusion reactor. Here, a new plasma confinement regime called fast ion roled enhancement (FIRE) mode is presented. This mode is realized at Korea Superconducting Tokamak Advanced Research (KSTAR) and subsequently characterized to show that it meets most of the requirements for fusion reactor commercialization. Through a comparison to other well-known plasma confinement regimes, the favourable properties of FIRE mode are further elucidated and concluded that the novelty lies in the high fraction of fast ions, which acts to stabilize turbulence and achieve steady-state operation for up to 20 s by self-organization. We propose this mode as a promising path towards commercial fusion reactors.

A mode identification method for slowly rotating (or non-rotating) n (toroidal mode number) = 1 plasma instabilities has been newly established with the signal compensation method used for an external time-varying magnetic field. The mode identification method is based on the Fourier decomposition scheme and processes the signal of the magnetic probes (MPs) on the passive stabilizer in the Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak. To exclude the non-plasma magnetic perturbation by the external current coils and their secondary eddy currents on the passive stabilizer that may not be easily characterized, the ARX-SISO (autoregressive with exogenous terms-single input single output) method has been introduced in the signal compensation process. Preliminary off-line analysis presented herein confirms that this method can adequately detect the time evolution of the mode-locking, along with a slowly rotating state, even in the presence of external magnetic perturbations.

Fast vertical control of shaped plasmas is essential for the successful realization of plasma operation near the limit of vertical control to achieve maximum confinement and stable, disruption free operation. In KSTAR, the normal conducting in-vessel vertical control coil (IVC coil) is employed to respond to vertical transients much faster than the superconducting coils are capable. The power supply for the IVC coil is capable of responding in a time commensurate with the expected vertical growth rates on KSTAR. The diagnostics used for the fast vertical control since the first operation with shaped plasmas in KSTAR, however, have a low signal-to-noise ratio which limits the gains that can be used successfully in the proportional and derivative control loops and thus the speed of the control loop. The successful use of relative flux for the Z-position estimate and of the loop voltage difference from a pair of up-down symmetric loops to provide sensitive and less noisy vertical estimate will be discussed. In addition, the control loop for the IVC coil is decoupled from the slow motion controlled by the superconducting coils using a high-pass filter in the control software. Finally the noticeable improvement in plasma control for plasmas near the vertical stability limit will be discussed.

Mitigation of deleterious heat flux from edge-localized modes (ELMs) on fusion reactors is often attempted with 3D perturbations of the confining magnetic fields. However, the established technique of resonant magnetic perturbations (RMPs) also degrades plasma performance, complicating implementation on future fusion reactors. In this paper, we introduce an adaptive real-time control scheme as a viable approach to simultaneously achieve both ELM-free states and recovered high-confinement (βN~1.91$ and HN~0.9), demonstrating successful handling of a volatile complex system through adaptive measures. We show that, by exploiting a salient hysteresis process to adaptively minimize the RMP strength, stable ELM suppression can be achieved while actively encouraging confinement recovery. This is made possible by a self-organized transport response in the plasma edge which reinforces the confinement improvement through a widening of the ion pedestal and promotes control stability, in contrast to the deteriorating effect on performance observed in standard RMP experiments. These results establish the real-time approach as an up-and-coming solution towards an optimized ELM-free state, which is an important step for the operation of ITER and reactor-grade tokamak plasmas. Notably, the real-time adaptive control scheme introduced here provides a path towards economic fusion reactors by maximizing the fusion gain while minimizing damage to machine components.

Major parts of an IR–visible two-color interferometer (TCI) on KSTAR have been upgraded for the multi-chord operation: (1) a diode-pumped-solid-state (DPSS) laser (660 nm) replacing the former HeNe laser (633 nm), (2) vacuum-compatible vibration isolator with titanium retro-reflectors, and (3) full digital phase comparator for multi-chord real-time density signals. The commercial compact DPSS laser suits the multiple chord configuration with its strong beam power (500 mW) and long coherent length (>100 m). Ti retro-reflectors are mounted on vacuum-compatible vibration isolators. The isolators are essential for the visible beams to avoid any fringe skips due to their short wavelength, considering the speed of the mechanical vibration (up to hundreds of μm). Field-programmable-gate-array (FPGA) modules count the entire fringes fast enough with a signal output rate up to 1.25 MHz, solving the fringe skip issues. The FPGA module enables the full digital processing of the phase comparator with a CORDIC algorithm after the sampling rate of 160 MS/s for the 40 MHz intermediate frequency of each beam. The full digital signals are transferred to the main plasma control system in real-time. Stable single-input-single-output operation of the KSTAR density control was demonstrated with the TCI. The real-time density profile control is also promising in the near future, with multiple actuators such as pellets and gas puffings.

