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The purpose of this work is the optical modeling and physical performances evaluations of the JT-60SA ECRF launcher system. The beams have been simulated with the electromagnetic code GRASP? and used as input for ECCD calculations performed with the beam tracing code GRAY, capable of modeling propagation, absorption and current drive of an EC Gaussion beam with general astigmatism. Full details of the optical analysis has been taken into account to model the launched beams. Inductive and advanced reference scenarios has been analysed for physical evaluations in the full poloidal and toroidal steering ranges for two slightly different layouts of the launcher system. [ABSTRACT FROM AUTHOR]

The importance of localized injection of Electron Cyclotron waves to control Magneto-HydroDynamic instability is well assessed in tokamak physics and the set of four Electron Cyclotron (EC) Upper Launchers (UL) in ITER is mainly designed for this purpose. Each of the 4 ULs uses quasi-optical mirrors (shaping and planes, fixed and steerable) to redirect and focus 8 beams (in two rows, with power close to 1 MW per beam coming from the EC transmission lines) in the plasma region where the instability appears. Small beam dimensions and maximum beam superposition guarantee the necessary localization of the driven current. To achieve the goal of MHD stabilization with minimum EC power to preserve the energy confinement in the outer half of the plasma cross section, optimization of the quasi-optical design is required and a guideline of a strategy is presented. As a result of this process and following the guidelines indicated, modifications of the design (new mirrors positions, rotation axes and/or focal properties) will be proposed for the next step of an iterative process, including the mandatory compatibility check with the mechanical constraints. [ABSTRACT FROM AUTHOR]

The breakdown and plasma start-up in ITER are well known issues studied in the last few years in many tokamaks with the aid of calculation based on simplified modeling. The thickness of ITER metallic wall and the voltage limits of the Central Solenoid Power Supply strongly limit the maximum toroidal electric field achievable (0.3 V/m), well below the level used in the present generation of tokamaks. In order to have a safe and robust breakdown, the use of Electron Cyclotron Power to assist plasma formation and current rump up has been foreseen. This has raised attention on plasma formation phase in presence of EC wave, especially in order to predict the required power for a robust breakdown in ITER. Few detailed theory studies have been performed up to nowadays, due to the complexity of the problems. A simplified approach, extended from that proposed in ref[1] has been developed including a impurity multispecies distribution and an EC wave propagation and absorption based on GRAY code. This integrated model (BK0D) has been benchmarked on ohmic and EC assisted experiments on FTU and AUG, finding the key aspects for a good reproduction of data. On the basis of this, the simulation has been devoted to understand the best configuration for ITER case. The dependency of impurity distribution content and neutral gas pressure limits has been considered. As results of the analysis a reasonable amount of power (1 - 2 MW) seems to be enough to extend in a significant way the breakdown and current start up capability of ITER. The work reports the FTU data reproduction and the ITER case simulations. [ABSTRACT FROM AUTHOR]

The grand aim of the Integrated Tokamak Modelling (ITM) task-force is to provide a ..exible, modular and reliable plasma simulator in view of planning and analyzing ITER discharges. Since radio-frequency (rf) heating in the ion cyclotron range of frequencies (ICRF) is foreseen as one of the main additional heating systems in ITER, physics modules that simulate ICRF wave propagation and absorption are necessary for the ITM project. Here, we report on the status of the benchmark activity of ICRF codes, already imported in ITM environment platform. We consider various scenarios for ITER, limiting the comparisons to wave propagation and absorption in Maxwellian plasmas. [ABSTRACT FROM AUTHOR]

The new Oblique ECE diagnostics of JET allows simultaneous measurement along three lines of sight at different toroidal angles. JET pulses, in which modulated LHCD power was applied, were analyzed by means of the SPECE emission code, which takes into account the fast electron tail generated by LH. The code results were compared to the ECE spectra from the oblique ECE diagnostic. The match between the computed and the experimental data from the three lines of sight provides an estimate of the density of superthermal electrons and of their maximum energy from which the fraction of the plasma current driven by LHCD is derived. [ABSTRACT FROM AUTHOR]

The possibility of coupling electron Bernstein waves (EBW) to the overdense plasma in RFX-mod has been explored. A frequency of 28 GHz has been chosen due to the plasma parameters and the commercial availability of this frequency. A two dimensional full-wave code has been used to model the O-X-B mode conversion process in which an incident O-mode is first converted to an X-mode and then to an EBW. Parameter studies have been carried out to optimise the mode-conversion efficiency. The maximum conversion efficiency for optimal launching conditions amounts to 56% for a single pass. The vacuum vessel has been included in the full-wave calculations to address the effects of multiple reflections between the vessel wall and the plasma boundary. A significant increase in conversion efficiency is observed as a result. [ABSTRACT FROM AUTHOR]

