Wave-Particle Studies in the Ion Cyclotron and Lower Hybrid Ranges of Frequencies in Alcator C-Mod

Abstract This paper reviews the physics and technology of wave-particle-interaction experiments in the ion cyclotron range of frequencies (ICRF) and the lower hybrid (LH) range of frequencies (LHRF) on the Alcator C-Mod tokamak. Operation of fixed frequency (80 MHz) and tunable (40- to 80-MHz) ICRF transmitters and the associated transmission system is described. Key fabrication issues that were solved in order to operate a four-strap ICRF antenna in the compact environment of C-Mod are discussed in some detail. ICRF heating experiments utilizing the hydrogen (H) and helium-3 (3He) minority heating schemes are described, and data are presented demonstrating an overall heating efficiency of 70 to 90% for the (H) minority scheme and somewhat lower efficiency for (3He) minority heating. Mode conversion electron heating experiments in D(3He), D(H), and H(3He) discharges are also reported as well as simulations of these experiments using an advanced ICRF full-wave solver. Measurements of mode-converted ion cyclotron waves and ion Bernstein waves using a phase contrast imaging diagnostic are presented and compared with the predictions of a synthetic diagnostic code that utilizes wave electric fields from a full-wave solver. The physics basis of the LH current profile control program on Alcator C-Mod is also presented. Computer simulations using a two-dimensional (velocity space) Fokker Planck solver indicate that ~200 kA of LH current can be driven in low-density H-mode discharges on C-Mod with ~3 MW of LHRF power. It is shown that this off-axis LH current drive can be used to create discharges with nonmonotonic profiles of the current density and reversed shear. An advanced tokamak operating regime near the ideal no-wall β limit is described for C-Mod, where ~70% of the current is driven through the bootstrap effect. The LH power is coupled to C-Mod through a waveguide launcher consisting of four rows (vertically) with 24 guides per row (toroidally). A detailed description of the LH launcher fabrication is given in this paper along with initial operation results.

[1]  I. Hutchinson,et al.  Effect of multipactor discharge on alcator C-Mod ion cyclotron range of frequency heating , 2006 .

[2]  B. Lipschultz Operation of Alcator C-Mod with high-Z plasma facing components and implications , 2005 .

[3]  P. Bonoli,et al.  Observation and modelling of ion cyclotron range of frequencies waves in the mode conversion region of Alcator C-Mod , 2005 .

[4]  J. Contributors,et al.  Long distance coupling of lower hybrid waves in JET plasmas with edge and core transport barriers , 2005 .

[5]  J. Irby,et al.  Calibration of Thomson scattering systems using electron cyclotron emission cutoff data , 2005 .

[6]  Ion cyclotron range of frequency mode conversion physics in Alcator C-Mod: Experimental measurements and modelinga) , 2005 .

[7]  P. T. Bonoli,et al.  ICRF loading studies on Alcator C-Mod , 2004 .

[8]  J. Snipes,et al.  Active and fast particle driven Alfven eigenmodes in Alcator C-Mod , 2004 .

[9]  P. T. Bonoli,et al.  Investigation of performance limiting phenomena in a variable phase ICRF antenna in Alcator C-Mod , 2004 .

[10]  D Mazon,et al.  Modeling of a lower-hybrid current drive by including spectral broadening induced by parametric instability in tokamak plasmas. , 2004, Physical review letters.

[11]  Alan Lynn,et al.  Investigation of ion cyclotron range of frequencies mode conversion at the ion–ion hybrid layer in Alcator C-Mod , 2004 .

[12]  Marco Brambilla,et al.  Full Wave Simulations of Fast Wave Mode Conversion and Lower Hybrid Wave Propagation in Tokamaks , 2004 .

[13]  P. T. Bonoli,et al.  Ion cyclotron range of frequencies mode conversion electron heating in deuterium–hydrogen plasmas in the Alcator C-Mod tokamak , 2003 .

[14]  E D'Azevedo,et al.  Sheared poloidal flow driven by mode conversion in tokamak plasmas. , 2003, Physical review letters.

[15]  M Porkolab,et al.  Experimental observations of mode-converted ion cyclotron waves in a tokamak plasma by phase contrast imaging. , 2003, Physical review letters.

[16]  K. Mima,et al.  Anomalous resistivity resulting from MeV-electron transport in overdense plasma. , 2003, Physical review letters.

[17]  Miklos Porkolab,et al.  Design of a Compact Lower Hybrid Coupler for Alcator C-Mod , 2003 .

[18]  J. Snipes,et al.  Experimental and theoretical study of quasicoherent fluctuations in enhanced D(alpha) plasmas in the Alcator C-Mod tokamak. , 2002, Physical review letters.

[19]  D. Hartmann,et al.  ICRF system enhancements at ASDEX Upgrade , 2001 .

[20]  A new internal matching impedance concept for ICRF antennas , 2001 .

[21]  David R. Smith,et al.  A study of molybdenum influxes and transport in Alcator C-Mod , 2001 .

[22]  P. T. Bonoli,et al.  Modelling of advanced tokamak scenarios with LHCD in Alcator C-Mod , 2000 .

[23]  S. J. Wukitch,et al.  Mode conversion electron heating in Alcator C-Mod: Theory and experiment , 2000 .

[24]  C. Domier,et al.  High resolution electron cyclotron emission temperature profile and fluctuation diagnostic for Alcator C-Mod , 1999 .