Results on the integration and the operation of the KSTAR plasma control system (PCS) upgrade are given. Real-time hardware, new realtime-capable operating system, and a brand-new data acquisition are assembled in order to extend the performance and compatibility with modern computer systems. The first full commissioning and eventual routine use performed in 2016 so that the system can now acquire more than 400 channels for more than 100 seconds of data with 5 kHz sampling. The performance test results are summarized, featuring In/Out streaming echo tests and the synchronization verifications. Examples of general performance improvements are demonstrated, and additional features added to the software are also described.

Method for automatic detection of L-H transition using Support Vector Machine (SVM), a popular tool of supervised machine learning tools, has been evaluated in order to improve plasma density control in KSTAR. Through the SVM, a nonlinear classifier is trained to distinguish L-mode and H-mode using two kinds of diagnostic data measured in KSTAR. The trained classifier has been analyzed for possible usage on the real-time detection through the truncation of the training samples. Study on the optimization of the training samples, and corresponding accuracy change is made for evaluating feasibility for real-time implementations.

Disruption avoidance is one of the most critical issues in KSTAR due to its high current, temperature and long operation characteristics of the superconducting tokamak. To minimize possible damages to the machine, we imposed a real time handling algorithm of off-normal events, named “forced landing” to ramp down the plasma with well-controlled plasma current and position. Two different plasma control schemes are implemented for different purposes and situations. Both schemes have been successfully demonstrated with careful classifications of actions on the machine in real experiments and they show routine performance with effective reduction of impacts on the machine. Such “machine-protection” schemes enable more aggressive operations such as mega-ampere or high beta experiment, resulting in an expansion of the KSTAR operation regime due to reduced less concerns regarding mechanical safety issues.

Recent control advances at KSTAR enabled us not only to establish but also to sustain the ITER-similar shape (ISS) in a stationary manner, matching the ITER-like dimensionless shape parameters in lower single null (LSN) configuration with vastly contrasting upper/lower triangularities. The kinetic parameters of the ISS are different from the typical KSTAR configurations seen in ELM-RMP suppression experiments. It is experimentally demonstrated the ISS-compatible RMP control in KSTAR for the first time, using the n=2, +90 degrees phasing RMP.

The improvements in the magnetic measurement are carried out to provide more accurate plasma parameters required for better plasma control in the KSTAR tokamak. Firstly, the large noise width in the magnetic diagnostic (MD) sensor signals (up to δV/V = ∼20%), which caused from the IVCC power supply being essential for sustaining high elongated plasmas, can be reduced down to ∼1% by using commercial anti-aliasing (AA) electronic filters with the cut-off frequency fc of 0.86 kHz. Secondly, the time response of ∼1.0 ms required for the fast vertical control is achieved by using new AA filter (fc = 2.2 kHz) which has been developed to minimize the time delay due to the previous filter. In this paper, the characteristics of the AA filters are described, and the improvements in the magnetic measurements are presented.

A polychrometer-type motional Stark effect (MSE) diagnostic technique, originally developed for the Alcator C-Mod tokamak, has been extended and applied to the Korea Superconducting Advanced Tokamak Research (KSTAR) device, the long-pulse superconducting tokamak, for the first time. It demonstrates a successful in situ subtraction of the polarized reflections off the vacuum vessel wall, sometimes up to half the total signal in some sightlines. To avoid the secondary neutral beam emission that may contaminate conventional beam-into-gas calibrations, a new approach, where the beam-into-gas measurements are made at various torus pressures with fixed vacuum fields, has been devised, which is possible with the stable superconducting coil systems of KSTAR. The validity of this new calibration scheme has been checked via plasma jog experiments. The experimental evidence of the polarized background light and the necessity of its correction in the MSE measurements made in KSTAR are presented as well.

