Edge operational space for high density/high confinement ELMY H-modes in JET

International Nuclear Information System (INIS)

Sartori, R.; Saibene, G.; Loarte, A.

2002-01-01

This paper discusses how the proximity to the L-H threshold affects the confinement of ELMy H-modes at high density. The largest reduction in confinement at high density is observed at the transition from the Type I to the Type III ELMy regime. At medium plasma triangularity, δ≅0.3 (where δ is the average triangularity at the separatrix), JET experiments show that by increasing the margin above the L-H threshold power and maintaining the edge temperature above the critical temperature for the transition to Type III ELMs, it is possible to avoid the degradation of the pedestal pressure with density, normally observed at lower power. As a result, the range of achievable densities (both in the core and in the pedestal) is increased. At high power above the L-H threshold power the core density was equal to the Greenwald limit with H97≅0.9. There is evidence that a mixed regime of Type I and Type II ELMs has been obtained at this intermediate triangularity, possibly as a result of this increase in density. At higher triangularity, δ≅0.5, the power required to achieve similar results is lower. (author)

A quantitative analysis of the effect of ELMs on H-mode thermal energy confinement in DIII-D

International Nuclear Information System (INIS)

Schissel, D.P.; Osborne, T.H.; Carlstrom, T.N.; Zohm, H.

1992-06-01

The desire to reach ignition in future tokamaks the energy confinement time critical parameter. The most promising enhanced (over L-mode) confinement regime is the H-mode, discovered on ASDEX with neutral beam heating, and then confirmed with various auxiliary heating sources on numerous machines. The knowledge of how H-mode τ E depends on different parameters is of chemical importance to the performance predictions for next generation devices. Inter-machine H-mode total and thermal energy confinement (τ th ) scalings, which are being utilized to predict ITER thermal energy confinement, have been created for discharges where the Edge Localized Mode (ELM) instability has not been present. Confinement scaling research hm concentrated on this ELM-free H-mode phase mostly owing to the difficulty of characterizing ELM behavior. To date, long pulse H-mode operation has only been achieved by utilizing ELMs to flush out unpurities and prevent radiative collapse of the discharge. Unfortunately, accompanying the ELMS is a decrease of the plasma stored energy due to the expulsion of particles near the edge of the discharge resulting in a reduction of the steep edge electron density gradient. In order to predict ITER's H-mode τ th in the presence of ELMS, an estimated 25% confinement degradation factor has been applied to the ELM-free predictions. Our work, summarized in this paper, indicates that this 25% reduction factor is too large and instead a value of approximately 15% would be more appropriate

Energy confinement in Ohmic H-mode in TUMAN-3M

International Nuclear Information System (INIS)

Andrejko, M.V.; Askinazi, L.G.; Golant, V.E.; Kornev, V.A.; Lebedev, S.V.; Levin, L.S.; Tukachinsky, A.S.

1997-01-01

The spontaneous transition from Ohmically heated limiter discharges into the regime with improved confinement termed as ''Ohmic H-mode'' has been investigated in ''TUMAN-3''. The typical signatures of H-mode in tokamaks with powerful auxiliary heating have been observed: sharp drop of D α radiation with simultaneous increase in the electron density and stored energy, suppression of the density fluctuations and establishing the steep gradient near the periphery. In 1994 new vacuum vessel had been installed in TUMAN-3 tokamak. The vessel has the same sizes as old one (R 0 =0.55 m, a 1 =0.24 m). New vessel was designed to reduce mechanical stresses in the walls during B T ramp phase of a shot. Therefore modified device - TUMAN-3M is able to produce higher B T and I p , up to 2 T and 0.2 MA respectively. During first experimental run device was operated in Ohmic Regime. In these experiments the possibility to achieve Ohmic H-mode was studied. The study of the parametric dependencies of the energy confinement time in both OH and Ohmic H-mode was performed. In Ohmic H-mode strong dependencies of τ E on plasma current and on input power and weak dependence on density were found. Energy confinement time in TUMAN-3/TUMAN-3M Ohmic H-mode has revealed good agreement with JET/DIII-D/ASDEX scaling for ELM-free H-mode, resulting in very long τ E at the high plasma current discharges. (author)

H-mode and confinement studies in ASDEX Upgrade

International Nuclear Information System (INIS)

Suttrop, W.; Ryter, F.; Mertens, V.; Gruber, O.; Murmann, H.; Salzmann, H.; Schweinzer, J.

2001-01-01

H-mode operational boundaries and H-mode confinement are investigated on ASDEX Upgrade. The local edge parameter threshold for H-mode holds independent of divertor geometry and changes little with ion mass. The deviation of the H-mode power threshold at densities near the Greenwald limit can be understood as a consequence of a confinement deterioration, caused by 'stiff' temperature profiles and lack of core density gradients in gas puff fuelled discharges. Ion and electron temperature profiles can be described by a lower limit of gradient length L T =T/T'. (author)

Confinement mechanisms in the radiatively improved mode

NARCIS (Netherlands)

Tokar, M. Z.; R. Jaspers,; Koslowski, H. R.; Kramer-Flecken, A.; Messiaen, A. M.; Ongena, J.; Rogister, A. A.; Unterberg, B.; Weynants, R. R.

1999-01-01

The characteristics of the toroidal ion temperature gradient (ITG) instability, considered as the main source of anomalous transport in the low (L) confinement mode of tokamaks, are analysed for the conditions of the radiatively improved (RI) mode triggered by seeding of impurities. Based on

Self-sustained turbulence and L-mode confinement in toroidal plasmas

International Nuclear Information System (INIS)

Itoh, K.; Itoh, S.; Fukuyama, A.; Yagi, M.; Azumi, M.

1993-04-01

Theory of the L-mode confinement in toroidal plasmas is developed. The quantitative effect of the anomalous transport, which is caused by microscopic fluctuations, on the pressure-gradient- driven modes is analyzed. The ExB nonlinearity is renormalized in a form of the transport coefficient such as the thermal diffusivity, the ion viscosity and the current diffusivity. The destabilization by the current-diffusivity and the stabilization by the thermal transport and ion viscosity are analyzed. By use of the mean-field approximations, the nonlinear dispersion relation is solved. Growth rate and stability condition are expressed in terms of the renormalized transport coefficients. The transport coefficients in the steady state are obtained by the marginal stability condition for the least stable mode. This method is applied to the microscopic ballooning mode for the toroidal plasma with the magnetic well (such as tokamak). The comparison with experimental observations are made. A good agreement is found in a various aspects of the L-mode plasmas; The typical wavenumber and level of the fluctuations for the self-sustained turbulence is also obtained. The analysis is also made for the plasma with magnetic hill and shear (such as torsatron/Heliotron devices). This method is applied to the interchange modes. Formula of the anomalous transport is obtained. Also investigated is the case of the magnetic well and low magnetic shear (conventional stellarator). The roles of the pressure gradient and the collisionless skin depth in determining the anomalous transport are found to be generic in toroidal plasmas. The difference in the magnetic configuration affects the transport coefficient. These formula explain major experimental observations. (J.P.N.)

Near-wall effects in improved plasma confinement regimes in tokamak FT-2

International Nuclear Information System (INIS)

Budnikov, V.N.; D'yachenko, V.V.; Esipov, L.A.

1997-01-01

Transition to the regime of improved plasma confinement (H-mode) revealed in experiments on low hybrid heating in tokamak ft-2 is analyzed. Main attention is paid to processes, taking place in near-wall region. The data are correlated with results of experiments in large tokamaks

Pattern recognition in probability spaces for visualization and identification of plasma confinement regimes and confinement time scaling

International Nuclear Information System (INIS)

Verdoolaege, G; Karagounis, G; Oost, G Van; Tendler, M

2012-01-01

Pattern recognition is becoming an increasingly important tool for making inferences from the massive amounts of data produced in fusion experiments. The purpose is to contribute to physics studies and plasma control. In this work, we address the visualization of plasma confinement data, the (real-time) identification of confinement regimes and the establishment of a scaling law for the energy confinement time. We take an intrinsically probabilistic approach, modeling data from the International Global H-mode Confinement Database with Gaussian distributions. We show that pattern recognition operations working in the associated probability space are considerably more powerful than their counterparts in a Euclidean data space. This opens up new possibilities for analyzing confinement data and for fusion data processing in general. We hence advocate the essential role played by measurement uncertainty for data interpretation in fusion experiments. (paper)

Turbulent edge transport in the Princeton Beta Experiment-Modified high confinement mode

Science.gov (United States)

Tynan, G. R.; Schmitz, L.; Blush, L.; Boedo, J. A.; Conn, R. W.; Doerner, R.; Lehmer, R.; Moyer, R.; Kugel, H.; Bell, R.; Kaye, S.; Okabayashi, M.; Sesnic, S.; Sun, Y.

1994-10-01

The first probe measurements of edge turbulence and transport in a neutral beam induced high confinement mode (H-mode) are reported. A strong negative radial electric field is directly observed in H-mode. A transient suppression of normalized ion saturation and floating potential fluctuation levels occurs at the low confinement mode to high confinement mode (L-H) transition, followed by a recovery to near low mode (L-mode) levels. The average poloidal wave number and the poloidal wave-number spectral width are decreased, and the correlation between fluctuating density and potential is reduced. A large-amplitude coherent oscillation, localized to the strong radial electric field region, is observed in H-mode but does not cause transport. In H-mode the effective turbulent diffusion coefficient is reduced by an order of magnitude inside the last closed flux surface and in the scrape-off layer. The results are compared with a heuristic model of turbulence suppression by velocity-shear stabilization.

Proceedings of the workshop of three large tokamak cooperation on energy confinement scaling under intensive auxiliary heating, May 18 ∼ 20, 1992, Naka

International Nuclear Information System (INIS)

1992-09-01

The workshop of three large tokamak cooperation W22 on 'Energy confinement scaling under intensive auxiliary heating' was held 18-20 May, 1992, at Naka Fusion Research Establishment. This proceedings compiles 14 synopses of contributions (5 from JET, 4 from JT-60, 3 from TFTR, and 1 each from DIII-D JFT-2M) and the summary of the workshop. Topic sections are ; (i) L-mode confinement and scaling, (ii) Confinement at high β P regimes, Supershots, High poloidal beta enhanced confinement mode etc., (iii) Confinement at various H-mode regimes and scaling (including the VH-mode), (iv) Characteristic time scales for present tokamak regimes, and (v) Theoretical comparison with experimental data. (author)

Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

Energy Technology Data Exchange (ETDEWEB)

Sung, C., E-mail: csung@physics.ucla.edu [University of California, Los Angeles, Los Angeles, California 90095 (United States); White, A. E.; Greenwald, M.; Howard, N. T. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Mikkelsen, D. R.; Churchill, R. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Holland, C. [University of California, San Diego, La Jolla, California 92093 (United States); Theiler, C. [Ecole Polytechnique Fédérale de Lausanne, SPC, Lausanne 1015 (Switzerland)

2016-04-15

Long wavelength turbulent electron temperature fluctuations (k{sub y}ρ{sub s} < 0.3) are measured in the outer core region (r/a > 0.8) of Ohmic L-mode plasmas at Alcator C-Mod [E. S. Marmar et al., Nucl. Fusion 49, 104014 (2009)] with a correlation electron cyclotron emission diagnostic. The relative amplitude and frequency spectrum of the fluctuations are compared quantitatively with nonlinear gyrokinetic simulations using the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] in two different confinement regimes: linear Ohmic confinement (LOC) regime and saturated Ohmic confinement (SOC) regime. When comparing experiment with nonlinear simulations, it is found that local, electrostatic ion-scale simulations (k{sub y}ρ{sub s} ≲ 1.7) performed at r/a ∼ 0.85 reproduce the experimental ion heat flux levels, electron temperature fluctuation levels, and frequency spectra within experimental error bars. In contrast, the electron heat flux is robustly under-predicted and cannot be recovered by using scans of the simulation inputs within error bars or by using global simulations. If both the ion heat flux and the measured temperature fluctuations are attributed predominantly to long-wavelength turbulence, then under-prediction of electron heat flux strongly suggests that electron scale turbulence is important for transport in C-Mod Ohmic L-mode discharges. In addition, no evidence is found from linear or nonlinear simulations for a clear transition from trapped electron mode to ion temperature gradient turbulence across the LOC/SOC transition, and also there is no evidence in these Ohmic L-mode plasmas of the “Transport Shortfall” [C. Holland et al., Phys. Plasmas 16, 052301 (2009)].

Energy confinement scaling from the international stellarator database

Energy Technology Data Exchange (ETDEWEB)

Stroth, U [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany); Murakami, M; Dory, R A; Yamada, H; Okamura, S; Sano, F; Obiki, T

1995-09-01

An international stellarator database on global energy confinement is presented comprising data from the ATF, CHS and Heliotron E heliotron/torsatrons and the W7-A and W7-AS shearless stellarators. Regression expressions for the energy confinement time are given for the individual devices and the combined dataset. A comparison with tokamak L mode confinement is discussed on the basis of various scaling expressions. In order to make this database available to interested colleagues, the structure of the database and the parameter list are explained in detail. More recent confinement results incorporating data from enhanced confinement regimes such as H mode are reported elsewhere. (author).

The quiescent H-mode regime for high performance edge localized mode-stable operation in future burning plasmas

Energy Technology Data Exchange (ETDEWEB)

Garofalo, A. M., E-mail: garofalo@fusion.gat.com; Burrell, K. H.; Meneghini, O.; Osborne, T. H.; Paz-Soldan, C.; Smith, S. P.; Snyder, P. B.; Turnbull, A. D. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Eldon, D.; Grierson, B. A.; Solomon, W. M. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States); Hanson, J. M. [Columbia University, 2960 Broadway, New York, New York 10027-6900 (United States); Holland, C. [University of California San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States); Huijsmans, G. T. A.; Liu, F.; Loarte, A. [ITER Organization, Route de Vinon sur Verdon, 13067 St Paul Lez Durance (France); Zeng, L. [University of California Los Angeles, P.O. Box 957099, Los Angeles, California 90095-7099 (United States)

2015-05-15

For the first time, DIII-D experiments have achieved stationary quiescent H-mode (QH-mode) operation for many energy confinement times at simultaneous ITER-relevant values of beta, confinement, and safety factor, in an ITER-like shape. QH-mode provides excellent energy confinement, even at very low plasma rotation, while operating without edge localized modes (ELMs) and with strong impurity transport via the benign edge harmonic oscillation (EHO). By tailoring the plasma shape to improve the edge stability, the QH-mode operating space has also been extended to densities exceeding 80% of the Greenwald limit, overcoming the long-standing low-density limit of QH-mode operation. In the theory, the density range over which the plasma encounters the kink-peeling boundary widens as the plasma cross-section shaping is increased, thus increasing the QH-mode density threshold. The DIII-D results are in excellent agreement with these predictions, and nonlinear magnetohydrodynamic analysis of reconstructed QH-mode equilibria shows unstable low n kink-peeling modes growing to a saturated level, consistent with the theoretical picture of the EHO. Furthermore, high density operation in the QH-mode regime has opened a path to a new, previously predicted region of parameter space, named “Super H-mode” because it is characterized by very high pedestals that can be more than a factor of two above the peeling-ballooning stability limit for similar ELMing H-mode discharges at the same density.

H-mode regimes and observators of central toroidal rotation in Alcator C-Mod

International Nuclear Information System (INIS)

Greenwald, M.; Rice, J.; Boivin, R.

1999-01-01

The Enhanced D α or EDA H-mode regime in Alcator C-Mod has been investigated and compared in detail to ELM-free plasmas. (In this paper, ELM-free will refer to discharges with no type I ELMs and with no sign of EDA, though technically, most EDA plasmas are ELM-free as well.) EDA discharges have only slightly lower energy confinement than comparable ELM-free ones, but show markedly reduced impurity confinement. Thus EDA discharges do not accumulate impurities and typically have a lower fraction of radiated power. EDA plasmas are seen to be more likely at low plasma current (q > 3.7 - 4), for moderate plasma shaping (0.35 - 0.55), and for high neutral pressures. No obvious trends were observed with input power or pressure (β). In both H-mode regimes, and in ICRF heated L-modes, central impurity toroidal rotation has been deduced, from the Doppler shifts of argon x-ray lines. Rotation velocities up to 1.3 x 10 5 m/s in the co-current direction have been observed in H-mode discharges that had no direct momentum input. There is a strong correlation between the increase in the central impurity rotation velocity and the increase in the plasma stored energy, induced by ICRF heating. In otherwise similar discharges with the same stored energy increase, plasmas with lower current rotate faster. The ion pressure gradient is an unimportant contributor to the central impurity rotation and the presence of a substantial core radial electric field is inferred during the ICRF pulse. An inward shift of ions induced by ICRF waves could give rise to a non-ambipolar electric field in the plasma core. Comparisons with a neo-classical ion orbit shift model show good agreement with the observations, both in magnitude, and in the scaling with plasma current. (author)

Improved confinement with ion cyclotron hydrogen minority heating on Tore Supra

International Nuclear Information System (INIS)

Hoang, G.T.; Monier-Garbet, P.; Aniel, T.; Bourdelle, C.; Eriksson, L.G.; Garbet, X.; Grisolia, C.; Platz, P.; Budny, R.V.

1999-02-01

Tore Supra experiments are presently devoted to study the high density and high radiation regimes with radio frequency heating. Recent results of ion cyclotron minority heating have been obtained with an improved L-mode confinement, close to ELMy H-mode, at relatively high density (up to 80% of Greenwald limit). Such a regime is very promising as possible scenario in a next step tokamak. (authors)

Confinement and stability in JET: recent results

International Nuclear Information System (INIS)

Campbell, D.J.

1990-01-01

The versatility of the JET device allows a wide range of tokamak operating regimes to be explored and plasmas bounded both by material limiters and by a magnetic separatrix have been investigated extensively. This has permitted the confinement and mhd stability properties of plasmas heated to temperatures above 10keV by neutral beam injection or ion cyclotron resonance heating to be studied in detail. The results of recent analyses of transport and confinement in the L- and H-mode regimes in JET are discussed and the properties of H-mode plasmas produced by both major forms of heating are compared. Several aspects of the mhd stability of such plasmas, particularly at high toroidal beta, β θ , and at the density limit, are reviewed. (author)

Energy confinement and transport of H-mode plasmas in tokamak

International Nuclear Information System (INIS)

Urano, Hajime

2005-02-01

A characteristic feature of the high-confinement (H-mode) regime is the formation of a transport barrier near the plasma edge, where steepening of the density and temperature gradients is observed. The H-mode is expected to be a standard operation mode in a next-step fusion experimental reactor, called ITER-the International Thermonuclear Experimental Reactor. However, energy confinement in the H-mode has been observed to degrade with increasing density. This is a critical constraint for the operation domain in the ITER. Investigation of the main cause of confinement degradation is an urgent issue in the ITER Physics Research and Development Activity. A key element for solving this problem is investigation of the energy confinement and transport properties of H-mode plasmas. However, the influence of the plasma boundary characterized by the transport barrier in H-modes on the energy transport of the plasma core has not been examined sufficiently in tokamak research. The aim of this study is therefore to investigate the energy confinement properties of H-modes in a variety of density, plasma shape, seed impurity concentration, and conductive heat flux in the plasma core using the experimental results obtained in the JT-60U tokamak of Japan Atomic Energy Research Institute. Comparison of the H-mode confinement properties with those of other tokamaks using an international multi-machine database for extrapolation to the next step device was also one of the main subjects in this study. Density dependence of the energy confinement properties has been examined systematically by separating the thermal stored energy into the H-mode pedestal component determined by MHD stability called the Edge Localized Modes (ELMs) and the core component governed by gyro-Bohm-like transport. It has been found that the pedestal pressure imposed by the destabilization of ELM activities led to a reduction in the pedestal temperature with increasing density. The core temperature for each

Characteristics of radiated power for various TFTR [Tokamak Fusion Test Reactor] regimes

International Nuclear Information System (INIS)

Bush, C.E.; Schivell, J.; McNeill, D.H.

1988-04-01

Power loss studies were carried out to determine the impurity radiation and energy transport characteristics of various TFTR operation and confinement regimes including L-Mode, detached plasma, co-only neutral beam injection (energetic ion regime), and the enhanced confinement (''supershot'') regime. Combined bolometric, spectroscopic, and infrared photometry measurements provide a picture of impurity behavior and power accounting in TFTR. The purpose of this paper is to make a survey of the various regimes with the aim of determining the radiated power signatures of each. 10 refs., 6 figs., 1 tab

Reduced transport and ER shearing in improved confinement regimes in JT-60U

International Nuclear Information System (INIS)

Shirai, H.; Kikuchi, M.; Takizuka, T.

2001-01-01

The global confinement and the local transport properties of improved core confinement plasmas in JT-60U have been studied in connection with E r shear formation. The improved core confinement mode with ITB, the internal transport barrier, is roughly classified into 'parabolic' type ITBs and 'box' type ITBs. The parabolic type ITB has the reduced thermal diffusivity, χ, in the core region; however, the E r shear, dE r /dr, is not so strong. The box type ITB has a very strong E r shear at the thin ITB layer and the χ value decreases to the level of neoclassical transport there. The estimated ExB shearing rate, ω ExB , becomes almost the same as the linear growth rate of the drift microinstability, γ L , at the ITB layer in the box type ITB. Experiments of hot ion mode plasmas during the repetitive L-H-L transition shows that the thermal diffusivity clearly depends on the E r shear and the strong E r shear contributes to the reduced thermal diffusivity. (author)

Reduced transport and Er shearing in improved confinement regimes in JT-60U

International Nuclear Information System (INIS)

Shirai, H.; Kikuchi, M.; Takizuka, T.

1999-01-01

The global confinement and the local transport properties of improved core confinement plasmas in JT-60U were studied in connection with E r shear formation. In the improved core confinement mode with internal transport barriers (ITBs), these are roughly classified into 'parabolic type' ITBs and 'box type' ITBs. The parabolic type ITB has a reduced thermal diffusivity χ in the core region; however, the E r shear, dE r /dr, is not as strong. The box type ITB has a very strong E r shear at the thin ITB layer and χ decreases to the level of neoclassical transport there. The estimated E x B shearing rate, ω ExB , becomes almost the same as the linear growth rate of the drift microinstability, γ L , at the ITB layer in the box type ITB. Experiments with hot ion mode plasmas during the repetitive L-H-L transition showed that the thermal diffusivity clearly depends on the E r shear and the strong E r shear contributes to the reduced thermal diffusivity. (author)

Regime of very high confinement in the boronized DIII-D tokamak

International Nuclear Information System (INIS)

Jackson, G.L.; Winter, J.; Taylor, T.S.; Burrell, K.H.; DeBoo, J.C.; Greenfield, C.M.; Groebner, R.J.; Hodapp, T.; Holtrop, K.; Lazarus, E.A.; Lao, L.L.; Lippmann, S.I.; Osborne, T.H.; Petrie, T.W.; Phillips, J.; James, R.; Schissel, D.P.; Strait, E.J.; Turnbull, A.D.; West, W.P.; DIII-D Team

1991-01-01

Following boronization, tokamak discharges in DIII-D have been obtained with confinement times up to a factor of 3.5 above the ITER89-P L-mode scaling and 1.8 times greater than the DIII-D/JET H-mode scaling relation. Very high confinement phases are characterized by relatively high central density with n e (0)∼1x10 20 m -3 , and central ion temperatures up to 13.6 keV at moderate plasma currents (1.6 MA) and heating powers (12.5--15.3 MW). These discharges exhibit a low fraction of radiated power, P≤25%, Z eff (0) close to unity, and lower impurity influxes than comparable DIII-D discharges before boronization

Dependence of L-mode confinement on the electron cyclotron power deposition profile in the TCV tokamak

Science.gov (United States)

Kirneva, N. A.; Razumova, K. A.; Pochelon, A.; Behn, R.; Coda, S.; Curchod, L.; Duval, B. P.; Goodman, T. P.; Labit, B.; Karpushov, A. N.; Rancic, M.; Sauter, O.; Silva, M.; TCV Team

2012-01-01

Scenarios with different electron cyclotron heating power profile distributions and widths were compared for the first time in experiments on the Tokamak à Configuration Variable (TCV). The heating profile was changed from shot to shot over a wide range from localized on-axis, with normalized minor radius half-width at half maximum σ1/2 ~ 0.1, up to a widely distributed heating power profile with σ1/2 ~ 0.4 and finally to a profile peaked far off-axis. The global confinement, MHD activity, density, temperature and electron pressure profile evolution were compared. In particular, the energy confinement properties of discharges with localized on-axis heating and distributed on-axis heating were very similar, with degradation close to that predicted by the ITER L-mode scaling; in the case of off-axis heating, on the other hand, the confinement degradation was even stronger.

Multiple-mirror plasma confinement

International Nuclear Information System (INIS)

Lichtenberg, A.J.; Lieberman, M.A.; Logan, B.G.

1975-01-01

A large enhancement of the confinement time can be achieved in a straight system of multiple mirrors over an equal length uniform magnetic field. The scaling is diffusive rather than that of flow, thereby scaling the square of the system length rather than linear with system length. Probably the most economic mode of operation for a reactor occurs when lambda/M is approximately l/sub c/, where lambda is the mean free path, M the mirror ratio, and l/sub c/ the length between mirrors; but where the scale length of the mirror field l/sub m/ is much less than lambda. The axial confinement time has been calculated theoretically and numerically for all important parameter regimes, and confirmed experimentally. A typical reactor calculation gives Q/sub E/ = 2 for a 400 meter system with 3000 MW(e) output. The main concern of a multiple-mirror system is stability. Linked quadrupoles can achieve average minimum-B stabilization of flute modes, and experiments have demonstrated this stabilization. Localized instabilities at finite β and enhanced diffusion resulting from the distorted flux surfaces and possibly from turbulent higher order modes still remain to be investigated

Ohmic H-mode and confinement in TCV

International Nuclear Information System (INIS)

Moret, J.M.; Anton, M.; Barry, S.

1995-01-01

The unique flexibility of TCV for the creation of a wide variety of plasma shapes has been exploited to address some aspects of tokamak physics for which the shape may play an important role. The electron energy confinement time in limited ohmic L-mode plasmas whose elongation and triangularity have been varied, has been observed to improve with elongation as κ 0.5 but to degrade with triangularity as (1-0.8 δ), for fixed safety factor. Ohmic H-modes have been obtained in several diverted and limited configurations, with some of the diverted discharges featuring large ELMs whose effects on the global confinement have been quantified. These effects depend on the configuration: in double null (DN) equilibria, a single ELM expels on average 2%, 6% and 2.5% of the particle, impurity and thermal energy content respectively, whilst in single null (SN) configurations, the corresponding numbers are 3.5%, 7% and 9%, indicative of larger ELM effects. The presence or absence of large ELMs in DN discharges has been actively controlled in a single discharge by alternately forcing one or other of the two X-points to lie on the separatrix, permitting stationary density and impurity content (Z eff ≅1.6) in long H-modes (1.5 s). (author) 9 figs., 9 refs

Status of global energy confinement studies

International Nuclear Information System (INIS)

Kaye, S.M.; Bell, M.G.; DeBoo, J.C.; Waltz, R.; Greenwald, M.; Sigmar, D.

1990-02-01

Empirical scaling expressions, reflecting the parametric dependence of the L-mode energy confinement time, have been used not only as benchmarks for tokamak operation and theories of energy transport, but for predicting the performance of proposed tokamak devices. Several scaling expressions based on data from small-and medium-sized devices have done well in predicting performance in larger devices, although great uncertainty exists in extrapolating yet farther, into the ignition regime. Several approaches exist for developing higher confidence scaling expressions. These include reducing the statistical uncertainty by identifying and filling in gaps in the present database, making use of more sophisticated statistical techniques, and developing scalings for confinement regimes within which future devices will operate. Confidence in the scaling expressions will be increased still if the expressions can be more directly tied to transport physics theory. This can be done through the use of dimensionless parameters, better describing the edge and core confinement regimes separately, and by incorporating transport models directly into the scaling expressions. 50 refs., 5 figs., 3 tabs

Improved particle confinement in transition from multiple-helicity to quasi-single-helicity regimes of a reversed-field pinch.

Science.gov (United States)

Frassinetti, L; Predebon, I; Koguchi, H; Yagi, Y; Hirano, Y; Sakakita, H; Spizzo, G; White, R B

2006-10-27

The quasi-single-helicity (QSH) state of a reversed-field pinch (RFP) plasma is a regime in which the RFP configuration can be sustained by a dynamo produced mainly by a single tearing mode and in which a helical structure with well-defined magnetic flux surfaces arises. In this Letter, we show that spontaneous transitions to the QSH regime enhance the particle confinement. This improvement is originated by the simultaneous and cooperative action of the increase of the magnetic island and the reduction of the magnetic stochasticity.

Confinement of a non cylindrical z discharge by a cusp geometry; Confinement d'une decharge lineaire non-cylindrique par une geometrie magnetique cuspidee

Energy Technology Data Exchange (ETDEWEB)

Watteau, J H [Commissariat a l' Energie Atomique, Limeil-Brevannes (France). Centre d' Etudes

1968-03-01

The plasma of a non-cylindrical z discharge is accumulated in the centre of a cusp geometry and then captured and confined by the rising cusp magnetic field. The cusp geometry is produced by two identical coaxial coils the currents of which are equal but in opposite directions. Stability and confinement properties of this zero minimum B geometry are recalled; in particular it is shown (the coils cross section being supposed punctual) that the magnetic well depth of the configuration without plasma is maximum for an optimum coils distance. Two modes of confinement are observed experimentally : - a collisional mode for which the plasma confinement is limited to 10 {mu}sec (temperature 5 eV, density 7 x 10{sup 16} cm{sup -3}) as a result of the gradual interpenetration of the plasma and of the magnetic field. - a collisionless mode (temperature 40 eV) where the radial leak thickness is of the order of the ion cyclotron radius. Plasma accumulation occurs even without confinement and is due to the non-cylindrical shape of the discharge chamber. The two-dimensional snow-plough model gives good account of the discharge dynamics. A comparison is made with plasma focus experiments: in particular experimental conditions (deuterium, pressure 1 torr,energy 3 kJ, current 100 kA) a 10{sup 7} neutron yield is detected which appears to be connected with the unstable behavior of the discharge. (authors) [French] Le plasma d'une decharge lineaire non-cylindrique s'accumule au centre d'une geometrie magnetique cuspidee ou il est capture et confine par l'induction croissante de la geometrie. On rappelle les proprietes de stabilite et de confinement de la geometrie cuspidee, geometrie a champ minimum nul produite par deux spires identiques, coaxiales et parcourues par des courants egaux et opposes; on montre en particulier que pour des spires de section ponctuelle la profondeur du puits magnetique de la geometrie sans plasma est maximum pour une distance optimum des spires. Deux

Radial transport in the far scrape-off layer of ASDEX upgrade during L-mode and ELMy H-mode

DEFF Research Database (Denmark)

Ionita, C.; Naulin, Volker; Mehlmann, F.

