Particle-in-Cell Simulations of the Near-Field of a Lower Hybrid Grill

Lower hybrid (LH) waves in the frequency range 1 to 10 GHz are used to heat and to drive current in a tokamak. A crucial issue for the future devices is the coupling of the wave power from the launching structure, the grill, to the plasma. A related problem is the formation of hot spots on the grill limiters and other components that are magnetically connected to the grill region. A probable explanation for these asymmetric heat loads is the parasitic absorption of the LH power. In parasitic absorption, the short-wavelength modes are absorbed by electrons within a very short distance in front of the grill. The cold edge electrons (Te ~ 25 eV) may reach energies up to 2 keV through stochastic acceleration in the electric field in front of the lower hybrid grill. The particle-in-cell (PIC) technique is one of the most popular methods of kinetic simulations of plasmas. In PIC codes, a spatial grid is used to describe the field quantities, while the particles move in the continuous space. The field and particle motion are solved self-consistently. The advantage of the PIC codes is that they take into account the kinetic effects and the non-linearities of the problem. They also give the deposition profiles unlike pure test particle simulations. In this thesis, the use of PIC codes has been extended to a whole new branch of applications, the near-field of the LH grill. During the work, the grill model used in the electrostatic PIC code has been developed. The parasitic absorption and the generation of fast electrons in front of the waveguide mouth have been explored. The absorption and the heat load on the grill limiter increases with the edge density, the edge temperature and the launched power density. A weak indication of a power threshold was observed. The simulation results can explain experimental observations in Tore Supra. According to the simulations, the heat loads are not a problem in the next generation launchers used in ITER.

[1]  L. Doceul,et al.  Overview of the ITER-FEAT LH system , 2003 .

[2]  Francesco Mirizzi,et al.  The PAM launcher for FTU: results of the preliminary tests , 2003 .

[3]  T. Tala,et al.  Simulations of Heat Loads on Plasma Facing Components , 2003 .

[4]  J. Lönnroth,et al.  Particle-in-cell simulation of ion Bernstein wave excitation , 2002 .

[5]  Tuomas Tala,et al.  Transport barrier and current profile studies on the JET tokamak , 2002 .

[6]  D. Tskhakaya,et al.  Effects of energetic electrons on magnetized electrostatic plasma sheaths , 2002 .

[7]  A. Salmi,et al.  Particle-in-Cell Simulations for Lower Hybrid Coupling near Cut-Off Density , 2002 .

[8]  A. Ekedahl,et al.  Coupling and power handling of the new Tore Supra LHCD launcher , 2001 .

[9]  C. Giroud,et al.  Impurity Behaviour in ITB Discharges with Reversed Shear on JET , 2001 .

[10]  P. Hertout,et al.  New advanced launcher for lower hybrid current drive on Tore Supra , 2000 .

[11]  M. Mantsinen,et al.  Parasitic Particle Acceleration and Rf Power Absorption in Edge Plasmas , 2000 .

[12]  M. Ye,et al.  2‐D PIC Simulation on Space‐Charge Limited Emission Current from Plasma‐Facing Components , 2000 .

[13]  R. Guirlet,et al.  Particle recirculation in the ergodic divertor of Tore Supra , 1999 .

[14]  Y. Demers,et al.  Enhanced heat flux in the scrape-off layer due to electrons accelerated in the near field of lower hybrid grills , 1998 .

[15]  V. Fuchs,et al.  ELECTRON ACCELERATION IN FRONT OF THE JET AND TORE SUPRA GRILLS , 1998 .

[16]  J. Harris,et al.  Plasma-surface interactions with ICRF antennas and lower hybrid grills in Tore Supra , 1997 .

[17]  J. Harris,et al.  Strong toroidal asymmetries in power deposition on divertor and first wall components during LHCD on TdeV and Tore Supra , 1997 .

[18]  M. Mantsinen,et al.  Local Current Profile Modification in Tokamak Reactors in Various Radiofrequency Ranges , 1997 .

[19]  V. Fuchs,et al.  Acceleration of electrons in the vicinity of a lower hybrid waveguide array , 1996 .

[20]  J. Harris,et al.  Acceleration of electrons in the near field of lower hybrid frequency grills , 1996 .

[21]  C. Laviron,et al.  Toward long-pulse, high-performance discharges in Tore Supra: Experimental knowledge and technological developments for heat exhaust , 1996 .

[22]  J. Harris,et al.  Lower-hybrid wave coupling and impurity generation in TORE SUPRA , 1995 .

[23]  John M. Dawson,et al.  Computer modeling of plasma: Past, present, and future , 1995 .

