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Development of tungsten brazing technology for the upgraded Korea superconducting tokamak advanced research divertor was launched in early 2013. ITER grade tungsten block was brazed on the CuCrZr alloy in vacuum at 980 °C for 30 min using silver free brazing alloy. An OFHC-copper was used as an interlayer between tungsten and the CuCuZr. The brazing alloy is a 0.05 mm thickness of plate of which component is a Ni–Cu–Mn. It is found that the optimal loading on mock-up is about 20 kPa. Ultrasonic test and shear strength test were carried out to check the strength between tungsten and substrate material. And the joint conditions were analyzed by scanning electron microscopy. Tungsten-brazed mock-ups with a cooling tube were tested at the electron beam facility, Korea heat load test facility-electron beam in Korea Atomic Energy Research Institute. The high heat flux test was performed for tungsten-brazed mock-ups under heat flux of about 5 MW/ \textm^2 with more than 2000 cycles. All the tungsten-brazed mock-ups met the requirements and there was no delamination or failure at the bonding joints. [ABSTRACT FROM PUBLISHER]

Tungsten (W) monoblock that consists of W according to ITER specifications, oxygen-free high conductive copper (Cu-OFHC), and CuCrZr has been designed in preparation for KSTAR upgrade for steady-state long-pulse operation with 27.5-MW heating power. Finite-element analysis has been performed by ANSYS Workbench. The hydraulic thermomechanical analysis is performed to investigate the optimal design parameters and the expected fatigue lifetime under the operating conditions with 5.4-MW/ \textm^2 incident heat flux at the divertor. For a single W monoblock, the optimization gives a W thickness of 5 mm, a side thickness of 2.5 mm, a thickness in the back part of 6 mm, and a Cu-OFHC interlayer thickness of 0.5 mm. For a mock-up consisting of five optimized W monoblocks, the thermal fatigue analysis is performed. As a result, the maximum value of equivalent total strain in the CuCrZr tube is found to be 0.266%, which corresponds to for a fatigue lifetime of 23 000 cycles. [ABSTRACT FROM AUTHOR]

The fourth KSTARcampaign in 2011 concentrated on active edge-localized mode (ELM) control by various methods such as non-axisymmetric magnetic perturbations, supersonic molecular beam injection (SMBI), vertical jogs of the plasma column and edge electron heating. The segmented in-vessel control coil (IVCC) system is capable of applying n ≤ 2 perturbed field with different phasing among top, middle and bottom coils. Application of an n = 1 perturbed field showed a desirable ELM suppression result. Fast vertical jogs of the plasma column achieved ELM pace-making and ELMs locked to 50 Hz vertical jogs were observed with a high probability of phase locking. A newly installed SMBI system was used for ELM control and the state of mitigated ELMs was sustained by the optimized repetitive SMBI pulse for a few tens of ELM periods. A change in ELM behaviour was seen due to edge electron heating although the effect of ECH launch needs supplementary analyses. The ECEI images of suppressed/mitigated ELM states showed apparent differences when compared with natural ELMy states. Further analyses are ongoing to explain the observed ELM control results. [ABSTRACT FROM AUTHOR]

In- and outboard plasma facing components (PFCs) of Korea Superconducting Tokamak Advanced Research (KSTAR) have been fully installed in 2010 for D-shaped diverted plasmas. Before the start of plasma operation, the PFCs were baked up to 200 ^\circ\C by hot nitrogen gas circulation system to remove impurities including water. The surface temperature of the PFC tiles was monitored by 200 thermocouple sensors during the plasma operation [plasma shot or glow discharge cleaning (GDC)], and the temporal and spatial (poloidal) temperature profiles are obtained. Depending on the heat flux on each tile, the surface temperature shows time-dependent behavior. After 1-h morning He GDC, the temperature of the PFCs at the inboard side has reached to 40 ^\circ\C. After an H-mode shot, the temperature of divertor tiles around the striking points was substantially increased. The time-averaged total heat flux after a few of L- and H-modes in 2010 was estimated to be approximately 0.010 \MW/m^2. [ABSTRACT FROM PUBLISHER]

The central solenoid (CS) coil system of the KSTAR device consists of four pairs of coils with up-down symmetry and a set of support structure. The CS coil system should endure various loads including thermal and electromagnetic load during operation. One of the most important roles of support structure is to preserve the structural stability of coil system from vertical forces by applying the pre-compression on the coil stack. The main assembly procedure of the coil stack is as follows: 1) coil subassembly and stacking, 2) structure assembly, 3) preloading process by heating shells in the support structure, and 4) measurement on the final dimension. The special jigs and heating system for the preloading were designed to apply pre-compression on the coil stack during the assembly at room temperature. Moreover, a few tens of thermocouples and strain gauges were installed for measuring temperature and thermal expansion of preloading structures. Since the final assembly of the CS coil was successfully completed with about 7.3 MN of preloading in 2006, the CS coil system has been experienced four thermal cycles from 300 K to 5 K until 2011. This paper describes the main results of applying the pre-compression on the coil stack and mechanical behaviors of preloading structures during thermal cycles. [ABSTRACT FROM PUBLISHER]

The Cable-In-Conduit Conductor (CICC) for the KSTAR buslines is made of NbTi superconducting (SC) strands. A busline consists of several electrical joints, which are the major heat load contributors to the busline cryo-system. In the poloidal field (PF) busline helium circuit, the supercritical helium is fed to the electrical joint of current lead end and comes out to the magnet terminal joint. This helium flow configuration has been verified to maintain the cryogenic stability of the buslines through the KSTAR operation. During the normal operation of the KSTAR PF coil, the heated helium coming out to both the coil and the busline meets at the magnet terminal and exchange heat, but the busline outlet temperature still remained less than magnet outlet temperature. As the buslines for the electrical connection in series of the upper and lower coils for PF1 and PF2 have the helium path through the two terminal joints of magnet, they experience higher temperature than the other buslines mainly due to the larger heat exchange. In this case, the connection buslines are considered to have very low safety margin and have the strong possibility of quenches. [ABSTRACT FROM PUBLISHER]