2013-01-01

The radial turbulent particle flux and the Reynolds stress in the scrape-off layer (SOL) of ASDEX Upgrade were investigated for two limited L-mode (low confinement) and one ELMy H-mode (high confinement) discharge. A fast reciprocating probe was used with a probe head containing five Langmuir...

Ohmic H-mode and confinement in TCV

International Nuclear Information System (INIS)

Moret, J.-M.; Anton, M.; Barry, S.

1995-01-01

The unique flexibility of TCV for the creation of a wide variety of plasma shapes has been exploited to address some aspects of tokamak physics for which the shape may play an important role. The electron energy confinement time in limited ohmic L-mode plasmas whose elongation and triangularity have been varied (κ = 1.3 - 1.9, δ 0.1 - 0.7) has been observed to improve with elongation as κ 0.5 but to degrade with triangularity as (1 - 0.8 δ), for fixed safety factor. Ohmic H-modes have been obtained in several diverted and limited configurations, with some of the diverted discharges featuring large ELMs whose effects on the global confinement have been quantified. These effects depend on the configuration: in double null (DN) equilibria, a single ELM expels on average 2%, 6% and 2.5% of the particle, impurity and thermal energy content respectively, whilst in single null (SN) configurations, the corresponding numbers are 3.5%, 7% and 9%, indicative of larger ELM effects. The presence of absence of large ELMs in DN discharges has been actively controlled in a single discharge by alternately forcing one or other of the two X-points to lie on the separatrix, permitting stationary density and impurity content (Z eff ∼ 1.6) in long H-modes (1.5 s). (Author)

High efficiency confinement mode by electron cyclotron heating

International Nuclear Information System (INIS)

Funahashi, Akimasa

1987-01-01

In the medium size nuclear fusion experiment facility JFT-2M in the Japan Atomic Energy Research Institute, the research on the high efficiency plasma confinement mode has been advanced, and in the experiment in June, 1987, the formation of a high efficiency confinement mode was successfully controlled by electron cyclotron heating, for the first time in the world. This result further advanced the control of the formation of a high efficiency plasma confinement mode and the elucidation of the physical mechanism of that mode, and promoted the research and development of the plasma heating by electron cyclotron heating. In this paper, the recent results of the research on a high efficiency confinement mode at the JFT-2M are reported, and the role of the JFT-2M and the experiment on the improvement of core plasma performance are outlined. Now the plasma temperature exceeding 100 million deg C has been attained in large tokamaks, and in medium size facilities, the various measures for improving confinement performance are to be brought forth and their scientific basis is elucidated to assist large facilities. The JFT-2M started the operation in April, 1983, and has accumulated the results smoothly since then. (Kako, I.)

An emerging understanding of H-mode discharges in tokamaks

International Nuclear Information System (INIS)

Groebner, R.J.

1992-12-01

A remarkable degree of consistency of experimental results from tokamaks throughout the world has developed with regard to the phenomenology of the transition from L-mode to H-mode confinement in tokamaks. The transition is initiated in a narrow layer at the plasma periphery where density fluctuations are suppressed and steep gradients of temperature and density form in a region with large first and second radial derivatives in the υ E → = (E x B)/B 2 flow velocity. These results are qualitatively consistent with theories which predict suppression of fluctuations by shear or curvature in υE. The required υE flow is generated very rapidly when the magnitude of the heating power or of an externally imposed radial current exceed threshold values and several theoretical models have been developed to explain the observed changes in the υE flow. After the transition occurs, the altered boundary conditions enable the development of improved confinement in the plasma interior on a confinement time scale. The resulting H-mode discharge has typically twice the confinement of L-mode discharges and regimes of further improved confinement have been obtained in some H-mode scenarios

Observations of core toroidal rotation reversals in Alcator C-Mod ohmic L-mode plasmas

International Nuclear Information System (INIS)

Rice, J.E.; Reinke, M.L.; Podpaly, Y.A.; Churchill, R.M.; Cziegler, I.; Dominguez, A.; Ennever, P.C.; Fiore, C.L.; Granetz, R.S.; Greenwald, M.J.; Hubbard, A.E.; Hughes, J.W.; Irby, J.H.; Ma, Y.; Marmar, E.S.; McDermott, R.M.; Porkolab, M.; Duval, B.P.; Bortolon, A.; Diamond, P.H.

2011-01-01

Direction reversals of intrinsic toroidal rotation have been observed in Alcator C-Mod ohmic L-mode plasmas following modest electron density or toroidal magnetic field ramps. The reversal process occurs in the plasma interior, inside of the q = 3/2 surface. For low density plasmas, the rotation is in the co-current direction, and can reverse to the counter-current direction following an increase in the electron density above a certain threshold. Reversals from the co- to counter-current direction are correlated with a sharp decrease in density fluctuations with k R ≥ 2 cm -1 and with frequencies above 70 kHz. The density at which the rotation reverses increases linearly with plasma current, and decreases with increasing magnetic field. There is a strong correlation between the reversal density and the density at which the global ohmic L-mode energy confinement changes from the linear to the saturated regime.

Improved confinement mode induced by the MARFE on the HT-7 superconducting tokamak

International Nuclear Information System (INIS)

Gao, X.; Zhao, Y.P.; Luo, J.R.; Jie, Y.X.; Gong, X.Z.; Wan, B.N.; Li, J.G.; Yin, F.X.; Kuang, G.L.; Zhang, X.D.; Zhang, S.Y.; Qiu, N.; Liu, X.N.; Zhao, J.Y.; Yang, Y.; Bao, Y.; Lin, B.L.; Wu, Z.W.; Li, Y.D.; Xu, Y.H.; Yang, K.; Wang, G.X.; Ye, W.W.; Chen, L.; Shi, Y.J.; Song, M.; Zhang, X.M.; Qin, P.J.; Gu, X.M.; Cui, N.Z.; Fan, H.Y.; Liu, S.X.; Chen, Y.F.; Hu, L.Q.; Hu, J.S.; Xia, C.Y.; Ruan, H.L.; Tong, X.D.; Mao, J.S.; Xie, J.K.; Wan, Y.X.

1999-01-01

In the HT-7 superconducting tokamak, the onset of a multifaceted asymmetric radiation from the edge (MARFE) usually occurs in the early ohmic discharges of each experimental campaign before wall conditioning. The occurrence and location of a MARFE is identified by different diagnostic systems. An improved confinement mode plasma which was induced by the MARFE is observed, and the global particle confinement time increases 1.9 times. The relaxation time between the MARFE event trigger and the L-H transition is about 1.4 ms, the following L-H transition time is 1.9 ms, and the improved confinement mode phase is maintained for about 40 ms. The MARFE cools the plasma edge, and the electron density profile is observed to become more narrow and peaked. The occurrence of a MARFE is strongly correlated with Z eff but not with the density, and it always occurs at Z eff = 3-8 ohmic discharges. In the case of a good wall condition (Z eff = 1-2), the onset of MARFEs has not been observed before reaching the Greenwald density limit. (author)

Confinement and Local Transport in the National Spherical Torus Experiment NSTX

International Nuclear Information System (INIS)

Kaye, S.M.; Levinton, F.M.; Stutman, D.; Tritz, K.; Yuh, H.; Bell, M.G.; Bell, R.E.; Domier, C.W.; Gates, D.; Horton, W.; Kim, J.; LeBlanc, B.P.; Luhmann, N.C. Jr.; Maingi, T.; Mazzucato, E.; Menard, J.E.; Mikkelsen, D.; Mueller, D; Park, H.; Rewoldt, G.; Sabbagh, S.A.; Smith, D.R.; Wang, W.

2007-01-01

NSTX operates at low aspect ratio (R/a∼1.3) and high beta (up to 40%), allowing tests of global confinement and local transport properties that have been established from higher aspect ratio devices. NSTX plasmas are heated by up to 7 MW of deuterium neutral beams with preferential electron heating as expected for ITER. Confinement scaling studies indicate a strong B T dependence, with a current dependence that is weaker than that observed at higher aspect ratio. Dimensionless scaling experiments indicate a strong increase of confinement with decreasing collisionality and a weak degradation with beta. The increase of confinement with B T is due to reduced transport in the electron channel, while the improvement with plasma current is due to reduced transport in the ion channel related to the decrease in the neoclassical transport level. Improved electron confinement has been observed in plasmas with strong reversed magnetic shear, showing the existence of an electron internal transport barrier (eITB). The development of the eITB may be associated with a reduction in the growth of microtearing modes in the plasma core. Perturbative studies show that while L-mode plasmas with reversed magnetic shear and an eITB exhibit slow changes of L Te across the profile after the pellet injection, H-mode plasmas with a monotonic q-profile and no eITB show no change in this parameter after pellet injection, indicating the existence of a critical gradient that may be related to the q-profile. Both linear and non-linear simulations indicate the potential importance of ETG modes at the lowest B T . Localized measurements of high-k fluctuations exhibit a sharp decrease in signal amplitude levels across the L-H transition, associated with a decrease in both ion and electron transport, and a decrease in calculated linear microinstability growth rates across a wide k-range, from the ITG/TEM regime up to the ETG regime

Heating, current drive and confinement regimes with the JET ICRH and LHCD systems

DEFF Research Database (Denmark)

Jacquinot, J.; Adams, J.M.; Altmann, H.

1991-01-01

by pellet injection. A value of n(d) tau-E T(i) = 7.8 x 10(20) m-3 s keV was obtained in this mode with T(e) approximately T(i) approximately 11 keV. In the L-mode regime, a regime, a record (140 kW) D-He-3 fusion power was generated with 10 - 14 MW of ICRH at the He-3 cyclotron frequency. Experiments were....... Paradoxically, LHCD induces central heating particularly in combination with ICRH. Finally we present the first observations of the synergistic acceleration of fast electrons by Transit Time Magnetic Pumping (TTMP) (from ICRH) and Electron Landau Damping (ELD) (from LHCD). The synergism generates TTMP current...

Sandwich structure of plasma edge during transition to improved confinement regime in L-2M stellarator

International Nuclear Information System (INIS)

Shchepetov, S V; Kholnov, Yu V; Fedyanin, O I; Kuznetsov, A B; Vasilkov, D G; Akulina, D K; Batanov, G M; Gladkov, G A; Grebenshchikov, S E; Meshcheryakov, A I

2008-01-01

Transitions to the regime with better confinement in the L-2M stellarator are presented. Transitions are indicated only at sufficiently high plasma densities, and for a given value of average density they appear only at higher heating powers. Each transition is easily identified by a sudden fast ( e ). In the bulk of the plasma parameters evolve slowly. Drastic changes are observed in the region close to the plasma boundary where two moderate order rational magnetic surfaces are located with the rotational transform μ taking the values 2/3 and 3/4. Relative values of plasma parameters' fluctuations and their spectrum widths decrease significantly in this region. The region has a definite sandwich structure being subdivided by the above-named moderate order rational magnetic surfaces into three smaller zones with different plasma parameter dynamics. Transition is triggered by local disturbances of plasma parameters that are caused by instabilities in the vicinity of magnetic surfaces where μ is equal to 2/3 or 3/4. Different hypotheses on the nature of the phenomenon are discussed

Core-SOL simulations of L-mode tokamak plasma discharges using BALDUR code

Directory of Open Access Journals (Sweden)

Yutthapong Pinanroj

2014-04-01

Full Text Available Core-SOL simulations were carried out of plasma in tokamak reactors operating in a low confinement mode (L-mode, for various conditions that match available experimental data. The simulation results were quantitatively compared against experimental data, showing that the average RMS errors for electron temperature, ion temperature, and electron density were lower than 16% or less for 14 L-mode discharges from two tokamaks named DIII-D and TFTR. In the simulations, the core plasma transport was described using a combination of neoclassical transport calculated by NCLASS module and anomalous transport by Multi-Mode-Model version 2001 (MMM2001. The scrape-off-layer (SOL is the small amount of residual plasma that interacts with the tokamak vessel, and was simulated by integrating the fluid equations, including sources, along open field lines. The SOL solution provided the boundary conditions of core plasma region on low confinement mode (L-mode. The experimental data were for 14 L-mode discharges and from two tokamaks, named DIII-D and TFTR.

Comparison of particle confinement in the high confinement mode plasmas with the edge localized mode of the Japan Atomic Energy Research Institute Tokamak-60 Upgrade and the DIII-D tokamak

International Nuclear Information System (INIS)

Takenaga, H.; Mahdavi, M.A.; Baker, D.R.

2001-01-01

Particle confinement was compared for the high confinement mode plasmas with the edge localized mode in the Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U) [S. Ishida, JT-60 Team, Nucl. Fusion 39, 1211 (1999)] and the DIII-D tokamak [J. L. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] considering separate confinement times for particles supplied by neutral beam injection (NBI) (center fueling) and by recycling and gas-puffing (edge fueling). Similar dependence on the NBI power was obtained in JT-60U and DIII-D. The particle confinement time for center fueling in DIII-D was smaller by a factor of 4 in the low density discharges and by a factor of 1.8 in the high density discharges than JT-60U scaling, respectively, suggesting the stronger dependence on the density in DIII-D. The particle confinement time for edge fueling in DIII-D was comparable with JT-60U scaling in the low density discharges. However, it decreased to a much smaller value in the high density discharges

The simulation of L-H transition in tokamak plasma using MMM95 transport model

International Nuclear Information System (INIS)

Intharat, P; Poolyarat, N; Chatthong, B; Onjun, T; Picha, R

2015-01-01

BALDUR integrative predictive modelling code together with a Multimode (MMM95) anomalous transport model is used to simulate the evolution profiles, including plasma current, temperature, density and energy in a tokamak reactor. It is found that a self - transition from low confinement mode (L-mode) to high confinement mode (H-mode) regimes can be achieved once a sufficient auxiliary heating applied to the plasma is reached. The result agrees with experimental observations from various tokamaks. A strong reduction of turbulent transport near the edge of plasma is also observed, which is related to the formation of steep radial electric field near the edge regime. From transport analysis, it appears that the resistive ballooning mode is the dominant term near the plasma edge regime, which is significantly reduced during the transition. (paper)

QUIESCENT H-MODE, AN ELM-FREE HIGH-CONFINEMENT MODE ON DIII-D WITH POTENTIAL FOR STATIONARY STATE OPERATION

Energy Technology Data Exchange (ETDEWEB)

WEST,WP; BURRELL,KH; deGRASSIE,JS; DOYLE,EJ; GREENFIELD,CM; LASNIER,CJ; SNYDER,PB; ZENG,L

2003-08-01

OAK-B135 The quiescent H-mode (QH-mode) is an ELM-free and stationary state mode of operation discovered on DIII-D. This mode achieves H-mode levels of confinement and pedestal pressure while maintaining constant density and radiated power. The elimination of edge localized modes (ELMs) and their large divertor loads while maintaining good confinement and good density control is of interest to next generation tokamaks. This paper reports on the correlations found between selected parameters in a QH-mode database developed from several hundred DIII-D counter injected discharges. Time traces of key plasma parameters from a QH-mode discharge are shown. On DIII-D the negative going plasma current (a) indicates that the beam injection direction is counter to the plasma current direction, a common feature of all QH-modes. The D{sub {alpha}} time behavior (c) shows that soon after high powered beam heating (b) is applied, the discharge makes a transition to ELMing H-mode, then the ELMs disappear, indicating the start of the QH period that lasts for the remainder of the high power beam heating (3.5 s). Previously published work showing density and temperature profiles indicates that long-pulse, high-triangularity QH discharges develop an internal transport barrier in combination with the QH edge barrier. These discharges are known as quiescent, double-barrier discharges (QDB). The H-factor (d) and stored energy (c) rise then saturate at a constant level and the measured axial and minimum safety factors remain above 1.0 for the entire QH duration. During QDB operation the performance of the plasma can be very good, with {beta}{sub N}*H{sub 89L} product reaching 7 for > 10 energy confinement times. These discharges show promise that a stationary state can be achieved.

QUIESCENT H-MODE, AN ELM-FREE HIGH-CONFINEMENT MODE ON DIII-D WITH POTENTIAL FOR STATIONARY STATE OPERATION

International Nuclear Information System (INIS)

WEST, WP; BURRELL, KH; DeGRASSIE, JS; DOYLE, EJ; GREENFIELD, CM; LASNIER, CJ; SNYDER, PB; ZENG, L.

2003-01-01

OAK-B135 The quiescent H-mode (QH-mode) is an ELM-free and stationary state mode of operation discovered on DIII-D. This mode achieves H-mode levels of confinement and pedestal pressure while maintaining constant density and radiated power. The elimination of edge localized modes (ELMs) and their large divertor loads while maintaining good confinement and good density control is of interest to next generation tokamaks. This paper reports on the correlations found between selected parameters in a QH-mode database developed from several hundred DIII-D counter injected discharges. Time traces of key plasma parameters from a QH-mode discharge are shown. On DIII-D the negative going plasma current (a) indicates that the beam injection direction is counter to the plasma current direction, a common feature of all QH-modes. The D α time behavior (c) shows that soon after high powered beam heating (b) is applied, the discharge makes a transition to ELMing H-mode, then the ELMs disappear, indicating the start of the QH period that lasts for the remainder of the high power beam heating (3.5 s). Previously published work showing density and temperature profiles indicates that long-pulse, high-triangularity QH discharges develop an internal transport barrier in combination with the QH edge barrier. These discharges are known as quiescent, double-barrier discharges (QDB). The H-factor (d) and stored energy (c) rise then saturate at a constant level and the measured axial and minimum safety factors remain above 1.0 for the entire QH duration. During QDB operation the performance of the plasma can be very good, with β N *H 89L product reaching 7 for > 10 energy confinement times. These discharges show promise that a stationary state can be achieved

Local transport analysis of L-mode plasmas in JT-60 tokamak

International Nuclear Information System (INIS)

Hirayama, Toshio; Kikuchi, Mitsuru; Shirai, Hiroshi; Shimizu, Katsuhiro; Yagi, Masatoshi; Koide, Yoshihiko; Ishida, Shinichi; Azumi, Masafumi.

1991-03-01

Local heat transport has been studied in auxiliary heated JT-60 plasmas with emphasis on understanding the deteriorated confinement observed in L-mode plasmas. The systematic experiment and analysis have been carried out in L-mode phase of divertor (single null, lower X-point), and limiter discharges with hydrogen neutral beam heating into hydrogen plasmas, based on sets of consistent experimental data including ion temperature profiles from CXR measurements. The deterioration in the energy confinement time with increasing the auxiliary heating power, so-called the power scaling, is mainly due to the degradation in ion energy transport. The confinement improvement as the plasma current increases is followed by both improvement in ion and electron transport properties. It is found that the ion thermal diffusivity has an approval dependence on the density. High ion temperature (T i (0) ≤ 12 keV) L-mode plasmas are attained at high β p up to 3.5. The centrally peaked ion temperature is significantly due to the improvement in ion transport property, which is reduced to the level of the electron thermal diffusivities. (author)

Analysis of tokamak plasma confinement modes using the fast

Indian Academy of Sciences (India)

The Fourier analysis is a satisfactory technique for detecting plasma confinement modes in tokamaks. The confinement mode of tokamak plasma was analysed using the fast Fourier transformation (FFT). For this purpose, we used the data of Mirnov coils that is one of the identifying tools in the IR-T1 tokamak, with and ...

Inhibited emission of electromagnetic modes confined in subwavelength cavities

International Nuclear Information System (INIS)

Le Thomas, N.; Houdre, R.

2011-01-01

We experimentally demonstrate the active inhibition of subwavelength confined cavity modes emission and quality factor enhancement by controlling the cavity optical surrounding. The intrinsic radiation angular spectrum of modes confined in planar photonics crystal cavities as well as its modifications depending on the environment are inferred via a transfer matrix modeling and k-space imaging.

Ohmic H-mode studies in TUMAN-3

International Nuclear Information System (INIS)

Lebedev, S.V.; Andrejko, M.V.; Askinazi, L.G.; Golant, V.E.; Kornev, V.A.; Levin, L.S.; Tukachinsky, A.S.; Tendler, M.

1994-01-01

The spontaneous transition from Ohmically heated limiter discharges into the regime with improved confinement termed as ''Ohmic H-mode'' has been investigated in ''TUMAN-3''. The typical signatures of H-mode in tokamaks with powerful auxiliary heating have been observed: sharp drop of D α radiation with simultaneous increase in the electron density and stored energy, suppression of the density fluctuations and establishing the steep gradient near the periphery. The crucial role of the radial electric field in the L-H transition was found in the experiments with boundary biasing. The possibility of initiating the H-mode using single pellet injection was demonstrated. In Ohmic H-mode strong dependencies of τ E on plasma current and on input power and weak dependence on density were found. Thermal energy confinement time enhanced by a factor of 10 compared to predictions of Neo-Alcator scaling. Longest energy confinement time (30 ms) was obtained in the small tokamak TUMAN-3. Absolute values of the energy confinement time are in agreement with scaling proposed for description of the ELM-free H-modes in devices with powerful auxiliary heating (''DIII-D/JET H-mode'' scaling). (author)

Dynamic Confinement of ITER Plasma by O-Mode Driver at Electron Cyclotron Frequency Range

Science.gov (United States)

Stefan, V. Alexander

2009-05-01

A low B-field side launched electron cyclotron O-Mode driver leads to the dynamic rf confinement, in addition to rf turbulent heating, of ITER plasma. The scaling law for the local energy confinement time τE is evaluated (τE ˜ 3neTe/2Q, where (3/2) neTe is the local plasma thermal energy density and Q is the local rf turbulent heating rate). The dynamics of unstable dissipative trapped particle modes (DTPM) strongly coupled to Trivelpiece-Gould (T-G) modes is studied for gyrotron frequency 170GHz; power˜24 MW CW; and on-axis B-field ˜ 10T. In the case of dynamic stabilization of DTPM turbulence and for the heavily damped T-G modes, the energy confinement time scales as τE˜(I0)-2, whereby I0(W/m^2) is the O-Mode driver irradiance. R. Prater et. al., Nucl. Fusion 48, No 3 (March 2008). E. P. Velikhov, History of the Russian Tokamak and the Tokamak Thermonuclear Fusion Research Worldwide That Led to ITER (Documentary movie; Stefan Studios Int'l, La Jolla, CA, 2008; E. P. Velikhov, V. Stefan.) M N Rosenbluth, Phys. Scr. T2A 104-109 1982 B. B. Kadomtsev and O. P. Pogutse, Nucl. Fusion 11, 67 (1971).

Power requirements for superior H-mode confinement on Alcator C-Mod: experiments in support of ITER

International Nuclear Information System (INIS)

Hughes, J.W.; Reinke, M.L.; Terry, J.L.; Brunner, D.; Greenwald, M.; Hubbard, A.E.; LaBombard, B.; Lipschultz, B.; Ma, Y.; Wolfe, S.; Wukitch, S.J.; Loarte, A.

2011-01-01

Power requirements for maintaining sufficiently high confinement (i.e. normalized energy confinement time H 98 ≥ 1) in H-mode and its relation to H-mode threshold power scaling, P th , are of critical importance to ITER. In order to better characterize these power requirements, recent experiments on the Alcator C-Mod tokamak have investigated H-mode properties, including the edge pedestal and global confinement, over a range of input powers near and above P th . In addition, we have examined the compatibility of impurity seeding with high performance operation, and the influence of plasma radiation and its spatial distribution on performance. Experiments were performed at 5.4 T at ITER relevant densities, utilizing bulk metal plasma facing surfaces and an ion cyclotron range of frequency waves for auxiliary heating. Input power was scanned both in stationary enhanced D α (EDA) H-modes with no large edge localized modes (ELMs) and in ELMy H-modes in order to relate the resulting pedestal and confinement to the amount of power flowing into the scrape-off layer, P net , and also to the divertor targets. In both EDA and ELMy H-mode, energy confinement is generally good, with H 98 near unity. As P net is reduced to levels approaching that in L-mode, pedestal temperature diminishes significantly and normalized confinement time drops. By seeding with low-Z impurities, such as Ne and N 2 , high total radiated power fractions are possible, along with substantial reductions in divertor heat flux (>4x), all while maintaining H 98 ∼ 1. When the power radiated from the confined versus unconfined plasma is examined, pedestal and confinement properties are clearly seen to be an increasing function of P net , helping to unify the results with those from unseeded H-modes. This provides increased confidence that the power flow across the separatrix is the correct physics basis for ITER extrapolation. The experiments show that P net /P th of one or greater is likely to lead to H

Sustainment of high confinement in JT-60U reversed shear plasmas

International Nuclear Information System (INIS)

Fujita, T.; Kamada, Y.; Ide, S.; Takeji, S.; Sakamoto, Y.; Isayama, A.; Suzuki, T.; Oikawa, T.; Fukuda, T.

2001-01-01

confinement is achieved owing to strong internal transport barriers (ITBs), are reported. In a high current plasma with an L-mode edge, deuterium-tritium-equivalent fusion power gain, Q DT eq =0.5 was sustained for 0.8 s (∼ energy confinement time) by adjusting plasma beta precisely using feedback control of stored energy. In a high triangularity plasma with an ELMy H-mode edge, the shrinkage of reversed shear region was suppressed and quasi steady sustainment of high confinement was achieved by raising the poloidal beta and enhancing the bootstrap current peaked at the ITB layer. High bootstrap current fraction (∼80%) was obtained in a high q regime (q 95 ∼9), which leaded to full non-inductive current drive condition. The normalized beta (β N ) of ∼ 2 and H-factor of H 89 ∼3.5 (HH 98y2 ∼2.2) were sustained for 2.7 s (∼ 6 times energy confinement time). (author)

Radiofrequency-heated enhanced confinement modes in the Alcator C-Mod tokamak

International Nuclear Information System (INIS)

Takase, Y.; Boivin, R.L.; Bombarda, F.; Bonoli, P.T.; Christensen, C.; Fiore, C.; Garnier, D.; Goetz, J.A.; Golovato, S.N.; Granetz, R.; Greenwald, M.; Horne, S.F.; Hubbard, A.; Hutchinson, I.H.; Irby, J.; LaBombard, B.; Lipschultz, B.; Marmar, E.; May, M.; Mazurenko, A.; McCracken, G.; OShea, P.; Porkolab, M.; Reardon, J.; Rice, J.; Rost, C.; Schachter, J.; Snipes, J.A.; Stek, P.; Terry, J.; Watterson, R.; Welch, B.; Wolfe, S.

1997-01-01

Enhanced confinement modes up to a toroidal field of B T =8T have been studied with up to 3.5 MW of radiofrequency (rf) heating power in the ion cyclotron range of frequencies (ICRF) at 80 MHz. H-mode is observed when the edge temperature exceeds a threshold value. The high confinement mode (H-mode) with higher confinement enhancement factors (H) and longer duration became possible after boronization by reducing the radiated power from the main plasma. A quasi-steady state with high confinement (H=2.0), high normalized beta (β N =1.5), low radiated power fraction (P rad main /P loss =0.3), and low effective charge (Z eff =1.5) has been obtained in Enhanced D α H-mode. This type of H-mode has enhanced levels of continuous D α emission and very little or no edge localized mode (ELM) activity, and reduced core particle confinement time relative to ELM-free H-mode. The pellet enhanced performance (PEP) mode is obtained by combining core fueling with pellet injection and core heating. A highly peaked pressure profile with a central value of 8 atmospheres was observed. The steep pressure gradient drives off-axis bootstrap current, resulting in a shear reversed safety factor (q) profile. Suppression of sawteeth appears to be important in maintaining the highly peaked pressure profile. Lithium pellets were found to be more effective than deuterium pellets in raising q 0 . copyright 1997 American Institute of Physics

Enhanced Confinement Scenarios Without Large Edge Localized Modes in Tokamaks: Control, Performance, and Extrapolability Issues for ITER

Energy Technology Data Exchange (ETDEWEB)

Maingi, R [PPPL

2014-07-01

Large edge localized modes (ELMs) typically accompany good H-mode confinement in fusion devices, but can present problems for plasma facing components because of high transient heat loads. Here the range of techniques for ELM control deployed in fusion devices is reviewed. The two baseline strategies in the ITER baseline design are emphasized: rapid ELM triggering and peak heat flux control via pellet injection, and the use of magnetic perturbations to suppress or mitigate ELMs. While both of these techniques are moderately well developed, with reasonable physical bases for projecting to ITER, differing observations between multiple devices are also discussed to highlight the needed community R & D. In addition, recent progress in ELM-free regimes, namely Quiescent H-mode, I-mode, and Enhanced Pedestal H-mode is reviewed, and open questions for extrapolability are discussed. Finally progress and outstanding issues in alternate ELM control techniques are reviewed: supersonic molecular beam injection, edge electron cyclotron heating, lower hybrid heating and/or current drive, controlled periodic jogs of the vertical centroid position, ELM pace-making via periodic magnetic perturbations, ELM elimination with lithium wall conditioning, and naturally occurring small ELM regimes.

Optimized profiles for improved confinement and stability in the Dill-D tokamak

International Nuclear Information System (INIS)

Taylor, T.S.; St John, H.; Turnbull, A.D.

1994-01-01

Simultaneous achievement of high energy confinement, τ E , and high plasma beta, β, leads to an economically attractive compact tokamak fusion reactor. High confinement enhancement, H τ E /τ E -ITER89P 4, and high normalized beta β N β/(I/aB) = 6%-m-T/MA. have been obtained in DIII-D experimental discharges. These improved confinement and/or improved stability limits are observed in several DIII-D high performance operational regimes: VH-mode, high l i H-mode, second stable core, and high beta poloidal. We have identified several important features of the improved performance in these discharges: details of the plasma shape, toroidal rotation or ExB flow profile, q profile and current density profile, and pressure profile. From our improved physics understanding of these enhanced performance regimes, we have developed operational scenarios which maintain the essential features of the improved confinement and which increase the stability limits using localized current profile control. The stability limit is increased by modifying the interior safety factor profile to be nonmonotonic with high central q, while maintaining the edge current density consistent with the improved transport regimes and the high edge bootstrap current. We have calculated high beta equilibria with β N 6.5, stable to ideal n=1 kinks and stable to ideal ballooning modes. The safety factor at the 95% flux surface is 6, the central q value is 3.9 and the minimum in q is 2.6. The current density profile is maintained by the natural profile of the bootstrap current, and a modest amount of electron cyclotron current drive. (Author)

The role of the radial electric field in confinement and transport in H-mode and VH-mode discharges in the DIII-D tokamak

International Nuclear Information System (INIS)

Gohil, P.; Burrell, K.H.; Groebner, R.J.; Osborne, T.H.; Doyle, E.J.; Rettig, C.L.

