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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]

The AC loss in a large superconducting magnet coil shows a tendency to be changed after assembly. For the ac loss measurement of the Korea Superconducting Tokamak Advanced Research (KSTAR) superconducting coils after assembly, several current scenarios, trapezoidal pulses and a DC offset sinusoidal pulses, were applied to the PF1 Upper (U) and Lower (L) coils during the commissioning. The measurement was done once before and once after the plasma discharge experiments. All coil data were obtained by the tokamak monitoring system and helium distribution system which were designed to measure temperature, pressure, and mass-flow at both inlets and outlets of the coils. The PF1 coils of the cable-in-conduit conductor type were made of Nb3Sn superconducting strands, whose winding scheme is 20 layers with each layer having 9 turns. Each has 10 cooling channels for the heat removal by the supercritical helium at 4.5 K. For the trapezoidal pulse tests, the current was increased up to 4 kA with several different ramp rates and a 2 kA DC offset and 0.5 kA sine waves with different frequencies from 0.1 Hz to 0.3 Hz were applied to the coil. According to the analyses, the AC loss was slightly decreased for the same condition after 700 plasma shots. It was believe that such a result was due to reduced inter-strand resistances which changed the transverse resistance between the inter-strands. The coupling time constant was estimated to be 32 ms in the trapezoidal tests and 13.6 ms for the DC offset sinusoidal pulses. The former is larger than the latter because of the effect of the jacket eddy current loss due to Incoloy 908 which is a ferromagnetic material. Considering the jacket eddy current losses, the coupling time constant was recalculated and the value estimated to be about 13 ms for all current wave forms during first commissioning. [ABSTRACT FROM AUTHOR]

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]

Provides an overview on the Korea Superconducting Tokamak Advanced Research (KSTAR) project for plasma diagnostics. Determination of plasma control, core plasma and divertor/edge plasma; Characteristics of the KSTAR diagnostics; Motional Stark effect system; Core Thomson scattering system; Machine access for diagnostics.

A piezoelectric valve, which has a flow rate of about 463 mbar l/s, has been installed to fuel the Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak. The valve flow rate is in situ calibrated by analyzing the pressure rise curve while fueling the vessel at a constant rate. The calibration method and results are presented. In addition to the flow rate, other vacuum system parameters, such as the pumping speed and the vessel volume, were experimentally obtained. Based on these measurements, a KSTAR vacuum system simulator was developed to calculate the valve drive signal to obtain a programmed pressure trace. An arbitrarily shaped pressure trace was successfully controlled in KSTAR with this hardware and software system. [ABSTRACT FROM AUTHOR]