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The high fraction of runaway current conversion following disruptions has an important effect on the first wall for next-generation tokamaks. Because of the potentially severe consequences of a large full current runaway beam on the first wall in an unmitigated disruption, runaway suppression is given a high priority. The behavior of runaway currents both in spontaneous disruptions and in D2 massive gas injection (MGI) shutdown experiments is investigated in the KSTAR tokamak. The experiments in KSTAR show that the toroidal magnetic field threshold, BT > 2 T, for runaway generation is not absolute. A high fraction of runaway current conversion following spontaneous disruptions is observed at a much lower toroidal magnetic field of BT = 1.3 T. A dedicated fast valve for high-pressure gas injection with 39.7 bar is developed for the study of disruptions. A study of runaway current parameters shows that the conversion efficiency of pre-disruptive plasma currents into runaway current can reach over 80% both in spontaneous disruptions and in D2 MGI shutdown experiments in KSTAR. [ABSTRACT FROM AUTHOR]

Nuclear fusion research has entered a new era of super-conducting tokamak research led by Asia toward ITER and demonstration power plants. The research goal is to sustain high integrated plasma performance satisfying high burning efficiency, high fusion power density, fully non-inductive plasma current drive, and reduced divertor heat flux in the steady-state. Toward this goal, the EAST device in China and the KSTAR device in Korea are extending experimental areas, and the JT-60SA device is under construction in Japan. [ABSTRACT FROM AUTHOR]

Korea Superconducting Tokamak Advanced Research (KSTAR) is a superconducting tokamak which adopts Nb3Sn and NbTi as superconductors and it has been operated since 2008. One of main issues is the performance of superconducting magnet system in the real operation. In view of this issue, the KSTAR magnet system shows the sufficient operational capability through the whole campaigns. For example, we have already achieved the maximum Toroidal Field (TF) current and the bipolar pulsed Poloidal Field (PF) operation up to \pm 10 kA. It is very important to operate stably the full superconducting magnet system such as KSTAR and ITER. Each KSTAR magnet consists of Cable-In-Conduit Conductors (CICC) cooled by forced flow of the supercritical helium in cryogenic temperature. The temperature, pressure and mass flow rate of coolant are interacted organically inside of CICC and the behaviors are also complicated during operation. The pressure drop between inlet and outlet of coil, the temperature increasing in accordance with coil current variation, and so on are critical issues related with the flexibility and reliability of superconducting tokamak. [ABSTRACT FROM PUBLISHER]

The helium refrigeration system (HRS) of the Korea Superconducting Tokamak Advanced Research (KSTAR), which was designed to provide an energetic equivalent cooling power of 9 kW at 4.5 K, has been operated successfully during the last three years since 2008. For the operation of KSTAR, all of the cold components, such as the superconducting (SC) magnets, magnet structure, thermal shields, SC buslines, and current leads, were cooled down to the aimed cryogenic temperature by generated helium in the HRS. The supercritical helium (4.5 K and 5.5 bar) of 300 g/s was delivered for cooling of the SC magnet (poloidal field (PF) magnet: 14; toroidal field (TF) magnet: 16) and magnet structure and was circulated by the PF and the TF circulators. Thermal loads due to magnet operation are removed at the thermal damper installed in the distribution box of the HRS. Moreover, the pressure change in the magnet will directly affect the circulators. In particular, the pressure drop of the PF circulator drastically changed due to the PF magnet operation depending on the plasma generation scenario. In the 2010 campaign, the operating range of the PF magnet expanded from \pm4 to \pm10 kA, and the plasma scenario was improved. Accordingly, the mass flow rate of the PF circuit was increased from 350 to 369 g/s in order to achieve cryogenic stability. However, the operating range of the PF circulator exceeded the allowable range during shot #2526 and shot #3878. Nevertheless, the circulator successfully operated without any significant fault. The operating plan of the PF magnet that will be further expanded in the operating range may cause damages to the circulator continuously. Consequently, the influence of PF operating scenarios on the PF circulator was analyzed to investigate the safety margin of the HRS. [ABSTRACT FROM PUBLISHER]

Abstract: Since Korea joined ITER as Korea was developing a fully super-conducting tokamak, KSTAR, the national plan for developing fusion energy was renewed and focused on a clear mission – developing a technological self-reliant program for a fusion demonstration device. A new technical roadmap was developed toward self-reliant technologies for constructing a fusion power plant in a similar time window as in the EU, Japan and the US. This looks tough and formidable but Korea could take advantage of their well-established nuclear technologies in power plant design, construction, and operation. The government and the legislature recognized the importance of this effort by establishing a special law for supporting it practically and for giving it a high priority in their R&D agenda. Under this favorable environment, various scenarios for finding the most effective and efficient path to achieve the goal were reviewed and some of the features of this review will be presented. [Copyright &y& Elsevier]