[25]  Marco Brambilla,et al.  Numerical simulation of ion cyclotron waves in tokamak plasmas , 1999 .

[26]  M. Brambilla,et al.  Electron Landau Damping of Ion Bernstein Waves in Tokamak Plasmas , 1998 .

[27]  Robert L. Miller,et al.  Synergism between cross-section and profile shaping in beta optimization of tokamak equilibria with negative central shear , 1998 .

[28]  C. Bathke,et al.  Physics basis for a reversed shear tokamak power plant , 1997 .

[29]  J. Rice,et al.  H mode confinement in Alcator C-Mod , 1997 .

[30]  P. T. Bonoli,et al.  Radiofrequency-heated enhanced confinement modes in the Alcator C-Mod tokamak , 1997 .

[31]  C. Kessel,et al.  Negative magnetic shear modes of operation in the Alcator C-Mod tokamak near the beta limit , 1997 .

[32]  F. X. Söldner,et al.  Shear optimization experiments with current profile control on JET , 1997 .

[33]  P. O'Shea Measurements of ICRF power deposition and thermal transport with an ECE grating polychromator on the Alcator C-Mod tokamak , 1997 .

[34]  J. Snipes,et al.  Electron heating via mode converted ion Bernstein waves in the Alcator C-Mod tokamak , 1996 .

[35]  E. D. Fredrickson,et al.  Ion cyclotron range of frequency experiments in the Tokamak Fusion Test Reactor with fast waves and mode converted ion Bernstein waves , 1996 .

[36]  Murakami,et al.  Mode conversion heating and current drive experiments in TFTR. , 1996, Physical review letters.

[37]  M. Rosenbluth,et al.  Model for the sawtooth period and amplitude , 1996 .

[38]  Haruyuki Kimura,et al.  CONFERENCES AND SYMPOSIA: Radiofrequency launchers for plasma heating and current drive , 1995 .

[39]  Francesco Porcelli,et al.  Local magnetic shear control in a tokamak via fast wave minority ion current drive : theory and experiments in jet , 1994 .

[40]  S. N. Golovato,et al.  Antennas for ICRF heating in the Alcator C-Mod tokamak , 1993, 15th IEEE/NPSS Symposium. Fusion Engineering.

[41]  R. W. Harvey,et al.  The CQL3D Fokker-Planck code , 1992 .

[42]  Paul T. Bonoli,et al.  Modelling of lower hybrid current drive in self-consistent elongated tokamak equilibria , 1992 .

[43]  S. Coda,et al.  A phase contrast interferometer on DIII‐D , 1992 .

[44]  Charles F. F. Karney,et al.  Approximate formula for radiofrequency current drive efficiency with magnetic trapping , 1991 .

[45]  J. Jacquinot,et al.  Impurity release from the ICRF antenna screens in JET , 1991 .

[46]  J. Jacquinot,et al.  A model of sheath-driven impurity production by ICRF antennas , 1991 .

[47]  H. Takeuchi,et al.  Invited paper: Interaction between RF and edge plasma during ICRF heating in JT-60 , 1990 .

[48]  D. Goebel,et al.  Invited paper: ICRF/Edge physics research on textor , 1990 .

[49]  James R. Wilson,et al.  RF-plasma interactions in the antenna near fields , 1990 .

[50]  ICRH-Team,et al.  Experimental results on edge effects during ICRF heating of ASDEX plasmas , 1990 .

[51]  N. A. Uckan ITER physics design guidelines: 1989 , 1990 .

[52]  H. Weisen The phase contrast method as an imaging diagnostic for plasma density fluctuations (invited) , 1988 .

[53]  Chris Marshall,et al.  Design guidelines , 1987 .

[54]  J. Adam REVIEW ARTICLE: Review of Tokamak plasma heating by wave damping in the ion cyclotron range of frequency , 1987 .

[55]  L. Lao,et al.  Reconstruction of current profile parameters and plasma shapes in tokamaks , 1985 .

[56]  R. Budny,et al.  The effects of ICRF heating on plasma edge conditions in PLT , 1985 .

[57]  H. Matsumoto,et al.  Impurity behaviour during ICRF heating in JFT-2M , 1984 .

[58]  P. T. Bonoli,et al.  Observation of lower-hybrid current drive at high densities in the Alcator C tokamak , 1984 .

[59]  K. Kawahata,et al.  IMPURITY ORIGIN DURING ICRF HEATING IN JIPP T-IIU TOKAMAK , 1984 .

[60]  F. Perkins,et al.  A Resonant-Cavity ICRF Coupler for Large Tokamaks , 1984, IEEE Transactions on Plasma Science.

[61]  J. Adam ICRF Heating in TFR and the problem of impurity release , 1984 .

[62]  Francis F. Chen Plasma Physics and Controlled Fusion , 1984 .

[63]  J. Manickam,et al.  Ideal MHD stability calculations in axisymmetric toroidal coordinate systems , 1982 .

[64]  S. Jardin,et al.  An iterative metric method for solving the inverse tokamak equilibrium problem , 1979 .

[65]  F. W. Perkins,et al.  Heating tokamaks via the ion-cyclotron and ion-ion hybrid resonances , 1977 .

[66]  Miklos Porkolab,et al.  Parametric Instabilities Due to Lower-Hybrid Radio Frequency Heating of Tokamak Plasmas , 1977 .

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

[68]  T. H. Stix Fast-wave heating of a two-component plasma , 1975 .