1993-08-01

Measurements of the radial electric field, E r , with high spatial and high time resolution in H-mode and VH-mode discharges in the DIII-D tokamak have revealed the significant influence of the shear in E r on confinement and transport in these discharges. These measurements are made using the DIII-D Charge Exchange Recombination (CER) System. At the L-H transition in DIII-D plasmas, a negative well-like E r profile develops just within the magnetic separatrix. A region of shear in E r results, which extends 1 to 2 cm into the plasma from the separatrix. At the transition, this region of sheared E r exhibits the greatest increase in impurity ion poloidal rotation velocity and the greatest reduction in plasma fluctuations. A transport barrier is formed in this same region of E x B velocity shear as is signified by large increases in the observed gradients of the ion temperature, the carbon density, the electron temperature and electron density. The development of the region of sheared E r , the increase in impurity ion poloidal rotation, the reduction in plasma turbulence, and the transport barrier all occur simultaneously at the L-H transition. Measurements of the radial electric field, plasma turbulence, thermal transport, and energy confinement have been performed for a wide range of plasma conditions and configurations. The results support the supposition that the progression of improving confinement at the L-H transition, into the H-mode and then into the VH-mode can be explained by the hypothesis of the suppression of plasma turbulence by the increasing penetration of the region of sheared E x B velocity into the plasma interior

The role of MHD instabilities in the improved H-mode scenario

International Nuclear Information System (INIS)

Flaws, Asher

2009-01-01

Recently a regime of tokamak operation has been discovered, dubbed the improved H-mode scenario, which simultaneously achieves increased energy confinement and stability with respect to standard H-mode discharges. It has been suggested that magnetohydrodynamic (MHD) instabilities play some role in establishing this regime. In this thesis MHD instabilities were identified, characterised, and catalogued into a database of improved H-mode discharges in order to statistically examine their behaviour. The onset conditions of MHD instabilities were compared to existing models based on previous H-mode studies. Slight differences were found, most notably a reduced β N onset threshold for the frequently interrupted regime for neoclassical tearing modes (NTM). This reduced threshold is due to the relatively low magnetic shear of the improved H-mode regime. This study also provided a first-time estimate for the seed island size of spontaneous onset NTMs, a phenomenon characteristic of the improved H-mode scenario. Energy confinement investigations found that, although the NTM impact on confinement follows the same model applicable to other operating regimes, the improved H-mode regime acts to mitigate the impact of NTMs by limiting the saturated island sizes for NTMs with toroidal mode number n ≥ 2. Surprisingly, although a significant loss in energy confinement is observed during the sawtooth envelope, it has been found that discharges containing fishbones and low frequency sawteeth achieve higher energy confinement than those without. This suggests that fishbone and sawtooth reconnection may indeed play a role in establishing the high confinement regime. It was found that the time evolution of the central magnetic shear consistently locks in the presence of sawtooth and fishbone reconnection. Presumably this is due to the periodic redistribution of the central plasma current, an effect which is believed to help establish and maintain the characteristic current profile

The role of MHD instabilities in the improved H-mode scenario

Energy Technology Data Exchange (ETDEWEB)

Flaws, Asher

2009-02-16

Recently a regime of tokamak operation has been discovered, dubbed the improved H-mode scenario, which simultaneously achieves increased energy confinement and stability with respect to standard H-mode discharges. It has been suggested that magnetohydrodynamic (MHD) instabilities play some role in establishing this regime. In this thesis MHD instabilities were identified, characterised, and catalogued into a database of improved H-mode discharges in order to statistically examine their behaviour. The onset conditions of MHD instabilities were compared to existing models based on previous H-mode studies. Slight differences were found, most notably a reduced {beta}{sub N} onset threshold for the frequently interrupted regime for neoclassical tearing modes (NTM). This reduced threshold is due to the relatively low magnetic shear of the improved H-mode regime. This study also provided a first-time estimate for the seed island size of spontaneous onset NTMs, a phenomenon characteristic of the improved H-mode scenario. Energy confinement investigations found that, although the NTM impact on confinement follows the same model applicable to other operating regimes, the improved H-mode regime acts to mitigate the impact of NTMs by limiting the saturated island sizes for NTMs with toroidal mode number n {>=} 2. Surprisingly, although a significant loss in energy confinement is observed during the sawtooth envelope, it has been found that discharges containing fishbones and low frequency sawteeth achieve higher energy confinement than those without. This suggests that fishbone and sawtooth reconnection may indeed play a role in establishing the high confinement regime. It was found that the time evolution of the central magnetic shear consistently locks in the presence of sawtooth and fishbone reconnection. Presumably this is due to the periodic redistribution of the central plasma current, an effect which is believed to help establish and maintain the characteristic current

Deuterium-tritium TFTR plasmas in the high poloidal beta regime

International Nuclear Information System (INIS)

Sabbagh, S.A.; Mauel, M.E.; Navratil, G.A.

1995-03-01

Deuterium-tritium plasmas with enhanced energy confinement and stability have been produced in the high poloidal beta, advanced tokamak regime in TFTR. Confinement enhancement H triple-bond τ E /τ E ITER-89P > 4 has been obtained in a limiter H-mode configuration at moderate plasma current I p = 0.85 - 1.46 MA. By peaking the plasma current profile, β N dia triple-bond 10 8 tperpendicular > aB 0 /I p = 3 has been obtained in these plasma,s exceeding the β N limit for TFTR plasmas with lower internal inductance, l i . Fusion power exceeding 6.7 MW with a fusion power gain Q DT = 0.22 has been produced with reduced alpha particle first orbit loss provided by the increased l i

Equilibrium current-driven tearing mode in the hydrodynamic regime

International Nuclear Information System (INIS)

Cozzani, F.; Mahajan, S.

1984-12-01

The effect of the parallel equilibrium current on the linear stability of the drift-tearing mode in the collisional regime is investigated analytically. In the appropriate parameter regime, a new unstable mode, driven by equilibrium current, is found and its relevance to tokamak discharges is discussed

Turbulent transport regimes and the scrape-off layer heat flux width

Science.gov (United States)

Myra, J. R.; D'Ippolito, D. A.; Russell, D. A.

2015-04-01

Understanding the responsible mechanisms and resulting scaling of the scrape-off layer (SOL) heat flux width is important for predicting viable operating regimes in future tokamaks and for seeking possible mitigation schemes. In this paper, we present a qualitative and conceptual framework for understanding various regimes of edge/SOL turbulence and the role of turbulent transport as the mechanism for establishing the SOL heat flux width. Relevant considerations include the type and spectral characteristics of underlying instabilities, the location of the gradient drive relative to the SOL, the nonlinear saturation mechanism, and the parallel heat transport regime. We find a heat flux width scaling with major radius R that is generally positive, consistent with the previous findings [Connor et al., Nucl. Fusion 39, 169 (1999)]. The possible relationship of turbulence mechanisms to the neoclassical orbit width or heuristic drift mechanism in core energy confinement regimes known as low (L) mode and high (H) mode is considered, together with implications for the future experiments.

Turbulent transport regimes and the scrape-off layer heat flux width

International Nuclear Information System (INIS)

Myra, J. R.; D'Ippolito, D. A.; Russell, D. A.

2015-01-01

Understanding the responsible mechanisms and resulting scaling of the scrape-off layer (SOL) heat flux width is important for predicting viable operating regimes in future tokamaks and for seeking possible mitigation schemes. In this paper, we present a qualitative and conceptual framework for understanding various regimes of edge/SOL turbulence and the role of turbulent transport as the mechanism for establishing the SOL heat flux width. Relevant considerations include the type and spectral characteristics of underlying instabilities, the location of the gradient drive relative to the SOL, the nonlinear saturation mechanism, and the parallel heat transport regime. We find a heat flux width scaling with major radius R that is generally positive, consistent with the previous findings [Connor et al., Nucl. Fusion 39, 169 (1999)]. The possible relationship of turbulence mechanisms to the neoclassical orbit width or heuristic drift mechanism in core energy confinement regimes known as low (L) mode and high (H) mode is considered, together with implications for the future experiments

Dispersion of strongly confined channel plasmon polariton modes

DEFF Research Database (Denmark)

Zenin, Vladimir; Volkov, Valentyn S.; Han, Zhanghua

2011-01-01

We report on experimental (by use of scanning near-field optical microscopy) and theoretical investigations of strongly confined (∼λ/5) channel plasmon polariton (CPP) modes propagating at telecom wavelengths (1425–1630 nm) along V-grooves cut in a gold film. The main CPP characteristics (mode in...

Comparison of low confinement mode transport simulations using the mixed Bohm/gyro-Bohm and the Multi-Mode-95 transport model

International Nuclear Information System (INIS)

Onjun, Thawatchai; Bateman, Glenn; Kritz, Arnold H.; Hannum, David

2001-01-01

Predictive transport simulations using the mixed Bohm/gyro-Bohm (JET) transport model [M. Erba , Plasma Phys. Controlled Fusion 39, 261 (1997)] are compared with simulations using the Multi-Mode-95 (MMM95) transport model [G. Bateman , Phys. Plasmas 5, 1793 (1998)]. Temperature and density profiles from these simulations are compared with experimental data for 13 low confinement mode (L-mode) discharges from the Doublet III-D Tokamak (DIII-D) [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] and the Tokamak Fusion Test Reactor (TFTR) [D. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)]. The selected discharges include systematic scans over gyro-radius, plasma power, current, and density. It is found that simulations using the two models match experimental data equally well, in spite of the fact that the JET model has predominantly Bohm scaling (proportional to gyro-radius) while the MMM95 model has a purely gyro-Bohm scaling (proportional to gyro-radius squared)

Transition from L mode to high ion temperature mode in CHS heliotron/torsatron plasmas

International Nuclear Information System (INIS)

Ida, K.; Osakabe, M.; Tanaka, K.

2001-01-01

A high ion temperature mode (high T i mode) is observed for neutral beam heated plasmas in the Compact Helical System (CHS) Heliotron/torsatron. The high T i mode plasma is characterized by a high central ion temperature, T i (0), and is associated with a peaked electron density profile produced by neutral beam fueling with low wall recycling. Transition from L mode to high T i mode has been studied in CHS. The central ion temperature in the high T i mode discharges reaches to 1 keV which is 2.5 times higher than that in the L mode discharges. The ion thermal diffusivity is significantly reduced by a factor of more than 2-3 in the high T i mode plasma. The ion loss cone is observed in neutral particle flux in the energy range of 1-6 keV with a narrow range of pitch angle (90±10 degree) in the high T i mode. However, the degradation of ion energy confinement due to this loss cone is negligible. (author)

Extremely confined gap surface-plasmon modes excited by electrons

DEFF Research Database (Denmark)

Raza, Søren; Stenger, Nicolas; Pors, Anders Lambertus

2014-01-01

High-spatial and energy resolution electron energy-loss spectroscopy (EELS) can be used for detailed characterization of localized and propagating surface-plasmon excitations in metal nanostructures, giving insight into fundamental physical phenomena and various plasmonic effects. Here, applying...... EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface-plasmon (GSP) modes excited by swift electrons in nanometre-wide gaps. We reveal the resonance behaviour associated with the excitation of the antisymmetric GSP mode for extremely small gap widths, down to ~5...... mode exploited in plasmonic waveguides with extreme light confinement is a very important factor that should be taken into account in the design of nanoplasmonic circuits and devices....

Discovery of stationary operation of quiescent H-mode plasmas with net-zero neutral beam injection torque and high energy confinement on DIII-D

Energy Technology Data Exchange (ETDEWEB)

Burrell, K. H.; Chen, X.; Garofalo, A. M.; Groebner, R. J.; Muscatello, C. M.; Osborne, T. H.; Petty, C. C.; Snyder, P. B. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Barada, K.; Rhodes, T. L.; Zeng, L. [University of California-Los Angeles, Los Angeles, California 90024 (United States); Solomon, W. M. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Yan, Z. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2016-05-15

Recent experiments in DIII-D [J. L. Luxon et al., in Plasma Physics and Controlled Nuclear Fusion Research 1996 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] have led to the discovery of a means of modifying edge turbulence to achieve stationary, high confinement operation without Edge Localized Mode (ELM) instabilities and with no net external torque input. Eliminating the ELM-induced heat bursts and controlling plasma stability at low rotation represent two of the great challenges for fusion energy. By exploiting edge turbulence in a novel manner, we achieved excellent tokamak performance, well above the H{sub 98y2} international tokamak energy confinement scaling (H{sub 98y2} = 1.25), thus meeting an additional confinement challenge that is usually difficult at low torque. The new regime is triggered in double null plasmas by ramping the injected torque to zero and then maintaining it there. This lowers E × B rotation shear in the plasma edge, allowing low-k, broadband, electromagnetic turbulence to increase. In the H-mode edge, a narrow transport barrier usually grows until MHD instability (a peeling ballooning mode) leads to the ELM heat burst. However, the increased turbulence reduces the pressure gradient, allowing the development of a broader and thus higher transport barrier. A 60% increase in pedestal pressure and 40% increase in energy confinement result. An increase in the E × B shearing rate inside of the edge pedestal is a key factor in the confinement increase. Strong double-null plasma shaping raises the threshold for the ELM instability, allowing the plasma to reach a transport-limited state near but below the explosive ELM stability boundary. The resulting plasmas have burning-plasma-relevant β{sub N} = 1.6–1.8 and run without the need for extra torque from 3D magnetic fields. To date, stationary conditions have been produced for 2 s or 12 energy confinement times, limited only by external hardware constraints

The H-mode Pedestal and Edge Localized Modes in NSTX

International Nuclear Information System (INIS)

Maingi, R.; Fredrickson, E.D.; Menard, J.E.; Nishino, N.; Roquemore, A.L.; Sabbagh, S.A.; Tritz, K.

2004-01-01

The research program of the National Spherical Torus Experiment (NSTX) routinely utilizes the H-mode confinement regime to test and extend beta and pulse length limits. As in conventional aspect ratio tokamaks, NSTX observes a variety of edge localized modes (ELMs) in H-mode. Hence a significant part of the research program is dedicated to ELMs studies

Mean and oscillating plasma flows and turbulence interactions across the L-H confinement transition.

Science.gov (United States)

Conway, G D; Angioni, C; Ryter, F; Sauter, P; Vicente, J

2011-02-11

A complex interaction between turbulence driven E × B zonal flow oscillations, i.e., geodesic acoustic modes (GAMs), the turbulence, and mean equilibrium flows is observed during the low to high (L-H) plasma confinement mode transition in the ASDEX Upgrade tokamak. Below the L-H threshold at low densities a limit-cycle oscillation forms with competition between the turbulence level and the GAM flow shearing. At higher densities the cycle is diminished, while in the H mode the cycle duration becomes too short to sustain the GAM, which is replaced by large amplitude broadband flow perturbations. Initially GAM amplitude increases as the H-mode transition is approached, but is then suppressed in the H mode by enhanced mean flow shear.

Remarks on saturation of energy confinement in high density regime on LHD

International Nuclear Information System (INIS)

Yamada, Hiroshi; Morita, Shigeru; Murakami, Sadayoshi

2003-01-01

A study on energy confinement times in currentless helical plasmas has indicated a preferable density dependence like τ E ∝ n-bar e 0.5-0.6 . However, saturation of energy confinement time has been often observed during the density ramping-up phase by gas puffing in NBI heated plasmas in LHD. The power balance analysis indicates that the thermal diffusivity is improved by the increase in local density while the global energy confinement time loses the dependence on the density. The flat or hollow density profile, which is distinguished in the density-ramping phase, promotes a broad heat power deposition. This change explains the apparent contradiction between the density dependence of the thermal diffusivity and the global energy confinement time. This result suggests that central heating can maintain a favorable density dependence of the energy confinement time in the high density regime. (author)

Energy Confinement of both Ohmic and LHW Plasma on EAST

International Nuclear Information System (INIS)

Yang Yao; Gao Xiang

2011-01-01

Study on the characters of energy confinement in both Ohmic and lower hybrid wave (LHW) discharges on EAST is conducted and the linear Ohmic confinement (LOC), saturated ohmic confinement (SOC) and improved Ohmic confinement (IOC) regimes are investigated in this paper. It is observed that an improved confinement mode characterized by both a drop of D α line intensity and an increase in line average density can be triggered by a gas puffing pulse. (magnetically confined plasma)

Intermittency in the Scrape-off Layer of the National Spherical Torus Experiment During H-mode Confinement

International Nuclear Information System (INIS)

Maqueda, R.J.; Stotler, D.P.; Zweben, S.J.

2010-01-01

A gas puff imaging diagnostic is used in the National Spherical Tokamak Experiment (M. Ono, et al., Nucl. Fusion 40, 557 (2000)) to study the edge turbulence and intermittency present during H-mode discharges. In the case of low power Ohmic H-modes the suppression of turbulence/blobs is maintained through the duration of the (short lived) H-modes. Similar quiescent edges are seen during the early stages of H-modes created with the use of neutral beam injection. Nevertheless, as time progresses following the L-H transition, turbulence and blobs reappear although at a lower level than that typically seen during L-mode confinement. It is also seen that the time-averaged SOL emission profile broadens, as the power loss across the separatrix increases. These broad profiles are characterized by a large level of fluctuations and intermittent events.

Neoclassical tearing modes on ASDEX Upgrade: Improved scaling laws, high confinement at high βN and new stabilization experiments

International Nuclear Information System (INIS)

Guenter, S.; Gude, A.; Igochine, V.; Maraschek, M.; Sips, A.C.C.; Zohm, H.; Gantenbein, G.; Sauter, O.

2003-01-01

In this paper recent results on the physics of neoclassical tearing modes (NTMs) achieved on ASDEX Upgrade are reported. A scaling law for NTM decay has been found, showing that the minimum local bootstrap current density required for mode growth is proportional to the ion gyro radius. As this scaling law does not depend on the seed island size, and thus on the background MHD activity, it is more reliable than previously derived scaling laws for the NTM onset. Furthermore, the recently reported Frequently Interrupted Regime (FIR) is discussed. In this new regime (m,n) NTMs are characterized by frequent amplitude drops caused by interaction with (m+1,n+1) background MHD activity. Due to the resulting reduced time averaged island size this leads to lower confinement degradation compared to that caused by the usual NTMs. As shown here, the transition into this regime can actively be triggered by lowering the magnetic shear at the q=(m+1)/=(n+1) rational surface. Further investigations regard mechanisms to increase the β N value for NTM onset such as plasma shaping, seed island size and density profile control. Using these studies, a scenario with high β N (β N = 3:5) at high density (n/n GW = 0.83) and confinement (H 98(y,2) = 1.2) has been developed. Moreover, this scenario is characterized by type II ELM activity and thus by moderate heat load to the target plates. Finally, new NTM stabilization experiments are reported, demonstrating an increase in β N after NTM stabilization. (author)

Electron heat transport in shaped TCV L-mode plasmas

International Nuclear Information System (INIS)

Camenen, Y; Pochelon, A; Bottino, A; Coda, S; Ryter, F; Sauter, O; Behn, R; Goodman, T P; Henderson, M A; Karpushov, A; Porte, L; Zhuang, G

2005-01-01

Electron heat transport experiments are performed in L-mode discharges at various plasma triangularities, using radially localized electron cyclotron heating to vary independently both the electron temperature T e and the normalized electron temperature gradient R/L T e over a large range. Local gyro-fluid (GLF23) and global collisionless gyro-kinetic (LORB5) linear simulations show that, in the present experiments, trapped electron mode (TEM) is the most unstable mode. Experimentally, the electron heat diffusivity χ e is shown to decrease with increasing collisionality, and no dependence of χ e on R/L T e is observed at high R/L T e values. These two observations are consistent with the predictions of TEM simulations, which supports the fact that TEM plays a crucial role in electron heat transport. In addition, over the broad range of positive and negative triangularities investigated, the electron heat diffusivity is observed to decrease with decreasing plasma triangularity, leading to a strong increase of plasma confinement at negative triangularity

H-mode confinement properties close to the power threshold in ASDEX Upgrade

International Nuclear Information System (INIS)

Ryter, F; Fuchs, J; Schneider, W; Sips, A; Staebler, A; Stober, J

2008-01-01

Confinement properties close to the H-mode power threshold are studied in the ASDEX Upgrade tokamak. The results show that good confinement can be obtained close to the threshold with Type-I ELMs. The existence of Type-I ELMs does not necessarily require the heating power to be higher than the H-Mode power threshold, but it requires collisionality to be low enough. At higher collisionality Type-III ELMs replace the Type-I ELMs and confinement time is reduced by about 20%

Collective oscillations and coupled modes in confined microfluidic droplet arrays

Science.gov (United States)

Schiller, Ulf D.; Fleury, Jean-Baptiste; Seemann, Ralf; Gompper, Gerhard

Microfluidic droplets have a wide range of applications ranging from analytic assays in cellular biology to controlled mixing in chemical engineering. Ensembles of microfluidic droplets are interesting model systems for non-equilibrium many-body phenomena. When flowing in a microchannel, trains of droplets can form microfluidic crystals whose dynamics are governed by long-range hydrodynamic interactions and boundary effects. In this contribution, excitation mechanisms for collective waves in dense and confined microfluidic droplet arrays are investigated by experiments and computer simulations. We demonstrate that distinct modes can be excited by creating specific `defect' patterns in flowing droplet trains. While longitudinal modes exhibit a short-lived cascade of pairs of laterally displacing droplets, transversely excited modes form propagating waves that behave like microfluidic phonons. We show that the confinement induces a coupling between longitudinal and transverse modes. We also investigate the life time of the collective oscillations and discuss possible mechanisms for the onset of instabilities. Our results demonstrate that microfluidic phonons can exhibit effects beyond the linear theory, which can be studied particularly well in dense and confined systems. This work was supported by Deutsche Forschungsgemeinschaft under Grant No. SE 1118/4.

Transport processes in magnetically confined plasmas in the nonlinear regime.

Science.gov (United States)

Sonnino, Giorgio

2006-06-01

A field theory approach to transport phenomena in magnetically confined plasmas is presented. The thermodynamic field theory (TFT), previously developed for treating the generic thermodynamic system out of equilibrium, is applied to plasmas physics. Transport phenomena are treated here as the effect of the field linking the thermodynamic forces with their conjugate flows combined with statistical mechanics. In particular, the Classical and the Pfirsch-Schluter regimes are analyzed by solving the thermodynamic field equations of the TFT in the weak-field approximation. We found that, the TFT does not correct the expressions of the ionic heat fluxes evaluated by the neoclassical theory in these two regimes. On the other hand, the fluxes of matter and electronic energy (heat flow) is further enhanced in the nonlinear Classical and Pfirsch-Schluter regimes. These results seem to be in line with the experimental observations. The complete set of the electronic and ionic transport equations in the nonlinear Banana regime, is also reported. A paper showing the comparison between our theoretic results and the experimental observations in the JET machine is currently in preparation.

Investigation of fluctuations in the HDH and H* regime of Wendelstein 7-AS

International Nuclear Information System (INIS)

Baeumel, S.; Werner, A.; McCormick, K.

2003-01-01

The High Density H-Mode Regime was discovered in Island Divertor operation of the Wendelstein 7-AS (W7-AS)stellerator. This regime is characterized by low impurity, high-energy confinement times - up to twice the value of the International Stellarator Scaling ISS95 - and edge radiated power fractions of up to 90% in detached state. Regarding the enhanced impurity transport at good energy confinement there are similarities to the enhanced D α H-mode found on the Alcator C-Mod tokamak. In W7-AS studies were performed in order to compare the HDH regime with the classical ELM-free discharges (H * ). Although both regimes are similar in collisionality and have almost the same n e (r)- and T e (r)-profile shapes, the H * regime suffers a radiation collapse due to impurity accumulation. The short impurity confinement times in HDH discharges requires enhanced transport at the plasma edge. The cause is not clear and this contribution looks for similarities to the enhanced D α H-mode of Alcator C-Mod, that is, whether quasicoherent modes exist in W7-AS causing enhanced edge transport. Discharges with a variation of magnetic configurations, densities (up to 4.10 20 m -3 ) and powers (up to 3.2 MW absorbed) will be discussed with respect to the different behaviour of fluctuations. (orig.)

Local transport in Joint European Tokamak edge-localized, high-confinement mode plasmas with H, D, DT, and T isotopes

International Nuclear Information System (INIS)

Budny, R. V.; Ernst, D. R.; Hahm, T. S.; McCune, D. C.; Christiansen, J. P.; Cordey, J. G.; Gowers, C. G.; Guenther, K.; Hawkes, N.; Jarvis, O. N.

2000-01-01

The edge-localized, high-confinement mode regime is of interest for future Tokamak reactors since high performance has been sustained for long durations. Experiments in the Joint European Tokamak [M. Keilhacker , Nuclear Fusion 39, 209 (1999)] have studied this regime using scans with the toroidal field and plasma current varied together in H, D, DT, and T isotopes. The local energy transport in more than fifty of these plasmas is analyzed, and empirical scaling relations are derived for energy transport coefficients during quasi-steady state conditions using dimensionless parameters. Neither the Bohm nor gyro-Bohm expressions give the shapes of the profiles. The scalings with β and ν * are in qualitative agreement with Ion Temperature Gradient theory

Origin of the various beta dependences of ELMy H-mode confinement properties

International Nuclear Information System (INIS)

Takizuka, T; Urano, H; Takenaga, H; Oyama, N

2006-01-01

Dependence of the energy confinement in ELMy H-mode tokamak on the beta has been investigated for a long time, but a common conclusion has not been obtained so far. Recent non-dimensional transport experiments in JT-60U demonstrated clearly the beta degradation. A database for JT-60U ELMy H-mode confinement was assembled. Analysis of this database is carried out, and the strong beta degradation consistent with the above experiments is confirmed. Two subsets of ASDEX Upgrade and JET data in the ITPA H-mode confinement database are analysed to find the origin of the various beta dependences. The shaping of the plasma cross section, as well as the fuelling condition, affects the confinement performance. The beta dependence is not identical for different devices and conditions. The shaping effect, as well as the fuelling effect, is a possible candidate for causing the variation of beta dependence

Analysis of the H-mode density limit in the ASDEX upgrade tokamak using bolometry

Energy Technology Data Exchange (ETDEWEB)

Bernert, Matthias

2013-10-23

The high confinement mode (H-mode) is the operational scenario foreseen for ITER, DEMO and future fusion power plants. At high densities, which are favourable in order to maximize the fusion power, a back transition from the H-mode to the low confinement mode (L-mode) is observed. This H-mode density limit (HDL) occurs at densities on the order of, but below, the Greenwald density. In this thesis, the HDL is revisited in the fully tungsten walled ASDEX Upgrade tokamak (AUG). In AUG discharges, four distinct operational phases were identified in the approach towards the HDL. First, there is a stable H-mode, where the plasma density increases at steady confinement, followed by a degrading H-mode, where the core electron density is fixed and the confinement, expressed as the energy confinement time, reduces. In the third phase, the breakdown of the H-mode and transition to the L-mode, the overall electron density is fixed and the confinement decreases further, leading, finally, to an L-mode, where the density increases again at a steady confinement at typical L-mode values until the disruptive Greenwald limit is reached. These four phases are reproducible, quasi-stable plasma regimes and provide a framework in which the HDL can be further analysed. Radiation losses and several other mechanisms, that were proposed as explanations for the HDL, are ruled out for the current set of AUG experiments with tungsten walls. In addition, a threshold of the radial electric field or of the power flux into the divertor appears to be responsible for the final transition back to L-mode, however, it does not determine the onset of the HDL. The observation of the four phases is explained by the combination of two mechanisms: a fueling limit due to an outward shift of the ionization profile and an additional energy loss channel, which decreases the confinement. The latter is most likely created by an increased radial convective transport at the edge of the plasma. It is shown that the

Analysis of the H-mode density limit in the ASDEX upgrade tokamak using bolometry

International Nuclear Information System (INIS)

Bernert, Matthias

2013-01-01

The high confinement mode (H-mode) is the operational scenario foreseen for ITER, DEMO and future fusion power plants. At high densities, which are favourable in order to maximize the fusion power, a back transition from the H-mode to the low confinement mode (L-mode) is observed. This H-mode density limit (HDL) occurs at densities on the order of, but below, the Greenwald density. In this thesis, the HDL is revisited in the fully tungsten walled ASDEX Upgrade tokamak (AUG). In AUG discharges, four distinct operational phases were identified in the approach towards the HDL. First, there is a stable H-mode, where the plasma density increases at steady confinement, followed by a degrading H-mode, where the core electron density is fixed and the confinement, expressed as the energy confinement time, reduces. In the third phase, the breakdown of the H-mode and transition to the L-mode, the overall electron density is fixed and the confinement decreases further, leading, finally, to an L-mode, where the density increases again at a steady confinement at typical L-mode values until the disruptive Greenwald limit is reached. These four phases are reproducible, quasi-stable plasma regimes and provide a framework in which the HDL can be further analysed. Radiation losses and several other mechanisms, that were proposed as explanations for the HDL, are ruled out for the current set of AUG experiments with tungsten walls. In addition, a threshold of the radial electric field or of the power flux into the divertor appears to be responsible for the final transition back to L-mode, however, it does not determine the onset of the HDL. The observation of the four phases is explained by the combination of two mechanisms: a fueling limit due to an outward shift of the ionization profile and an additional energy loss channel, which decreases the confinement. The latter is most likely created by an increased radial convective transport at the edge of the plasma. It is shown that the

Unified approach for calculating the number of confined modes in multilayered waveguiding structures

Science.gov (United States)

Ruschin, S.; Griffel, G.; Hardy, A.; Croitoru, N.

1986-01-01

A general formalism is developed in order to find the number of modes and mode cutoff conditions in multilayer waveguiding structures. An explicit expression is presented for the number of confined modes that allows the modes to be counted without having to analyze the specific eigenvalue equation of the structure. The method is illustrated by its application to several structures: the buried layer, the directional coupler, and the three-guide symmetrical arrangement. By a suitable extension of the formalism, the number of well-confined modes is found for a four-layer structure.

Role of zonal flow predator-prey oscillations in triggering the transition to H-mode confinement.

Science.gov (United States)

Schmitz, L; Zeng, L; Rhodes, T L; Hillesheim, J C; Doyle, E J; Groebner, R J; Peebles, W A; Burrell, K H; Wang, G

2012-04-13

Direct evidence of zonal flow (ZF) predator-prey oscillations and the synergistic roles of ZF- and equilibrium E×B flow shear in triggering the low- to high-confinement (L- to H-mode) transition in the DIII-D tokamak is presented. Periodic turbulence suppression is first observed in a narrow layer at and just inside the separatrix when the shearing rate transiently exceeds the turbulence decorrelation rate. The final transition to H mode with sustained turbulence and transport reduction is controlled by equilibrium E×B shear due to the increasing ion pressure gradient.