A 26 MW Electron Cyclotron Heating and Current Drive (EC H&CD) system is to be installed for ITER. The main objectives are to provide, start-up assist, central H&CD and control of MHD activity. These are achieved by a combination of two types of launchers, one located in an equatorial port and the second type in four upper ports. The physics applications are partitioned between the two launchers, based on the deposition location and driven current profiles. The equatorial launcher (EL) will access from the plasma axis to mid radius with a relatively broad profile useful for central heating and current drive applications, while the upper launchers (ULs) will access roughly the outer half of the plasma radius with a very narrow peaked profile for the control of the Neoclassical Tearing Modes (NTM) and sawtooth oscillations. The EC power can be switched between launchers on a time scale as needed by the immediate physics requirements. A revision of all injection angles of all launchers is under consideration for increased EC physics capabilities while relaxing the engineering constraints of both the EL and ULs. A series of design reviews are being planned with the five parties (EU, IN, JA, RF, US) procuring the EC system, the EC community and ITER Organization (IO). The review meetings qualify the design and provide an environment for enhancing performances while reducing costs, simplifying interfaces, predicting technology upgrades and commercial availability. In parallel, the test programs for critical components are being supported by IO and performed by the Domestic Agencies (DAs) for minimizing risks. The wide participation of the DAs provides a broad representation from the EC community, with the aim of collecting all expertise in guiding the EC system optimization. Still a strong relationship between IO and the DA is essential for optimizing the design of the EC system and for the installation and commissioning of all ex-vessel components when several teams from several DAs will be involved together in the tests on the ITER site. [ABSTRACT FROM AUTHOR]

Deviations of the electron function velocity distribution from Maxwellian behavior in the high energy range have been extensively studied during the past two decades. A brief review of the experimental techniques and findings on the subject is given in this paper. There are indications that the electron distribution function in thermonuclear plasmas could be significantly different from the Maxwellian one even near the thermal velocity range when particular circumstances occur. These reasons motivate a renewed effort in the measurements that could detect low energies distortions, among which is the new Oblique Electron Cyclotron Emission diagnostics that has entered operations during 2006 experimental campaign at JET and aims to resolve relatively small differences in the ECE spectra taken at three toroidal angles. Such measurements allow insight into the characteristics of the electron distribution function. First results of such experimental system are discussed in this paper, along with emission simulations. [ABSTRACT FROM AUTHOR]

Low frequency, relativistic sub-cycle localised (soliton-like) concentrations of the electromagnetic (em) energy are found in two-dimensional (2D) and in three-dimensional (3D) Particle in Cell simulations of the interaction of ultra-short, high-intensity laser pulses with homogeneous and inhomogeneous plasmas. These solitons consist of electron and ion density depressions and intense em field concentrations with a frequency definitely lower than that of the laser pulse. The downshift of the pulse frequency, due to the depletion of the pulse energy, causes a significant portion of the pulse em energy to become trapped as solitons, slowly propagating inside the plasma. In an earlier phase solitons are formed due to the trapping of the em radiation inside an electron cavity, while ions can be assumed to remain at rest. Later on, after (m[SUBi]/m[SUBi])[SUP1/2] times the laser period, ions start to move and the ion depletion occurs producing a slowly growing hole in the plasma density. In inhomogeneous plasmas the solitons are accelerated toward the plasma vacuum interface where they radiate away their energy in the form of bursts of low frequency em radiation. In the frame of a 1D cold hydrodynamic model for an electron-ion plasma, the existence of multipeaked em solitons has been investigated both analytically and numerically. The analytical expression for a sub-cycle relativistic soliton has been derived for circularly polarized pulses in a cold isotropic plasma, and in the presence of an externally applied magnetic field. Recently, em relativistic solitons in a hot multi-component plasma have been investigated in the frame of an hydrodynamic (adiabatic) model and of a kinetic (isothermal) model. An overview of the most recent analytical and numerical results on the soliton dynamics is given. [ABSTRACT FROM AUTHOR]

A set of nonlinear differential equations, that describes the moving relativistic solitons with the ion response taken into account, is investigated analytically and solved numerically. We study the influence of the ion motion on the soliton structure and show that depending on the propagation velocity we have either the bright, dark solitons or electromagnetic collisionless shock waves. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The review of the results obtained recently in the theory and in the computer simulations with 2D and 3D PIC codes of the interaction of high-intensity, ultra-short laser pulses with plasmas is presented. The laser interaction with underdense plasmas and its application to the problem of charged particle acceleration, of laser frequency upshifting, of relativistic self focusing, and of the generation of a quasistatic magnetic field is discussed. We present the results of the analytical description and of the PIC simulations of nonlinear coherent structures such as relativistic solitons and vortices and the production of high harmonics. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

With 2D particle in cell simulations we show that during the interaction of a high intensity ultra short laser pulse with a collisionless plasma in the wake of the laser pulse electromagnetic relativistically strong solitons are formed, which evolve asymptotically into post-solitons. A post-soliton is a slowly expanding cavity in the ion and electron densities which traps electromagnetic energy. Fast ions are accelerated during the post-soliton formation. The long time evolution of the post-solitons in an inhomogeneous plasma slab is investigated. The spectra of the electromagnetic energy radiated by the post-solitons are analyzed. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]