The plasma control system (PCS) has been one of essential systems in annual KSTAR plasma campaigns: starting from a single-process version in 2008, extensive upgrades are done through the previous 7 years in order to achieve major goals of KSTAR performance enhancement. Major implementations are explained in this paper. In consequences of successive upgrades, the present KSTAR PCS is able to achieve ∼48 s of 500 kA plasma pulses with full real-time shaping controls and real-time NB power controls. It has become a huge system capable of dealing with 8 separate categories of algorithms, 26 actuators directly controllable during the shot, and real-time data communication units consisting of +180 analog channels and +600 digital input/outputs through the reflective memory (RFM) network. The next upgrade of the KSTAR PCS is planned in 2015 before the campaign. An overview of the upgrade layout will be given for this paper. The real-time system box is planned to use the CERN MRG-Realtime OS, an ITER-compatible standard operating system. New hardware is developed for faster real-time streaming system for future installations of actuators/diagnostics.

A newly upgraded IVCC (In-Vessel Control Coil) system equipped with four broadband power supplies, along with a current connection patch panel, are introduced with a discussion of their capabilities on various KSTAR experiments. Until the 2014 KSTAR experimental campaign, the non-axisymmetric field configuration could not be changed in a shot, let alone the limited number of accessible configurations. With the installation of the new power supplies, such restrictions have been greatly reduced. Based on the 2015 KSTAR run-campaign, this new system was confirmed to easily cope with various dynamic demands for toroidal and poloidal phases of the 3D magnetic field in a shot. With newly equipped magnetic sensors, this enables us to extend the operational options and further explore the 3D physics for tokamak plasmas.

Excellent reproducibility of KSTAR resonant magnetic perturbation (RMP)-driven, edge-localized mode (ELM)-crash suppression enables us to construct a database reliably for the study of ELM-crash suppression conditions. To establish a high-fidelity database, we have selected one of the frequently used RMP configurations in KSTAR, n = 1, + 90 ° phasing RMP-coil configuration. A series of fitting curves based on edge profile diagnostics data is used for normalized electron collisionality ( ν e *) and plasma toroidal rotation ( V tor) at pedestal top. Since ITER is expected to employ slowly rotating, low-collisionality, high-density plasmas whose conditions are not readily accessible in the existing devices, the exploration and understanding of these two parameters would be important not only for RMP-driven, ELM-crash-suppression physics but also for the success of ITER. The data points for the ELM-crash suppression phase are in the range of 0.2 40 km/s. Suppression thresholds or boundaries in ν e , ped * or V tor , ped are not confirmed in the investigated parameter ranges so far. The KSTAR database still needs additional experimental datasets in ITER-relevant conditions ( ν e , ped * ∼ 0.1 and low-torque low-rotation) to confirm the boundary of the ELM-crash suppression window in KSTAR and reduce the uncertainties of the RMP ELM-crash control technique in ITER. In both ν e , ped * and V tor , ped parameters, the phase-space distribution of the ELM-crash suppression has no clear distinction from that of the ELM-crash mitigation. Linear discriminant analysis provides a linear combination of parameters relevant to ELM-crash suppression, best separating two data categories. Recursive feature elimination indicates that n e , ped and I RMP, as well as ν e , ped * and V tor , ped, are critical variables in the separation of the data groups.