Deuterium-tritium plasmas in novel regimes in the Tokamak Fusion Test Reactor

International Nuclear Information System (INIS)

Bell, M.G.; Beer, M.

1997-02-01

Experiments in the Tokamak Fusion Test Reactor (TFTR) have explored several novel regimes of improved tokamak confinement in deuterium-tritium (D-T) plasmas, including plasmas with reduced or reversed magnetic shear in the core and high-current plasmas with increased shear in the outer region (high-l i ). New techniques have also been developed to enhance the confinement in these regimes by modifying the plasma-limiter interaction through in-situ deposition of lithium. In reversed-shear plasmas, transitions to enhanced confinement have been observed at plasma currents up to 2.2 MA (q a ∼ 4.3), accompanied by the formation of internal transport barriers, where large radial gradients develop in the temperature and density profiles. Experiments have been performed to elucidate the mechanism of the barrier formation and its relationship with the magnetic configuration and with the heating characteristics. The increased stability of high-current, high-l i plasmas produced by rapid expansion of the minor cross-section, coupled with improvement in the confinement by lithium deposition has enabled the achievement of high fusion power, up to 8.7 MW, with D-T neutral beam heating. The physics of fusion alpha-particle confinement has been investigated in these regimes, including the interactions of the alphas with endogenous plasma instabilities and externally applied waves in the ion cyclotron range of frequencies. In D-T plasmas with q 0 > 1 and weak magnetic shear in the central region, a toroidal Alfven eigenmode instability driven purely by the alpha particles has been observed for the first time. The interactions of energetic ions with ion Bernstein waves produced by mode-conversion from fast waves in mixed-species plasmas have been studied as a possible mechanism for transferring the energy of the alphas to fuel ions

L-H Power Threshold, Pedestal Stability and Confinement in JET with a Metallic Wall

Energy Technology Data Exchange (ETDEWEB)

Beurskens, M.; Alper, B.; Challis, C.; Flanagan, J.; Giroud, C.; Kempenaars, M.; Lomas, P.; Maslov, M.; Matthews, G.; Mayoral, M. L.; Snyder, P. B.; Saarelma, S., E-mail: marc.beurskens@ccfe.ac.uk [EURATOM /CCFE Fusion Association, Culham Science Centre, Abingdon (United Kingdom); Frassinetti, L. [Division of Fusion Plasma Physics, Association EURATOM-VR , Stockholm (Sweden); Maggi, C.; Angioni, C.; Hobirk, J.; Neu, R. [IPP Garching, Garching (Germany); Calabro, G.; Buratti, P.; Giovannozzi, E. [Associazione EURATOM-ENEA sulla Fusione, Frascati (Italy); Bourdelle, C.; Joffrin, E. [Association Euratom-CEA, IRFM, St-Paul-Lez-Durance (France); Brezinsek, S. [Forschungszentrum Juelich, Juelich (Germany); Groth, M. [Association EURATOM/Helsinki University of Technology, Espoo (Finland); Leyland, M. [Department of Physics, University of York, Heslington, York (United Kingdom); De la Luna, E. [Ciemat, Madrid (Spain); Mantica, P. [Istituto di Fisica del Plasma ' P. Caldirola' , Milano (Italy); Nunes, I. [Centro de Fusao Nuclear, Associacao EURATOM-IST, Lisboa (Portugal); Osborne, T. [General Atomics, San Diego (United States); De Vries, P. [FOM DIFFER, Nieuwegein (Netherlands)

2012-09-15

Full text: After the change-over from the Carbon-Fibre Composite (CFC) wall to an ITER-like metallic wall (ILW) the baseline type I ELMy H-mode scenario has been re-established in JET with the new plasma-facing materials Be and W. A key finding for ITER is that the power required to enter H-mode has reduced with respect to that in JET with the CFC wall. In JET with the ILW the power threshold to enter H-mode (P{sub L-H}) is below the international L-H power threshold scaling P{sub Martin-08}. The minimum threshold is P{sub L-H} = 1.8 MW compared to P{sub Martin-08} = 4 MW with a pedestal density of n{sub ped} = 2 x 10{sup 19} m{sup -3} in plasmas with I{sub p} = 2.0 MA, B{sub t} = 2.4 T. However the threshold depends strongly on density; using slow ion cyclotron heating (ICRH) power ramps P{sub L-H} varies from 1.8 to 4.5 MW in a range of lower and upper plasma triangularity ({delta}{sub L} = 0.32 - 0.4, {delta}{sub U} = 0.19 - 0.38). Stationary Type I ELMy H-mode operation has been re-established at both low and high triangularity with I{sub p} {<=} 2.5 MA, q{sub 95} = 2.8 - 3.6 and H{sub 98} {<=} 1. The achieved plasma collisionality is relatively high, in the range of 1 < v{sub eff} < 4 due to the required strong gas dosing. Stability analysis with the linear MHD stability code ELITE show that the pedestal is marginally unstable with respect to the Peeling Ballooning boundary. Due to the stabilising effect of the global pressure on the pedestal stability, a strong coupling between core and edge confinement is expected. Indeed in an H-mode profile database comparison with 119 CFC- (0.1 < v{sub eff} < 1) and 40 ILW-H-modes a strong coupling of the core versus edge confinement is found, independent of wall material. In addition, the pedestal predictions using the EPED predictive pedestal code coincide with the measured pedestal height over a wide range of normalised pressure 1.5 < {beta}{sub N} < 3.5. Due to the strong core-edge coupling, beneficial effects of core

Theory-based transport simulations of TFTR L-mode temperature profiles

International Nuclear Information System (INIS)

Bateman, G.

1991-01-01

The temperature profiles from a selection of TFTR L-mode discharges are simulated with the 1-1/2-D BALDUR transport code using a combination of theoretically derived transport models, called the Multi-Mode Model. The present version of the Multi-Mode Model consists of effective thermal diffusivities resulting from trapped electron modes and ion temperature gradient (η i ) modes, which dominate in the core of the plasma, together with resistive ballooning modes, which dominate in the periphery. Within the context of this transport model and the TFTR simulations reported here, the scaling of confinement with heating power comes from the temperature dependence of the η i and trapped electron modes, while the scaling with current comes mostly from resistive ballooning modes. 24 refs., 16 figs., 3 tabs

Expression for the thermal H-mode energy confinement time under ELM-free conditions

International Nuclear Information System (INIS)

Ryter, F.; Gruber, O.; Kardaun, O.J.W.F.; Menzler, H.P.; Wagner, F.; Schissel, D.P.; DeBoo, J.C.; Kaye, S.M.

1992-07-01

The design of future tokamaks, which are supposed to reach ignition with the H-mode, requires a reliable scaling expression for the H-mode energy confinement time. In the present work, an H-mode scaling expression for the thermal plasma energy confinement time has been developed by combining data from four existing divertor tokamaks, ASDEX, DIII-D, JET and PBX-M. The plasma conditions, which were as similar as possible to ensure a coherent set of data, were ELM-free deuterium discharges heated by deuterium neutral beam injection. By combining four tokamaks, the parametric dependence of the thermal energy confinement on the main plasma parameters, including the three main geometrical variables, was determined. (orig./WL)

Coupling of an ICRF compact loop antenna to H-mode plasmas in DIII-D

International Nuclear Information System (INIS)

Mayberry, M.J.; Baity, F.W.; Hoffman, D.J.; Luxon, J.L.; Owens, T.L.; Prater, R.

1987-01-01

Low power coupling tests have been carried out with a prototype ICRF compact loop antenna on the DIII-D tokamak. During neutral-beam-heated L-mode discharges the antenna loading is typically R≅1-2Ω for an rf frequency of 32 MHz (B/sub T/ = 21 kG, ω = 2Ω/sub D/(0)). When a transition into the H-mode regime of improved confinement occurs, the loading drops to R≅0.5-1.0Ω. During ELMs, transient increases in loading up to several Ohms are observed. The apparent sensitivity of ICRF antenna coupling to changes in the edge plasma profiles associated with the H-mode regime could have important implications for the design of future high power systems

Characteristics of the First H-mode Discharges in NSTX

International Nuclear Information System (INIS)

Maingi, R.; Bell, M.G.; Bell, R.E.; Bush, C.E.; Fredrickson, E.D.; Gates, D.A.; Kaye, S.M.; Kugel, H.W.; LeBlanc, B.P.; Menard, J.E.; Mueller, D.; Sabbagh, S.A.; Stutman, D.; Taylor, G.; Johnson, D.W.; Kaita, R.; Maqueda, R.J.; Ono, M.; Paoletti, F.; Peng, Y-K.M.; Roquemore, A.L.; Skinner, C.H.; Soukhanovskii, V.A.; Synakowski, E.J.

2001-01-01

We report observations of the first low-to-high (L-H) confinement mode transitions in the National Spherical Torus Experiment (NSTX). The H-mode energy confinement time increased over reference L-mode discharges transiently by 100-300%, as high as ∼150 ms. This confinement time is ∼1.8-2.3 times higher than predicted by a multi-machine ELM-free H-mode scaling. This achievement extends the H-mode window of fusion devices down to a record low aspect ratio (R/a) ∼ 1.3, challenging both confinement and L-H power thresholds scalings based on conventional aspect ratio tokamaks

The Physics Basis of ITER Confinement

International Nuclear Information System (INIS)

Wagner, F.

2009-01-01

ITER will be the first fusion reactor and the 50 year old dream of fusion scientists will become reality. The quality of magnetic confinement will decide about the success of ITER, directly in the form of the confinement time and indirectly because it decides about the plasma parameters and the fluxes, which cross the separatrix and have to be handled externally by technical means. This lecture portrays some of the basic principles which govern plasma confinement, uses dimensionless scaling to set the limits for the predictions for ITER, an approach which also shows the limitations of the predictions, and describes briefly the major characteristics and physics behind the H-mode--the preferred confinement regime of ITER.

Banana fluxes in the plateau regime for a nonaxisymmetrically confined plasma

International Nuclear Information System (INIS)

Balescu, R.; Fantechi, S.

1990-01-01

The banana (or banana-plateau) fluxes, related to the generalized stresses left-angle B·∇·π α(n) right-angle, left-angle B T ·∇·π α(n) right-angle have been determined in the plateau regime, for a plasma confined by a toroidal magnetic field of arbitrary geometry. The complete set of transport coefficients for both the ''parallel'' (ambipolar) and ''toroidal'' (nonambipolar) banana fluxes was obtained in the 13-moment (13M) approximation, going beyond the previously known expressions in the nonaxisymmetric case. The main emphasis is laid on the structure of the transport matrix and of its coefficients. It is shown that the Onsager symmetry of this matrix partly breaks down (for the mixed electron--ion coefficients) in a nonaxisymmetrically confined plasma

Observation of the L-H confinement bifurcation triggered by a turbulence-driven shear flow in a tokamak plasma.

Science.gov (United States)

Yan, Z; McKee, G R; Fonck, R; Gohil, P; Groebner, R J; Osborne, T H

2014-03-28

Comprehensive 2D turbulence and eddy flow velocity measurements on DIII-D demonstrate a rapidly increasing turbulence-driven shear flow that develops ∼100  μs prior to the low-confinement (L mode) to high-confinement (H mode) transition and appears to trigger it. These changes are localized to a narrow layer 1-2 cm inside the magnetic boundary. Increasing heating power increases the Reynolds stress, the energy transfer from turbulence to the poloidal flow, and the edge flow shearing rate that then exceeds the decorrelation rate, suppressing turbulence and triggering the transition.

Observation of an improved energy-confinement regime in neutral-beam--heated divertor discharges in the DIII-D tokamak

International Nuclear Information System (INIS)

Burrell, K.H.; Ejima, S.; Schissel, D.P.

1987-01-01

Tokamak discharges using the expanded boundary divertor in the DIII-D device exhibit H-mode confinement. With neutral-beam power up to 6 MW, energy confinement remains comparable to the Ohmic value at a plasma current of 1 MA. Confinement is also independent of plasma density and toroidal field. Confinement increases with plasma current, but the exact functional dependence is, as yet, uncertain. These results show that the H mode can be achieved in a reactor-compatible open divertor configuration

Pellet fuelling and ELMy H-mode physics at JET

International Nuclear Information System (INIS)

Horton, L.D.

2001-01-01

As the reference operating regime for ITER, investigations of the ELMy H-mode have received high priority in the JET experimental programme. Recent experiments have concentrated in particular on operation simultaneously at high density and high confinement using high field side (HFS) pellet launch. The enhanced fuelling efficiency of HFS pellet fuelling is found to scale favourably to a large machine such as JET. The achievable density of ELMy H-mode plasmas in JET has been significantly increased using HFS fuelling although at the expense of confinement degradation back to L-mode levels. Initial experiments using control of the pellet injection frequency have shown that density and confinement can simultaneously be increased close to the values necessary for ITER. The boundaries of the available ELMy H-mode operational space have also been extensively explored. The power necessary to maintain the high confinement normally associated with ELMy H-mode operation is found to be substantially higher than the H-mode threshold power. The compatibility of ELMy H-modes with divertor operation acceptable for a fusion device has been studied. Narrow energy scrape-off widths are measured which place stringent limits on divertor power handling. Deuterium and tritium codeposition profiles are measured to be strongly in/out asymmetric. Successful modelling of these profiles requires the inclusion of the (measured) scrape-off layer flows and of the production in the divertor of hydrocarbon molecules with sticking coefficients below unity. Helium exhaust and compression are found to be within the limits sufficient for a reactor. (author)

The relationship between turbulence measurements and transport in different heating regimes in TFTR

International Nuclear Information System (INIS)

Bretz, N.L.; Mazzucato, E.; Nazikian, R.; Paul, S.F.; Hammett, G.; Rewoldt, G.; Tang, W.M.; Zarnstorff, M.C.

1992-01-01

The scaling of broad band density fluctuations in the confinement zone of TFTR measured by microwave scattering, beam emission spectroscopy (BES), and reflectometry show a relationship between these fluctuations and energy transport measured from power balance calculations. In L-mode plasmas scattering and BES indicates that the density fluctuation level, δn 2 , in the confinement zone for 0.2 aux and I p in a way that is consistent with variations in energy transport. Fluctuation levels measured with all systems increase strongly toward the edge in all heating regimes following increases in energy transport coefficients. Measurements using BES have shown that poloidal and radial correlation lengths in the confinement zone of L-mode and supershot plasmas fall in the range of 1 to 2 cm. with a wave structure which has k max ∼ 1 cm -1 (k perpendicular ps ∼ 0.2) in the poloidal direction and k max approaching zero in the radial direction. A simple estimate of the diffusion coefficient based on a measured radial correlation length and correlation time indicates good agreement with power balance calculations. Similar estimates using reflectometry give radial coherence lengths at 10 to 20 kHz in low density ohmic and supershot plasmas of between I and 2 cm

Random nanolasing in the Anderson localized regime

DEFF Research Database (Denmark)

Liu, Jin; Garcia, P. D.; Ek, Sara

2014-01-01

The development of nanoscale optical devices for classical and quantum photonics is affected by unavoidable fabrication imperfections that often impose performance limitations. However, disorder may also enable new functionalities, for example in random lasers, where lasing relies on random...... multiple scattering. The applicability of random lasers has been limited due to multidirectional emission, lack of tunability, and strong mode competition with chaotic fluctuations due to a weak mode confinement. The regime of Anderson localization of light has been proposed for obtaining stable multimode...... random lasing, and initial work concerned macroscopic one-dimensional layered media. Here, we demonstrate on-chip random nanolasers where the cavity feedback is provided by the intrinsic disorder. The strong confinement achieved by Anderson localization reduces the spatial overlap between lasing modes...

VH mode accessibility and global H-mode properties in previous and present JET configurations

Energy Technology Data Exchange (ETDEWEB)

Jones, T T.C.; Ali-Arshad, S; Bures, M; Christiansen, J P; Esch, H P.L. de; Fishpool, G; Jarvis, O N; Koenig, R; Lawson, K D; Lomas, P J; Marcus, F B; Sartori, R; Schunke, B; Smeulders, P; Stork, D; Taroni, A; Thomas, P R; Thomsen, K [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking

1994-07-01

In JET VH modes, there is a distinct confinement transition following the cessation of ELMs, observed in a wide variety of tokamak operating conditions, using both NBI and ICRF heating methods. Important factors which influence VH mode accessibility such as magnetic configuration and vessel conditions have been identified. The new JET pumped divertor configuration has much improved plasma shaping control and power and particle exhaust capability and should permit exploitation of plasmas with VH confinement properties over an even wider range of operating regimes, particularly at high plasma current; first H-modes have been obtained in the 1994 JET operating period and initial results are reported. (authors). 7 refs., 6 figs.

Analysis of tokamak plasma confinement modes using the fast Fourier transformation

International Nuclear Information System (INIS)

Mirmoeini, S.R.; Salar Elahi, A.; Ghoranneviss, M.

2016-01-01

The Fourier analysis is a satisfactory technique for detecting plasma confinement modes in tokamaks. The confinement mode of tokamak plasma was analysed using the fast Fourier transformation (FFT). For this purpose, we used the data of Mirnov coils that is one of the identifying tools in the IR-T1 tokamak, with and without external field (electric biasing), and then compared it with each other. After the Fourier analysis of Mirnov coil data, the diagram of power spectrum density was depicted in different angles of Mirnov coils in the 'presence of external field' as well as in the 'absence of external field'. The power spectrum density (PSD) interprets the manner of power distribution of a signal with frequency. In this article, the number of plasma modes and the safety factor q were obtained by using the mode number of q = m/n (m is the mode number). The maximum MHD activity was obtained in 30-35 kHz frequency, using the density of the energy spectrum. In addition, the number of different modes across 0-35 ms time was compared with each other in the presence and absence of the external field. (author)

Confinement of acoustical modes due to the electron-phonon interaction within 2D-electron gas

International Nuclear Information System (INIS)

Kochelap, V.A.; Gulseren, O.

1992-09-01

We study the confinement of acoustical modes within 2DEG due only to the electron-phonon interaction. The confined modes split out from the bulk phonons even at uniform lattice parameters, when the 2DEG is created by means of modulation doping. The effect is more pronounced when the wave vector q of the modes increases and is maximum at q = 2 k F (k F is the Fermi wave vector). In the case of several electron sheets the additional features of the confinement effect appear. In the limit of the strong electron-phonon coupling and high surface concentration of the electrons the considered system can suffer Peierls-type phase transition. In this case periodical deformation of the lattice and charge density wave are confined within the electron sheet. (author). 18 refs, 2 figs

Offset linear scaling for H-mode confinement

International Nuclear Information System (INIS)

Miura, Yukitoshi; Tamai, Hiroshi; Suzuki, Norio; Mori, Masahiro; Matsuda, Toshiaki; Maeda, Hikosuke; Takizuka, Tomonori; Itoh, Sanae; Itoh, Kimitaka.

1992-01-01

An offset linear scaling for the H-mode confinement time is examined based on single parameter scans on the JFT-2M experiment. Regression study is done for various devices with open divertor configuration such as JET, DIII-D, JFT-2M. The scaling law of the thermal energy is given in the MKSA unit as W th =0.0046R 1.9 I P 1.1 B T 0.91 √A+2.9x10 -8 I P 1.0 R 0.87 P√AP, where R is the major radius, I P is the plasma current, B T is the toroidal magnetic field, A is the average mass number of plasma and neutral beam particles, and P is the heating power. This fitting has a similar root mean square error (RMSE) compared to the power law scaling. The result is also compared with the H-mode in other configurations. The W th of closed divertor H-mode on ASDEX shows a little better values than that of open divertor H-mode. (author)

Integrated core-SOL simulations of L-mode plasma in ITER and Indian demo

International Nuclear Information System (INIS)

Wisitsorasak, Apiwat; Onjun, Thawatchai; Kanjanaput, Wittawat

2015-01-01

Core-SOL simulations are carried out using 1.5D BALDUR integrated predictive modeling code to investigate tokamak plasma in ITER and Indian DEMO reactors operating in low confinement mode (L-Mode). In each simulation, the plasma current, temperature, and density profiles in both core and SOL region are evolved self-consistency. The SOL is simulated by integrating the fluid equations, including sources, along the field lines. The solutions in SOL subsequently provide as the boundary conditions of core plasma region on low-confinement mode. The core plasma transport model is described using a combination of anomalous transport by Multi-Mode-Model version 2001 (MMM2001) and neoclassical transport calculated by NCLASS module together with the toroidal velocity based on the torque due to Neoclassical Toroidal Viscosity (NTV). In addition, a sensitivity analysis is explored by varying plasma parameters, such as plasma density and auxiliary heating power. Furthermore, the ignition tests are conducted to observed plasma response in each design after shutting down an auxiliary heating. (author)

Changes in core electron temperature fluctuations across the ohmic energy confinement transition in Alcator C-Mod plasmas

International Nuclear Information System (INIS)

Sung, C.; White, A.E.; Howard, N.T.; Oi, C.Y.; Rice, J.E.; Gao, C.; Ennever, P.; Porkolab, M.; Parra, F.; Ernst, D.; Walk, J.; Hughes, J.W.; Irby, J.; Kasten, C.; Hubbard, A.E.; Greenwald, M.J.; Mikkelsen, D.

2013-01-01

The first measurements of long wavelength (k y ρ s < 0.3) electron temperature fluctuations in Alcator C-Mod made with a new correlation electron cyclotron emission diagnostic support a long-standing hypothesis regarding the confinement transition from linear ohmic confinement (LOC) to saturated ohmic confinement (SOC). Electron temperature fluctuations decrease significantly (∼40%) crossing from LOC to SOC, consistent with a change from trapped electron mode (TEM) turbulence domination to ion temperature gradient (ITG) turbulence as the density is increased. Linear stability analysis performed with the GYRO code (Candy and Waltz 2003 J. Comput. Phys. 186 545) shows that TEMs are dominant for long wavelength turbulence in the LOC regime and ITG modes are dominant in the SOC regime at the radial location (ρ ∼ 0.8) where the changes in electron temperature fluctuations are measured. In contrast, deeper in the core (ρ < 0.8), linear stability analysis indicates that ITG modes remain dominant across the LOC/SOC transition. This radial variation suggests that the robust global changes in confinement of energy and momentum occurring across the LOC/SOC transition are correlated to local changes in the dominant turbulent mode near the edge. (paper)

H-modes studies in PDX

International Nuclear Information System (INIS)

Fonck, R.J.; Beirsdorfer, P.; Bell, M.

1984-07-01

A regime of enhanced energy confinement during neutral beam heating has been obtained routinely in the PDX tokamak after modifications to form a closed divertor geometry. Plasma density profiles were broad and the electron temperature at the plasma edge reached values of approx. 400 eV in the H-mode phase of a discharge. A comparison of closed divertor discharges with moderate and intense gas puffing indicates that a requirement for obtaining high confinement times is the localization of the plasma fueling source in the divertor throat region. While high confinement was attained at moderate injected powers (P/sub INJ/ less than or equal to 3 MW), confinement was degraded at higher powers due to both increased edge instabilities and, especially, the intense gas puffing needed to prevent disruptions. Initial results with a particle scoop limiter indicate high particle confinement times and energy confinement times approaching those of diverted H-mode plasmas

Transition to the improved confinement mode in torsatron U-3M in range of rare collision frequencies

International Nuclear Information System (INIS)

Pashnev, V.K.; Sorokovov, E.L.; Berezhnyj, V.L. and others

2010-01-01

Transition to the mode of improved plasma confinement in U-3M facility earlier was discussed in works [1-3]. In these studies discussed the various processes in the confinement volume and in the peripheral plasma that accompany the transition process. Study of plasma confinement and process of transition into the mode of improved confinement just at rare collisions between plasma particles is very important because future fusion reactor based on a toroidal magnetic trap will operate under plasma parameters with rare collision frequencies ('banana' mode). The peculiarity of experiments on torsatron U-3M is that they are conducted at small density n-bar e ≤ 2 lover case x 10 12 cm -3 and, thereby, the frequency of collisions in the confinement area is in the 'banana' mode [4]. And herewith, time of collisions is essentially smaller (up to several orders for electrons and up to the order for ions) than the lifetime of plasma particles. It ensures maxwellization of distribution function and possibility to compare the obtained results with data from other experiments. The objective of this work is to study the main regularity of transition into the mode of improved confinement. Also it is interesting to compare the results with data from other facilities.

Influence of an external gas puff on the RI-mode confinement properties in TEXTOR

International Nuclear Information System (INIS)

Kalupin, D.

2002-06-01

An actual subject of experimental and theoretical studies in present day fusion research is the development of an operational scenario combining simultaneously high confinement, with at least H-mode quality, and high densities, around or above the empirical Greenwald limit. Recently, this subject was studied in TEXTOR radiative improved (RI) mode discharges, in which the seeding of a small amount of impurities is helpful in a transition to the improved confinement stage. It was found that by the careful tailoring of external fuelling and optimisation of the wall conditions it is possible to maintain the H-mode or even higher quality confinement at densities much above Greenwald density limit. However, more intense fuelling, aimed to extend maximal achievable densities, led to the progressive confinement deterioration. The theory explains the transition to the RI-mode as a bifurcation into the stage where the transport governed by the ion temperature gradient (ITG) instability is significantly reduced due to a high density gradient and high value of the effective charge. The numerical studies of an influence of the gas puff intensity on confinement properties of plasma, done with the help of the 1-D transport code RITM, show that the same theory can be used for an explanation of the confinement rollover triggered by a strong gas puff. The code was modified in order to simulate the effect of the gas puff on the confinement properties. The anomalous transport coefficients in the plasma core include contributions from the ITG and dissipative trapped electron (DTE) instabilities. The transport at the plasma edge under RI-mode conditions might be described by the electrostatic turbulence caused by electric currents in the scrape-off layer of the limiter. The present computations show that this assumption for the edge transport does not allow the modeling of an effect of the gas puff intensity on the profiles evolution in agreement with experimental observations. The

Investigation of the Energy Confinement in Ohmic and LHCD Plasmas in HT-7

International Nuclear Information System (INIS)

Zhang Xiaoqing; Wan Baonian; Shen Biao; Hu Xiwei; Qian Jinping; Fan Hengyu; Ding Yonghua

2006-01-01

Investigation of the energy confinement in ohmic and lower hybrid current drive (LHCD) plasmas in HT-7 has been performed. In ohmic discharges at low densities the global energy confinement time τ E increases almost linearly with the density, saturates at a critical density (2.5 x 10 13 /cm 3 for HT-7) and is nearly constant at higher densities. The energy confinement time is in good agreement with the Neo-Alcator scaling law at different densities and currents. In the LHCD plasmas the global energy confinement time similar to that of the L-mode discharges has been observed to be in good agreement with the low confinement mode (L mode) scaling law of ITER89-P in higher electron density and plasma current

Turbulence at the transition to the high density H-mode in Wendelstein 7-AS plasmas

DEFF Research Database (Denmark)

Basse, N.P.; Zoletnik, S.; Baumel, S.

2003-01-01

Recently a new improved confinement regime was found in the Wendelstein 7-AS (W7-AS) stellarator (Renner H. et al 1989 Plasma Phys. Control. Fusion 31 1579). The discovery of this high density high confinement mode (HDH-mode) was facilitated by the installation of divertor modules. In this paper,...

Theoretical investigation of flute modes in a magnetic quadrupole

International Nuclear Information System (INIS)

Wu, H.S.

1988-01-01

This research developed theories and conducted numerical investigations of electrostatic flute modes in a plasma confined in a magnetic quadrupole. Chapter I presents the discussion of relevant background. Chapter II contains a brief discussion of the basic flute-mode operator L 0 for intermediate- and low-frequency regimes. Chapter III develops a simple theory for a flute mode with frequency between the electron and ion bounce frequencies in the uniform density and temperature regions of a magnetic quadrupole. The frequency is predicted to be inversely proportional to the wave number. Chapter IV describes the kinetic approach. Chapter V contains the derivation of an eigenvalue equation for electrostatic waves with frequencies below the ion frequency in the private flux region of a magnetic quadrupole. Chapter VI develops a theory for electrostatic waves with frequency below the ion bounce frequency in the shared flux region of a magnetic quadrupole. Chapter VII contains the derivation of a dispersion equation for flute modes with frequencies between the electron and ion bounce frequencies in a plasma confined to a magnetic quadrupole. Chapter VIII presents a summary of the research described

Confinement and exhaust in the Mega Ampere Spherical Tokamak

International Nuclear Information System (INIS)

Counsell, G F; Ahn, J-W; Akers, R; Arends, E; Buttery, R; Field, A R; Gryaznevich, M; Helander, P; Kirk, A; Meyer, H; Valovic, M; Wilson, H R; Yang, Y

2002-01-01

The Mega Ampere Spherical Tokamak (MAST) is now accessing regimes with high normalized confinement relative to international scalings, H H (IPB98(y, 2))>1 at high normalized density, n-bar e >60% of the Greenwald density. Data from MAST H-modes suggest that the aspect ratio dependency of international confinement and L-H threshold scalings may need to be modified to improve predictions for ITER. Access to H-mode on MAST is strongly affected by both the divertor magnetic geometry and fuelling location, with the formation of an edge transport barrier being facilitated by operation near the symmetric, connected double-null configuration and with poloidally localized inboard gas puffing. The ELMs on MAST appear to be Type III in nature, even in the highest performance plasmas and with the maximum available auxiliary heating power. ELM energy losses are less than 4% of stored energy in all regimes so far explored. These Type III ELMs are associated with a reduction in the pedestal density but no significant change in the pedestal temperature or temperature profile, indicating that energy is convected from the pedestal region into the scrape-off layer. Analysis of the energy observed to arrive at the divertor targets indicates that ELM losses are predominantly on the low field side. ELM effluxes are observed up to 20 cm from the plasma edge at the outboard mid-plane and are associated with the radial motion of a feature at an average velocity of 1.2 km s -1

Learning on probabilistic manifolds in massive fusion databases: Application to confinement regime identification

International Nuclear Information System (INIS)

Verdoolaege, Geert; Van Oost, Guido

2012-01-01

Highlights: ► We present an integrated framework for pattern recognition in fusion data. ► We model measurement uncertainty through an appropriate probability distribution. ► We use the geodesic distance on probabilistic manifolds as a similarity measure. ► We apply the framework to confinement mode classification. ► The classification accuracy benefits from uncertainty information and its geometry. - Abstract: We present an integrated framework for (real-time) pattern recognition in fusion data. The main premise is the inherent probabilistic nature of measurements of plasma quantities. We propose the geodesic distance on probabilistic manifolds as a similarity measure between data points. Substructure induced by data dependencies may further reduce the dimensionality and redundancy of the data set. We present an application to confinement mode classification, showing the distinct advantage obtained by considering the measurement uncertainty and its geometry.

