Non-linear temperature oscillations in the plasma centre on Tore Supra and their interplay with MHD
V. S. Udintsev, G. Giruzzi, F. Imbeaux, J. -F. Artaud, X. Garbet, G. Huysmans, P. Maget, J. -L. Segui, A. Becoulet, G. T. Hoang, E. Joffrin, X. Litaudon, B. Sao… 展开作者
V. S. Udintsev, G. Giruzzi, F. Imbeaux, J. -F. Artaud, X. Garbet, G. Huysmans, P. Maget, J. -L. Segui, A. Becoulet, G. T. Hoang, E. Joffrin, X. Litaudon, B. Saoutic, The Tore Supra Team
备注：
12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)
Regular oscillations of the central electron temperature have been observed by means of ECE and SXR diagnostics during non-inductively driven discharges on Tore Supra. These oscillations are sustained by LHCD, do not have a helical structure and, therefore, cannot be ascribed as MHD phenomena. The most probable explanation of this oscillating regime (O-regime) is the assumption that the plasma current density (and, thus, the q-profile) and the electron temperature evolve as a non-linearly coupled predator-pray system. The integrated modelling code CRONOS has been used to demonstrate that the coupled heat transport and resistive diffusion equations admit solutions for the electron temperature and the current density which have a cyclic behaviour. Recent experimental results in which the O-regime co-exists with MHD modes will be presented. Because both phenomena are linked to details of the q-profile, some interplay between MHD and oscillations may occur. The localisation of magnetic islands allows to obtain an accurate picture of the q-profile in the plasma core. In some case, MHD-driven reconnection helps in maintaining a weakly inverted q-profile that is found to be, in the CRONOS simulations, a necessary condition to trigger the oscillations.
Electron temperature fluctuation studies can help to understand the nature of the turbulent transport in to-kamak plasmas. At Tore Supra, a 32-channel heterodyne ECE radiometer has been upgraded with two chan-nels of 100 MHz bandwidth and tunable central frequencies allowing the shift of the plasma sample volume in the radial direction. With the sufficiently large video bandwidth and the long sampling time, it is possible to reduce significantly the thermal noise and to identify "true" high frequency components up to 200 kHz from the cross-correlation between these channels. First results of t…
Direct coupling of the fast magnetosonic wave to the electrons has been studied on the tokamak TORE SUPRA. Preliminary experiments were dedicated to optimise the scenario for Fast Wave Electron Heating (FWEH) and Current Drive (FWCD). In a first part, thermal kinetic and diamagnetic energy are compared when fast wave is applied to the plasma in two different regimes: 1/ the minority hydrogen heating scenario (ICRH), 2/ the direct electron damping. Effects of ion resonant layers, marginally present in the plasma in the later regime (FWEH), is then presented and discussed.
The Tore Supra tokamak is the largest superconducting magnetic fusion facility, has been devoted to long-duration high-performance discharge research. With a steady-state magnetic field and water cooled plasma facing components, discharges up to 6 minutes 24 seconds duration with injected / extracted energy up to 1 GJ have been performed. The Tore Supra real time measurements and control (RTMC) system has been upgraded to address schemes dedicated to long pulse operation with simultaneous control of an increasing number of plasma parameters. This includes plasma equilibrium control with possib…
The last experimental campaign of Tore Supra was also the last one with a set of plasma facing components mainly dating from the assembly of the machine in 1988. This campaign was interrupted a few days ahead of schedule because of the rupture of one coolant tube of the Inner First Wall (IFW). The rupture was observed by an abrupt increase of the pressure in the vessel. It was caused by a water leak which occurred two seconds after the end of the lower hybrid heating pulse during the current ramp-down. Investigations show that the accident is not related to the operation of the machine or a we…
The sputtering of inside wall components of tokamaks can lead to the injection of supersaturated vapour in the plasma edge. The resulting condensation favours the formation of clusters which can give rise to solid particulates by further accretion. Sputtering discharges are proposed to have highlight on the formation of carbonaceous dust observed in the tokamaks with graphite based wall components. The flux of the sputtered carbon atoms is evaluated in the conditions of our laboratory discharges as well as the evolution of their energy distribution. It is shown that a cooling mechanism occurs …
An analytical model previously developed to study the structure of the magnetic field for the TEXTOR-DED [S.S. Abdullaev et al. Phys. Plasmas, 6, 153 (1999)] is applied to the similar study of the Ergodic Divertor of Tore Supra tokamak [Ph. Ghendrih, Plasma Phys. Control. Fusion, 38, 1653 (1996)]. The coil configuration of ED Tore Supra consists of six modules equidistantly located along the toroidal direction on the low-field-side of the torus with given toroidal and poloidal extensions. The Hamiltonian formulation of field line equations in straight-field-line coordinates (Boozer coordinates…
During the 2003 experimental campaign, the aim of realizing reliable fully non inductive discharges has been successfully completed in Tore Supra. One the major difficulties in optimizing this scenario comes from MHD stability issues. Indeed, the current profile obtained with LH antennas in these experiments is prone to the triggering of single or double tearing modes. Under certain conditions, the discharges enters in a regime of permanent MHD activity. The present work investigates the MHD properties of these fully non-inductive discharges in the operational space defined by the toroidal mag…
Traditionally devoted to electron density profile measurement we show that fast frequency sweeping reflectometry technique can bring valuable and innovative measurements onto plasma turbulence. While fast frequency sweeping technique is traditionally devoted to electron density radial profile measurements we show in this paper how we can handle the fluctuations of the reflected signal to recover plasma density fluctuation measurements with a high spatial and temporal resolution. Large size turbulence related to magneto-hydrodynamic (MHD) activity and the associated magnetic islands can be dete…