During the early campaigns of the KSTAR project, feedback control of plasma density has been successfully commissioned at the very first attempt by using a transfer function analysis. In order to minimize a chance of any risk happening, a stable and robust Ohmic discharge was chosen as a test-bed of 300 kA ( I p ) circular limited plasma in 2.0 T ( B t ). Pre-programmed fueling modulation was carried out first by puffing the deuterium gas via a piezoelectric valve. Line-averaged plasma density was measured in real-time by a 280 GHz interferometer system. From those modulations, both the density decay time ( τ i * ) and the external fueling efficiency ( f ex ) were approximated in windows: 3.0–5.0 s and 10–20% respectively. By using the results, a simple plant model has been established based on a global particle balance equation. Then several transient responses such as rising time, settling time and overshoot ratio were estimated in a certain range depending on the windows of τ i * and f ex . It is found that τ i * has little effect on those response characteristics while f ex plays primary role together with magnitude of the proportional gain G P . This is due to predominance of valve response whose characteristic time τ v was approximately 60 ms, which is much shorter than τ i * . Considering the responses, G P for closed-loop control were set initially very low i.e. 2.5 being concerned on excessive fueling. It was followed by several stepwise increments to reduce steady-state error instead of using any integral gain G I to avoid any chance of instability and uncertainty. Similarly, the target density was also initially low and gradually growing. In this way the very first density feedback control was successfully completed although some of the transient responses were different from the anticipated results while the predicted steady-state error was in good agreement with the experimental undershoot. By investigating an arbitrary time delay τ a , it is found that the digital-low-pass filter embedded in the plasma control system (PCS) of 50 ms also plays crucial role together with the τ v . In such way, settling time τ s and low overshoot case were well agreed but rising time t r and strong overshoot were not able to be found with those time delays. Considering well predicted steady-state error, with settling time t s , the transfer function analysis with the simple particle balance model is appropriate for relatively slow responses but not applicable for the faster responses and strong overshoot, which may not be linear-time-invariant (LTI) system anymore. More comprehensive physics-basis modeling will be necessary for more accurate prediction including fast responses and strong overshoot of feedback control of the density.

In order to automate the control of ELM and plasma density, an algorithm for classification of L-H transition and the first ELM burst in real-time has been developed with KSTAR campaign data. We applied a Long Short-term Memory (LSTM) which is a special kind of recurrent neural networks for storing long time-series data to classify the L-H transition phenomena and the first ELM burst. For training the LSTM classifier, we used D α and line-averaged electron density diagnostic data that indicate the characteristic patterns of the L-H transition. After the training, we tested two versions for real-time experimental data and post-processed data. In addition, through the results related to the long intermediate states, we examined whether the statistical approach can reflect physical aspect of the KSTAR plasmas.

An overview of advances and progress on the KSTAR plasma control improvement is given. The enhancement of the KSTAR plasma control system (PCS) continues in order to enable implementations of more sophisticated control algorithms and capabilities of integrated controls on magnets, gas, heating and off-normal event handling. Features and functionalities on the generic magnetic controls, kinetic controls and new fault scheme design are added for the operation space expansion, mainly regarding recent achievements of high plasma current up to 1.1 MA for 10 s, high-performance long pulse up to 90 s, and discharges relevant to ITER research. Technical challenges and prospective upgrades in the near future are described.

For the advanced tokamak operation in Korea Superconducting Tokamak Advanced Research (KSTAR), up to 6 MW of electron cyclotron heating (ECH) is planned. The ECH launcher should be able to operate in steady state and serve as a central/off-axis heating and current drive, q-profile control, and control of the neoclassical tearing mode (NTM) and sawtooth. The water cooled launchers have been upgraded to include continuous operation with precise, high-speed real-time control of the beams by integration with the plasma control system (PCS) for supporting the experiments, in particular for suppressing NTM. In this study, the launcher was successfully operated for 78 s with about 650 kW EC power, where the temperature of the coolant, with a flow rate of 9.6 lpm, is saturated and approximately 2 °C. The launcher control system had a maximum control cycle of 5 kHz and a motor latency of about 10 ms, and the poloidal scanning speed of the beam was 20°/s. Additionally, for the higher localization of power deposition, the curvature and size of the mirrors in the launcher were optimized. This paper presents the ECH launcher design and its control system with the operation results.