Impurity toroidal rotation and transport in Alcator C-Mod ohmic high confinement mode plasmas

International Nuclear Information System (INIS)

Rice, J. E.; Goetz, J. A.; Granetz, R. S.; Greenwald, M. J.; Hubbard, A. E.; Hutchinson, I. H.; Marmar, E. S.; Mossessian, D.; Pedersen, T. Sunn; Snipes, J. A.

2000-01-01

Central toroidal rotation and impurity transport coefficients have been determined in Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] Ohmic high confinement mode (H-mode) plasmas from observations of x-ray emission following impurity injection. Rotation velocities up to 3x10 4 m/sec in the co-current direction have been observed in the center of the best Ohmic H-mode plasmas. Purely ohmic H-mode plasmas display many characteristics similar to ion cyclotron range of frequencies (ICRF) heated H-mode plasmas, including the scaling of the rotation velocity with plasma parameters and the formation of edge pedestals in the electron density and temperature profiles. Very long impurity confinement times (∼1 sec) are seen in edge localized mode-free (ELM-free) Ohmic H-modes and the inward impurity convection velocity profile has been determined to be close to the calculated neoclassical profile. (c) 2000 American Institute of Physics

Optimized profiles for improved confinement and stability in the DIII-D tokamak

International Nuclear Information System (INIS)

Taylor, T.S.; St. John, H.; Turnbull, A.D.

1995-02-01

Simultaneous achievement of high energy confinement, τ E , and high plasma beta, β, leads to an economically attractive compact tokamak fusion reactor. High confinement enhancement, H = τ E /τ E-ITER89P = 4, and high normalized beta β N = β/(I/aB) = 6%-m-T/MA, have been obtained in DIII-D experimental discharges. These improved confinement and/or improved stability limits are observed in several DIII-D high performance operational regimes: VH-mode, high ell i H-mode, second stable core, and high beta poloidal. The authors have identified several important features of the improved performance in these discharges: details of the plasma shape, toroidal rotation or ExB flow profile, q profile and current density profile, and pressure profile. From the improved physics understanding of these enhanced performance regimes, they have developed operational scenarios which maintain the essential features of the improved confinement and which increase the stability limits using localized current profile control. The stability limit is increased by modifying the interior safety factor profile to be nonmonotonic with high central q, while maintaining the edge current density consistent with the improved transport regimes and the high edge bootstrap current. They have calculated high beta equilibria with β N = 6.5, stable to ideal n = 1 kinks and stable to ideal ballooning modes. The safety factor at the 95% flux surface is 6, the central q value is 3.9 and the minimum in q is 2.6. The current density profile is maintained by the natural profile of the bootstrap current, and a modest amount of electron cyclotron current drive

Verification of GENE and GYRO with L-mode and I-mode plasmas in Alcator C-Mod

Science.gov (United States)

Mikkelsen, D. R.; Howard, N. T.; White, A. E.; Creely, A. J.

2018-04-01

Verification comparisons are carried out for L-mode and I-mode plasma conditions in Alcator C-Mod. We compare linear and nonlinear ion-scale calculations by the gyrokinetic codes GENE and GYRO to each other and to the experimental power balance analysis. The two gyrokinetic codes' linear growth rates and real frequencies are in good agreement throughout all the ion temperature gradient mode branches and most of the trapped electron mode branches of the kyρs spectra at r/a = 0.65, 0.7, and 0.8. The shapes of the toroidal mode spectra of heat fluxes in nonlinear simulations are very similar for kyρs ≤ 0.5, but in most cases GENE has a relatively higher heat flux than GYRO at higher mode numbers. The ratio of ion to electron heat flux is similar in the two codes' simulations, but the heat fluxes themselves do not agree in almost all cases. In the I-mode regime, GENE's heat fluxes are ˜3 times those from GYRO, and they are ˜60%-100% higher than GYRO in the L-mode conditions. The GYRO under-prediction of Qe is much reduced in GENE's L-mode simulations, and it is eliminated in the I-mode simulations. This largely improved agreement with the experimental electron heat flux is offset, however, by the large overshoot of GENE's ion heat fluxes, which are 2-3 times the experimental level, and its electron heat flux overshoot at r/a = 0.80 in the I-mode. Rotation effects can explain part of the difference between the two codes' predictions, but very significant differences remain in simulations without any rotation effects.

Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas

Science.gov (United States)

Garcia, O. E.; Kube, R.; Theodorsen, A.; LaBombard, B.; Terry, J. L.

2018-05-01

Plasma fluctuations in the scrape-off layer of the Alcator C-Mod tokamak in ohmic and high confinement modes have been analyzed using gas puff imaging data. In all cases investigated, the time series of emission from a single spatially resolved view into the gas puff are dominated by large-amplitude bursts, attributed to blob-like filament structures moving radially outwards and poloidally. There is a remarkable similarity of the fluctuation statistics in ohmic plasmas and in edge localized mode-free and enhanced D-alpha high confinement mode plasmas. Conditionally averaged waveforms have a two-sided exponential shape with comparable temporal scales and asymmetry, while the burst amplitudes and the waiting times between them are exponentially distributed. The probability density functions and the frequency power spectral densities are similar for all these confinement modes. These results provide strong evidence in support of a stochastic model describing the plasma fluctuations in the scrape-off layer as a super-position of uncorrelated exponential pulses. Predictions of this model are in excellent agreement with experimental measurements in both ohmic and high confinement mode plasmas. The stochastic model thus provides a valuable tool for predicting fluctuation-induced plasma-wall interactions in magnetically confined fusion plasmas.

Suppression of large edge-localized modes in high-confinement DIII-D plasmas with a stochastic magnetic boundary.

Science.gov (United States)

Evans, T E; Moyer, R A; Thomas, P R; Watkins, J G; Osborne, T H; Boedo, J A; Doyle, E J; Fenstermacher, M E; Finken, K H; Groebner, R J; Groth, M; Harris, J H; La Haye, R J; Lasnier, C J; Masuzaki, S; Ohyabu, N; Pretty, D G; Rhodes, T L; Reimerdes, H; Rudakov, D L; Schaffer, M J; Wang, G; Zeng, L

2004-06-11

A stochastic magnetic boundary, produced by an applied edge resonant magnetic perturbation, is used to suppress most large edge-localized modes (ELMs) in high confinement (H-mode) plasmas. The resulting H mode displays rapid, small oscillations with a bursty character modulated by a coherent 130 Hz envelope. The H mode transport barrier and core confinement are unaffected by the stochastic boundary, despite a threefold drop in the toroidal rotation. These results demonstrate that stochastic boundaries are compatible with H modes and may be attractive for ELM control in next-step fusion tokamaks.

Tearing mode growth in a regime of weak magnetic shear

International Nuclear Information System (INIS)

Riyopoulos, S.; Hazeltine, R.D.

1987-06-01

The nonlinear growth for the m/n ≥ 2 resistive tearing mode is studied in case when the rational surface q(r 0 ) = m/n falls in a regime of weak magnetic shear, q'(r 0 ) ≅ 0. The island width is determined self-consistently from the nonlinear, zero-helicity component of the perturbed magnetic flux that provides the local shear. It is found that the magnetic perturbation keeps growing exponentially in the nonlinear regime on a hybrid resistive-Alfvenic time scale, while the island width and the vorticity grow on a much slower time scale. Accordingly, much faster release of magnetic energy results for modes growing near minima of hollow q profiles

H-mode edge rotation in W7-AS

International Nuclear Information System (INIS)

Hirsch, M.; Baldzuhn, J.; Ehmler, H.; Grigull, P.; Maassberg, H.; McCormick, K.; Wagner, F.; Wobig, H.

2005-01-01

In W7-AS three regimes of improved confinement exist which base on negative radial electric fields at the plasma edge resulting there from ion-root conditions of the ambipolar radial fluxes. Experimental control besides the magnetic configuration is given via the edge density profile i.e. the recycling and fuelling conditions. However, the ordering element seems to be the radial electric field profile (respectively its shear) and its interplay with the gradients of ion temperature and density. At low to medium densities the so called optimum confinement regime occurs with maximum density gradients located well inside the plasma boundary and large negative values of E r extending deep in the bulk plasma. For a large inner fraction of the bulk the ion temperature can be sufficiently high that ion transport conditions already can be explained by neoclassics. This regime delivers maximum values of T i , τ e and n τ e T i . Density gradients located right inside the plasma boundary result in the classical H-mode phenomena reminiscent to other toroidal devices with the capability of an edge layer with nearly complete suppression of turbulence either quasi stationary (in a quiescent H-mode) or intermittently (in between ELMs). At even higher densities and highly collisional plasmas with the maximum of ∇n shifted to or even out of the plasma boundary the High Density H-mode (HDH) opens access to steady state conditions with no measurable impurity accumulation. These improved confinement regimes are accessed and left via significant transitions of the transport properties albeit these transitions occur on rather different timescales. A comprehensive picture of improved edge confinement regimes in W7-AS is drawn based on the assumption that a weak edge bounded transport barrier resulting from the ion root conditions (thus E r <0) is the ground state of the (turbulent) edge plasma and already behaves as a barrier for anomalous transport. On top of that the classical H-mode

Comparisons of theoretically predicted transport from ion temperature gradient instabilities to L-mode tokamak experiments

International Nuclear Information System (INIS)

Kotschenreuther, M.; Wong, H.V.; Lyster, P.L.; Berk, H.L.; Denton, R.; Miner, W.H.; Valanju, P.

1991-12-01

The theoretical transport from kinetic micro-instabilities driven by ion temperature gradients is a sheared slab is compared to experimentally inferred transport in L-mode tokamaks. Low noise gyrokinetic simulation techniques are used to obtain the ion thermal transport coefficient X. This X is much smaller than in experiments, and so cannot explain L-mode confinement. Previous predictions based on fluid models gave much greater X than experiments. Linear and nonlinear comparisons with the fluid model show that it greatly overestimates transport for experimental parameters. In addition, disagreements among previous analytic and simulation calculations of X in the fluid model are reconciled

Numerical simulation of L.E.L. in Compton regime. Part II, GONDOLE, a three-dimensional code

International Nuclear Information System (INIS)

Deck, D.

1992-07-01

In the first part of this report, the BIWI two-dimensional numerical simulation code of L.E.L. in Compton regime has been described; the question was to simulate L.E.L. experiments in 'optical mode', that is to say for wavelengths of the order of one micron. The axisymmetric cylindrical geometry (r,z) of the BIWI code is adapted to these experiments. However, the increasingly frequent use of L.E.L. in the regime of microwaves requires the presence of a waveguide within the inverter, which breaks the cylindrical symmetry and forces us to adopt another geometry. On the other hand, the desire to take into account fields of inverters having a gradient in the direction transverse to the direction of propagation of the beam, and thus allowing various focalizations (quadrupole, parabolic, etc.), leads to work in Cartesian geometry. For these reasons (and for others that will appear later), the GONDOLE code has been written and is described in this note. The Gondole code is three-dimensional (x, y, z) and allows to simulate a large variety of L.E.L experiences. Then, all the inverter fields that the GONDOLE code takes into account are introduced. These fields are responsible for the existence of a current J(vector) perpendicular to the Z axis of propagation, and source of radiation. The dynamics of the electrons is then deduced, which derives directly from these fields, and it is shown to which equations of propagation of the laser wave each different J(vector) is coupling [fr

Flow regime analysis for fluid injection into a confined aquifer: implications for CO2 sequestration

Science.gov (United States)

Guo, B.; Zheng, Z.; Celia, M. A.; Stone, H.

2015-12-01

Carbon dioxide injection into a confined saline aquifer may be modeled as an axisymmetric two-phase flow problem. Assuming the two fluids segregate in the vertical direction due to strong buoyancy, and neglecting capillary pressure and miscibility, the lubrication approximation leads to a nonlinear advection-diffusion equation that describes the evolution of the sharp fluid-fluid interface. The flow behaviors in the system are controlled by two dimensionless groups: M, the viscosity ratio of the displaced fluid relative to injected fluid, and Γ , the gravity number, which represents the relative importance of buoyancy and fluid injection. Four different analytical solutions can be derived as the asymptotic approximations, representing specific values of the parameter pairs. The four solutions correspond to: (1) Γ 1; and (4) Γ >> 1, any M values. The first two of these solutions are new, while the third corresponds to the solution of Nordbotten and Celia (2006) for confined injections and the fourth corresponds to the solution of (Lyle et al., 2005) for gravity currents in an unconfined aquifer. Overall, the various axisymmetric flows can be summarized in a Γ-M regime diagram with five distinct dynamic behaviors including the four asymptotic regimes and an intermediate regime (Fig. 1). Data from a number of CO2 injection sites around the world can be used to compute the two dimensionless groups Γ and M associated with each injection. When plotted on the regime diagram, these values show the flow behavior for each injection and how the values vary from site to site. For all the CO2 injections, M is always larger than 1, while Γ can range from 0.01 up to 100. The pairs of (Γ, M) with lower Γ values correspond to solution (3), while the ones with higher Γ values can move up to the intermediate regime and the flow regime for solution (4). The higher values of Γ correspond to pilot-scale injections with low injection rates; most industrial-scale injection

SUPPESSION OF LARGE EDGE LOCALIZED MODES IN HIGH CONFINEMENT DIII-D PLASMAS WITH A STOCHASTIC MAGNETIC BOUNDARY

International Nuclear Information System (INIS)

EVANS, TE; MOYER, RA; THOMAS, PR; WATKINS, JG; OSBORNE, TH; BOEDO, JA; FENSTERMACHER, ME; FINKEN, KH; GROEBNER, RJ; GROTH, M; HARRIS, JH; LAHAYE, RJ; LASNIER, CJ; MASUZAKI, S; OHYABU, N; PRETTY, D; RHODES, TL; REIMERDES, H; RUDAKOV, DL; SCHAFFER, MJ; WANG, G; ZENG, L.

2003-01-01

OAK-B135 A stochastic magnetic boundary, produced by an externally applied edge resonant magnetic perturbation, is used to suppress large edge localized modes (ELMs) in high confinement (H-mode) plasmas. The resulting H-mode displays rapid, small oscillations with a bursty character modulated by a coherent 130 Hz envelope. The H-mode transport barrier is unaffected by the stochastic boundary. The core confinement of these discharges is unaffected, despite a three-fold drop in the toroidal rotation in the plasma core. These results demonstrate that stochastic boundaries are compatible with H-modes and may be attractive for ELM control in next-step burning fusion tokamaks

Local Physics Basis of Confinement Degradation in JET ELMy H-Mode Plasmas and Implications for Tokamak Reactors

International Nuclear Information System (INIS)

Budny, R.V.; Alper, B.; Borba, D.; Cordey, J.G.; Ernst, D.R.; Gowers, C.

2001-01-01

First results of gyrokinetic analysis of JET [Joint European Torus] ELMy [Edge Localized Modes] H-mode [high-confinement modes] plasmas are presented. ELMy H-mode plasmas form the basis of conservative performance predictions for tokamak reactors of the size of ITER [International Thermonuclear Experimental Reactor]. Relatively high performance for long duration has been achieved and the scaling appears to be favorable. It will be necessary to sustain low Z(subscript eff) and high density for high fusion yield. This paper studies the degradation in confinement and increase in the anomalous heat transport observed in two JET plasmas: one with an intense gas puff and the other with a spontaneous transition between Type I to III ELMs at the heating power threshold. Linear gyrokinetic analysis gives the growth rate, gamma(subscript lin) of the fastest growing modes. The flow-shearing rate omega(subscript ExB) and gamma(subscript lin) are large near the top of the pedestal. Their ratio decreases approximately when the confinement degrades and the transport increases. This suggests that tokamak reactors may require intense toroidal or poloidal torque input to maintain sufficiently high |gamma(subscript ExB)|/gamma(subscript lin) near the top of the pedestal for high confinement

Mode dynamics and confinement in the reversed field pinch

International Nuclear Information System (INIS)

Brunsell, P.R.; Bergsaker, H.; Brzozowski, J.H.; Cecconello, M.; Drake, J.R.; Malmberg, J.-A.; Scheffel, J.; Schnack, D.D.

2001-01-01

Tearing mode dynamics and toroidal plasma flow in the RFP has been experimentally studied in the Extrap T2 device. A toroidally localised, stationary magnetic field perturbation, the 'slinky mode' is formed in nearly all discharges. There is a tendency of increased phase alignment of different toroidal Fourier modes, resulting in higher localised mode amplitudes, with higher magnetic fluctuation level. The fluctuation level increases slightly with increasing plasma current and plasma density. The toroidal plasma flow velocity and the ion temperature has been measured with Doppler spectroscopy. Both the toroidal plasma velocity and the ion temperature clearly increase with I/N. Initial, preliminary experimental results obtained very recently after a complete change of the Extrap T2 front-end system (first wall, shell, TF coil), show that an operational window with mode rotation most likely exists in the rebuilt device, in contrast to the earlier case discussed above. A numerical code DEBSP has been developed to simulate the behaviour of RFP confinement in realistic geometry, including essential transport physics. Resulting scaling laws are presented and compared with results from Extrap T2 and other RFP experiments. (author)

H-mode physics

International Nuclear Information System (INIS)

Itoh, Sanae.

1991-06-01

After the discovery of the H-mode in ASDEX ( a tokamak in Germany ) the transition between the L-mode ( Low confinement mode ) and H-mode ( High confinement mode ) has been observed in many tokamaks in the world. The H-mode has made a breakthrough in improving the plasma parameters and has been recognized to be a universal phenomena. Since its discovery, the extensive studies both in experiments and in theory have been made. The research on H-mode has been casting new problems of an anomalous transport across the magnetic surface. This series of lectures will provide a brief review of experiments for explaining H-mode and a model theory of H-mode transition based on the electric field bifurcation. If the time is available, a new theoretical model of the temporal evolution of the H-mode will be given. (author)

Scaling Behavior of Dilute Polymer Solutions Confined between Parallel Plates

NARCIS (Netherlands)

Vliet, J.H. van; Luyten, M.C.; Brinke, G. ten

1992-01-01

The average size and shape of a polymer coil confined in a slit between two parallel plates depends on the distance L between the plates. On the basis of numerical results, four different regimes can be distingubhed. For large values of L the coil is essentially unconfined. For intermediate values

Simulation of transition dynamics to high confinement in fusion plasmas

DEFF Research Database (Denmark)

Nielsen, Anders Henry; Xu, G. S.; Madsen, Jens

2015-01-01

The transition dynamics from the low (L) to the high (H) confinement mode in magnetically confined plasmas is investigated using a first-principles four-field fluid model. Numerical results are in agreement with measurements from the Experimental Advanced Superconducting Tokamak - EAST...

Pellet injection and confinement in the tore supra tokamak; Injection de glacons et confinement dans le tokamak tore supra

Energy Technology Data Exchange (ETDEWEB)

Maget, P

1998-09-23

Pellet injection in the centre of tokamak plasmas can lead to an improved confinement regime called PEP (Pellet Enhanced Performance). The present work is dedicated to the mechanisms involved in the PEP regimes obtained in the tokamak Tore Supra. A neoclassical approach of transport shows that it is the anomalous transport, due to plasma turbulence, that causes the enhanced confinement. A linear model describing electrostatic instabilities has been developed in order to study the roles of density profile and current profile during the PEP, in the limit of large growth rates. The effect ofradial shear in flows is taken into account by removing the ExB shear flow rate from the linear growth rate, as suggested by non-linear numerical simulations of turbulence. A local transport coefficient is estimated from the knowledge of the linear growth rate and the mode width. We find that the peaked density profile in PEP regime lowers the diffusion coefficient, and that the velocity shear amplifies this effect. The evolution of the current profile is also stabilizing, but this parameter is not known with sufficient accuracy, so that its role in Tore Supra PEP experiments remains uncertain. (author)

Giant enhancement of reflectance due to the interplay between surface confined wave modes and nonlinear gain in dielectric media.

Science.gov (United States)

Kim, Sangbum; Kim, Kihong

2017-12-11

We study theoretically the interplay between the surface confined wave modes and the linear and nonlinear gain of the dielectric layer in the Otto configuration. The surface confined wave modes, such as surface plasmons or waveguide modes, are excited in the dielectric-metal bilayer by obliquely incident p waves. In the purely linear case, we find that the interplay between linear gain and surface confined wave modes can generate a large reflectance peak with its value much greater than 1. As the linear gain parameter increases, the peak appears at smaller incident angles, and the associated modes also change from surface plasmons to waveguide modes. When the nonlinear gain is turned on, the reflectance shows very strong multistability near the incident angles associated with surface confined wave modes. As the nonlinear gain parameter is varied, the reflectance curve undergoes complicated topological changes and sometimes displays separated closed curves. When the nonlinear gain parameter takes an optimally small value, a giant amplification of the reflectance by three orders of magnitude occurs near the incident angle associated with a waveguide mode. We also find that there exists a range of the incident angle where the wave is dissipated rather than amplified even in the presence of gain. We suggest that this can provide the basis for a possible new technology for thermal control in the subwavelength scale.

MHD instabilities and their effects on plasma confinement in the large helical device plasmas

International Nuclear Information System (INIS)

Toi, K.

2002-01-01

MHD stability of NBI heated plasmas and impacts of MHD modes on plasma confinement are intensively studied in the Large Helical Device (LHD). Three characteristic MHD instabilities were observed, that is, (1) pressure driven modes excited in the plasma edge, (2) pressure driven mode in the plasma core, and (3) Alfven eigenmodes (AEs) driven by energetic ions. MHD mode excited in the edge region accompanies multiple satellites, and is called Edge Harmonic Modes (EHMs). EHM sometimes has a bursting character. The bursting EHM transiently decreases the stored energy by about 15 percent. In the plasma core region, m=2/n=1 pressure driven mode is typically destabilized. The mode often induces internal collapse in the higher beta regime more than 1 percent. The internal collapse appreciably affects the global confinement. Energetic ion driven AEs are often detected in NBI-heated LHD plasmas. Particular AE with the frequency 8-10 times larger than TAE-frequency was detected in high beta plasmas more than 2 percent. The AE may be related to helicity-induced AE. Excitation of these three types of MHD instabilities and their impacts on plasma confinement are discussed. (author)

Direct observation of current in type-I edge-localized-mode filaments on the ASDEX upgrade tokamak

DEFF Research Database (Denmark)

Vianello, N.; Zuin, M.; Cavazzana, R.

2011-01-01

Magnetically confined plasmas in the high confinement regime are regularly subjected to relaxation oscillations, termed edge localized modes (ELMs), leading to large transport events. Present ELM theories rely on a combined effect of edge current and the edge pressure gradients which result...

Dimensionally similar studies of confinement and H-mode transition in ASDEX Upgrade and JET

International Nuclear Information System (INIS)

Ryter, F.; Stober, J.; Suttrop, W.

2001-01-01

Joint experiments on confinement and L-H transition were performed in ASDEX Upgrade and JET. The confinement experiments suggest that the invariance principle is not always fulfilled at high density. For the L-H transition studies, the dimensionless variables taken at the plasma edge can be in general only made identical per pair, due to the condition imposed by the L-H transition. This new approach to investigate the L-H physics suggests a weak dependence of the L-H transition mechanism on collisionality. (author)

Dimensionally similar studies of confinement and H-mode transition in ASDEX Upgrade and JET

International Nuclear Information System (INIS)

Ryter, F.; Stober, J.; Suttrop, W.

1999-01-01

Joint experiments on confinement and L-H transition were performed in ASDEX Upgrade and JET. The confinement experiments suggest that the invariance principle is not always fulfilled at high density. For the L-H transition studies, the dimensionless variables taken at the plasma edge can be in general only made identical per pair, due to the condition imposed by the L-H transition. This new approach to investigate the L-H physics suggests a weak dependence of the L-H transition mechanism on collisionality. (author)

Theory of self-sustained turbulence in confined plasmas

International Nuclear Information System (INIS)

Itoh, K.; Itoh, S.-I.; Fukuyama, A.; Yagi, M.

1996-01-01

This article reviews some aspects of recent theoretical activities in Japan on the problem of turbulent transport in confined plasmas. The method of self-sustained turbulence is discussed. The process of the renormalization is shown and the turbulent Prandtl number is introduced. Nonlinear destabilization by the electron momentum diffusion is explained. The nonlinear eigenmode equation is derived for the dressed-test-mode for the inhomogeneous plasma in the shear magnetic field. The eigenvalue equation is solved, and the least stable mode determines the anomalous transport coefficient. The formula of the thermal conductivity is presented for the system of bad average magnetic curvature (current diffusive interchange mode (CDIM) turbulence) and that for the average good magnetic curvature (current diffusive ballooning mode (CDBM) turbulence). The transport coefficient, scale length of fluctuations and fluctuation level are shown to be an increasing function of the pressure gradient. Verification by use of the nonlinear simulation is shown. The bifurcation of the electric field and improved confinement are addressed, in order to explain the H-mode physics. The improved confinement and dynamics such as ELMs are explained. Application to the transport analysis of tokamaks is also presented, including explanations of the L-mode confinement, internal transport barrier, and the role of the current profile control

Edge localized mode physics and operational aspects in tokamaks

Energy Technology Data Exchange (ETDEWEB)

Becoulet, M [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Huysmans, G [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Sarazin, Y [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Garbet, X [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Ghendrih, Ph [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Rimini, F [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Joffrin, E [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Litaudon, X [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Monier-Garbet, P [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Ane, J-M [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Thomas, P [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Grosman, A [Association Euratom-CEA, CEA Cadarache, F-13108 St Paul-lez-Durance (France); Parail, V [Euratom/UKAEA Association, Fusion Culham Science Centre, Abingdon, OX14 3EA (United Kingdom); Wilson, H [Euratom/UKAEA Association, Fusion Culham Science Centre, Abingdon, OX14 3EA (United Kingdom); Lomas, P [Euratom/UKAEA Association, Fusion Culham Science Centre, Abingdon, OX14 3EA (United Kingdom); Vries, P de[Euratom/UKAEA Association, Fusion Culham Science Centre, Abingdon, OX14 3EA (United Kingdom); Zastrow, K-D [Euratom/UKAEA Association, Fusion Culham Science Centre, Abingdon, OX14 3EA (United Kingdom); Matthews, G F [Euratom/UKAEA Association, Fusion Culham Science Centre, Abingdon, OX14 3EA (United Kingdom); Lonnroth, J [Euratom/UKAEA Association, Fusion Culham Science Centre, Abingdon, OX14 3EA (United Kingdom); Gerasimov, S [Euratom/UKAEA Association, Fusion Culham Science Centre, Abingdon, OX14 3EA (United Kingdom)] [and others

2003-12-01

Recent progress in experimental and theoretical studies of edge localized mode (ELM) physics is reviewed for the reactor relevant plasma regimes, namely the high confinement regimes, that is, H-modes and advanced scenarios. Theoretical approaches to ELM physics, from a linear ideal magnetohydrodynamic (MHD) stability analysis to non-linear transport models with ELMs are discussed with respect to experimental observations, in particular the fast collapse of pedestal pressure profiles, magnetic measurements and scrape-off layer transport during ELMs. High confinement regimes with different types of ELMs are addressed in this paper in the context of development of operational scenarios for ITER. The key parameters that have been identified at present to reduce the energy losses in Type I ELMs are operation at high density, high edge magnetic shear and high triangularity. However, according to the present experimental scaling for the energy losses in Type I ELMs, the extrapolation of such regimes for ITER leads to unacceptably large heat loads on the divertor target plates exceeding the material limits. High confinement H-mode scenarios at high triangularity and high density with small ELMs (Type II), mixed regimes (Type II and Type I) and combined advanced regimes at high beta{sub p} are discussed for present-day tokamaks. The optimum combination of high confinement and small MHD activity at the edge in Type II ELM scenarios is of interest to ITER. However, to date, these regimes have been achieved in a rather narrow operational window and far from ITER parameters in terms of collisionality, edge safety factor and beta{sub p}. The compatibility of the alternative internal transport barrier (ITB) scenario with edge pedestal formation and ELMs is also addressed. Edge physics issues related to the possible combination of small benign ELMs (Type III, Type II ELMs, quiescent double barrier) and high performance ITBs are discussed for present-day experiments (JET, JT-60U

Edge localized mode physics and operational aspects in tokamaks

International Nuclear Information System (INIS)

Becoulet, M; Huysmans, G; Sarazin, Y; Garbet, X; Ghendrih, Ph; Rimini, F; Joffrin, E; Litaudon, X; Monier-Garbet, P; Ane, J-M; Thomas, P; Grosman, A; Parail, V; Wilson, H; Lomas, P; Vries, P de; Zastrow, K-D; Matthews, G F; Lonnroth, J; Gerasimov, S; Sharapov, S; Gryaznevich, M; Counsell, G; Kirk, A; Valovic, M; Buttery, R; Loarte, A; Saibene, G; Sartori, R; Leonard, A; Snyder, P; Lao, L L; Gohil, P; Evans, T E; Moyer, R A; Kamada, Y; Chankin, A; Oyama, N; Hatae, T; Asakura, N; Tudisco, O; Giovannozzi, E; Crisanti, F; Perez, C P; Koslowski, H R; Eich, T; Sips, A; Horton, L; Hermann, A; Lang, P; Stober, J; Suttrop, W; Beyer, P; Saarelma, S

2003-01-01

Recent progress in experimental and theoretical studies of edge localized mode (ELM) physics is reviewed for the reactor relevant plasma regimes, namely the high confinement regimes, that is, H-modes and advanced scenarios. Theoretical approaches to ELM physics, from a linear ideal magnetohydrodynamic (MHD) stability analysis to non-linear transport models with ELMs are discussed with respect to experimental observations, in particular the fast collapse of pedestal pressure profiles, magnetic measurements and scrape-off layer transport during ELMs. High confinement regimes with different types of ELMs are addressed in this paper in the context of development of operational scenarios for ITER. The key parameters that have been identified at present to reduce the energy losses in Type I ELMs are operation at high density, high edge magnetic shear and high triangularity. However, according to the present experimental scaling for the energy losses in Type I ELMs, the extrapolation of such regimes for ITER leads to unacceptably large heat loads on the divertor target plates exceeding the material limits. High confinement H-mode scenarios at high triangularity and high density with small ELMs (Type II), mixed regimes (Type II and Type I) and combined advanced regimes at high beta p are discussed for present-day tokamaks. The optimum combination of high confinement and small MHD activity at the edge in Type II ELM scenarios is of interest to ITER. However, to date, these regimes have been achieved in a rather narrow operational window and far from ITER parameters in terms of collisionality, edge safety factor and beta p . The compatibility of the alternative internal transport barrier (ITB) scenario with edge pedestal formation and ELMs is also addressed. Edge physics issues related to the possible combination of small benign ELMs (Type III, Type II ELMs, quiescent double barrier) and high performance ITBs are discussed for present-day experiments (JET, JT-60U, DIII-D) in

SAFETY FACTOR SCALING OF ENERGY TRANSPORT IN L-MODE PLASMAS ON THE DIII-D TOKAMAK

International Nuclear Information System (INIS)

PETTY, C.C.; KINSEY, J.E.; LUCE, T.C.