The Inner First Wall (IFW) is the main limiter in Tore Supra for long and powerful discharges. The original graphite IFW was partly damaged by 8 years of operation and a sector of 60{\textdegree} was replaced between 1995 and 1997 by CFC brazed elements. They are designed to accept twice as much flux (2 MW/m${}^2$) as the older ones and are expected to be more resilient. The new elements gave the opportunity to install diagnostics (thermocouples and langmuir probes) on a poloidal sector, to characterise the behaviour of the new IFW and especially the heat flux profile. The pattern doesn't foll…
The paper presents a relativistic mechanism that can create a poloidal non-uniformity of a radial electric field on a magnetic surface in a tokamak plasma. This mechanism is associated with a significant current velocity of electrons in plasma for many experimental modes of tokamak operations. It is important that electric fields arise without the traditional separation of charges in plasma. The presented mechanism can explain the previously experimentally measured poloidal non-uniformity of the C+6 carbon ion toroidal rotation velocity in the TORE-SUPRA tokamak plasma
SATIR is a new test-bed installed at Tore Supra to perform non destructive examination of actively cooled plasma facing components. Hot and cold water flow successively in the cooling tube of the component and the surface temperature is recorded with an infrared camera. Defects are detected by a slower temperature response above unbrazed areas. The connection between temperature differences and defect sizes is the main difficulty. It is established by tests of standard defects and thermal transient calculations of defective geometries. SATIR has been in use for two years and has proved to be v…
The acceleration of charged particles by interplanetary shocks can drain a non-negligible fraction of the upstream ram pressure. For a sample of shocks observed in-situ at 1 AU by the ACE and Wind spacecraft, time-series of the non-Maxwellian components (supra-thermal and higher-energy) of the ion and electron energy spectra were acquired for each event. These were averaged for one hour before and after the time of the shock passage to determine their partial pressure. Using the MHD Rankine-Hugoniot jump conditions, we find that the fraction of the total upstream energy flux transferred to non…
Recent development of real-time equilibrium code Equinox [1] using a fixed-point algorithm [2] allow major plasma magnetic parameters to be identified in real-time, using rigorous analytical method. The code relies on the boundary flux code providing flux values on the first wall of vacuum vessel. By means of least-square minimization of differences between magnetic field obtained from previous solution and the next measurements the code identifies the source term of the non-linear Grad-Shafranov equation [3]. The strict use of analytical equations together with a flexible algorithm offers an …
We present two generalized hybrid kinetic-Hall magnetohydrodynamics (MHD) models describing the interaction of a two-fluid bulk plasma, which consists of thermal ions and electrons, with energetic, suprathermal ion populations described by Vlasov dynamics. The dynamics of the thermal components are governed by standard fluid equations in the Hall MHD limit with the electron momentum equation providing an Ohm's law with Hall and electron pressure terms involving a gyrotropic electron pressure tensor. The coupling of the bulk, low-energy plasma with the energetic particle dynamics is accomplishe…
Starting from the Braginskii equations, relevant for the tokamak edge region, a complete set of nonlinear equations for the geodesic acoustic modes (GAM) has been derived which includes collisionality, plasma beta and external sources of particle, momentum and heat. Local linear analysis shows that the GAM frequency increases with collisionality at low radial wave number $k_{r}$ and decreases at high $k_{r}$. GAM frequency also decreases with plasma beta. Radial profiles of GAM frequency for two Tore Supra shots, which were part of a collisionality scan, are compared with these calculations. D…
The observation of distinct peaks in tokamak core reflectometry measurements - named quasi-coherent-modes (QCMs) - are identified as a signature of Trapped-Electron-Mode (TEM) turbulence [H. Arnichand et al. 2016 Plasma Phys. Control. Fusion 58 014037]. This phenomenon is investigated with detailed linear and nonlinear gyrokinetic simulations using the \gene code. A Tore-Supra density scan is studied, which traverses through a Linear (LOC) to Saturated (SOC) Ohmic Confinement transition. The LOC and SOC phases are both simulated separately. In the LOC phase, where QCMs are observed, TEMs are r…
The acceleration of charged particles by interplanetary shocks (IPs) can drain a non-negligible fraction of the plasma pressure. In this study, we have selected 17 IPs observed in-situ at $1\,\text{au}$ by the Advanced Composition Explorer (ACE) and the Wind spacecraft, and 1 shock at $0.8\,\text{au}$ observed by Parker Solar Probe (PSP). We have calculated the time-dependent partial pressure of supra-thermal and energetic particles (smaller and greater than $50\,\text{keV}$ for protons and $30\,\text{keV}$ for electrons, respectively) in both the upstream and downstream regions. The particle …
The understanding of the mechanisms responsible for particle transport is of the utmost importance for magnetized fusion plasmas. A peaked density profile is attractive to improve the fusion rate, which is proportional to the square of the density, and to self-generate a large fraction of non-inductive current required for continuous operation. Experiments in various tokamak devices (AUG, DIII-D, JET, TCV, TEXT, TFTR) have indicated the existence of an anomalous inward particle pinch. Recently, such an anomalous pinch has been unambiguously identified in Tore Supra very long discharges, in abs…
In many plasmas, in particular in space science, protons govern much of the essential physics. Minority ions, suprathermal tails, and electrons at times account for additional details. However, electron effects usually appear on much smaller spatial and temporal scales. For more than two decades, scientists have refined computational models that concentrate on the dominating and larger-scale ion kinetic physics, while treating the much lighter electrons as a charge-neutralizing fluid. These physics-based, algorithmic model descriptions are called hybrid codes, which have established an invalua…
