Thermohydraulic Behaviors of KSTAR PF Superconducting Magnet System in Operation
Korea Superconducting Tokamak Advanced Research (KSTAR) is a superconducting tokamak which adopts 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 ± 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. Most of all, we agree that the analysis of thermohydraulic behavior is absolutely needed for more stable operation and higher plasma performance. So we are checking the related data and the tendency at every campaign and we are optimizing the operational procedure to fit the plasma scenario. In this paper, we introduce the significant thermohydraulic behaviors of KSTAR PF coils up to now.
Pressure drop analysis in the CS insert coil
The Central Solenoid Model Coil (CSMC) and the CS Insert Coil (CSIC) were tested during the spring and summer of 2000 at JAERI Naka, Japan, within the framework of the ITER large projects. The CSIC is a single-layer one-in-hand solenoid inserted in the bore of the CSMC. It uses a Nb3Sn dual-channel cable-in-conduit conductor (CICC), about 140 m long, cooled by forced flow supercritical HeI nominally at 4.5 K and 0.6 MPa. The friction of the helium flow in the conductor plays a fundamental role in assessing the total mass-flow rate and its repartition between the central cooling channel and the annular bundle region. In turn, these may significantly influence, e.g., quench and/or heat slug propagation in the coil. In the CSIC these issues are complicated further by the fact that different friction characteristics were observed in different phases (e.g., with or without current) of the experimental campaign. Here we present and discuss a selection of the CSIC experimental data of pressure drop vs. mass-flow...
The Unusual Variability of the Large Magellanic Cloud Planetary Nebula RPJ 053059–683542
We present images and light curves of the bipolar planetary nebula RPJ 053059-683542 that was discovered in the Reid-Parker AAO UKST Hα survey of the Large Magellanic Cloud. The emission from this object appears entirely nebular, with the central star apparently obscured by a central band of absorption that bisects the nebula. The light curves, which were derived from images from the SuperMACHO project at CTIO, showed significant, spatially resolved variability over the period 2002 January through 2005 December. Remarkably, the emission from the two bright lobes of the nebula vary either independently or similarly but with a phase lag of at least 1 yr. The optical spectra show a low level of nebular excitation, and only modest N enrichment. Infrared photometry from the 2MASS and SAGE surveys indicates the presence of a significant quantity of dust. The available data imply that the central star has a close binary companion and that the system has undergone some kind of outburst event that caused the nebular emission to first brighten and then fade. Further monitoring, high-resolution imaging, and detailed IR polarimetry and spectroscopy would uncover the nature of this nebula and the unseen ionizing source.