The world clock based automatic sequential operation manipulator has been developed and begin to work on the 7th campaign in KSTAR Tokamak. The Pulse Automation and Scheduling System (PASS) divided into Pulse Automation System (PAS) and Pulse Scheduling System (PSS). The PAS is on the online control system and it has communicated with many other local control systems. Before PASS, the plasma experiment was performed manually by using Central Control System (CCS). However the PASS currently manipulates the sequential operation of KSTAR with the programmed shot interval time. It provides readiness check routine, shot time handler, and local system monitoring functions. The PASS has no hardware dependency and it was configured with EPICS extensions. The Real Time Monitoring System, PCS_GATE, Automatic Reporting System, Central Control System, and Timing Synchronization System are well organized and they communicate to each other. The PASS provides perceptual operation status, easy time manipulator, and intuitive man machine interface. The plasma disruption information which is used in the KSTAR standard software framework also comes from the PASS. We describe the functions and system architecture of the Pulse Automation System in this paper. The PSS will be specified inside PASS for the purpose of intelligent system parameterization.

Sustaining the plasma in a stable and a high performance condition is one of the important control issues for future steady state tokamaks. In the 2014 KSTAR campaign, we have developed a real-time poloidal beta (βp) control technique and carried out preliminary experiments to identify its feasibility. In the control system, the βp is calculated in real time using the measured diamagnetic loop signal, and compared with the target value leading to the change of the neutral beam (NB) heating power using a feedback PID control algorithm. To match the requested power of NB which is operated with constant voltage, the on-time periods of the intervals were adjusted as the ratio of the required power to the maximum achievable one. This paper will present the overall procedures of the βp control, the βp estimation process and NB operation scheme implemented in the plasma control system (PCS), and the analysis on the preliminary experimental results.

Superconducting tokamaks like KSTAR, EAST and ITER need elaborate magnetic controls mainly due to either the demanding experiment schedule or tighter hardware limitations caused by the superconducting coils. In order to reduce the operation runtime requirements, two types of plasma simulators for the KSTAR plasma control system (PCS) have been developed for improving axisymmetric magnetic controls. The first one is an open-loop type, which can reproduce the control done in an old shot by loading the corresponding diagnostics data and PCS setup. The other one, a closed-loop simulator based on a linear nonrigid plasma model, is designed to simulate dynamic responses of the plasma equilibrium and plasma current (Ip) due to changes of the axisymmetric poloidal field (PF) coil currents, poloidal beta, and internal inductance. The closed-loop simulator is the one that actually can test and enable alteration of the feedback control setup for the next shot. The simulators have been used routinely in 2012 plasma campaign, and the experimental performances of the axisymmetric shape control algorithm are enhanced. Quality of the real-time EFIT has been enhanced by utilizations of the open-loop type. Using the closed-loop type, the decoupling scheme of the plasma current control and axisymmetric shape controls are verified through both the simulations and experiments. By combining with the relay feedback tuning algorithm, the improved controls helped to maintain the shape suitable for longer H-mode (10–16 s) with the number of required commissioning shots largely reduced.

We use a newly developed simulation tool to numerically study fast-ion loading on plasma-facing components (PFCs) at the Korea Superconducting Tokamak Advanced Research facility in the high-poloidal-β plasma operation regime. The new code can calculate neutral beam ionization and follow the guiding center orbit of ionized particles. The results of the simulation indicate that fast ions ionized in the high-field side drift out and strike the PFCs as they rotate poloidally. Momentum projection onto a phase space defined by canonical toroidal angular momentum and magnetic moment leads to a simple criterion to avoid fast-ion loading on poloidal limiters (PLs), which are PFCs that are toroidally localized on the low-field side. Control of fast-ion loss is examined by varying the plasma current and plasma boundary. A larger plasma current and inner shifting of the outer plasma boundary is predicted to substantially reduce fast-ion loading on the PLs. The proposed phase-space criterion is qualitatively consistent with the results of the simulation of fast-ion control.

韓国National Fusion Research Instituteのトカマク実験装置KSTARでは高速イオンによるプラズマ対向壁の熱負荷が問題となっていた。そこで高速イオンによるプラズマ対向壁の熱負荷を評価するための数値計算コードを開発した。さらに、開発したコードによる解析結果をもとに対向壁の熱負荷を避けるための指標を与える簡易式を導出した。本論文で、数値コードの詳細とその結果、導出した簡易式と実験との比較について報告する。