The Korea Superconducting Tokamak Advanced Research (KSTAR) is a medium size, fully superconducting tokamak, which is scheduled to begin operation in year 2006. The control system of KSTAR consists of a supervisory system, plasma control system, and local control systems for various subsystems. Modular system, high reliability, flexibility and long time maintainability are major factors for the system design. The EPICS is the first choice for the distributed system control and the MDSPlus will be utilized for the data handling and analysis. The reflective memory network will be used for the real time plasma control. A pilot system has been being developed with VME and Compact PCI buses. Current status of the development of KSTAR control system will be presented. [Copyright &y& Elsevier]

Investigates the design of the central solenoid superconducting magnet of a tokamak device. Maximum repulsive force between the coils; Axial compression testing of the magnet; Thermal contraction; Preload structure of the magnet.

A new electron cyclotron emission (ECE) diagnostics system was installed for the Second Korea Superconducting Tokamak Advanced Research (KSTAR) campaign. The new ECE system consists of an ECE collecting optics system, an overmode circular corrugated waveguide system, and 48 channel heterodyne radiometer with the frequency range of 110-162 GHz. During the 2 T operation of the KSTAR tokamak, the electron temperatures as well as its radial profiles at the high field side were measured and sawtooth phenomena were also observed. We also discuss the effect of a window on in situ calibration. [ABSTRACT FROM AUTHOR]

Installs a fast reciprocating ion cyclotron range of frequencies (ICRF) probe on the TORE SUPRA tokamak. Parts consisting the probe; Distances where the probe was operated.

Abstract: The neutral beam injection (NBI) system was designed to provide plasma heating and current drive for high performance and long pulse operation of the Korean Superconducting Tokamak Advanced Research (KSTAR) device using two co-current beam injection systems. Each neutral beam injection system was designed to inject three beams using three ion sources and each ion source has been designed to deliver more than 2.0MW of deuterium neutral beam power for the 100-keV beam energy. Consequently, the final goal of the KSTAR NBI system aims to inject more than 12MW of deuterium beam power with the two NBI for the long pulse operation of the KSTAR. As an initial step toward the long pulse (∼300s) KSTAR NBI system development, the first neutral beam injection system equipped with one ion source was constructed for the KSTAR 2010 campaign and successfully commissioned. During the KSTAR 2010 campaign, a MW-deuterium neutral beam was successfully injected to the KSTAR plasma with maximum beam energy of 90keV and the L-H transition was observed with neutral beam heating. In recent 2011 campaign, the beam power of 1.5MW is injected with the beam energy of 95keV. With the beam injection, the ion and electron temperatures increased significantly, and increase of the toroidal rotation speed of the plasma was observed as well. This paper describes the design, construction, commissioning results of the first NBI system leading the successful heating experiments carried in the KSTAR 2010 and 2011 campaign and the trial of 300-s long pulse beam extraction. [Copyright &y& Elsevier]

Abstract: The in-vessel control coil (IVCC) system, which has been designed for dedication of various active feedback plasma control functions, successfully fabricated and installed in the vacuum vessel of the Korea Superconducting Tokamak Advanced Research (KSTAR). The IVCC system consists of sixteen segmented coils that were independently fabricated outside the vacuum vessel and installed without any inside welding or brazing joints. The segmented coil system has several advantages such as eliminating possibility of cooling water leakage at the welded or brazed joints, simplification in fabrication and installation, and easy repair and maintenance of the coil system. Each segment contains eight oxygen-free high conductive coppers, which are grouped to four pairs, called as sections. Consequently, a segmented coil forms four sections for position control, field error correction (FEC), and resistive wall mode (RWM) control in accordance with electrical connection outside the cryostat. The eight conductors (or four sections) with internal coolant holes were enclosed in a rectangular welded jacket made of stainless steel 316LN and electrically insulated from the conductors by epoxy/glass composite layers. This coil system was commissioned up to 5kA (30kA-turns) for 5s to achieve tentative use for the fast vertical plasma position control in the 2010 campaign of the KSTAR. This paper describes the several remarkable results in the fabrication and installation of the IVCC as well as commissioning results. [Copyright &y& Elsevier]