2003-01-01

OAK-B135 The scaling of energy transport with safety factor (q) at fixed magnetic shear has been measured on the DIII-D tokamak [Nucl. Fusion 42, 614 (2002)] for low confinement (L) mode discharges. At constant density, temperature, and toroidal magnetic field strength, such that the toroidal dimensionless parameters other than q are held fixed, the one-fluid thermal diffusivity is found to scale like χ ∝ q 0.84±0.15 , with the ion channel having a stronger q dependence than the electron channel in the outer half of the plasma. The measured q scaling is in good agreement with the predicted scaling by the GLF23 transport model for the ion temperature gradient and trapped electron modes, but it is significantly weaker than the inferred scaling from empirically-derived confinement scaling relations

Dynamical vanishing of the order parameter in a confined Bardeen-Cooper-Schrieffer Fermi gas after an interaction quench

Science.gov (United States)

Hannibal, S.; Kettmann, P.; Croitoru, M. D.; Axt, V. M.; Kuhn, T.

2018-01-01

We present a numerical study of the Higgs mode in an ultracold confined Fermi gas after an interaction quench and find a dynamical vanishing of the superfluid order parameter. Our calculations are done within a microscopic density-matrix approach in the Bogoliubov-de Gennes framework which takes the three-dimensional cigar-shaped confinement explicitly into account. In this framework, we study the amplitude mode of the order parameter after interaction quenches starting on the BCS side of the BEC-BCS crossover close to the transition and ending in the BCS regime. We demonstrate the emergence of a dynamically vanishing superfluid order parameter in the spatiotemporal dynamics in a three-dimensional trap. Further, we show that the signal averaged over the whole trap mirrors the spatiotemporal behavior and allows us to systematically study the effects of the system size and aspect ratio on the observed dynamics. Our analysis enables us to connect the confinement-induced modifications of the dynamics to the pairing properties of the system. Finally, we demonstrate that the signature of the Higgs mode is contained in the dynamical signal of the condensate fraction, which, therefore, might provide a new experimental access to the nonadiabatic regime of the Higgs mode.

Suppression of large edge localized modes with edge resonant magnetic fields in high confinement DIII-D plasmas

International Nuclear Information System (INIS)

Thomas, P.R.; Becoulet, M.; Evans, T.E.; Osborne, T.H.; Groebner, R.J.; Jackson, G.L.; Haye, R.J. La; Schaffer, M.J.; West, W.P.; Moyer, R.A.; Rhodes, T.L.; Rudakov, D.L.; Watkins, J.G.; Boedo, J.A.; Doyle, E.J.; Wang, G.; Zeng, L.; Fenstermacher, M.E.; Groth, M.; Lasnier, C.J.; Finken, K.H.; Harris, J.H.; Pretty, D.G.; Masuzaki, S.; Ohyabu, N.; Reimerdes, H.; Wade, M.R.

2005-01-01

Large divertor heat pulses due to Type-I edge localized modes (ELMs) have been eliminated reproducibly in DIII-D with small dc currents driven in a simple magnetic perturbation coil. The current required to eliminate all but a few isolated Type-I ELMs, during a coil pulse, is less than 0.4% of plasma current. Modelling shows that the perturbation fields resonate with plasma flux surfaces across most of the pedestal region (0.9 ≤ N ≤ 1.0), when q95 = 3.7±0.2 creating small remnant magnetic islands surrounded by weakly stochastic field lines. The stored energy, N , H-mode quality factor and global energy confinement time are unaltered by the magnetic perturbation. At high collisionality (ν* ∼0.5-1), there is no obvious effect of the perturbation on the edge profiles and yet ELMs are suppressed, nearly completely, for up to 9τ E . At low collisionality (ν* <0.1), there is a density pump-out and complete ELM suppression, reminiscent of the DIIID QH- mode. Other differences, specifically in the resonance condition and the magnetic fluctuations, suggest that different mechanisms are at play in the different collisionality regimes. In addition to a description and interpretation of the DIIID data, the application of this method to ELM control on other machines, such as JET and ITER will be discussed. (author)

High-confinement-mode edge stability of Alcator C-mod plasmas

International Nuclear Information System (INIS)

Mossessian, D.A.; Snyder, P.; Hubbard, A.; Hughes, J.W.; Greenwald, M.; La Bombard, B.; Snipes, J.A.; Wolfe, S.; Wilson, H.

2003-01-01

For steady state high-confinement-mode (H-mode) operation, a relaxation mechanism is required to limit build-up of the edge gradient and impurity content. Alcator C-Mod [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] sees two such mechanisms--EDA (enhanced D-alpha H mode) and grassy ELMs (edge localized modes), but not large type I ELMs. In EDA the edge relaxation is provided by an edge localized quasicoherent (QC) electromagnetic mode that exists at moderate pedestal temperature T 95 >3.5, and does not limit the buildup of the edge pressure gradient. The q boundary of the operational space of the mode depends on plasma shape, with the q 95 limit moving down with increasing plasma triangularity. At high edge pressure gradients and temperatures the mode is replaced by broadband fluctuations ( f<50 kHz) and small irregular ELMs are observed. Ideal MHD (magnetohydrodynamic) stability analysis that includes both pressure and current driven edge modes shows that the discharges where the QC mode is observed are stable. The ELMs are identified as medium n (10< n<50) coupled peeling/ballooning modes. The predicted stability boundary of the modes as a function of pedestal current and pressure gradient is reproduced in experimental observations. The measured dependence of the ELMs' threshold and amplitude on plasma triangularity is consistent with the results of ideal MHD analysis performed with the linear stability code ELITE [Wilson et al., Phys. Plasmas 9, 1277 (2002)

Transport modeling of L- and H-mode discharges with LHCD on EAST

Science.gov (United States)

Li, M. H.; Ding, B. J.; Imbeaux, F.; Decker, J.; Zhang, X. J.; Kong, E. H.; Zhang, L.; Wei, W.; Shan, J. F.; Liu, F. K.; Wang, M.; Xu, H. D.; Yang, Y.; Peysson, Y.; Basiuk, V.; Artaud, J.-F.; Yuynh, P.; Wan, B. N.

2013-04-01

High-confinement (H-mode) discharges with lower hybrid current drive (LHCD) as the only heating source are obtained on EAST. In this paper, an empirical transport model of mixed Bohm/gyro-Bohm for electron and ion heat transport was first calibrated against a database of 3 L-mode shots on EAST. The electron and ion temperature profiles are well reproduced in the predictive modeling with the calibrated model coupled to the suite of codes CRONOS. CRONOS calculations with experimental profiles are also performed for electron power balance analysis. In addition, the time evolutions of LHCD are calculated by the C3PO/LUKE code involving current diffusion, and the results are compared with experimental observations.

Turbulent regimes in the tokamak scrape-off layer

International Nuclear Information System (INIS)

Mosetto, A.

2014-01-01

The tokamak scrape-off layer (SOL) is the plasma region characterized by open field lines that start and end on the vessel walls. The plasma dynamics in the SOL plays a crucial role in determining the overall performance of a tokamak, since it controls the plasma-wall interactions, being responsible of exhausting the tokamak power, it regulates the overall plasma confinement, and it governs the plasma refueling and the removal of fusion ashes. Scrape-off layer physics is intrinsically non-linear and characterized by phenomena that occur on a wide range of spatio-temporal scales. Free energy sources drive a number of unstable modes that develop into turbulence and lead to transport of particles and heat across the magnetic field lines. Depending on the driving instability, different SOL turbulent regimes can be identified. As the SOL turbulent regimes determine the plasma confinement properties and the SOL width (and, consequently, the power flux on the vessel wall, for example), it is of crucial importance to understand which turbulent regimes are active in the SOL, under which conditions they develop, and which are the main properties of the associated turbulent transport. In the present thesis we define the SOL turbulent regimes, and we provide a framework to identify them, given the operational SOL parameters. Our study is based on the drift-reduced Braginskii equations and it is focused on a limited tokamak SOL configuration. We first describe the main SOL linear instabilities, such as the inertial and resistive branches of the drift waves, the resistive, inertial and ideal branches of the ballooning modes, and the ion temperature gradient mode. Then, we find the SOL turbulent regimes depending on the instability driving turbulent transport, assuming that turbulence saturates when the radial gradient associated to the pressure fluctuations is comparable to the equilibrium one. Our methodology for the turbulent regime identification is supported by the analysis

Experimental investigation of different regimes of mode-locking in a high repetition rate passively mode-locked semiconductor quantum-dot laser.

Science.gov (United States)

Kéfélian, Fabien; O'Donoghue, Shane; Todaro, Maria Teresa; McInerney, John; Huyet, Guillaume

2009-04-13

We report experimental investigations on a two-section 16-GHz repetition rate InAs/GaAs quantum dot passively mode-locked laser. Near the threshold current, pseudo-periodic Q-switching with complex dynamics is exhibited. Mode-locking operation regimes characterized by different repetition rates and timing jitter levels are encountered up to twice the threshold current. Evolution of the RF spectrum and optical spectrum with current is compared. The different mode-locked regimes are shown to be associated with different spectral and temporal shapes, ranging from 1.3 to 6 ps. This point is discussed by introducing the existence of two different supermodes. Repetition rate evolution and timing jitter increase is attributed to the coupling between the dominant and the secondary supermodes.

Confinement properties of JET plasmas with different temperature and density profiles

International Nuclear Information System (INIS)

Watkins, M.L.; Balet, B.; Bhatnagar, V.P.

1989-01-01

The confinement properties of plasmas with substantially different temperature and density profiles have been analysed. The effects of fast particles and energy pedestals on the overall confinement of plasma energy in limiter (L-mode) and X-point (L- and H-modes) discharges heated by NBI or ICRF or both are determined. The importance of the bootstrap current when such energy pedestals are formed is noted. Using sets of consistent experimental data, including ion temperature profile measurements, the local transport properties are compared in the L- and H-phases of a single null X-point medium density NBI heated discharge, the ''enhanced'' confinement phase of a limiter high density pellet-fuelled and ICRF heated discharge, the hot-ion phase of a double null X-point low density NBI heated discharge and the hot-ion and H-phases of a double null X-point low density high temperature NBI heated discharge. (author)

Pellet injection and confinement in the tore supra tokamak

International Nuclear Information System (INIS)

Maget, P.

1998-01-01

Pellet injection in the centre of tokamak plasmas can lead to an improved confinement regime called PEP (Pellet Enhanced Performance). The present work is dedicated to the mechanisms involved in the PEP regimes obtained in the tokamak Tore Supra. A neoclassical approach of transport shows that it is the anomalous transport, due to plasma turbulence, that causes the enhanced confinement. A linear model describing electrostatic instabilities has been developed in order to study the roles of density profile and current profile during the PEP, in the limit of large growth rates. The effect of radial shear in flows is taken into account by removing the ExB shear flow rate from the linear growth rate, as suggested by non-linear numerical simulations of turbulence. A local transport coefficient is estimated from the knowledge of the linear growth rate and the mode width. We find that the peaked density profile in PEP regime lowers the diffusion coefficient, and that the velocity shear amplifies this effect. The evolution of the current profile is also stabilizing, but this parameter is not known with sufficient accuracy, so that its role in Tore Supra PEP experiments remains uncertain. (author)

Advances in measurement and modeling of the high-confinement-mode pedestal on the Alcator C-Mod tokamak

International Nuclear Information System (INIS)

Hughes, J.W.; LaBombard, B.; Mossessian, D.A.; Hubbard, A.E.; Terry, J.; Biewer, T.

2006-01-01

Edge transport barrier (ETB) studies on the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511 (1994)] investigate pedestal scalings and the radial transport of plasma and neutrals. Pedestal profiles show trends with plasma operational parameters such as total current I P . A ballooning-like I P 2 dependence is seen in the pressure gradient, despite calculated stability to ideal ballooning modes. A similar scaling is seen in the near scrape-off layer for both low-confinement (L-mode) and H-mode discharges, possibly due to electromagnetic fluid drift turbulence setting transport near the separatrix. Neutral density diagnosis allows an examination of D 0 fueling in H-modes, yielding profiles of effective particle diffusivity in the ETB, which vary as I P is changed. Edge neutral transport is studied using a one-dimensional kinetic treatment. In both experiment and modeling, the C-Mod density pedestal exhibits a weakly increasing pedestal density and a nearly invariant density pedestal width as the D 0 source rate increases. Identical modeling performed on pedestal profiles typical of DIII-D [Nucl. Fusion 42, 614 (2002)] reveal differences in pedestal scalings qualitatively similar to experimental results

Comparison of hybrid and baseline ELMy H-mode confinement in JET with the carbon wall

NARCIS (Netherlands)

Beurskens, M. N. A.; Frassinetti, L.; Challis, C.; Osborne, T.; Snyder, P. B.; Alper, B.; Angioni, C.; Bourdelle, C.; Buratti, P.; Crisanti, F.; Giovannozzi, E.; Giroud, C.; Groebner, R.; Hobirk, J.; Jenkins, I.; Joffrin, E.; Leyland, M. J.; Lomas, P.; Mantica, P.; McDonald, D.; Nunes, I.; Rimini, F.; Saarelma, S.; Voitsekhovitch, I.; P. de Vries,; Zarzoso, D.

2013-01-01

The confinement in JET baseline type I ELMy H-mode plasmas is compared to that in so-called hybrid H-modes in a database study of 112 plasmas in JET with the carbon fibre composite (CFC) wall. The baseline plasmas typically have beta(Nu) similar to 1.5-2, H-98 similar to 1, whereas the hybrid

Confinement and transport properties during current ramps in the ASDEX Upgrade tokamak

Science.gov (United States)

Fable, E.; Angioni, C.; Hobirk, J.; Pereverzev, G.; Fietz, S.; Hein, T.; ASDEX Upgrade Team

2011-04-01

A detailed analysis of experimental data from the ASDEX Upgrade tokamak is carried out to shed light on the properties of confinement and transport in the current ramp-up and ramp-down phases of the plasma discharge. The experimental database is used to identify the relevant ranges of parameters explored during the ramp-up and the ramp-down. The energy confinement time observed in the two ramps displays interesting evolution, in many cases attaining different values at the same current level between ramp-up and ramp-down. The possible reasons for this behaviour are investigated. Interpretative transport simulations are used as a tool to clarify the interplay between different parameters, which are coupled in a non-linear way. In addition, a theory-based transport model is used to understand the behaviour of confinement as observed in the experiment, evidencing the role of both turbulent and neoclassical transport. Linear gyrokinetic calculations are performed to identify the relevant turbulence regime, showing that a broad range of frequencies, in the trapped electron modes (TEMs) and in the ion temperature gradient modes (ITGs) regimes, is explored during both the ramp-up and ramp-down. In the same framework, a quasi-linear model is applied to calculate the value of the local logarithmic density gradient and compare it with the experimental value. Finally, first non-linear simulations of heat transport during the current ramps are presented.

Physics of the H-mode

International Nuclear Information System (INIS)

Hinton, F.L.; Chu, M.S.; Dominguez, R.R.

1985-01-01

A theoretical picture of the H-mode is proposed which explains some of the most important features of this good confinement mode in neutral beam heated plasmas with divertors. From consideration of the transport through the separatrix and along the open field lines outside the separatrix, as well as the stability of the plasma inside the separatrix, we show that a bifurcation in the operating parameters is possible. At high edge temperatures, very large particle confinement times are possible because of the Ware pinch. The transport of particles and heat along the open field lines to the divertor region depends on temperature in a non-monotonic way, and the bifurcation of the thermal equilibrium which is implied may correspond to the L- to H-mode transition. The improvement of the interior confinement in the H-mode, when the edge temperature is higher, is shown to follow from the tearing mode stability properties of current profiles with pedestals. (author)

Ignition in net for different energy confinement time scalings

International Nuclear Information System (INIS)

Johner, J.; Prevot, F.

1988-06-01

A zero-dimensional profile dependent model is used to assess the feasibility of ignition in the extended version of NET. Five recent scalings for the energy confinement time (Goldston, Kaye All, Kaye Big, Shimomura-Odajima, Rebut-Lallia) are compared in the frame of two different scenarii, i.e., H-mode with a flat density profile or L-mode with a peaked density profile. For the flat density H-mode case, ignition is accessible with none of the scalings except Rebut-Lallia's. For the peaked density L-mode case, ignition is accessible with none of the scalings except Rebut-Lallia's. For the two Kaye's scalings, ignition is forbidden in H-mode even with the peaked density profile. For the Rebut-Lallia scaling, ignition is allowed in L-mode even with the flat density profile

Mode-selective symmetry control for indirect-drive inertial confinement fusion hohlraums

International Nuclear Information System (INIS)

Vesey, R. A.; Slutz, S. A.; Herrmann, M. C.; Mehlhorn, T. A.; Campbell, R. B.

2008-01-01

Achieving a high degree of radiation symmetry is a critical feature of target designs for indirect-drive inertial confinement fusion. Typically, the radiation flux incident on the capsule is required to be uniform to 1% or better. It is generally possible to design a hohlraum that provides low values of higher-order asymmetry (Legendre mode P 10 and above) due to geometric averaging effects. Because low-order intrinsic asymmetry (e.g., Legendre modes P 2 and P 4 ) are less strongly reduced by geometric averaging alone, the development of innovative control techniques has been an active area of research in the inertial fusion community over the years. Shields placed inside the hohlraum are one example of a technique that has often been proposed and incorporated into hohlraum target designs. Simple mathematical considerations are presented indicating that radiation shields may be designed to specifically tune lower-order modes (e.g., P 4 ) without deleterious effects on the higher order modes. Two-dimensional view factor and radiation-hydrodynamics simulations confirm these results and support such a path to achieving a highly symmetric x-ray flux. The term ''mode-selective'' is used because these shields, essentially ring structures offset from the capsule, are designed to affect only a specific Legendre mode (or multiple modes) of interest

Role of magnetic flux perturbations in confinement bifurcations in TUMAN-3M

International Nuclear Information System (INIS)

Lebedev, S.V.; Andreiko, M.V.; Askinazi, L.G.

2003-01-01

Poloidal magnetic flux variations in the small tokamak TUMAN-3M allowed observation of transitions between different confinement modes. The possibility of switching on/off the ohmic H-mode by edge poloidal magnetic flux perturbations has been found. The flux perturbations were created by fast current ramp up/down or by magnetic compression/decompression produced by fast increase/decrease in the toroidal magnetic field. It was found that positive flux perturbations (current ramp-up and magnetic compression scenarios) are useful means of H-mode triggering. If a negative flux perturbation (current ramp-down or magnetic decompression) is applied, the H-mode terminated. Various mechanisms involved in the L-H and H-L transition physics in the flux perturbation experiments were analyzed. The experimental observations of the transitions between confinement modes might be understood in terms of the model of a sheared radial electric field generation, which takes into account the electron Ware drift in a perturbed longitudinal electric field. Another scenario of improved confinement was observed in the initial phase of an ohmic discharge, when change in the poloidal flux is associated with current ramp-up. Variation of the rates of current ramp-up and working gas puffing in the beginning of a discharge resulted in a fast increase in the electron temperature near the axis. The increase correlates with low m/n MHD mode growth. The observed core electron confinement improvement is apparently connected with the rate of current ramp. Deviation from the optimal rate results in disappearance of the improvement. The role of magnetic shear profile and rational magnetic surfaces in the core electron confinement improvement in the initial phase of ohmic discharges is discussed. (author)

New steady-state quiescent high-confinement plasma in an experimental advanced superconducting tokamak.

Science.gov (United States)

Hu, J S; Sun, Z; Guo, H Y; Li, J G; Wan, B N; Wang, H Q; Ding, S Y; Xu, G S; Liang, Y F; Mansfield, D K; Maingi, R; Zou, X L; Wang, L; Ren, J; Zuo, G Z; Zhang, L; Duan, Y M; Shi, T H; Hu, L Q

2015-02-06

A critical challenge facing the basic long-pulse high-confinement operation scenario (H mode) for ITER is to control a magnetohydrodynamic (MHD) instability, known as the edge localized mode (ELM), which leads to cyclical high peak heat and particle fluxes at the plasma facing components. A breakthrough is made in the Experimental Advanced Superconducting Tokamak in achieving a new steady-state H mode without the presence of ELMs for a duration exceeding hundreds of energy confinement times, by using a novel technique of continuous real-time injection of a lithium (Li) aerosol into the edge plasma. The steady-state ELM-free H mode is accompanied by a strong edge coherent MHD mode (ECM) at a frequency of 35-40 kHz with a poloidal wavelength of 10.2 cm in the ion diamagnetic drift direction, providing continuous heat and particle exhaust, thus preventing the transient heat deposition on plasma facing components and impurity accumulation in the confined plasma. It is truly remarkable that Li injection appears to promote the growth of the ECM, owing to the increase in Li concentration and hence collisionality at the edge, as predicted by GYRO simulations. This new steady-state ELM-free H-mode regime, enabled by real-time Li injection, may open a new avenue for next-step fusion development.

Effects of triangularity on confinement, density limit and profile stiffness of H-modes on ASDEX upgrade

International Nuclear Information System (INIS)

Stober, J.; Gruber, O.; Kallenbach, A.; Mertens, V.; Ryter, F.; Staebler, A.; Suttrop, W.; Treutterer, W.

2000-01-01

At ASDEX Upgrade the influence of triangularity on the H-mode performance has been studied intensively. It has been found that confinement increases with δ for a fixed line-averaged density. Though confinement decreases with increasing density for all analysed values of δ, H-factors (ITERH-98P) at the Greenwald density could be raised to 1 for the highest δ values achieved so far. The H-mode density limit could be increased by approx. 20%. There is a scatter of about 30% on the confinement data, which is anti-correlated to the average density in the scrape-off layer or the neutral fluxes outside the plasma. For nearly all discharges analysed so far, the temperature profiles are self-similar. This indication of profile stiffness could be verified by changing the heat-flux profile by changing the beam-voltage of the neutral-beam injection (NBI) at high density. At low density, first results indicate a deviation from this stiff behaviour. (author)

Rovibrational states of Wigner molecules in spherically symmetric confining potentials

Energy Technology Data Exchange (ETDEWEB)

Cioslowski, Jerzy [Institute of Physics, University of Szczecin, Wielkopolska 15, 70-451 Szczecin, Poland and Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Str. 38, D-01187 Dresden (Germany)

2016-08-07

The strong-localization limit of three-dimensional Wigner molecules, in which repulsively interacting particles are confined by a weak spherically symmetric potential, is investigated. An explicit prescription for computation of rovibrational wavefunctions and energies that are asymptotically exact at this limit is presented. The prescription is valid for systems with arbitrary angularly-independent interparticle and confining potentials, including those involving Coulombic and screened (i.e., Yukawa/Debye) interactions. The necessary derivations are greatly simplified by explicit constructions of the Eckart frame and the parity-adapted primitive wavefunctions. The performance of the new formalism is illustrated with the three- and four-electron harmonium atoms at their strong-correlation limits. In particular, the involvement of vibrational modes with the E symmetry is readily pinpointed as the origin of the “anomalous” weak-confinement behavior of the {sup 1}S{sub +} state of the four-electron species that is absent in its {sup 1}D{sub +} companion of the strong-confinement regime.

Slow Dynamics and Structure of Supercooled Water in Confinement

Directory of Open Access Journals (Sweden)

Gaia Camisasca

2017-04-01

Full Text Available We review our simulation results on properties of supercooled confined water. We consider two situations: water confined in a hydrophilic pore that mimics an MCM-41 environment and water at interface with a protein. The behavior upon cooling of the α relaxation of water in both environments is well interpreted in terms of the Mode Coupling Theory of glassy dynamics. Moreover, we find a crossover from a fragile to a strong regime. We relate this crossover to the crossing of the Widom line emanating from the liquid-liquid critical point, and in confinement we connect this crossover also to a crossover of the two body excess entropy of water upon cooling. Hydration water exhibits a second, distinctly slower relaxation caused by its dynamical coupling with the protein. The crossover upon cooling of this long relaxation is related to the protein dynamics.

Global energy confinement in TORE SUPRA

International Nuclear Information System (INIS)

Hoang, G.T.; Bizarro, J.P.; Genile, B. de; Hutter, Th.; Laurent, L.; Litaudon, X.; Moreau, D.; Peysson, Y.; Tonon, G.; Houtte, D. van

1992-01-01

The global energy confinement behaviour of mixed Ohmic/Lower Hybrid driven Tore Supra plasmas has been analysed at various densities. In contradiction with L-mode ITER scaling law, this analysis indicates that the global energy confinement time depends strongly on the plasma density and the isotopic dependence seems not to be observed. The thermal electron energy content of steady-state discharges is in good agreement with the offset linear Rebut-Lallia scaling law. During current ramp experiments, the global energy confinement time was found to depend on the internal self-inductance (li). Improved confinement has been obtained for a steady-state 0.8 MA plasma where the plasma current profile is peaked by LH waves (li ∼1.8). In this case, the global confinement time is found to be about 40% higher than the value predicted by the Rebut-Lallia scaling law. (author) 3 refs., 6 figs

Topology of polymer chains under nanoscale confinement.

Science.gov (United States)

Satarifard, Vahid; Heidari, Maziar; Mashaghi, Samaneh; Tans, Sander J; Ejtehadi, Mohammad Reza; Mashaghi, Alireza

2017-08-24

Spatial confinement limits the conformational space accessible to biomolecules but the implications for bimolecular topology are not yet known. Folded linear biopolymers can be seen as molecular circuits formed by intramolecular contacts. The pairwise arrangement of intra-chain contacts can be categorized as parallel, series or cross, and has been identified as a topological property. Using molecular dynamics simulations, we determine the contact order distributions and topological circuits of short semi-flexible linear and ring polymer chains with a persistence length of l p under a spherical confinement of radius R c . At low values of l p /R c , the entropy of the linear chain leads to the formation of independent contacts along the chain and accordingly, increases the fraction of series topology with respect to other topologies. However, at high l p /R c , the fraction of cross and parallel topologies are enhanced in the chain topological circuits with cross becoming predominant. At an intermediate confining regime, we identify a critical value of l p /R c , at which all topological states have equal probability. Confinement thus equalizes the probability of more complex cross and parallel topologies to the level of the more simple, non-cooperative series topology. Moreover, our topology analysis reveals distinct behaviours for ring- and linear polymers under weak confinement; however, we find no difference between ring- and linear polymers under strong confinement. Under weak confinement, ring polymers adopt parallel and series topologies with equal likelihood, while linear polymers show a higher tendency for series arrangement. The radial distribution analysis of the topology reveals a non-uniform effect of confinement on the topology of polymer chains, thereby imposing more pronounced effects on the core region than on the confinement surface. Additionally, our results reveal that over a wide range of confining radii, loops arranged in parallel and cross

An Abrupt Transition to an Intergranular Failure Mode in the Near-Threshold Fatigue Crack Growth Regime in Ni-Based Superalloys

Science.gov (United States)

Telesman, J.; Smith, T. M.; Gabb, T. P.; Ring, A. J.

2018-06-01

Cyclic near-threshold fatigue crack growth (FCG) behavior of two disk superalloys was evaluated and was shown to exhibit an unexpected sudden failure mode transition from a mostly transgranular failure mode at higher stress intensity factor ranges to an almost completely intergranular failure mode in the threshold regime. The change in failure modes was associated with a crossover of FCG resistance curves in which the conditions that produced higher FCG rates in the Paris regime resulted in lower FCG rates and increased ΔK th values in the threshold region. High-resolution scanning and transmission electron microscopy were used to carefully characterize the crack tips at these near-threshold conditions. Formation of stable Al-oxide followed by Cr-oxide and Ti-oxides was found to occur at the crack tip prior to formation of unstable oxides. To contrast with the threshold failure mode regime, a quantitative assessment of the role that the intergranular failure mode has on cyclic FCG behavior in the Paris regime was also performed. It was demonstrated that even a very limited intergranular failure content dominates the FCG response under mixed mode failure conditions.

Impurity transport model for the normal confinement and high density H-mode discharges in Wendelstein 7-AS

International Nuclear Information System (INIS)

Ida, K; Burhenn, R; McCormick, K; Pasch, E; Yamada, H; Yoshinuma, M; Inagaki, S; Murakami, S; Osakabe, M; Liang, Y; Brakel, R; Ehmler, H; Giannone, L; Grigull, P; Knauer, J P; Maassberg, H; Weller, A

2003-01-01

An impurity transport model based on diffusivity and the radial convective velocity is proposed as a first approach to explain the differences in the time evolution of Al XII (0.776 nm), Al XI (55 nm) and Al X (33.3 nm) lines following Al-injection by laser blow-off between normal confinement discharges and high density H-mode (HDH) discharges. Both discharge types are in the collisional regime for impurities (central electron temperature is 0.4 keV and central density exceeds 10 20 m -3 ). In this model, the radial convective velocity is assumed to be determined by the radial electric field, as derived from the pressure gradient. The diffusivity coefficient is chosen to be constant in the plasma core but is significantly larger in the edge region, where it counteracts the high local values of the inward convective velocity. Under these conditions, the faster decay of aluminium in HDH discharges can be explained by the smaller negative electric field in the bulk plasma, and correspondingly smaller inward convective velocity, due to flattening of the density profiles

Unifying role of radial electric field shear in the confinement trends of transitionless regimes in TFTR

International Nuclear Information System (INIS)

Ernst, D.R.; Beer, M.; Batha, S.

2001-01-01

Turbulence suppression by radial electric field shear (E r ) is shown to be important in the enhanced confinement of TFTR supershot plasmas. Simulations of supershot ion temperature profiles are performed using an existing parameterization of transport due to toroidal ion temperature gradient modes, extended to include suppression by E r shear. New spectroscopic measurements of E r differ significantly from prior neoclassical estimates. Supershot temperature profiles appear to be consistent with a criterion describing near-complete turbulence suppression by intrinsically generated E r shear. Helium spoiling and xenon puffing experiments are simulated to illustrate the role of E r shear in the confinement changes observed. (author)

Unifying role of radial electric field shear in the confinement trends of transitionless regimes in TFTR

International Nuclear Information System (INIS)

Ernst, D.R.; Beer, M.; Batha, S.