A decade long operation of KSTAR has contributed significantly to operation of superconducting tokamak device and advancement of tokamak physics which will be beneficial for the ITER and K-DEMO programs. Even with limited heating capability, various conventional as well as new operating regimes have been explored and achieved great performance. As examples, a long pulse H-mode operation with and without the ELM-crash was well over 60 seconds and over 30 seconds, respectively. Unique capabilities of KSTAR allowed to improve control capability of harmful instabilities and have been instrumental for many exciting new physics. The intricate IVCC system has been a great perturbation tool in studying of threshold power of the L/H transition in the presence of non-axisymmetric fields, rotation physics due to NTV effects, heat dispersal in divertor system and predictive control of the ELM-crash with a priori modeling. The state-of-the-art 2D/3D microwave imaging systems uncovered many new exciting new physics in the MHD and turbulence transport physics. They are validation of q0agt;1 right after the sawtooth crash, self-consistent asymmetric distribution of plasma turbulence amplitude and flow in the presence of 2/1 island, and underlying physics of low frequency turbulence induced by 3D resonant fields in suppression of the ELM-crash through non-linear interaction with the ELMs. In the turbulence area, non-diffusive "avalanche" transport event and role of quiescent coherent mode in confinement are studied. To accommodate anticipating higher performance of the KSTAR plasmas with the increased heating powers (NBI and ECH), new divertor/internal interface with full active cooling system will be implemented after the increased heating power systems and new current drive systems are fully tested. Upgrade plan for the internal hardware and efficient current drive system may allow a long pulse operation of higher performance plasmas at βNagt;3.0 with fbs~0.5 and Tiagt;10keV. a#13; a#13

Since the first plasma in Korea Superconducting Tokamak Advanced Research (KSTAR), the electron cyclotron heating (ECH) system has been an essential tool for ECH-assisted start-up using second-harm...

The Korea Superconducting Tokamak Advanced Research (KSTAR) device is aimed at advanced tokamak (AT) research. Three years have passed since it achieved its first plasma in 2008. Because it is a superconducting machine and is working toward AT research, it has unique features in terms of the machine engineering and operation. The toroidal field (TF) magnet coils are made of Nb3Sn, which provide high TFs up to 3.5 T, and have been fully tested. The poloidal field (PF) magnet coils, consisting of both Nb3Sn and NbTi, which have a maximum current of 25 kA in their design, were tested up to 15 kA. A thermal hydraulic analysis is being conducted for PF magnet coil operation. All plasma-facing components (PFCs) are equipped with water cooled graphite tiles and have the capability of being baked up to 350°C. A startup scenario, which considered both the effect of the ferromagnetic material in the cable in conduit conductor jacket of the magnet coils as well as a nonferromagnetic up-down asymmetry in the cryostat structure, was developed and demonstrated its effectiveness by the last two year's reliable operations. Passive stabilizers and in-vessel control coils (IVCCs) are key components to realize AT operation in KSTAR. The segmented IVCC coils were connected to form circular coils for internal vertical control in 2010, and diverted plasmas with high elongation (κ~1.8, δ>;0.6) were achieved. A neutral beam injection (NBI) system was developed aiming at 2 MW, 300 s per ion source which meets the long-pulse requirement of KSTAR. An NBI ion source with a power of 1.7 MW at 100 kV has been commissioned for 10 s. Finally, ELMy H-modes were successfully produced with 1.3-MW NBI power at a plasma current of 0.6 MA in the 2010 campaign. The first H-mode discharge (#4200) in KSTAR was achieved one year earlier than officially planned and was done at BT = 2 T with Ip = 0.6 MA in a well-balanced double null configuration after boronization on the PFC. Successful operations in the early days of KSTAR including H-mode experiments revealed the capability of advanced and steady-state operation which is essential for the international thermonuclear experimental reactor (ITER) and future fusion reactors.

