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Title: The TORE SUPRA Cryogenic System Behaviour During Long Plasma Discharges with a High Injected Energy

Abstract

After the CIEL project completion including the upgrade of the plasma facing components and the water cooling system, the superconducting Tore Supra Tokamak achieved a world record of injected energy (1.1 GJ), during long duration (6 min) plasma discharges, which was enabled by the upgrade of the transfer system capacities, but also by the steady state toroidal field. The Tore Supra cryogenic refrigerator enables the toroidal field coils to be operated at nominal current along the full daily plasma operation shift. It has capacities of 300 W at 1.8 K, 750 W at 4.5 K and 30 kW at 80 K and was operated with a high reliability for more than 16 years. After a brief recall on the cryogenic refrigeration of the toroidal superconducting magnet, the distribution of the heat loads at the various levels of temperature (in standby mode 150W at 1.8 K and 200W at 4.5 K) is presented. The inventory of the calculated static and variable heat loads deposited within each part of toroidal field coils and thermal shields, is given with the factors of dependence. This analysis identifies and quantifies the major magnetic disturbances like a disruption (about 12 kJ onto the coils and 300more » kJ onto the thick casings) which generate additional heat loads for the refrigerator.The measurements associated with the He II saturated bath pumping system, and the supercritical helium loop cooling the thick casings, allow us to verify thereafter the behaviour of the cryo-refrigerator during the long duration discharges, and the compliance with the theoretical model.The conclusions bring results also applicable to the cyoplant of future plant like ITER which will operate with long duration discharges.« less

Authors:
; ; ; ;  [1]
  1. Departement de Recherches sur la Fusion Controlee, Association, Euratom-CEA, CEA/Cadarache, F-13108 Saint Paul-lez-Durance (France)
Publication Date:
OSTI Identifier:
20800203
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 823; Journal Issue: 1; Conference: Cryogenic engineering conference, Keystone, CO (United States), 29 Aug - 2 Sep 2005; Other Information: DOI: 10.1063/1.2202563; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; COOLING SYSTEMS; CRYOGENICS; DISTURBANCES; ELECTRIC CURRENTS; ELECTRIC DISCHARGES; FIRST WALL; HEATING LOAD; HELIUM; ITER TOKAMAK; OPERATION; PLASMA; PUMPING; REFRIGERATION; REFRIGERATORS; STANDBY MODE; STEADY-STATE CONDITIONS; SUPERCONDUCTING COILS; SUPERCONDUCTING MAGNETS; THERMAL SHIELDS; TORE SUPRA TOKAMAK

