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Reference CRPP-CONF-2006-067 URL: http://eps2006.frascati.enea.it Record created on 2008-05-13, modified on 2017-05-12
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ABSTRACT A common feature of the Vlasov equation is that it develops fine-scale filamentation as time evolves, as observed, for example, in global nonlinear simulations of the ion-temperature-gradient instability. From a numerical point... more
ABSTRACT A common feature of the Vlasov equation is that it develops fine-scale filamentation as time evolves, as observed, for example, in global nonlinear simulations of the ion-temperature-gradient instability. From a numerical point of view, it is not trivial to simulate nonlinear regimes characterized by increasingly smaller scales, which eventually become smaller than the (finite) grid size. When very small structures occur, higher order interpolation schemes have a tendency to produce overshoots and negative-density regions unless some additional dissipative procedure is applied. Different interpolation schemes for the distribution function are compared and discussed.
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Direct and indirect poloidal rotation measurements with improved accuracy were performed and compared in the TCV tokamak. The indirect measurement argues that, provided the plasma flow is divergence free on a flux surface, poloidal... more
Direct and indirect poloidal rotation measurements with improved accuracy were performed and compared in the TCV tokamak. The indirect measurement argues that, provided the plasma flow is divergence free on a flux surface, poloidal rotation can be inferred from the toroidal rotation at the high and low field sides of a flux surface. The key advantage of the method is an intrinsic amplification factor: instead of measuring poloidal rotation directly (typically few km/s i.e. of the order of the measurement accuracy), a difference in toroidal rotation is measured that is 4 to 10 times larger. Here, the main uncertainties arise from the flux surface mapping that are, however, largely compensated by this amplification factor. In TCV, the C^6+ toroidal rotation was measured across the whole plasma diameter by charge exchange (CX) spectroscopy for a series of low collisionality (0.1<&*circ;<1.5) OH and ECH L-mode plasmas, including positive and negative plasma current and toroidal ma...
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The capability of any given e.m.-wave plasma heating system to be utilized for physics applications depends strongly on the technical properties of the launching antenna (or launcher). An effective ECH launcher must project a small... more
The capability of any given e.m.-wave plasma heating system to be utilized for physics applications depends strongly on the technical properties of the launching antenna (or launcher). An effective ECH launcher must project a small mm-wave beam spot size far into the plasma and `steer&amp;amp;#39; the beam across a large fraction of the plasma cross section (along the resonance surface).
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The TCV tokamak program is centred on flexible plasma shaping matched by a flexible auxiliary-heating system based entirely on ECH at 2nd and 3rd harmonics. This paper reviews some of the recent highlights of TCV ECW (Electron Cyclotron... more
The TCV tokamak program is centred on flexible plasma shaping matched by a flexible auxiliary-heating system based entirely on ECH at 2nd and 3rd harmonics. This paper reviews some of the recent highlights of TCV ECW (Electron Cyclotron Waves) results. Very high elongation high q plasmas, which would be vertically unstable in Ohmic conditions, are stabilised by broadening the current
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Note: 36th Annual Meeting APS Division of Plasma Physics, Minneapolis, MN, USA, November 1994, Bull of APS, Vol. 39, 1720 (1994) Reference CRPP-CONF-1994-033 Record created on 2008-05-13, modified on 2017-05-12
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Note: Proc. Joint Varenna-Lausanne International Workshop Theory of Fusion Plasmas, Varenna, Italy, August 28 - September 1, 2000, ISPP-19, ISBN88-7794-248-7, 327 - 332 (2000) Reference CRPP-CONF-2000-009 Record created on 2008-05-13,... more
Note: Proc. Joint Varenna-Lausanne International Workshop Theory of Fusion Plasmas, Varenna, Italy, August 28 - September 1, 2000, ISPP-19, ISBN88-7794-248-7, 327 - 332 (2000) Reference CRPP-CONF-2000-009 Record created on 2008-05-13, modified on 2017-05-12
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The control of ELMs is a crucial requirement for future Tokamak reactors. The possibility to achieve ELM pacing using ECH locally deposited near the pressure pedestal has been explored on TCV. With constant power, the frequency of type I... more
The control of ELMs is a crucial requirement for future Tokamak reactors. The possibility to achieve ELM pacing using ECH locally deposited near the pressure pedestal has been explored on TCV. With constant power, the frequency of type I ELMs was observed to increase by a factor 1.5 to 2 when the deposition region was moved towards the edge, despite the decreased absorption. Power modulation synchronized with the ELM cycle was also used for a real-time control of individual ELM occurrence as well as ELM frequency and regularity, measured by the standard deviation of their period. An ad-hoc 0-D model for the ELM cycle is proposed in support to these observations.