1999-01-01

Turbulence suppression by radial electric field shear (E r ) is shown to be important in the enhanced confinement of TFTR supershot plasmas. Simulations of supershot ion temperature profiles are performed using an existing parameterization of transport due to toroidal ion temperature gradient modes, extended to include suppression by E r shear. New spectroscopic measurements of E r differ significantly from prior neoclassical estimates. Supershot temperature profiles appear to be consistent with a criterion describing near-complete turbulence suppression by intrinsically generated E r shear. Helium spoiling and xenon puffing experiments are simulated to illustrate the role of E r shear in the confinement changes observed. (author)

Microtearing modes

International Nuclear Information System (INIS)

Garbet, X.; Mourgues, F.; Samain, A.; Zou, X.

1990-01-01

A serious degradation of confinement with additional heating is commonly observed on most tokamaks. The microtearing modes could provide an explanation for this experimental fact. They are driven linearly unstable by diamagnetism in collisional regimes, but it may be shown that the collisions in non linear regimes provide a small diffusion coefficient which can be only significant at the plasme edge. In the bulk of the plasma, the microtearing turbulence could play a basic role if it is unstable in the collisionless regime. While it is linearly stable without collisions, it could be driven unstable in realistic regimes by the radial diffusion it induces. To study this effect, we have used a model where the non linear action of the modes on a given helicity component is represented by a diffusion operator. They are found unstable for reasonable β p =2μ o nT/B 2 p , with a special radial profile of the potential vector A. The problem arises the validity of this model where non linearities in the trajectories behaviour are replaced by the diffusion which broadens resonances. To test this procedure, we calculate the actual electron distribution function when it is determined by the ergodicity of the field lines. We compute the correlations of the distribution function with the magnetic perturbation and compare them with the analytical expressions derived from the resonance broadening model. (author) 3 refs., 2 figs

Investigation of impurity confinement in lower hybrid wave heated plasma on EAST tokamak

Science.gov (United States)

Xu, Z.; Wu, Z. W.; Zhang, L.; Gao, W.; Ye, Y.; Chen, K. Y.; Yuan, Y.; Zhang, W.; Yang, X. D.; Chen, Y. J.; Zhang, P. F.; Huang, J.; Wu, C. R.; Morita, S.; Oishi, T.; Zhang, J. Z.; Duan, Y. M.; Zang, Q.; Ding, S. Y.; Liu, H. Q.; Chen, J. L.; Hu, L. Q.; Xu, G. S.; Guo, H. Y.; the EAST Team

2018-01-01

The transient perturbation method with metallic impurities such as iron (Fe, Z  =  26) and copper (Cu, Z  =  29) induced in plasma-material interaction (PMI) procedure is used to investigate the impurity confinement characters in lower hybrid wave (LHW) heated EAST sawtooth-free plasma. The dependence of metallic impurities confinement time on plasma parameters (e.g. plasma current, toroidal magnetic field, electron density and heating power) are investigated in ohmic and LHW heated plasma. It is shown that LHW heating plays an important role in the reduction of the impurity confinement time in L-mode discharges on EAST. The impurity confinement time scaling is given as 42IP0.32Bt0.2\\overline{n}e0.43Ptotal-0.4~ on EAST, which is close to the observed scaling on Tore Supra and JET. Furthermore, the LHW heated high-enhanced-recycling (HER) H-mode discharges with ~25 kHz edge coherent modes (ECM), which have lower impurity confinement time and higher energy confinement time, provide promising candidates for high performance and steady state operation on EAST.

Mode 1 drive asymmetry in inertial confinement fusion implosions on the National Ignition Facility

International Nuclear Information System (INIS)

Spears, Brian K.; Edwards, M. J.; Hatchett, S.; Kritcher, A.; Lindl, J.; Munro, D.; Patel, P.; Robey, H. F.; Town, R. P. J.; Kilkenny, J.; Knauer, J.

2014-01-01

Mode 1 radiation drive asymmetry (pole-to-pole imbalance) at significant levels can have a large impact on inertial confinement fusion implosions at the National Ignition Facility (NIF). This asymmetry distorts the cold confining shell and drives a high-speed jet through the hot spot. The perturbed hot spot shows increased residual kinetic energy and reduced internal energy, and it achieves reduced pressure and neutron yield. The altered implosion physics manifests itself in observable diagnostic signatures, especially the neutron spectrum which can be used to measure the neutron-weighted flow velocity, apparent ion temperature, and neutron downscattering. Numerical simulations of implosions with mode 1 asymmetry show that the resultant simulated diagnostic signatures are moved toward the values observed in many NIF experiments. The diagnostic output can also be used to build a set of integrated implosion performance metrics. The metrics indicate that P 1 has a significant impact on implosion performance and must be carefully controlled in NIF implosions

Mode 1 drive asymmetry in inertial confinement fusion implosions on the National Ignition Facility

Energy Technology Data Exchange (ETDEWEB)

Spears, Brian K., E-mail: spears9@llnl.gov; Edwards, M. J.; Hatchett, S.; Kritcher, A.; Lindl, J.; Munro, D.; Patel, P.; Robey, H. F.; Town, R. P. J. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551-0808 (United States); Kilkenny, J. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Knauer, J. [Laboratory for Laser Energetics, 250 E. River Road Rochester, New York 14623-1212 (United States)

2014-04-15

Mode 1 radiation drive asymmetry (pole-to-pole imbalance) at significant levels can have a large impact on inertial confinement fusion implosions at the National Ignition Facility (NIF). This asymmetry distorts the cold confining shell and drives a high-speed jet through the hot spot. The perturbed hot spot shows increased residual kinetic energy and reduced internal energy, and it achieves reduced pressure and neutron yield. The altered implosion physics manifests itself in observable diagnostic signatures, especially the neutron spectrum which can be used to measure the neutron-weighted flow velocity, apparent ion temperature, and neutron downscattering. Numerical simulations of implosions with mode 1 asymmetry show that the resultant simulated diagnostic signatures are moved toward the values observed in many NIF experiments. The diagnostic output can also be used to build a set of integrated implosion performance metrics. The metrics indicate that P{sub 1} has a significant impact on implosion performance and must be carefully controlled in NIF implosions.

Confinement of a self-stabilized tokamak under average magnetic well conditions

International Nuclear Information System (INIS)

Demchenko, V.V.; Fu, G.Y.; Van Dam, J.W.

1987-05-01

It is well known that the average favorable magnetic curvature of a tokamak is stabilizing with respect to pressure-driven magnetohydrodynamic instabilities at low beta and that self-stabilization occurs at finite beta in the so-called second stability regime. Here we self-consistently investigate how these two effects, viz., the mean magnetic well and the self-stabilization, influence the energy confinement time in a tokamak, using the ballooning mode transport model

Plasma confinement in self-consistent, one-dimensional transport equilibria in the collisionless-ion regime of EBT operation

International Nuclear Information System (INIS)

Chang, C.S.; Miller, R.L.

1983-01-01

It has long been recognized that if an EBT-confined plasma could be maintained in the collisionless-ion regime, characterized by positive ambipolar potential and positive radial electric field, the particle loss rates could be reduced by a large factor. The extent to which the loss rate of energy could be reduced has not been as clearly determined, and has been investigated recently using a one-dimensional, time-dependent transport code developed for this purpose. We find that the energy confinement can be improved by roughly an order of magnitude by maintaining a positive radial electric field that increases monotonically with radius, giving a large ExB drift near the outer edge of the core plasma. The radial profiles of heat deposition required to sustain these equilibria will be presented, and scenarios for obtaining dynamical access to the equilibria will be discussed

Competitive Modes for the Detection of Chaotic Parameter Regimes in the General Chaotic Bilinear System of Lorenz Type

Science.gov (United States)

Mallory, Kristina; van Gorder, Robert A.

We study chaotic behavior of solutions to the bilinear system of Lorenz type developed by Celikovsky and Vanecek [1994] through an application of competitive modes. This bilinear system of Lorenz type is one possible canonical form holding the Lorenz equation as a special case. Using a competitive modes analysis, which is a completely analytical method allowing one to identify parameter regimes for which chaos may occur, we are able to demonstrate a number of parameter regimes which admit a variety of distinct chaotic behaviors. Indeed, we are able to draw some interesting conclusions which relate the behavior of the mode frequencies arising from writing the state variables for the Celikovsky-Vanecek model as coupled oscillators, and the types of emergent chaotic behaviors observed. The competitive modes analysis is particularly useful if all but one of the model parameters are fixed, and the remaining free parameter is used to modify the chaos observed, in a manner analogous to a bifurcation parameter. Through a thorough application of the method, we are able to identify several parameter regimes which give new dynamics (such as specific forms of chaos) which were not observed or studied previously in the Celikovsky-Vanecek model. Therefore, the results demonstrate the advantage of the competitive modes approach for detecting new parameter regimes leading to chaos in third-order dynamical systems.

The role of electric field shear stabilization of turbulence in the H-mode to VH-mode transition in DIII-D

International Nuclear Information System (INIS)

Burrell, K.H.; Osborne, T.H.; Groebner, R.J.; Rettig, C.L.

1993-01-01

VH-mode plasma exhibit energy confinement times up to 2.4 times the DIII-D/JET H-mode scaling relation and up to 3.9 times the value given by ITER89-P L-mode scaling. If this confinement improvement can be exploited in reactor plasmas, smaller prototype reactors with significantly lower unit cost can be produced. Accordingly, understanding and optimizing the confinement improvement is of significant interest. One of the possible explanations for this bulk confinement improvement is stabilization of turbulence by shear in the radial electric field, similar to the present explanation for the confinement improvement at the extreme plasma edge at the L to H transition. Preliminary measurements have shown that the region of the plasma where the electric field gradient is steepest broadens when the plasma goes from H-mode to VH-mode. More recent measurements have confirmed this broadening and have shown that the change in the electric field gradient occurs prior to the change in the thermal transport. In addition, transport analysis shows that the electric field shear increases in the same region between magnetic flux coordinate p=0.6 and 0.9 where the local thermal transport decreases. Furthermore, far infra-red (FIR) scattering measurements have detected density fluctuations in the region around p=0.8 which could be responsible for enhanced transport and which disappear at the time that the electric shear increases. These fluctuations appear as bursts of density fluctuations in the 0.5 to 1.5 MHz range. The time between bursts increases as the electric field shear increases. Once these bursts disappear, the major change in confinement takes place in most discharges. When isolated bursts occur, the heat and angular momentum pulse connected with the burst are detectable on the plasma profile diagnostics. (author) 13 refs., 4 figs

Hybrid rib-slot-rib plasmonic waveguide with deep-subwavelength mode confinement and long propagation length

Directory of Open Access Journals (Sweden)

Kai Zheng

2016-08-01

Full Text Available We propose a hybrid plasmonic waveguide where a combined rib-slot-rib structure is added on the metal substrate within a low-index gap region. The optical properties of the quasi-TM fundamental mode are numerically calculated using the finite element method. Compared to the traditional hybrid plasmonic waveguide, our designed waveguiding structure can support modes with tighter confinement and longer propagation length, by properly adjusting the geometry of the rib-slot-rib structure and the gap height. In details, it can provide the hybrid mode with mode area λ2/12000 and reasonable propagation distance 23.78 μm, simultaneously. Its excellent optical performance can facilitate potential applications in ultra-compact nanophotonic devices and circuits.

Study of neutral particle behavior and particle confinement in JT-60U

International Nuclear Information System (INIS)

Takenaga, Hidenobu; Shimizu, Katsuhiro; Asakura, Nobuyuki; Shimada, Michiya; Kikuchi, Mitsuru; Tsuji-Iio, Shunji; Uchino, Kiichiro; Muraoka, Katsunori.

1995-07-01

In order to understand the particle confinement properties in JT-60U, the particle confinement time was estimated through analyses of the neutral particle behavior. First, the neutral particle transport simulation code DEGAS using a Monte-Carlo technique was combined with the simple divertor code for calculating the edge plasma parameters, and was developed to calculate under the experimental conditions in JT-60U. Then, the charged particle source in the main plasma due to the ionization of the neutral particles was evaluated from the analyses of the neutral particle penetration to the main plasma based on results of the simulation code and measurements of D α emission intensities. Finally, the particle confinement time was estimated from the analysis of particle balance. The analyses were performed systematically for the L-mode plasma and H-mode plasma of JT-60U, and a data base of the particle confinement time was obtained. The dependence of the particle confinement time on the plasma parameters and the relationship between the properties of the particle confinement and the energy confinement were examined. (author)

Flux-driven turbulence GDB simulations of the IWL Alcator C-Mod L-mode edge compared with experiment

Science.gov (United States)

Francisquez, Manaure; Zhu, Ben; Rogers, Barrett

2017-10-01

Prior to predicting confinement regime transitions in tokamaks one may need an accurate description of L-mode profiles and turbulence properties. These features determine the heat-flux width upon which wall integrity depends, a topic of major interest for research aid to ITER. To this end our work uses the GDB model to simulate the Alcator C-Mod edge and contributes support for its use in studying critical edge phenomena in current and future tokamaks. We carried out 3D electromagnetic flux-driven two-fluid turbulence simulations of inner wall limited (IWL) C-Mod shots spanning closed and open flux surfaces. These simulations are compared with gas puff imaging (GPI) and mirror Langmuir probe (MLP) data, examining global features and statistical properties of turbulent dynamics. GDB reproduces important qualitative aspects of the C-Mod edge regarding global density and temperature profiles, within reasonable margins, and though the turbulence statistics of the simulated turbulence follow similar quantitative trends questions remain about the code's difficulty in exactly predicting quantities like the autocorrelation time A proposed breakpoint in the near SOL pressure and the posited separation between drift and ballooning dynamics it represents are examined This work was supported by DOE-SC-0010508. This research used resources of the National Energy Research Scientific Computing Center (NERSC).

Confinement improvement in H-mode-like plasmas in helical systems

International Nuclear Information System (INIS)

Itoh, K.; Sanuki, H.; Itoh, S.; Fukuyama, A.; Yagi, M.

1993-06-01

The reduction of the anomalous transport due to the inhomogeneous radial electric field is theoretically studied for toroidal helical plasmas. The self-sustained interchange-mode turbulence is analysed for the system with magnetic shear and magnetic hill. For the system with magnetic well like conventional stellarators, the ballooning mode turbulence is studied. Influence of the radial electric field inhomogeneity on the transport coefficients and fluctuations are quantitatively shown. Unified theory of the transport coefficients in the L-mode and H-mode-like plasmas are presented. (author)

Optical Control of Mechanical Mode-Coupling within a MoS2 Resonator in the Strong-Coupling Regime.

Science.gov (United States)

Liu, Chang-Hua; Kim, In Soo; Lauhon, Lincoln J

2015-10-14

Two-dimensional (2-D) materials including graphene and transition metal dichalcogenides (TMDs) are an exciting platform for ultrasensitive force and displacement detection in which the strong light-matter coupling is exploited in the optical control of nanomechanical motion. Here we report the optical excitation and displacement detection of a ∼ 3 nm thick MoS2 resonator in the strong-coupling regime, which has not previously been achieved in 2-D materials. Mechanical mode frequencies can be tuned by more than 12% by optical heating, and they exhibit avoided crossings indicative of strong intermode coupling. When the membrane is optically excited at the frequency difference between vibrational modes, normal mode splitting is observed, and the intermode energy exchange rate exceeds the mode decay rate by a factor of 15. Finite element and analytical modeling quantifies the extent of mode softening necessary to control intermode energy exchange in the strong coupling regime.

Investigation of energy confinement during ICRF heating on EAST

Science.gov (United States)

Yang, Y. Q.; Zhang, X. J.; Zhao, Y. P.; Qin, C. M.; Cheng, Y.; Mao, Y. Z.; Yang, H.; Yuan, S.; Wang, L.; Ju, S. Q.; Chen, G.; Zhang, J. H.; Wang, J. H.; Chen, Z.; Wan, B. N.; Gong, X. Z.; Qian, J. P.; Zhang, T.; Li, J. G.; Song, Y. T.; Lin, Y.; Taylor, G.; Hosea, J. C.; Perkins, R. J.; Wukitch, S.; Noterdaeme, J. M.; Kumazawa, R.; Seki, T.; Saito, K.; Kasahara, H.

2017-09-01

A summary is given on recent experiments in L-mode with ion cyclotron resonance heating (ICRH) of hydrogen minority in deuterium plasmas on EAST. Experiments show a degradation of confinement with increasing power. Furthermore, the energy confinement time increases with plasma current and magnetic field, whereas it is insensitive to line averaged density. Minority heating has been found to be efficient, and parameters were optimized to maximize its efficiency. ICRH in lower hybrid waves heated plasma was also investigated.

New fluctuation phenomena in the H-mode regime of PDX tokamak plasmas

International Nuclear Information System (INIS)

Slusher, R.E.; Surko, C.M.; Valley, J.F.; Crowley, T.; Mazzucato, E.; McGuire, K.

1984-05-01

A new kind of quasi-coherent fluctuation is observed near the edge of plasmas in the PDX tokamak during H-mode operation. (The H-mode occurs in neutral beam heated divertor plasmas and is characterized by improved energy containment as well as large density and temperature gradients near the plasma edge.) These fluctuations are evidenced as VUV and density fluctuation bursts at well-defined frequencies (Δω/ω less than or equal to 0.1) in the frequency range between 50 and 180 kHz. They affect the edge temperature-density product, and therefore they may be important for understanding the relationship between the large edge density and temperature gradients and the improved energy confinement

Observation of transverse and longitudinal modes in non-neutral electron clouds confined in a magnetic mirror

International Nuclear Information System (INIS)

Eckhouse, S.; Fisher, A.; Rostoker, N.

1979-01-01

Electrostatic modes on non-neutral electron clouds confined in a magnetic mirror field have been investigated. The cloud contains 2 x 10 11 electrons at an average kinetic energy of 0.3 MeV for a magnetic field with a peak intensity of 9 kG at the midplane. It was found that the cloud is moving azimuthally as well as longitudinally. The azimuthal motion has an m=1 spatial nature. The longitudinal modes have a more complicated nature, but their frequency equals that of the azimuthal mode

Transverse mode control in proton-implanted and oxide-confined VCSELs via patterned dielectric anti-phase filters

Science.gov (United States)

Kesler, Benjamin; O'Brien, Thomas; Dallesasse, John M.

2017-02-01

A novel method for controlling the transverse lasing modes in both proton implanted and oxide-confined vertical- cavity surface-emitting lasers (VCSELs) with a multi-layer, patterned, dielectric anti-phase (DAP) filter is pre- sented. Using a simple photolithographic liftoff process, dielectric layers are deposited and patterned on individual VCSELs to modify (increase or decrease) the mirror reflectivity across the emission aperture via anti-phase reflections, creating spatially-dependent threshold material gain. The shape of the dielectric pattern can be tailored to overlap with specific transverse VCSEL modes or subsets of transverse modes to either facilitate or inhibit lasing by decreasing or increasing, respectively, the threshold modal gain. A silicon dioxide (SiO2) and titanium dioxide (TiO2) anti-phase filter is used to achieve a single-fundamental-mode, continuous-wave output power greater than 4.0 mW in an oxide-confined VCSEL at a lasing wavelength of 850 nm. A filter consisting of SiO2 and TiO2 is used to facilitate injection-current-insensitive fundamental mode and lower order mode lasing in proton implanted VCSELs at a lasing wavelength of 850 nm. Higher refractive index dielectric materials such as amorphous silicon (a-Si) can be used to increase the effectiveness of the anti-phase filter on proton implanted devices by reducing the threshold modal gain of any spatially overlapping modes. This additive, non-destructive method allows for mode selection at any lasing wavelength and for any VCSEL layer structure without the need for semiconductor etching or epitaxial regrowth. It also offers the capability of designing a filter based upon available optical coating materials.

Pedestal structure and stability in H-mode and I-mode: a comparative study on Alcator C-Mod

International Nuclear Information System (INIS)

Hughes, J.W.; Walk, J.R.; Davis, E.M.; LaBombard, B.; Baek, S.G.; Churchill, R.M.; Greenwald, M.; Hubbard, A.E.; Lipschultz, B.; Marmar, E.S.; Reinke, M.L.; Rice, J.E.; Theiler, C.; Terry, J.; White, A.E.; Whyte, D.G.; Snyder, P.B.; Groebner, R.J.; Osborne, T.; Diallo, A.

2013-01-01

New experimental data from the Alcator C-Mod tokamak are used to benchmark predictive modelling of the edge pedestal in various high-confinement regimes, contributing to greater confidence in projection of pedestal height and width in ITER and reactors. ELMy H-modes operate near stability limits for ideal peeling–ballooning modes, as shown by calculations with the ELITE code. Experimental pedestal width in ELMy H-mode scales as the square root of β pol at the pedestal top, i.e. the dependence expected from theory if kinetic ballooning modes (KBMs) were responsible for limiting the pedestal width. A search for KBMs in experiment has revealed a short-wavelength electromagnetic fluctuation in the pedestal that is a candidate driver for inter-edge localized mode (ELM) pedestal regulation. A predictive pedestal model (EPED) has been tested on an extended set of ELMy H-modes from C-Mod, reproducing pedestal height and width reasonably well across the data set, and extending the tested range of EPED to the highest absolute pressures available on any existing tokamak and to within a factor of three of the pedestal pressure targeted for ITER. In addition, C-Mod offers access to two regimes, enhanced D-alpha (EDA) H-mode and I-mode, that have high pedestals, but in which large ELM activity is naturally suppressed and, instead, particle and impurity transport are regulated continuously. Pedestals of EDA H-mode and I-mode discharges are found to be ideal magnetohydrodynamic (MHD) stable with ELITE, consistent with the general absence of ELM activity. Invocation of alternative physics mechanisms may be required to make EPED-like predictions of pedestals in these kinds of intrinsically ELM-suppressed regimes, which would be very beneficial to operation in burning plasma devices. (paper)

Electron transport and improved confinement on Tore Supra

International Nuclear Information System (INIS)

Hoang, G.T.; Bourdelle, C.; Garbet, X.; Aniel, T.; Giruzzi, G.; Ottaviani, M.; Horton, W.; Zhu, P.; Budny, R.V.

2001-01-01

Magnetic shear is found to play an important role for triggering various improved confinement regimes through the electron channel. A wide database of hot electron plasmas (T e >2T i ) heated by fast wave electron heating (FWEH) is analyzed for electron thermal transport. A critical gradient is clearly observed. It is found that the critical gradient linearly increases with the ratio between local magnetic shear (s) and safety factor (q). The Horton model, based on the electromagnetic turbulence driven by the electron temperature gradient (ETG) mode, is found to be a good candidate for electron transport modeling. (author)

Scalings of energy confinement and density limit in stellarator/heliotron

International Nuclear Information System (INIS)

Sudo, S.; Takeiri, Y.; Zushi, H.; Sano, F.; Itoh, K.; Kondo, K.; Iiyoshi, A.

1989-04-01

Empirical scaling of energy confinement observed experimentally in stellarator/heliotron (Heliotron E, Wendelstein 7A, L2, Heliotron DR) under the condition that plasmas are heated by ECH and/or NbI is proposed. Empirical scaling of density limit obtainable under the optimum condition is proposed. These scalings are compared with those of tokamaks. The energy confinement scaling has similar power dependence as 'L mode scaling' of tokamaks. The density limit scaling seems also to indicate the upper limit of achievable density in many tokamaks. Combining the energy confinement time and the density limit scaling a transport-limited beta value is also deduced. Thus, from the viewpoint of designing a machine, there should be some compromise in determing magnetic field strength on plasma axis, average minor radius and major radius, because their dependence on confinement time and transport-limited beta value is contradicting. (J.P.N.)

Confined longitudinal acoustic phonon modes in free-standing Si membranes coherently excited by femtosecond laser pulses

OpenAIRE

Hudert, Florian; Bruchhausen, Axel; Issenmann, Daniel; Schecker, Olivier; Waitz, Reimar; Erbe, Artur; Scheer, Elke; Dekorsy, Thomas; Mlayah, Adnen; Huntzinger, Jean-Roch

2009-01-01

In this Rapid Communication we report the first time-resolved measurements of confined acoustic phonon modes in free-standing Si membranes excited by fs laser pulses. Pump-probe experiments using asynchronous optical sampling reveal the impulsive excitation of discrete acoustic modes up to the 19th harmonic order for membranes of two different thicknesses. The modulation of the membrane thickness is measured with fm resolution. The experimental results are compared with a theoretical model in...

New advanced operational regime on the W7-AS stellarator

International Nuclear Information System (INIS)

McCormick, K.; Grigull, P.; Burhenn, R.; Brakel, R.; Ehmler, H.; Feng, Y.; Gadelmeier, F.; Giannone, L.; Hildebrandt, D.; Hirsch, M.; Jaenicke, R.; Kisslinger, J.; Klinger, T.; Klose, S.; Knauer, J. P.; Koenig, R.; Kuehner, G.; Laqua, H. P.; Naujoks, D.; Niedermeyer, H.

2002-01-01

A promising new plasma operational regime on the Wendelstein stellarator W7-AS has been discovered. It is extant above a threshold density and characterized by flat density profiles, high energy and low impurity confinement times, and edge-localized radiation. Impurity accumulation is avoided. Quasistationary discharges with line-averaged densities n-bar e to 4x10 20 m -3 , radiation levels to 90% , and partial plasma detachment at the divertor target plates can be simultaneously realized. Energy confinement is up to twice that of a standard scaling. At B t =0.9 T , an average β value of 3.1% is achieved. The high n-bar e values allow demonstration of electron Bernstein wave heating using linear mode conversion

A fission-fusion hybrid reactor in steady-state L-mode tokamak configuration with natural uranium

International Nuclear Information System (INIS)

Reed, Mark; Parker, Ronald R.; Forget, Benoit

2012-01-01

This work develops a conceptual design for a fusion-fission hybrid reactor operating in steady-state L-mode tokamak configuration with a subcritical natural or depleted uranium pebble bed blanket. A liquid lithium-lead alloy breeds enough tritium to replenish that consumed by the D-T fusion reaction. The fission blanket augments the fusion power such that the fusion core itself need not have a high power gain, thus allowing for fully non-inductive (steady-state) low confinement mode (L-mode) operation at relatively small physical dimensions. A neutron transport Monte Carlo code models the natural uranium fission blanket. Maximizing the fission power gain while breeding sufficient tritium allows for the selection of an optimal set of blanket parameters, which yields a maximum prudent fission power gain of approximately 7. A 0-D tokamak model suffices to analyze approximate tokamak operating conditions. This fission blanket would allow the fusion component of a hybrid reactor with the same dimensions as ITER to operate in steady-state L-mode very comfortably with a fusion power gain of 6.7 and a thermal fusion power of 2.1 GW. Taking this further can determine the approximate minimum scale for a steady-state L-mode tokamak hybrid reactor, which is a major radius of 5.2 m and an aspect ratio of 2.8. This minimum scale device operates barely within the steady-state L-mode realm with a thermal fusion power of 1.7 GW. Basic thermal hydraulic analysis demonstrates that pressurized helium could cool the pebble bed fission blanket with a flow rate below 10 m/s. The Brayton cycle thermal efficiency is 41%. This reactor, dubbed the Steady-state L-mode non-Enriched Uranium Tokamak Hybrid (SLEUTH), with its very fast neutron spectrum, could be superior to pure fission reactors in terms of breeding fissile fuel and transmuting deleterious fission products. It would likely function best as a prolific plutonium breeder, and the plutonium it produces could actually be more

Numerical modeling of the transition from low to high confinement in magnetically confined plasma

DEFF Research Database (Denmark)

Rasmussen, Jens Juul; Nielsen, Anders Henry; Madsen, Jens

2016-01-01

The transition dynamics from low (L) to high (H) mode confinement in magnetically confined plasmas is investigated using a four-field drift fluid model—HESEL (Hot Edge-Sol-Electrostatic). The model includes profile evolution and is solved in a 2D domain at the out-board mid-plane of a tokamak......–I–H transition with an intermediate I-phase displaying limit-cycle oscillations (LCO). The model recovers the power threshold for the L–H transition, the scaling of the threshold with the density and with the loss-rate in the SOL, indicating a decrease in power threshold when switching from single to double null...... including both open and closed field lines. The results reveal different types of L–H-like transitions in response to ramping up the input power by increasing the ion temperature in the edge region. For a fast rising input power we obtain an abrupt transition, and for a slow rising power we obtain a L...

Report on the combined meeting of the core confinement and internal transport barrier expert group, confinement database and modeling expert group and edge pedestal expert group, 12-16 April 1999, Garching

International Nuclear Information System (INIS)

Janeschitz, G.; Connor, J.W.; Cordey, G.; Kardaun, O.; Mukhovatov, V.; Stambaugh, R.; Ryter, F.; Wakatani, M.

1999-01-01

This contribution to the ITER EDA Newsletter reports on the combined meeting of the core confinement and internal transport barrier expert group, confinement database and modeling expert group and edge pedestal expert group in Garching, Germany. This is the first workshop of its kind after the re-organisation of the expert groups. The new scheme of the meetings, namely to permit more interaction between groups by arranging them at the same time and location turned out to be very successful. The main issues discussed were for the Confinement Database: merging of edge pedestal and confinement data, improvement of the density- and magnetic shape parameters, addition of new dedicated threshold data, the effect of different divertors in JET; for the H-Mode Power Threshold Database: assembly of a new version of the database with about 650 time points from 10 tokamaks; for the 1-D Modelling Workshop: management of the database after the re-organisation of the Joint Central Team an ongoing efforts in plasma transport modelling; for the newly formed pedestal group: issues of the H-mode shear layer at the plasma edge. There was also an executive summary given of a recent USA workshop on internal transport barriers and regimes with weak or negative magnetic shear

On confinement and duality

Energy Technology Data Exchange (ETDEWEB)

Strassler, M J [University of Pennsylvania, Philadelphia, PA (United States)

2002-05-15

Confinement in four-dimensional gauge theories is considered from several points of view. General features are discussed, and the mechanism of confinement is investigated. Dualities between field theories, and duality between field theory and string theory, are both put to use. In these lectures I have given an overview of some of the key ideas underlying confinement as a property of field theory, and now, of string theory as well. This is a tiny fraction of what field theory (and now string theory) is capable of, and we are still uncovering new features on a monthly basis. In fact, most field theories do not have confinement, for reasons entirely different from those of QCD. Many become nontrivial conformal field theories at low energy. Others become composite, weakly-coupled gauge theories. Dualities of many stripes are found everywhere. Ordinary dimensional analysis in string theory is totally wrong in the regime where it looks like weakly-coupled field theory, and ordinary dimensional analysis in field theory is totally wrong in the regime where it looks like weakly-coupled supergravity.

