Experimental Advanced Superconducting Tokamak

Le tokamak supraconducteur avancé expérimental (Experimental Advanced Superconducting Tokamak ou EAST, en chinois 先进实验超导托卡马克实验装置), désigné en interne par HT-7U (ou 人造太阳”、东方超环), est un réacteur tokamak supraconducteur à fusion par confinement magnétique expérimental situé dans le Hefei, en Chine. Les instituts de sciences physiques de Hefei mènent l'expérience pour l'Académie chinoise des sciences. Il fonctionne depuis 2006. C'est le premier tokamak à utiliser des aimants supraconducteurs toroïdaux et poloïdaux. Il vise des impulsions plasma allant jusqu'à . Il remplace le réacteur HT-7, et sera suivi dans les années 2020 par China Fusion Engineering Test Reactor. Historique EAST a suivi le premier dispositif tokamak supraconducteur de Chine, baptisé HT-7, construit par l'Institut de physique du plasma en partenariat avec la Russie au début des années 1990. Le projet a été proposé en 1996 et approuvé en 1998. Selon un calendrier de 2003 bâtiments et installations du

Heat Transfer between the Superconducting Cables of the LHC Accelerator Magnets and the Superfluid Helium Bath

Pier Paolo Granieri

In this thesis work we investigate the heat transfer through the electrical insulation of superconducting cables cooled by super fluid helium. The cable insulation constitutes the most severe barrier for heat extraction from the superconducting magnets of the CERN Large Hadron Collider (LHC). We performed an experimental analysis, a theoretical modeling and a fundamental research to characterize the present LHC insulation and to develop new ideas of thermally enhanced insulations. The outcome of these studies allowed to determine the thermal stability of the magnets for the LHC and its future upgrades. An innovative measurement technique was developed to experimentally analyze the heat transfer between the cables and the super fluid helium bath. It allowed to describe the LHC coil behavior using the real cable structure, an appropriate thermometry and controlling the applied pressure. We developed a new thermally enhanced insulation scheme based on an increased porosity to super uid helium. It aims at withstanding large heat loads, as needed for the High Luminosity LHC upgrade (HL-LHC). Experimental measurements of the new insulation showed a major improvement of heat extraction compared to the present state-of-the-art used in the LHC. We developed a theoretical heat transfer model quantitatively explaining the experimental results of the LHC and HL-LHC insulations. We identified the heat extraction mechanisms, mainly occurring through super fluid helium micro-channels. The average micro-channels dimensions were estimated to vary between few and dozens of µm, depending on the insulation scheme. In the model we considered the known laws describing the dynamic regimes of super fluid helium. However such laws were never demonstrated to be valid in the narrow channels typical of the cable insulation. We developed a new experimental device to investigate heat transport through microchannels. Micro-fabrication techniques were used to etch the channels down to a depth of 16 µm. We measured the classical laminar and turbulent regimes, thus demonstrating the validity of such heat transport laws independently from the channel geometrical shape and size down to these dimensions. To conclude, we used the obtained experimental and theoretical heat transfer results to determine the LHC and HL-LHC magnets stability. We estimated their quench margin and compared it to the beam induced heat deposit. The resulting difference allows a safe operation of the magnets.

EPFL2012

Improved Plasma Vertical Position Control on TCV Using Model-Based Optimized Controller Synthesis

Stefano Coda, Federico Alberto Alfredo Felici, Cristian Galperti, Federico Pesamosca

Elongated plasmas lead to improved performance in tokamaks but make the plasma prone to vertical instability, which requires active feedback control, a critical issue for future fusion reactors. Vertical control was optimized for the TCV tokamak by applying modern control theory to electromagnetic models for the plasma-vessel-coils dynamics. Two different optimal combinations of poloidal field coils for vertical control actuation are derived from linear plasma response models and used on different timescales for controlling the plasma vertical position. On fast timescales, the priority is input minimization, while on long timescales position control is designed to be compatible with shape control. A structured H-infinity design extending classical H-infinity to fixed-structure control systems was subsequently applied to obtain an optimized controller using all available coils for position control. Closed-loop performance improvement was demonstrated in dedicated TCV experiments, showing a reduction of input requirement for stabilizing the same plasma, thus reducing the risk of power supply saturation and consequent loss of vertical control. This novel algorithm is adaptable to different plasma equilibria as it is designed for model-based automated coil selection and controller tuning, thus avoiding extensive experimental gain scans when performing plasma discharges in TCV. The presented technique is general and can be applied to any present tokamak with independent coils or for the design of future tokamak magnetic control systems.

TAYLOR & FRANCIS INC2022

Heat Transfer between the Superconducting Cables of the LHC Accelerator Magnets and the Superfluid Helium Bath

Pier Paolo Granieri

EPFL2012