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The function of the current feeder system (CFS) is for conducting large currents from the power supplies to the KSTAR superconducting (SC) magnets. The CFS consists of SC bus-lines, joints, and current leads. The bus-line conductor is a circular cable-in-conduit conductor (CICC), which consists of a 4.5 mm thick stainless steel 316L seamless pipe containing 324 strands of chrome coated NbTi superconductor and 243 strands of OFHC. The ends of the CICC are assembled with specially designed lap joints. The joining resistance is controlled to less than 2.5 nano-ohm to minimize Joule heating. The outer surfaces of the CICC were electrically insulated up to 15 kV with jackets made of Kapton film and prepreged E-glass tape. Helically wrapped conducting fiber was used to measure the voltages of bus-line quenches. Two pairs of prototype brass leads for poloidal field (PF) and toroidal field (TF) coils have been fabricated and tested up to the currents of 26 kA for the PF leads and 35 kA for the TF leads. The test results satisfied all the requirements so that all 18 leads were manufactured and assembled on site. This paper will describe the detailed manufacturing progress and commissioning results of the KSTAR CFS. [ABSTRACT FROM AUTHOR]

To protect the KSTAR (Korea Superconducting Tokamak Advanced Research) superconducting coils against a quench, the quench detection system based on voltage measurement was fabricated. It used a detect/dump scheme which detects the presence of non-recovering normal zones and activates a dump circuit that transfers most of the stored energy into a dump resistor. Even though it is desirable to discharge the coil energy as fast as possible after quench detection, a time delay between the quench detection and the complete dump circuit actuation will be necessary in order that the quench voltage is to be distinguished from various noises. The quench threshold voltage and the delay time should be set before operation for quench voltage detection so that the maximum hot-spot temperature could be limited to 150 K. This paper describes the hardware techniques to prevent the malfunction of the quench detection due to voltage noises arising from the KSTAR operating scenarios. During the first operation of the KSTAR machine, the inductive voltages and other voltage noises were measured and effectively compensated below voltage thresholds. A quench did not occur and the quench detection system was well operated without any false activation. [ABSTRACT FROM AUTHOR]

The magnet system comprises sixteen toroidal field (TF) coils and fourteen poloidal field (PF) coils for KSTAR (Korea Superconducting Tokamak Advanced Research) Tokamak. All the TF coils and 10 PF coils (PF1~ 5 UL) are made of Nb3 Sn strands and 4 PF coils (PF6 ~ 7 UL) are made of NbTi strands. Before operating the superconducting coils, it is critical to verify the operation conditions such as thermo-hydraulic parameters and stability boundaries. In this regards, the TF model coil and CSMC (Central Solenoid Model Coil) have been tested and the operating conditions have been analyzed. Before cool down, parameters such as helium flow through conduits, electrical insulation and coil geometry have been measured at room temperature to confirm the manufacturing soundness. During cool down and current charging, thermo-hydraulic and mechanical parameters by using mechanical sensors have been measured. Also measured was the magnetic field strength in various positions of the coil conductor. Measured data have been analyzed and the results have been compared with the model analysis by simulation code. [ABSTRACT FROM AUTHOR]

The Korea Superconducting Tokamak Advanced Research (KSTAR) Central Solenoid Model Coil (CSMC) was tested at the National Fusion Research Center (NFRC) to verify the design and manufacturing engineering and to ensure reliable operation. The CSMC reached 8.6 T at 20 kA DC operation successfully. We also assessed the AC loss of the CSMC by means of both a sinusoidal wave with a DC offset as well as a triangular pulse. We derived a friction factor correlation of CSMC at room temperature and at cryogenic temperature (4 ∼ 6 K). We also investigated the variation of the friction factor during current charging. The KSTAR PF coil simulation code was validated with inlet and outlet helium temperature, mass flow rate, and pressure drop from the experimental results. The operation temperature margin of the CS1 coil of KSTAR was calculated with the revised KSTAR PF coil simulation coil. [ABSTRACT FROM AUTHOR]

The KSTAR Central Solenoid Model Coils (CSMC), which are in the form of split coils with same dimension, have been tested. The CSMC were successfully charged up to 20 kA and down to zero with different ramp rates. Various pulse waveforms were applied to the CSMC to analyse the AC-loss characteristics of the coils. The measurement method was a gas-flow calorimetry. In this work, two types of waveforms, the DC-biased sinusoidal wave (Idc = 2, 4 kA; ΔIac = 1 kA; ƒ = 0.08 ∼ 0.67 Hz) and a single triangular pulse (Imax = 6 ∼ 10 kA; dI/dt = 0.5 ∼ 2 kA/s), are selected and analysed. From the measured data at the one outlet where helium channel 3 and 4 are merged, the AC loss parameters, related with the hysteresis loss and the coupling loss, are calculated. The B-field strength differs depending on the position within the cooling channels. The spatial field variation and the ramp rate were 0.048∼ 1.9T and 8.1∼ 71 mT/s for the DC-biased sinusoidal waves, while 0.29∼ 4.3 T and 0.024∼ 0.86 T/s for the triangular pulses. The measured AC losses are compared with estimated values and the behavior agrees well. The coupling time constant (nτ) varies with the field strength. In case of the triangular pulses, nτ increases by increasing the field amplitude and the maximum value of nτ is 41 ms with Imax = 10 kA. [ABSTRACT FROM AUTHOR]