Abstract: In-vessel components of the Korea Superconducting Tokamak Advanced Research (KSTAR) were developed for 2010 campaign to provide a crucial circumstance for achieving the strongly shaped and diverted plasma. Moreover, the in-vessel components such as limiter, divertor, passive stabilizer, in-vessel control coil (IVCC) system demonstrated good performances satisfying the original design concepts. In addition to the plasma facing components and the IVCC, in-vessel cryo-pump (IVCP) system was also installed to leverage divertor operation. Besides the in-vessel components, there have been substantial progresses in development of the heating and current drive system. The KSTAR heating and current drive system includes all kinds of the major heating systems such as neutral beam injection (NBI), ion cyclotron range of frequency (ICRF), electron cyclotron resonance heating and current drive (ECH and ECCD), lower hybrid current drive (LHCD) systems. As an initial stage for full equipment of the heating systems to total power of 26MW, several key systems such as 1st NBI (called NBI-1), ICRF, and ECH-assisted startup system successfully demonstrated their excellent feasibilities in the design and performances for dedication to the 2010 campaign. [Copyright &y& Elsevier]

Abstract: An un-calibrated sensitive 3He detector was used to monitor the KSTAR neutron rate during Ohmically heated discharges. Neutrons were detected for every shot. If the neutrons were from D–D reactions then there should be a dependence on the ion temperature. We obtained ion temperature, electron density, Ohmic heating input power measurements, etc. from standard diagnostics. The study shows no observable dependence on the Ohmic power, ion temperature, or calculated source strength. It appears that the neutrons are from sources other than D–D reactions. The most probable source is high-energy runaway electrons. [Copyright &y& Elsevier]

Abstract: Wave enhanced runaway generation is expected to play an important role in the conversion of plasma current into runaway current during major disruptions. The fast electrons created by electron cyclotron heating (ECH) were used to study this issue in KSTAR. It is found that the fast electrons driven by ECH can enhance runaway production in the flat top phase with high loop voltage. The runaway current in disruptions was not enhanced by the ECH produced fast electron population due to the strong magnetic fluctuations which inhibited the generation of runaway electrons. It is found that a complete loss of existing REs during thermal quench has occurred in KSTAR limiter configuration discharges. [Copyright &y& Elsevier]

Abstract: It is possible to detect the presence of small field errors in a tokamak with an electron beam. This was demonstrated earlier on T-15 and TEXTOR. This paper discusses the concept, past experience on these tokamaks, calculations for the Korea Superconducting Tokamak Advanced Research (KSTAR) device, an electron beam source, measurement devices for these measurements, and some results. It is shown that small toroidally averaged field errors can be detected by this method. A low voltage electron beam (e-beam) gun and fluorescent screen were mounted in a vertical port and inserted into the vacuum vessel at the end of the KSTAR 2nd campaign plasma experiments. A camera with a narrow field of view was mounted in midplane port in a tube tangent to the field lines at R ∼1.3m and photographed the beam striking the screen. The poloidal field (PF) currents were held constant during the camera exposure period. Many shots with various PF coils energized were made and the deflections of the e-beam were measured. The measurements were made with a camera integration time of 300ms because of the low light intensity. The results show that there are large field errors that diminish as the PF currents are raised. There appears to be no significant up–down asymmetry for static fields. Measurements with a 7 PF coil scenario with a calculated field null located at e-beam radial position show much larger fields than calculated. KSTAR was constructed with Incoloy 908 conduit using cable-in-conduit conductors (CICC) in 10 of the 14 PF coils and all 16 of the toroidal field (TF) coils. Incoloy 908 has a relative magnetic permeability, μ, of about 10. The field errors appear to be largely due to Incoloy 908. [Copyright &y& Elsevier]

Abstract: After successful achieving first plasma, Korea Superconducting Tokamak Advanced Research (KSTAR) is now preparing second operation that includes power supplies with full power operation and more diagnostic systems. During first campaign the Experimental Physics and Industrial Control System (EPICS) was adopted as a control middleware of the KSTAR control system showed stable and reliable results and did not reveal any significant system failures. The EPICS based plant control system is used for data acquisition, data archiving and data visualization and is interfaced with Central Control System (CCS). A plant control system requires an EPICS Input Output Controller (IOC) and its own DAQ system. During the first operation the EPICS based control systems were mainly used slow data acquisition at a rate less than 10Hz. The hardware platforms were Programmable Logic Controller (PLC) and PCI eXtensions for Instrumentation (PXI). In this paper we will describe following items: the details of control function, implementation of each plant control system, operation results and analysis, focusing on the Tokamak Monitoring System (TMS), the Vacuum Monitoring System (VMS), the Current Lead System (CLS), the Helium Distribution System (HDS), and the Heating Systems. [ABSTRACT FROM AUTHOR]