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E.Lazzaro,R.J.Buttery,T.C.Hender,M.Bigi,T.Bolzonella,R.Coelho,M.DeBenedetti, S.Nowak,O.Sauter,M.Stamp,P.Zancaand contributors to the EFDA-JET work programme Istituto di Fisica del Plasma del CNR, Assoc. EURATOM-ENEA-CNR per la Fusione,... more
E.Lazzaro,R.J.Buttery,T.C.Hender,M.Bigi,T.Bolzonella,R.Coelho,M.DeBenedetti, S.Nowak,O.Sauter,M.Stamp,P.Zancaand contributors to the EFDA-JET work programme Istituto di Fisica del Plasma del CNR, Assoc. EURATOM-ENEA-CNR per la Fusione, Via R.Cozzi 53, 20125 Milan, Italy 2 EURATOM-UKAEA Fusion Assoc.Culham Science Centre, Abingdon OX14 3DB, UK CRPP / EPFL Assoc. EURATOM-Switzerland, Lausanne, Switzerland CRE ENEA Assoc. EURATOM-ENEA per la Fusione, Via E. Fermi 7, Frascati, Italy CONSORZIO RFX Assoc. EURATOM-ENEA-CNR per la Fusione, C.so Stati Uniti 4 Padova, Italy Associação EURATOM/IST, Centro de Fusão Nuclear, 1096 Lisbon,CODEX, Portugal
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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... more
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.
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Electron cyclotron current drive experiments in the DIII-D and TCV tokamaks provide excellent data sets for evaluating radial transport effects on the driven current. In the lower power density DIII-D EC experiments quasilinear effects... more
Electron cyclotron current drive experiments in the DIII-D and TCV tokamaks provide excellent data sets for evaluating radial transport effects on the driven current. In the lower power density DIII-D EC experiments quasilinear effects and synergy between the EC current drive (CD) and toroidal electric field are significant, placing experiment in accord with calculations using the CQL3D bounce-averaged Fokker- Planck code,(C.C. Petty, et al., 14th Conf. on RF Power, Oxnard, California (2001).) which includes a radial transport model. Radial transport at levels consistent with ITER scaling can double the radial width of the ECCD, although the calculated widths are near the radial resolution limit of the DIII-D MSE diagnostic. For the high power TCV ECCD experiment, both the quasilinear formation of nonthermal distributions and the transport effects are dramatic: For a particular shot,(O. Sauter, et al., Phys. Rev. Lett. 84), 3322 (2000). a radial diffusion coefficient consistent with...
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ABSTRACT Tokamak disruptions are events of fatal collapse of the magnetohydrodynamic (MHD) confinement configuration, which cause a rapid loss of the plasma thermal energy and the impulsive release of magnetic energy and heat on the... more
ABSTRACT Tokamak disruptions are events of fatal collapse of the magnetohydrodynamic (MHD) confinement configuration, which cause a rapid loss of the plasma thermal energy and the impulsive release of magnetic energy and heat on the tokamak first wall components. The physics of the disruptions is very complex and non-linear, strictly associated with the dynamics of magnetic tearing perturbations. The crucial problem of the response to the effects of localized heat deposition and current driven by external (rf) sources to avoid or quench the MHD tearing instabilities has been investigated both experimentally and theoretically on the ASDEX Upgrade tokamak. The analysis of the conditions under which a disruption can be prevented by injection of electron cyclotron (EC) rf power, or, alternatively, may be caused by it, shows that the local EC heating can be more significant than EC current drive in ensuring neoclassical tearing modes (NTMs) stability, due to two main reasons: first, the drop of temperature associated with the island thermal short circuit tends to reduce the neoclassical character of the instability and to limit the EC current drive generation; second, the different effects on the mode evolution of both the location of the power deposition relative to the island separatrix and the island shape deformation lead to less strict requirements of precise power deposition focussing. A contribution to the validation of theoretical models of the events associated with NTM is given and can be used to develop concepts for their control, relevant also for ITER-like scenarios. [http://dx.doi.org/10.1063/1.4752423]
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Theoretical study and experimental observations suggest that rotation can play a crucial role in determining plasma stability. Since conventional magnetohydrodynamic (MHD) analysis ignores rotation, more advanced computational tools are... more
Theoretical study and experimental observations suggest that rotation can play a crucial role in determining plasma stability. Since conventional magnetohydrodynamic (MHD) analysis ignores rotation, more advanced computational tools are being developed to confirm the theoretical understanding and to perform comparison between theory and experiment. In a previous work, the authors reported on the formulation and computation of MHD modes in plasmas with a small (subsonic) toroidal rotation. R.otation is found to have a substantial stabilizing effect under many circumstances. In this work, they extend the formulation in Ref. 4 to include an arbitrary (large) toroidal plasma rotation. It is the purpose of this work to examine the difference between these two formulations and report on results from computations using these formulations.
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Initial ideal MHD stability results for the Tokamak Configuration Variable (TCV) tokamak with variable elongation are presented. Two configurations have been studied: a racetrack shape and a D-shape at a fixed elongation of 2.5. Low beta... more
Initial ideal MHD stability results for the Tokamak Configuration Variable (TCV) tokamak with variable elongation are presented. Two configurations have been studied: a racetrack shape and a D-shape at a fixed elongation of 2.5. Low beta studies indicate the existence of stable racetrack equilibria at currents up to an edge safety factor value of qs = 2, but the window of operation is limited in qo to narrow bands above each integer value. For the D-shape, qs = 3 gives the current limit at low beta, but the operating range in q0 is much wider than that for the racetrack. Beta optimization studies show that the maximum beta set by the n= 1 freeboundary stability limit decreases as the current increases, except for the lowest currents in the range studied. Although further optimization cannot be ruled out, considerable enhancement of the beta over that for an equivalent circular cross-section of the same major radius and aspect ratio can be obtained by elongation of the plasma cross-section.