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.
4C code analysis of thermal-hydraulic transients in the KSTAR PF1 superconducting coil
Abstract The KSTAR tokamak, in operation since 2008 at the National Fusion Research Institute in Korea, is equipped with a full superconducting magnet system including the central solenoid (CS), which is made of four symmetric pairs of coils PF1L/U–PF4L/U. Each of the CS coils is pancake wound using Nb 3 Sn cable-in-conduit conductors with a square Incoloy jacket. The coils are cooled with supercritical He in forced circulation at nominal 4.5 K and 5.5 bar inlet conditions. During different test campaigns the measured temperature increase due to AC losses turned out to be higher than expected, which motivates the present study. The 4C code, already validated against and applied to different types of thermal–hydraulic transients in different superconducting coils, is applied here to the thermal–hydraulic analysis of a full set of trapezoidal current pulses in the PF1 coils, with different ramp rates. We find the value of the coupling time constant nτ that best fits, at each current ramp rate, the temperature increase up to the end of the heating at the coil outlet. The agreement between computed results and the whole set of measured data, including temperatures, pressures and mass flow rates, is then shown to be very good both at the inlet and at the outlet of the coil. The nτ values needed to explain the experimental results decrease at increasing current ramp rates, consistently with the results found in the literature.
M&M: Multi-conductor Mithrandir code for the simulation of thermal-hydraulic transients in superconducting magnets
Abstract The analysis of superconducting magnets can require the simultaneous simulation of several conductors. The multi-conductor Mithrandir (MM14:25), which was used for the simulation of thermal-hydraulic transients of single two-channel cable-in-conduit conductors (CICCs) cooled by supercritical helium. The M&M code is able to describe simultaneously an arbitrary number of one- or two-channel conductors, allowing for different kinds of coupling between them, and for different topologies of the assembly. The new code has been validated in three different situations, leading to good agreement both with results obtained with Mithrandir and with experimental data.