Abstract: The supervisory interlock system (SIS), the personal safety interlock (PSI) and the radiation monitoring system (RMS) are the safety and protection system for the KSTAR operations. The supervisory interlock system prevents men and devices from an accident and it protects auxiliary systems and the superconducting tokamak against the propagation hazardous events. SIS is collecting events of the tokamak and auxiliary systems and decides a level of the event and command to stop the actions of local I&C for the KSTAR operation. The local interlock system is self-protecting from local accidents and executing orders from supervisory interlock system. SIS had accomplished its own functions at the first campaign of the KSTAR. Even though several unexpected incidents and mismanagement had occurred, the interlock function had been properly responding. We have test result of the emergency stop function for the superconducting magnet power supplies against accidents. We measured different shutdown time of each magnet power supply, which is about 1min, but we need to more analysis to the source of delay. We had inserted the current and density fault protection logics to stop the ECH and the ICRF at central control system through the first campaign. The short message system (SMS) had helped to restore fast of faults in local and KSTAR integrated control system (ICS). The processor regular scanning time is about 75ms that is longer than recommended scanning time of the redundancy system. We had reduced it <20ms by optimization of logic program during the maintenance period. This paper describes the interlock system functions of the first campaign, operation results, and update contents and results. [ABSTRACT FROM AUTHOR]

Abstract: The construction of the Korea Superconducting Tokamak Advanced Research (KSTAR) device has been completed by August 2007. Key achievements in the KSTAR construction are (i) fabrication process establishment in the Nb3Sn superconducting coils including interface components, (ii) development of magnet structures to resist high magnetic force and thermal loads of TF and PF coils, (iii) accurate assembling of all components using special assembly tools, and (iv) development of ancillary systems including a control system, magnet power supplies, diagnostic systems, heating systems, and cryogenic facility. Device commissioning has been started and the milestone for first plasma discharge is by the end of 2008. The KSTAR operation plan is targeted on the high performance plasma confinement research and long pulse operation achievement using the fully superconducting tokamak device. There is a lot of engineering similarity between KSTAR and ITER, such as using Nb3Sn superconductor for TF and CS magnets. The experience of the KSTAR device could be an important technical basis for the design, procurement, and initial operation of the ITER device, as a role of a ITER pilot device. [Copyright &y& Elsevier]

Abstract: KSTAR is fully superconducting tokamak under construction, capable of quasi-steady state, and long pulse operation. KSTAR has two parts of vacuum system. One is the cryostat vacuum system to maintain low temperature (4/80K) for thermal shielding of superconducting magnets. Other is the vacuum vessel to contain the plasma in double-walled evacuated space. For integration of KSTAR machine control, we chose experimental physics and industrial control system (EPICS) as a middleware at the engineering phase. Because EPICS is a good solution to implement the distributed control and the real time control for the tokamak, aiming at long pulse operation. The vacuum control system is the first local control system implemented using EPICS, and becomes an important pilot system to demonstrate the capability of EPICS on the machine control system. In this paper, we describe a procedure from designing hardware drivers to realizing operation panel. [Copyright &y& Elsevier]

Abstract: The Korea Superconducting Tokamak Advanced Research (KSTAR) control system will be developed with several subsystems, which consist of the central control system (e.g. plasma control, machine control, diagnostic control, time synchronization, and interlock systems) and local control systems for various subsystems. We are planning to connect the entire system with several networks, viz. a reflective-memory-based real-time network, an optical timing network, a gigabit Ethernet network for generic machine control, and a storage network. Then it will evolve into a network-based, distributed real-time control system. Thus, we have to consider the standard communication protocols among the subsystems and how to handle the various kinds of hardware in a homogeneous way. To satisfy these requirements, EPICS has been chosen for the KSTAR control. The EPICS framework provides network-based real-time distributed control, operating system independent programming tools, operator interface tools, archiving tools, and interface tools with other commercial and non-commercial software. The most important advantage of the use of the EPICS framework is in providing homogeneity of the system for the control system developer. The developer does not have to be concerned about the specifics of the local system, but can concentrate on the implementation of the control logic with EPICS tools. We will present the details of the integration issues and also will give a brief summary of the entire KSTAR control system from an integration point of view. [Copyright &y& Elsevier]

Abstract: Low density slide away discharges with anomalous Doppler resonance (ADR) effects have been observed in the KSTAR tokamak. When the line averaged electron density was lower than , the discharges went into the slide-away regime with relaxations in the electron cyclotron emission due to the ADR effects which transferred the runaway electron energy from parallel to perpendicular motion. The suppression of the ADR effects has been achieved by electron cyclotron resonance heating which enhanced the perpendicular energy of electrons and led to an isotropization of the electron distribution function. [Copyright &y& Elsevier]