The design of the integrated quench protection (QP) system for the high current superconducting magnet (SCM) has been fabricated and tested for the toroidal field (TF) coil system of the Korea Superconducting Tokamak Advanced Research (KSTAR) device. The QP system is capable of protecting the TF SCM, which consists of 16 identical coils serially connected with a stored energy of 495 MJ at the design operation level at 35.2 kA per turn. Given that the power supply for the TF coils can only ramp up and maintain the coil current, the design of the QP system includes two features. The first is a basic fast discharge function to protect the TF SCM by a dump resistor circuit with a 7 s time constant in case of coil quench event. The second is a slow discharge function with a time constant of 360 s for a daily TF discharge or for a stop demand from the tokamak control system. The QP system has been successfully tested up to 40 kA with a short circuit and up to 34 kA with TF SCM in the second campaign of KSTAR. This paper describes the characteristics of the TF QP systems and test results of the plasma experiment of KSTAR in 2009.

The q-profile control is essential for tokamaks exploring the advanced tokamak scenarios, which is expected to be able to provide a possible route toward a steady-state high performance operation in a fully non-inductive current drive state. This is because the pressure and current profiles must remain optimal for the scenario during the injection of large amounts of heating and current drive. Here, essential tools for the q-profile control are the motional Stark effect diagnostic for measuring the radial magnetic pitch angle profile and a state-of-the-art plasma control system. The pulse duration of the H-mode discharge at KSTAR has been extended year by year with improved control performance, and the experiment of internal transport barrier (ITB) formation in a weakly reversed q-profile with a marginal neutral beam injection majority heating successfully demonstrated that the ITB is an alternative candidate to achieve a high performance regime in KSTAR. These recent achievements are attributed to reliable profile measurement, which means that profile feedback control has become a necessary step to ensure a robust and reliable approach to advanced scenarios as the next step of research in KSTAR. In this paper, we discuss the technical and conceptual requirements for q-profile control according to the upgrade plan for heating and current drive systems in the coming years.

The DIII-D digital plasma control system (D3PCS) has been in use since 1993 controlling DIII-D plasmas. Control research and D3PCS development at DIII-D has revealed aspects of advanced tokamak control which can help inform the ITER design. The D3PCS has also been adapted for use at several fusion devices worldwide, which has allowed the DIII-D team to obtain a significant understanding of common requirements for plasma control on multiple fusion devices, along with substantial experience in the alternative computing, data acquisition, and networking technologies presently available. We describe some of what has been learned and highlight the relevance of these lessons for ITER Control, Data Access and Communication (CODAC). Several capabilities of the D3PCS are described in the context of ITER requirements. This description touches on multiple subsystems described in the CODAC conceptual design. We also discuss features of D3PCS architecture that are appropriate for today's experimental devices but may not be appropriate for ITER, which requires a much more comprehensive system for ensuring device safety. Even for these applications, the knowledge gained in implementing methods to aid in ensuring device safety on present devices provides useful guidance for an eventual ITER solution.

The DIII-D digital plasma control system (PCS) has been adapted and used at a number of tokamaks around the world over the past several years. Implementations of the DIII-D PCS at KSTAR and EAST in particular have made use of, and improved upon, the methodology for off-normal event/fault detection and response that was originally incorporated into the DIII-D PCS. This work discusses the lessons learned implementing and installing codes for detecting and responding to off-normal events in both plasma discharges and tokamak systems. In particular, we discuss the implementation details for codes at DIII-D, EAST, and KSTAR, and discuss how those experiences are being incorporated into a proposed finite state machine architecture in support of ITER research at DIII-D.

The current DIII-D plasma control system (PCS) has evolved through several iterations into a robust platform that has been adopted at several fusion devices around the world. Each installation, as well as each new upgrade at DIII-D, has presented new challenges. Each of these challenges has provided an additional opportunity to expand our understanding of the requirements, alternative operational methods, and differing real-time implementations for Tokamak plasma control. This paper presents a brief historical overview of PCS hardware evolutions and describes some of the design, structure, and techniques that have allowed the PCS to be a productive component at many fusion facilities. It will also discuss some of the major differences between the individual PCS installations and bring to light some of the major challenges that were overcome during integration. The lessons learned from these experiences provide general solutions and can inform control system designs for other next-generation devices. We also describe some limitations of the PCS relative to identified present and future needs at DIII-D and other devices, and discuss planned upgrades to the PCS to address these needs.