Citation Formats

Henry, D., Hertout, P., Journeaux, J. Y., Duchateau, J. L., and Reynaud, P.. The TORE SUPRA Cryogenic System Behaviour During Long Plasma Discharges with a High Injected Energy. United States: N. p., 2006. Web. doi:10.1063/1.2202563.
Henry, D., Hertout, P., Journeaux, J. Y., Duchateau, J. L., & Reynaud, P.. The TORE SUPRA Cryogenic System Behaviour During Long Plasma Discharges with a High Injected Energy. United States. doi:10.1063/1.2202563.
Henry, D., Hertout, P., Journeaux, J. Y., Duchateau, J. L., and Reynaud, P.. Thu . "The TORE SUPRA Cryogenic System Behaviour During Long Plasma Discharges with a High Injected Energy". United States. doi:10.1063/1.2202563.
@article{osti_20800203,
title = {The TORE SUPRA Cryogenic System Behaviour During Long Plasma Discharges with a High Injected Energy},
author = {Henry, D. and Hertout, P. and Journeaux, J. Y. and Duchateau, J. L. and Reynaud, P.},
abstractNote = {After the CIEL project completion including the upgrade of the plasma facing components and the water cooling system, the superconducting Tore Supra Tokamak achieved a world record of injected energy (1.1 GJ), during long duration (6 min) plasma discharges, which was enabled by the upgrade of the transfer system capacities, but also by the steady state toroidal field. The Tore Supra cryogenic refrigerator enables the toroidal field coils to be operated at nominal current along the full daily plasma operation shift. It has capacities of 300 W at 1.8 K, 750 W at 4.5 K and 30 kW at 80 K and was operated with a high reliability for more than 16 years. After a brief recall on the cryogenic refrigeration of the toroidal superconducting magnet, the distribution of the heat loads at the various levels of temperature (in standby mode 150W at 1.8 K and 200W at 4.5 K) is presented. The inventory of the calculated static and variable heat loads deposited within each part of toroidal field coils and thermal shields, is given with the factors of dependence. This analysis identifies and quantifies the major magnetic disturbances like a disruption (about 12 kJ onto the coils and 300 kJ onto the thick casings) which generate additional heat loads for the refrigerator.The measurements associated with the He II saturated bath pumping system, and the supercritical helium loop cooling the thick casings, allow us to verify thereafter the behaviour of the cryo-refrigerator during the long duration discharges, and the compliance with the theoretical model.The conclusions bring results also applicable to the cyoplant of future plant like ITER which will operate with long duration discharges.},
doi = {10.1063/1.2202563},
journal = {AIP Conference Proceedings},
number = 1,
volume = 823,
place = {United States},
year = {Thu Apr 27 00:00:00 EDT 2006},
month = {Thu Apr 27 00:00:00 EDT 2006}
}
  • In view of high-power, long pulse steady-state operation, Tore Supra has incorporated in its design the active control of heat and particles in a realistic environment. A new inner-wall technology was developed in 1994 and is to be tested in 1995-1996 with a totally rebuilt 40-deg toroidal sector. A carbon-fiber-reinforced carbon-metal compound is based on the newest brazing technology and regorous quality control. Components such as the toroidal pump limiter and the guard limiters of plasma-heating antennas are being developed in the same way. For structures where brazing is difficult, boron carbide-coated components have been developed and installed in Toremore » Supra. For lower heat fluxes, a bolted concept has been designed and tested. The influence of inner-first-wall misalignment in Tore Supra on the power exhaust limitation of brazed components has been studied. Results from the technological development for the different power exhaust systems and the associated experimental knowledge obtained during plasma operation in Tore Supra are presented. 63 refs., 34 figs., 2 tabs.« less
  • Reliable and repetitive high power and long pulse tokamak operation is strongly dependant of the ability to secure the Plasma Facing Components (PFCs). In Tore Supra, a network of 7 infrared (IR) video cameras is routinely used to prevent PFCs overheating and damage in selected regions. Real time feedback control and offline analysis are essential for basic protection and understanding of abnormal thermal events. One important limitation detected by the IR real time feed-back loop during high power RF operation (injected power of 9.5 MW over 26 s and 12 MW over 10 s have been achieved respectively in 2006more » and 2008) is due to the interaction between fast ions which increase the power flux density and flaking of the boron carbide coatings on the Faraday screen box of the ICRH antennas. An IR-based experimental procedure is proposed in order to detect new flakes during plasma operation. The thermal response of the B4C coating is studied with and without flaking during plasma operation. The experimental heat flux deposited by fast ion losses on the Faraday screen is calculated for high (3.8 T) and low magnetic field (2 T) during high RF power operation (with fundamental hydrogen minority and second harmonic ICRH heating schemes respectively). The paper addresses both thermal science issues applied to machine protection and limitation due to fast ions issues during high RF power, long pulse operation. Safety margin to critical heat flux and number of fatigue cycles under heat load are presented in the paper.« less
  • On many tokamaks (C-Mod, EAST, FTU, JET, HT-7, TS), a decrease in current drive efficiency of the Lower Hybrid (LH) waves is observed in high electron density plasmas. The cause of this behaviour is believed to be: Parametric Instabilities (PI) and Scattering from Density Fluctuations (SDF). For the ITER LH system, our knowledge must be improved to avoid such effects and to maintain the LH current drive efficiency at high density. The ITPA IOS group coordinates this effort [1] and all experimental data are essential to validate the numerical codes in progress. Usually the broadening of the LH wave frequencymore » spectrum is measured by a probe located in the plasma edge. For this study, the frequency spectrum of a reflected power signal from the LH antenna was used. In addition, the spectrum measurements are compared with the density fluctuations observed on RF probes located at the antenna mouth. Several plasma currents (0.6 to 1.4 MA) and densities up to 5.2 × 10{sup 19} m−3 have been realised on Tore Supra (TS) long pulses and with high injected RF power, up to 5.4 MW-30s. This allowed using a spectrum analyser to make several measurements during the plasma pulse. The side lobe amplitude, shifted by 20-30MHz with respect to the main peak, grows with increasing density. Furthermore, for an increase of plasma current at the same density, the spectra broaden and become asymmetric. Some parametric dependencies are shown in this paper.« less
  • The lower hybrid current drive (LHCD) system of Tore Supra has been upgraded for long pulse operation at higher power (7–8 MW). The two launchers have coupled on plasma 3.8 MW and 2.7 MW separately. This new power capability allows extending the operational domain of Tore Supra for long pulses at higher current and density. 38 long (20 s –155 s) discharges with very low loop voltage (V{sub L} = 30-60 mV) were performed with combined LHCD (5-5.7 MW) and ICRH (1–3 MW) powers, with up to 1 GJ of injected energy. Higher LHCD efficiency, with respect to the previous long discharges, is reported. MHD stability of these discharges ismore » very sensitive to the LHCD power and parallel wave index, in particular in the preforming phase. For theses evanescent loop voltage plasmas, the ICRH power, in excess of 1 MW, is found to have a beneficial effect on the MHD stability.« less
  • The upgraded 3.7 GHz Lower Hybrid Current Drive (LHCD) system for the Tore Supra (TS) tokamak is in the process of installation. When complete, it will permit long pulse injection (1000s) at coupled power level up to 6, 5 MW. Steady state operation of high power RF sources and components is challenging and requires careful validation before the system can be commissioned on the tokamak.Results on the validation of CW klystrons, improvements on the RF components forming part of the power generation circuit and the development of an RF water load to sustain CW pulses under 700 kW RF powermore » are presented.« less