[24]  John P. Verboncoeur,et al.  An object-oriented electromagnetic PIC code , 1995 .

[25]  Gilles Berger-By,et al.  Experimental and Theoretical Results Concerning the Development of the Main RF Components for Next Tore Supra LHCD Antennae , 1995 .

[26]  T. Pättikangas,et al.  Analysis of velocity diffusion of electrons with Vlasov-Poisson simulations , 1994 .

[27]  M. Lieberman,et al.  Verification of frequency scaling laws for capacitive radio‐frequency discharges using two‐dimensional simulations* , 1993 .

[28]  X. Litaudon,et al.  Lower hybrid wave coupling in TORE SUPRA through multijunction launchers , 1992 .

[29]  F. Miyawaki,et al.  Sheath and Heat Flow of a Two-Electron-Temperature Plasma in the Presence of Electron Emission , 1992 .

[30]  T. H. Stix.  Waves in plasmas , 1992 .

[31]  R. A. Cairns.  Radiofrequency heating of plasmas , 1991 .

[32]  F. Leuterer,et al.  Characteristics of Toroidal Energy Deposition Asymmetries in ASDEX , 1990 .

[33]  D. Moreau,et al.  Coupling of slow waves near the lower hybrid frequency in JET , 1990 .

[34]  Xavier Litaudon.  Etude théorique et expérimentale du couplage de l'onde hybride dans Tore-Supra et jet au moyen d'antennes à multijonctions , 1990 .

[35]  James R. Wilson,et al.  Power transmission and coupling for radiofrequency heating of plasmas , 1989 .

[36]  Nathaniel J. Fisch,et al.  Theory of current-drive in plasmas , 1987 .

[37]  C. Birdsall,et al.  Plasma Physics via Computer Simulation , 2018 .

[38]  K. Rönnmark.  Kinetic theory of plasma waves , 1985 .

[39]  Didier Moreau,et al.  Lower-hybrid plasma heating via a new launcher – the multijunction grill , 1985 .

[40]  M. Porkolab.  Survey of Lower Hybrid Experiments , 1984, IEEE Transactions on Plasma Science.

[41]  Paul Bonoli,et al.  Linear Theory of Lower Hybrid Heating , 1984, IEEE Transactions on Plasma Science.

[42]  B. McNamara.  Radiation in plasmas , 1984 .

[43]  R. Itatani,et al.  Energy and Momentum Deposition to Plasmas due to the Lower Hybrid Wave by a Finite Source , 1981 .

[44]  R. Itatani,et al.  Propagation and plasma heating of the lower hybrid wave in the nonuniform density plasma , 1979 .

[45]  B. Chirikov.  A universal instability of many-dimensional oscillator systems , 1979 .

[46]  M. Brambilla,et al.  Slow-wave launching at the lower hybrid frequency using a phased waveguide array , 1976 .

[47]  M. Porkolab,et al.  Experimental studies of lower hybrid wave propagation , 1976 .

[48]  市川 芳彦,et al.  S. Ichimaru : Basic Principles of Plasma Physics ; A Statistical Approach, W. A. Benjamin, Massachusetts, 1973, 324ページ, 23×16cm, 6,840円. , 1974 .

[49]  P. Lallia,et al.  A LHR Heating Slow Wave Launching Structure Suited for Large Toroidal Experiments , 1974 .

[50]  S. Ichimaru,et al.  Basic Principles of Plasma Physics: a Statistical Approach. , 1973 .

[51]  R. Parker,et al.  TRANSPORT OF rf ENERGY TO THE LOWER HYBRID RESONANCE IN AN INHOMOGENEOUS PLASMA. , 1972 .

[52]  V. Glagolev.  Propagation and absorption of ion hybrid waves in a weakly inhomogeneous plasma laser. I , 1972 .

[53]  R. W. Gould,et al.  Resonance Cones in the Field Pattern of a Radio Frequency Probe in a Warm Anisotropic Plasma , 1971 .

[54]  R. W. Gould,et al.  Resonance cones in the field pattern of a short antenna in an anisotropic plasma , 1969 .

[55]  T. H. Stix.  Radiation and absorption via mode conversion in an in homogeneous collisionfree plasma. , 1965 .

[56]  C. B. Wharton,et al.  COLLISIONLESS DAMPING OF ELECTROSTATIC PLASMA WAVES , 1964 .

[57]  H. H. Kuehl.  Electromagnetic Radiation from an Electric Dipole in a Cold Anisotropic Plasma , 1962 .

[58]  Lev Davidovich Landau,et al.  On the vibrations of the electronic plasma , 1946 .