Yeong-Kook Oh

OVERVIEW OF KSTAR INTEGRATED CONTROL SYSTEM

After more than 10 years construction, KSTAR (Korea Superconducting Tokamak Advanced Research) had finally completed its assembly in June 2007, and then achieved the goal of first-plasma in July 2008 through the four months commissioning. KSTAR was constructed with fully superconducting magnets with material of and NbTi, and their operation temperatures are maintained below 4.5K by the help of Helium Refrigerator System. During the first-plasma operation, plasmas of maximum current of 133kA and maximum pulse width of 865ms were obtained. The KSTAR Integrated Control System (KICS) has successfully fulfilled its missions of surveillance, device operation, machine protection interlock, and data acquisition and management. These and more were all KSTAR commissioning requirements. For reliable and safe operation of KSTAR, 17 local control systems were developed. Those systems must be integrated into the logically single control system, and operate regardless of their platforms and location installed. In order to meet these requirements, KICS was developed as a network-based distributed system and adopted a new framework, named as EPICS (Experimental Physics and Industrial Control System). Also, KICS has some features in KSTAR operation. It performs not only 24 hour continuous plant operation, but the shot-based real-time feedback control by exchanging the initiatives of operation between a central controller and a plasma control system in accordance with the operation sequence. For the diagnosis and analysis of plasma, 11 types of diagnostic system were implemented in KSTAR, and the acquired data from them were archived using MDSpius (Model Driven System), which is widely used in data management of fusion control systems. This paper will cover the design and implementation of the KSTAR integrated control system and the data management and visualization systems. Commissioning results will be introduced in brief.

Initial phase wall conditioning in KSTAR

The initial phase wall conditioning in KSTAR is depicted. The KSTAR wall conditioning procedure consists of vessel baking, glow discharge cleaning (GDC), ICRH wall conditioning (ICWC) and boronization (Bz). Vessel baking is performed for the initial vacuum conditioning in order to remove various kinds of impurities including H2O, carbon and oxygen and for the plasma operation. The total outgassing rates after vessel baking in three successive KSTAR campaigns are compared. GDC is regularly performed as a standard wall cleaning procedure. Another cleaning technique is ICWC, which is useful for inter-shot wall conditioning under a strong magnetic field. In order to optimize the operation time and removal efficiency of ICWC, a parameter scan is performed. Bz is a standard technique to remove oxygen impurity from a vacuum vessel. KSTAR has used carborane powder which is a non-toxic boron-containing material. The KSTAR Bz has been successfully performed through two campaigns: water and oxygen levels in the vacuum vessel are reduced significantly. As a result, KSTAR has achieved its first L–H mode transition, although the input power was marginal for the L–H transition threshold. The characteristics of boron-containing thin films deposited for boronization are investigated.

CURRENT STATUS OF NUCLEAR FUSION ENERGY RESEARCH IN KOREA

The history of nuclear fusion research in Korea is rather short compared to that of advanced countries. However, since the mid-1990s, at which time the construction of KSTAR was about to commence, fusion research in Korea has been actively carried out in a wide range of areas, from basic plasma physics to fusion reactor design. The flourishing of fusion research partly owes to the fact that industrial technologies in Korea including those related to the nuclear field have been fully matured, with their quality being highly ranked in the world. Successive pivotal programs such as KSTAR and ITER have provided diverse opportunities to address new scientific and technological problems in fusion as well as to draw young researchers into related fields. The frame of the Korean nuclear fusion program is now changing from a small laboratory scale to a large national agenda. Coordinated strategies from different views and a holistic approach are necessary in order to achieve optimal efficiency and effectiveness. Upon this background, the present paper reflects upon the road taken to arrive at this point and looks ahead at the coming future in nuclear fusion research activities in Korea.

CONSTRUCTION, ASSEMBLY AND COMMISSIONING OF KSTAR MAIN STRUCTURES

The KSTAR device succeeded in first plasma generation on June of 2008 through comprehensive system test and commissioning. Among various kinds of the key factors that decisively affected the project, success in the construction and assembly of the major tokamak structure was most important one. Every engineering aspects of each structure were finally confirmed in the integrated commissioning period, and there were no severe troubles and failures prevented the KSTAR device from operating during the commissioning and the first plasma experiments. As a result, all of the experiences and technologies achieved through the KSTAR construction process are expected to be important fundamentals for future construction projects of superconducting fusion devices. This paper summarizes key engineering features of the major structures and of the machine assembly.

Thermo-hydraulic analysis of the KSTAR central solenoid model coil

The Korea Superconducting Tokamak Advanced Research (KSTAR) Central Solenoid Model Coil (CSMC) has been developed to validate the design of KSATR CS coil. The thermo-hydraulic characteristics were analyzed for the KSTAR CSMC. The major thermo-hydraulic parameters of the coil are AC losses, strand temperature, coolant temperature, pressure drop and temperature margin. A numerical code has been developed for the thermo-hydaulic analysis of the KSTAR CSMC according to the operating conditions. In this paper, the description of the thermo-hydraulic analysis models and analysis results of CSMC are presented. The total energy deposition due to AC losses in CSMC winding will induce a flow reversal of supercritical helium. The minimum temperature margin is estimated approximately 0.5 K. The maximum temperature in CSMC winding is about 7.6 K.

Superconductor Application to the Magnetic Fusion Devices for the Steady-State Plasma Confinement Achievement

The exploitation of the new energy source is necessary in upcoming century due to the rapid increasing of energy consumption and the shortage of the fossil energy sources in the world. There have been a lot of scientific and engineering efforts to make realization of the fusion energy production as a clean and limitless energy source to the mankind. The fusion energy has great advantages in the points of the energy density and the amount of resources, and it is a dominant energy source in the universe like the sun and stars. To achieve a reliable fusion reaction, a good confinement technology is required to overcome the repulsive force between nucleuses of light atoms like hydrogen isotopes as shown in Fig. 1. Among the confinement technologies two kinds of methods are dominant in the fusion researches. The one is the inertial confinement which focusing the high power laser beams in to the small size fuel pellet. The other is the magnetic confinement which confining the fuel gas in plasma state in vacuum by applying the high magnetic fields.

Development of Numerical Model of KSTAR PF Conductor and Magnet for the Analyses of AC Loss on the Results of KSTAR PF Magnet Test Run

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.