To analyse the experimental results of PF magnet during the commissioning test of KSTAR, a numerical model of the PF1 magnet and its CICC was developed for the evaluation of Joule heat from the AC loss due to the time varying field profile along the conductor during ramping-up or down taking into account the ferromagnetic effect of Incoloy 908 jacket. The calculation routines was carefully updated to make a proper estimation of the AC loss and applied to the estimation of AC loss parameters of the CICC of the KSTAR PF magnet.

A finite-state off-normal and fault response (ONFR) system is presented that provides the supervisory logic for comprehensive disruption avoidance and machine protection in tokamaks. Robust event handling is critical for ITER and future large tokamaks, where plasma parameters will necessarily approach stability limits and many systems will operate near their engineering limits. Events can be classified as off-normal plasmas events, e.g. neoclassical tearing modes or vertical displacements events, or faults, e.g. coil power supply failures. The ONFR system presented provides four critical features of a robust event handling system: sequential responses to cascading events, event recovery, simultaneous handling of multiple events and actuator prioritization. The finite-state logic is implemented in Matlab®/Stateflow® to allow rapid development and testing in an easily understood graphical format before automated export to the real-time plasma control system code. Experimental demonstrations of the ONFR algorithm on the DIII-D and KSTAR tokamaks are presented. In the most complex demonstration, the ONFR algorithm asynchronously applies 'catch and subdue' electron cyclotron current drive (ECCD) injection scheme to suppress a virulent 2/1 neoclassical tearing mode, subsequently shuts down ECCD for machine protection when the plasma becomes over-dense, and enables rotating 3D field entrainment of the ensuing locked mode to allow a safe rampdown, all in the same discharge without user intervention. When multiple ONFR states are active simultaneously and requesting the same actuator (e.g. neutral beam injection or gyrotrons), actuator prioritization is accomplished by sorting the pre-assigned priority values of each active ONFR state and giving complete control of the actuator to the state with highest priority. This early experience makes evident that additional research is required to develop an improved actuator sharing protocol, as well as a methodology to minimize the number and topological complexity of states as the finite-state ONFR system is scaled to a large, highly constrained device like ITER.

Recent commissioning of two major fully superconducting (SC)-shaped tokamaks, Experimental Advanced Superconducting Tokamak (EAST) and Korean Superconducting Tokamak Advanced Research (KSTAR), represents a significant advance in magnetic fusion research. The key to commissioning success in these complex and unique tokamaks was as follows: 1) use of a robust, flexible plasma control system (PCS) based on the validated DIII-D design; 2) use of the TokSys design and modeling environment, which is tightly coupled with the DIII-D PCS architecture for first-plasma scenario development and plasma diagnosis; and 3) collaborations with experienced internationally recognized teams of tokamak operations and control experts. We provide an overview of the generic modeling environment and plasma control tools developed and validated within the DIII-D experimental program and applied through an international collaborative program to successfully address the unique constraints associated with the startup of these next-generation tokamaks. The unique characteristics of each tokamak and the machine constraints that must be included in device modeling and simulation, such as SC coil current slew rate limits and the presence of nonlinear magnetic materials, are discussed, along with commissioning and initial operational results. Lessons learned from the startup experience in these devices are summarized, with special emphasis on ramifications for International Thermonuclear Experimental Reactor (ITER).

The Korea Superconducting Tokamak Advanced Research (KSTAR) control system has been developed as a network-based distributed control system composed of several sub-systems. There are many local control systems for various sub-systems, and the central control system includes discharge control, machine control, and safety interlocks which aim for integrated control of the entire system. We have chosen the Experimental Physics and Industrial Control System (EPICS) as the middleware of the KSTAR control system because EPICS provides a software framework to integrate heterogeneous systems. The discharge control system, which is implemented in a part of the supervisory control system, performs the discharge sequence execution. The plasma control system, which has been implemented with general atomics and modified for KSTAR, is involved in the discharge control. The plasma control system performs real-time plasma control algorithms and provides the results of the control algorithms to the magnet power supplies. We are using a reflective memory-based real-time network for communication between the plasma control system and the magnet power supplies, thus we developed a fully digital control for the magnet power supplies. We have implemented the discharge control system with state notation language (SNL) in EPICS and also developed interface software among the sub-systems. We will present the details of the development of the KSTAR discharge control system and commissioning results.