Edge-localized mode avoidance and pedestal structure in I-mode plasmas

Energy Technology Data Exchange (ETDEWEB)

Walk, J. R., E-mail: jrwalk@psfc.mit.edu; Hughes, J. W.; Hubbard, A. E.; Terry, J. L.; Whyte, D. G.; White, A. E.; Baek, S. G.; Reinke, M. L.; Theiler, C.; Churchill, R. M.; Rice, J. E. [MIT Plasma Science and Fusion Center, Cambridge, MA 02139-4307 (United States); Snyder, P. B.; Osborne, T. [General Atomics, San Diego, CA 92186-5608 (United States); Dominguez, A [Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451 (United States); Cziegler, I. [UCSD Center for Momentum Transport and Flow Organization, La Jolla, CA 92093-0417 (United States)

2014-05-15

I-mode is a high-performance tokamak regime characterized by the formation of a temperature pedestal and enhanced energy confinement, without an accompanying density pedestal or drop in particle and impurity transport. I-mode operation appears to have naturally occurring suppression of large Edge-Localized Modes (ELMs) in addition to its highly favorable scalings of pedestal structure and overall performance. Extensive study of the ELMy H-mode has led to the development of the EPED model, which utilizes calculations of coupled peeling-ballooning MHD modes and kinetic-ballooning mode (KBM) stability limits to predict the pedestal structure preceding an ELM crash. We apply similar tools to the structure and ELM stability of I-mode pedestals. Analysis of I-mode discharges prepared with high-resolution pedestal data from the most recent C-Mod campaign reveals favorable pedestal scalings for extrapolation to large machines—pedestal temperature scales strongly with power per particle P{sub net}/n{sup ¯}{sub e}, and likewise pedestal pressure scales as the net heating power (consistent with weak degradation of confinement with heating power). Matched discharges in current, field, and shaping demonstrate the decoupling of energy and particle transport in I-mode, increasing fueling to span nearly a factor of two in density while maintaining matched temperature pedestals with consistent levels of P{sub net}/n{sup ¯}{sub e}. This is consistent with targets for increased performance in I-mode, elevating pedestal β{sub p} and global performance with matched increases in density and heating power. MHD calculations using the ELITE code indicate that I-mode pedestals are strongly stable to edge peeling-ballooning instabilities. Likewise, numerical modeling of the KBM turbulence onset, as well as scalings of the pedestal width with poloidal beta, indicates that I-mode pedestals are not limited by KBM turbulence—both features identified with the trigger for large ELMs

Confinement of vibrational modes within crystalline lattices using thin amorphous layers

International Nuclear Information System (INIS)

Bagolini, Luigi; Mattoni, Alessandro; Lusk, Mark T

2017-01-01

It is possible to confine vibrational modes to a crystal by encapsulating it within thin disordered layers with the same average properties as the crystal. This is not due to an impedance mismatch between materials but, rather, to higher order moments in the distribution of density and stiffness in the disordered phase—i.e. it is a result of material substructure. The concept is elucidated in an idealized one-dimensional setting and then demonstrated for a realistic nanocrystalline geometry. This offers the prospect of specifically engineering higher order property distributions as an alternate means of managing phonons. (paper)

Gate-defined Quantum Confinement in Suspended Bilayer Graphene

Science.gov (United States)

Allen, Monica

2013-03-01

Quantum confined devices in carbon-based materials offer unique possibilities for applications ranging from quantum computation to sensing. In particular, nanostructured carbon is a promising candidate for spin-based quantum computation due to the ability to suppress hyperfine coupling to nuclear spins, a dominant source of spin decoherence. Yet graphene lacks an intrinsic bandgap, which poses a serious challenge for the creation of such devices. We present a novel approach to quantum confinement utilizing tunnel barriers defined by local electric fields that break sublattice symmetry in suspended bilayer graphene. This technique electrostatically confines charges via band structure control, thereby eliminating the edge and substrate disorder that hinders on-chip etched nanostructures to date. We report clean single electron tunneling through gate-defined quantum dots in two regimes: at zero magnetic field using the energy gap induced by a perpendicular electric field and at finite magnetic fields using Landau level confinement. The observed Coulomb blockade periodicity agrees with electrostatic simulations based on local top-gate geometry, a direct demonstration of local control over the band structure of graphene. This technology integrates quantum confinement with pristine device quality and access to vibrational modes, enabling wide applications from electromechanical sensors to quantum bits. More broadly, the ability to externally tailor the graphene bandgap over nanometer scales opens a new unexplored avenue for creating quantum devices.

Steady state plasma operation in RF dominated regimes on EAST

Energy Technology Data Exchange (ETDEWEB)

Zhang, X. J.; Zhao, Y. P.; Gong, X. Z.; Hu, C. D.; Liu, F. K.; Hu, L. Q.; Wan, B. N., E-mail: bnwan@ipp.ac.cn; Li, J. G. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)

2015-12-10

Significant progress has recently been made on EAST in the 2014 campaign, including the enhanced CW H&CD system over 20MW heating power (LHCD, ICRH and NBI), more than 70 diagnostics, ITER-like W-monoblock on upper divertor, two inner cryo-pumps and RMP coils, enabling EAST to investigate long pulse H mode operation with dominant electron heating and low torque to address the critical issues for ITER. H-mode plasmas were achieved by new H&CD system or 4.6GHz LHCD alone for the first time. Long pulse high performance H mode has been obtained by LHCD alone up to 28s at H{sub 98}∼1.2 or by combing of ICRH and LHCD, no or small ELM was found in RF plasmas, which is essential for steady state operation in the future Tokamak. Plasma operation in low collision regimes were implemented by new 4.6GHz LHCD with core Te∼4.5keV. The non-inductive scenarios with high performance at high bootstrap current fraction have been demonstrated in RF dominated regimes for long pulse operation. Near full non-inductive CD discharges have been achieved. In addition, effective heating and decoupling method under multi-transmitter for ICRF system were developed in this campaign, etc. EAST could be in operation with over 30MW CW heating and current drive power (LHCD ICRH NBI and ECRH), enhanced diagnostic capabilities and full actively-cooled metal wall from 2015. It will therefore allow to access new confinement regimes and to extend these regimes towards to steady state operation.

Characterisation of edge turbulence in relation to edge magnetic field configuration in L-mode plasmas in the Mega Amp Spherical Tokamak.

Science.gov (United States)

Dewhurst, J.; Hnat, B.; Dudson, B.; Dendy, R. O.; Counsell, G. F.; Kirk, A.

2007-12-01

Almost all astrophysical and magnetically confined fusion plasmas are turbulent. Here, we examine ion saturation current (Isat) measurements of edge plasma turbulence for three MAST L-mode plasmas that differ primarily in their edge magnetic field configurations. First, absolute moments of the coarse grained data are examined to obtain accurate values of scaling exponents. The dual scaling behaviour is identified in all samples, with the temporal scale τ ≍ 40-60 μs separating the two regimes. Strong universality is then identified in the functional form of the probability density function (PDF) for Isat fluctuations, which is well approximated by the Fréchet distribution on temporal scales τ ≤ 40μs. For temporal scales τ > 40μs, the PDFs appear to converge to the Gumbel distribution, which has been previously identified as a universal feature of many other complex phenomena. The optimal fitting parameters k=1.15 for Fréchet and a=1.35 for Gumbel provide a simple quantitative characterisation of the full spectrum of fluctuations. We conclude that, to good approximation, the properties of the edge turbulence are independent of the edge magnetic field configuration.

Improved H-mode access in connected DND in MAST

International Nuclear Information System (INIS)

Meyer, H; Carolan, P G; Conway, N J; Counsell, G F; Cunningham, G; Field, A R; Kirk, A; McClements, K G; Price, M; Taylor, D

2005-01-01

In the Mega-Amp Spherical Tokamak, MAST, the formation of the edge transport barrier leading to the high-confinement (H-mode) regime is greatly facilitated by operating in a double null diverted (DND) configuration where both X-points are practically on the same flux surface. Ohmic H-modes are presently only obtained in these connected double null diverted (CDND) configurations. The ease of H-mode access is lost if the two flux surfaces passing through the X-points are radially separated by more than one ion Larmor radius (ρ i ∼ 6 mm) at the low-field-side mid-plane. The change of the magnetic configuration from disconnected to CDND is accompanied by a change in the radial electric field of about ΔE ψ ∼ -1 kV m -1 and a reduction of the electron temperature decay length in the high-field-side scrape-off-layer. Other parameters at the plasma edge, in particular those affecting the H-mode access criteria of common L/H transition theories, are not affected by the slight changes to the magnetic configuration. It is believed that the observed change in E ψ , which may result from differences in ion orbit losses, leads to a higher initial E x B flow shear in CDND configurations which could lead to the easier H-mode access

Nonlocal quasinormal modes for arbitrarily shaped three-dimensional plasmonic resonators

DEFF Research Database (Denmark)

Kamandar Dezfouli, Mohsen; Tserkezis, Christos; Mortensen, N. Asger

2017-01-01

Nonlocal effects have been shown to be responsible for a variety of non-trivial optical effects in small-size plasmonic nanoparticles, beyond classical electrodynamics. However, it is not clear whether optical mode descriptions can be applied to such extreme confinement regimes. Here, we present...... quasinormal modes, even at the single mode level. We exemplify the use of this theory by calculating the Purcell factors of single quantum emitters, the electron energy-loss spectroscopy spatial maps, as well as the Mollow triplet spectra of field-driven quantum dots with and without nonlocal effects...... for different size nanoresonators. Our nonlocal quasinormal mode theory offers a reliable and efficient technique to study both classical and quantum optical problems in nanoplasmonics....

Thermal transport in Si and Ge nanostructures in the 'confinement' regime.

Science.gov (United States)

Kwon, Soonshin; Wingert, Matthew C; Zheng, Jianlin; Xiang, Jie; Chen, Renkun

2016-07-21

Reducing semiconductor materials to sizes comparable to the characteristic lengths of phonons, such as the mean-free-path (MFP) and wavelength, has unveiled new physical phenomena and engineering capabilities for thermal energy management and conversion systems. These developments have been enabled by the increasing sophistication of chemical synthesis, microfabrication, and atomistic simulation techniques to understand the underlying mechanisms of phonon transport. Modifying thermal properties by scaling physical size is particularly effective for materials which have large phonon MFPs, such as crystalline Si and Ge. Through nanostructuring, materials that are traditionally good thermal conductors can become good candidates for applications requiring thermal insulation such as thermoelectrics. Precise understanding of nanoscale thermal transport in Si and Ge, the leading materials of the modern semiconductor industry, is increasingly important due to more stringent thermal conditions imposed by ever-increasing complexity and miniaturization of devices. Therefore this Minireview focuses on the recent theoretical and experimental developments related to reduced length effects on thermal transport of Si and Ge with varying size from hundreds to sub-10 nm ranges. Three thermal transport regimes - bulk-like, Casimir, and confinement - are emphasized to describe different governing mechanisms at corresponding length scales.

Calibration and fluctuation of the secular frequency peak amplitude versus initial condition distribution of the ion cloud confined into a three-dimensional quadrupole ion trap using a fourier transform operating mode and a steady ion flow injection mode

International Nuclear Information System (INIS)

Janulyte, A.; Andre, J.; Carette, M.; Mercury, M.; Reynard, C; Zerega, Y.

2009-01-01

A specific Fourier transform operating mode is applied to a 3-dimensional quadrupolar ion trap for mass analysis (Fourier Transform Quadrupolar Ion Trap (FTQIT) Operating Mode or Mass Spectrometer). With this operating mode, an image signal, which is representative of the collective motion of simultaneously confined ions, is made up from a set of recorded time-of-flight histograms. In an ion trap, the secular frequency of ion motion depends on m/Z ratio of the ion. By Fourier transformation of the image signal, one observes the frequency peak of each confined ionic species. When only one ionic species is confined, the peak amplitude is proportional to the maximal amplitude of the image signal. The maximal amplitude of the image signal is expressed according to the operating parameters, the initial conditions of the ions and the number of ions. Simulation tools lead to fluctuation calculation of the maximal amplitude of the image signal. Two origins are explored: (1) the fluctuation of the numbers of ions according to the steady ion flow injection mode (SIFIM) used with this operating mode and (2) the distribution fluctuation of the initial positions and velocities. Initial confinement conditions, obtained with SIFIM injection mode, lead to optimal detection with small fluctuations of the peak amplitude for Fourier transform operating mode applied to an ion trap. (authors)

Structural behavior of supercritical fluids under confinement

Science.gov (United States)

Ghosh, Kanka; Krishnamurthy, C. V.

2018-01-01

The existence of the Frenkel line in the supercritical regime of a Lennard-Jones (LJ) fluid shown through molecular dynamics (MD) simulations initially and later corroborated by experiments on argon opens up possibilities of understanding the structure and dynamics of supercritical fluids in general and of the Frenkel line in particular. The location of the Frenkel line, which demarcates two distinct physical states, liquidlike and gaslike within the supercritical regime, has been established through MD simulations of the velocity autocorrelation (VACF) and radial distribution function (RDF). We, in this article, explore the changes in the structural features of supercritical LJ fluid under partial confinement using atomistic walls. The study is carried out across the Frenkel line through a series of MD simulations considering a set of thermodynamics states in the supercritical regime (P =5000 bar, 240 K ≤T ≤1500 K ) of argon well above the critical point. Confinement is partial, with atomistic walls located normal to z and extending to "infinity" along the x and y directions. In the "liquidlike" regime of the supercritical phase, particles are found to be distributed in distinct layers along the z axis with layer spacing less than one atomic diameter and the lateral RDF showing amorphous-like structure for specific spacings (packing frustration) and non-amorphous-like structure for other spacings. Increasing the rigidity of the atomistic walls is found to lead to stronger layering and increased structural order. For confinement with reflective walls, layers are found to form with one atomic diameter spacing and the lateral RDF showing close-packed structure for the smaller confinements. Translational order parameter and excess entropy assessment confirms the ordering taking place for atomistic wall and reflective wall confinements. In the "gaslike" regime of the supercritical phase, particle distribution along the spacing and the lateral RDF exhibit features

Trapped particle confinement studies in L = 2 torsatrons for additional helical coils, radial electric field and finite beta effect

International Nuclear Information System (INIS)

Kato, A.; Nakamura, Y.; Wakatani, M.

1990-07-01

L = 2 torsatrons are studied to improve the high energy trapped particle confinement with additional l = 1 and/or l = 3 helical coils. The winding laws are selected in two ways. One is to realize 'σ - optimization' by the additional helical coils, but this approach loses magnetic well region. The other selection is to produce or deepen the magnetic well by the additional helical coils. L=3 helical coils are usable to this end. In this case the improvement of the trapped particle confinement depends on magnetic axis position. Radial electric field producing sheared rotational motion is also considered to improve the trapped particle confinement in a standard l = 2 torsatron. By excluding cancellation between E x B and ΔB drift motion occurred for the parabolic potential profiles, all deeply trapped particles can be confined in the central region. Degradation of the trapped particle confinement by the Shafranov shift is mitigated by shifting the magnetic axis inside in the vacuum configuration. (author)

Temperature oscillating regimes in Tore Supra diagnosed by MHD activity

International Nuclear Information System (INIS)

Maget, P.; Imbeaux, F.; Giruzzi, G.; Udintsev, V.S.; Huysmans, G.T.A.; Segui, J.-L.; Goniche, M.; Moreau, Ph.; Sabot, R.; Garbet, X.

2006-01-01

This paper describes what we can learn on the regimes of spontaneous electron temperature oscillations discovered in Tore Supra from the analysis of MHD activity. Since the first observations of this oscillating behaviour of plasma equilibrium, and its interpretation as a predator-prey system involving lower hybrid waves power deposition and electron confinement, analysis of MHD modes has confirmed the reality of safety factor profile oscillations. This points towards the importance of rational values of the safety factor in the transition to transport barriers in reversed magnetic shear plasmas

Comparison between measured and predicted turbulence frequency spectra in ITG and TEM regimes

Science.gov (United States)

Citrin, J.; Arnichand, H.; Bernardo, J.; Bourdelle, C.; Garbet, X.; Jenko, F.; Hacquin, S.; Pueschel, M. J.; Sabot, R.

2017-06-01

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 (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 robustly predicted unstable in linear studies. In the later SOC phase, where QCMs are no longer observed, ion-temperature-gradient (ITG) modes are identified. In nonlinear simulations, in the ITG (SOC) phase, a broadband spectrum is seen. In the TEM (LOC) phase, a clear emergence of a peak at the TEM frequencies is seen. This is due to reduced nonlinear frequency broadening of the underlying linear modes in the TEM regime compared with the ITG regime. A synthetic diagnostic of the nonlinearly simulated frequency spectra reproduces the features observed in the reflectometry measurements. These results support the identification of core QCMs as an experimental marker for TEM turbulence.

Low-frequency fluctuation regime in a multimode semiconductor laser subject to a mode-selective optical feedback

International Nuclear Information System (INIS)

Rogister, F.; Sciamanna, M.; Deparis, O.; Megret, P.; Blondel, M.

2002-01-01

We study numerically the dynamics of a multimode laser diode subject to a mode-selective optical feedback by using a generalization of the Lang-Kobayashi equations. In this configuration, only one longitudinal mode of the laser is reinjected into the laser cavity; the other modes are free. When the laser operates in the low-frequency fluctuation regime, our model predicts intensity bursts in the free modes simultaneously with dropouts in the selected mode, in good agreement with recent experiments. In the frame of our model, intensity bursts and dropouts are associated with collisions of the system trajectory in phase space with saddle-type antimodes

Beyond dipolar regime in high-order plasmon mode bowtie antennas

Science.gov (United States)

Cuche, Aurélien; Viarbitskaya, Sviatlana; Kumar, Upkar; Sharma, Jadab; Arbouet, Arnaud; Girard, Christian; Dujardin, Erik

2017-03-01

Optical nanoantennas have shown their great potential for far-field to near-field coupling and for light confinement in subwavelength volumes. Here, we report on a multimodal configuration for bright and polarization-dependent bowtie antenna based on large and highly crystalline gold prisms. Each individual prism constituting an antenna arm sustains high order plasmon modes in the visible and near infrared range that allow for high field confinement and two-dimensional optical information propagation. We demonstrate by scanning two-photon luminescence (TPL) microscopy and numerical simulations based on the Green dyadic method that these bowtie antennas result in intense hot spots in different antenna locations as a function of the incident polarization. Finally, we quantify the local field enhancement above the antennas by computing the normalized total decay rate of a molecular system placed in the near field of the antenna gap as a function of the dipole orientation. We demonstrate the existence of a subtle relation between antenna geometry, polarization dependence and field enhancement. These new multimodal optical antennas are excellent far field to near field converter and they open the door for new strategies in the design of coplanar optical components for a wide range of applications including sensing, energy conversion or integrated information processing.

Attainment of high confinement in neutral beam heated divertor discharges in the PDX tokamak

International Nuclear Information System (INIS)

Kaye, S.M.; Bell, M.; Bol, K.

1983-11-01

The PDX divertor configuration has recently been converted from an open to a closed geometry to inhibit the return of neutral gas from the divertor region to the main chamber. Since then, operation in a regime with high energy confinement in neutral beam heated discharges (ASDEX H-mode) has been routine over a wide range of operating conditions. These H-mode discharges are characterized by a sudden drop in divertor density and H/sub α/ emission and a spontaneous rise in main chamber plasma density during neutral beam injection. The confinement time is found to scale nearly linearly with plasma current, but it can be degraded due to either the presence of edge instabilities or heavy gas puffing. Detailed Thomson scattering temperature profiles show high values of Te near the plasma edge (approx. 450 eV) with sharp radial gradients (approx. 400 eV/cm) near the separatrix. Density profiles are broad and also exhibit steep gradients close to the separatrix

Curvature-induced electrostatic drift modes in a toroidal plasma

International Nuclear Information System (INIS)

Venema, M.

1985-01-01

This thesis deals with a number of problems in the theory of linear stability of a hot, fully ionized plasma immersed in a strong magnetic field. The most widely used system to magnetically confine a plasma is the tokamak. This is a toroidal, current carrying device with a strong, externally imposed, magnetic field. The author discusses the linear theory of unstable, low-frequency waves in the gradient region, restricted to electrostatic waves. In that case the resulting radial fluxes of particles and energy are due to electric cross-field drifts. In the presence of magnetic fluctuations and small-scale reconnection phenomena, radial transport could also be predominantly along field lines. At present, it is not clear which of the two mechanisms is the dominant feature of the observed anomalous transport. First, the author introduces the theory of drift waves in toroidal geometry. Next, the electrostratic drift modes in toroidal geometry (weakly collisional regime), the equations for low-frequency waves in the strongly collisional regime and the electrostatic drift modes (strongly collisional regime) are discussed. (Auth.)

Confinement in W7-AS and the role of radial electric field and magnetic shear

International Nuclear Information System (INIS)

Brakel, R.; Anton, M.; Baldzuhn, J.; Burhenn, R.; Erckmann, V.; Fiedler, S.; Geiger, J.; Hartfuss, H.J.; Heinrich, O.; Hirsch, M.; Jaenicke, R.; Kick, M.; Kuehner, G.; Maassberg, H.; Stroth, U.; Wagner, F.; Weller, A.

1997-01-01

Improved neoclassical electron confinement in the centre of low-density ECRH plasmas has been observed in the presence of a strong positive radial electric field, which resembles the electron root solution of the neoclassical ambipolarity condition but is obviously driven by the loss of ECRH-generated suprathermal electrons. At higher densities and with NBI heating, a high confinement regime substantially above the ISS95-scaling and different from the H-mode is established with a strongly sheared negative radial electric field at the boundary. The application of plasma-current induced magnetic shear reveals that confinement in W7-AS is essentially determined by perturbations at high-order rational surfaces. For optimum confinement, these resonances have either to be avoided in the boundary region or magnetic shear must be sufficiently large. Independent of its sign, magnetic shear can reduce electron energy transport which is enhanced in the presence of such resonances to the neoclassical level. (author)

High brightness photonic band crystal semiconductor lasers in the passive mode locking regime

International Nuclear Information System (INIS)

Rosales, R.; Kalosha, V. P.; Miah, M. J.; Bimberg, D.; Posilović, K.; Pohl, J.; Weyers, M.

2014-01-01

High brightness photonic band crystal lasers in the passive mode locking regime are presented. Optical pulses with peak power of 3 W and peak brightness of about 180 MW cm −2  sr −1 are obtained on a 5 GHz device exhibiting 15 ps pulses and a very low beam divergence in both the vertical and horizontal directions.

High β experiment and confinement regimes in a compact helical system

International Nuclear Information System (INIS)

Matsuoka, K.; Okamura, S.; Nishimura, K.; Tsumori, K.; Akiyama, R.; Yamada, H.; Sakakibara, S.; Lazaros, A.; Xu, J.; Ida, K.; Tanaka, K.; Morisaki, T.; Morita, S.; Arimoto, H.; Fujiwara, M.; Idei, H.; Iguchi, H.; Kaneko, O.; Kawamoto, T.; Kubo, S.; Kuroda, T.; Motojima, O.; Ozaki, T.; Pustovitov, V.D.; Sagara, A.; Takahashi, C.; Toi, K.; Watari, T.; Yamada, I.

1995-01-01

A volume-averaged equilibrium β value left angle β eq right angle of 2.14% is achieved in a compact helical system using two neutral beam lines with balanced injection and intense wall conditioning with Ti gettering. This value is the highest β value realized so far in helical systems. Reheat mode, where the stored energy increases after turn-off of a strong gas puff, is employed in the experiment. Discharge conditions are as follows: B t =0.61T; beam power through the port, 1.1MW (coinjection) and 0.8MW (counterinjection); line-averaged electron density n e =6.5x10 13 cm -3 . Amplitudes of magnetic fluctuations integrated over the frequency range from 3kHz to 100kHz become saturated at left angle β eq right angle higher than 1%. Dominant coherent modes are m/n=2/1 and 1/1 when left angle β eq right angle is lower and higher respectively than 1%. Dependence of the energy confinement time τ E on n e (up to 8x10 13 cm -3 ) and B t (from 0.6 to 1.8T) is also studied in this high β experiment. When the density increases τ E degrades compared with the LHD scaling; the density dependence exhibits Bohm-like behaviour. On the contrary, τ E scales as B ∼0.75 t , which is rather close to the LHD scaling (gyro-Bohm-like behaviour). ((orig.))

Vacuum background fields in QCD as a source of confinement

International Nuclear Information System (INIS)

Simonov, Yu.A.

1987-01-01

Large distance behaviour of quark and gluon Green functions is studied in vacuum background fields. Periodic and bounded stochastic fields do not ensure confinement. New stochastic vacuum configurations are suggested, which generate a superlocalization regime, i.e. a large distance decay of Green functions faster than the exponential one. This latter regime corresponds to the confinement

JT-60U high performance regimes

International Nuclear Information System (INIS)

Ishida, S.

1999-01-01

High performance regimes of JT-60U plasmas are presented with an emphasis upon the results from the use of a semi-closed pumped divertor with W-shaped geometry. Plasma performance in transient and quasi steady states has been significantly improved in reversed shear and high- βp regimes. The reversed shear regime elevated an equivalent Q DT eq transiently up to 1.25 (n D (0)τ E T i (0)=8.6x10 20 m-3·s·keV) in a reactor-relevant thermonuclear dominant regime. Long sustainment of enhanced confinement with internal transport barriers (ITBs) with a fully non-inductive current drive in a reversed shear discharge was successfully demonstrated with LH wave injection. Performance sustainment has been extended in the high- bp regime with a high triangularity achieving a long sustainment of plasma conditions equivalent to Q DT eq ∼0.16 (n D (0)τ E T i (0)∼1.4x10 20 m -3 ·s·keV) for ∼4.5 s with a large non-inductive current drive fraction of 60-70% of the plasma current. Thermal and particle transport analyses show significant reduction of thermal and particle diffusivities around ITB resulting in a strong Er shear in the ITB region. The W-shaped divertor is effective for He ash exhaust demonstrating steady exhaust capability of τ He */τ E ∼3-10 in support of ITER. Suppression of neutral back flow and chemical sputtering effect have been observed while MARFE onset density is rather decreased. Negative-ion based neutral beam injection (N-NBI) experiments have created a clear H-mode transition. Enhanced ionization cross- section due to multi-step ionization processes was confirmed as theoretically predicted. A current density profile driven by N-NBI is measured in a good agreement with theoretical prediction. N-NBI induced TAE modes characterized as persistent and bursting oscillations have been observed from a low hot beta of h >∼0.1-0.2% without a significant loss of fast ions. (author)

MHD mode evolutions prior to minor and major disruptions in SST-1 plasma

Energy Technology Data Exchange (ETDEWEB)

Dhongde, Jasraj; Pradhan, Subrata, E-mail: pradhan@ipr.res.in; Bhandarkar, Manisha

2017-01-15

Highlights: • Observation of different regimes of MHD phenomena in SST-1 plasma. • MHD mode (m/n = 1/1, m/n = 2/1) evolutions prior to minor and major disruptions in SST-1 plasma. • MHD mode characteristics such as mode frequency, mode number, island width etc. in different regimes. - Abstract: Steady State Superconducting Tokamak (SST-1) is a medium size Tokamak (R{sub 0} = 1.1 m, a = 0.2 m, B{sub T} = 1.5T, Ip ∼ 110 kA) in operation at the Institute for Plasma Research, India. SST-1 uniquely experiments large aspect ratio (∼5.5) plasma in different operation regimes. In these experiments, repeatable characteristic MHD phenomena have been consistently observed. As the large aspect ratio plasma pulse progresses, these MHD phenomena display minor-major disruptions ably indicated in Mirnov oscillations, Mirnov oscillations with saw teeth and locked modes etc. Even though somewhat similar observations have been found in some other machines, these observations are found for the first time in large aspect ratio plasma of SST-1. This paper elaborates the magnetic field perturbations and mode evolutions due to MHD activities from Mirnov coils (poloidal and toroidal), Soft X-ray diagnostics, ECE diagnostics etc. This work further, for the first time reports quantitatively different regimes of MHD phenomena observed in SST-1 plasma, their details of mode evolutions characteristics as well as the subsequently observed minor, major disruptions supported with the physical explanations. This study will help developing disruption mitigation and avoidance scenarios for having better confinement plasma experiments.

Fluctuating zonal flows in the I-mode regime in Alcator C-Moda)

Science.gov (United States)

Cziegler, I.; Diamond, P. H.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M.; Churchill, R. M.; Hubbard, A. E.; Lipschultz, B.; Sierchio, J. M.; Terry, J. L.; Theiler, C.

2013-05-01

Velocity fields and density fluctuations of edge turbulence are studied in I-mode [F. Ryter et al., Plasma Phys. Controlled Fusion 40, 725 (1998)] plasmas of the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] tokamak, which are characterized by a strong thermal transport barrier in the edge while providing little or no barrier to the transport of both bulk and impurity particles. Although previous work showed no clear geodesic-acoustic modes (GAM) on C-Mod, using a newly implemented, gas-puff-imaging based time-delay-estimate velocity inference algorithm, GAM are now shown to be ubiquitous in all I-mode discharges examined to date, with the time histories of the GAM and the I-mode specific [D. Whyte et al., Nucl. Fusion 50, 105005 (2010)] Weakly Coherent Mode (WCM, f = 100-300 kHz, Δf/f≈0.5, and kθ≈1.3 cm-1) closely following each other through the entire duration of the regime. Thus, the I-mode presents an example of a plasma state in which zero frequency zonal flows and GAM continuously coexist. Using two-field (density-velocity and radial-poloidal velocity) bispectral methods, the GAM are shown to be coupled to the WCM and to be responsible for its broad frequency structure. The effective nonlinear growth rate of the GAM is estimated, and its comparison to the collisional damping rate seems to suggest a new view on I-mode threshold physics.

H-mode pedestal characteristics, ELMs, and energy confinement in ITER shape discharges on DIII-D

International Nuclear Information System (INIS)

Osborne, T.H.; Groebner, R.J.; Lao, L.L.; Leonard, A.W.; Miller, R.L.; Thomas, D.M.; Waltz, R.E.; Maingi, R.; Porter, G.D.

1997-12-01

The H-mode confinement enhancement factor, H, is found to be strongly correlated with the height of the edge pressure pedestal in ITER shape discharges. In discharges with Type I ELMs the pedestal pressure is set by the maximum pressure gradient before the ELM and the width of the H-mode transport barrier. The pressure gradient before Type I ELMs is found to scale as would be expected for a stability limit set by ideal ballooning modes, but with values significantly in excess of that predicted by stability code calculations. The width of the H-mode transport barrier is found to scale equally well with pedestal P(POL)(2/3) or B(POL)(1/2). The improved H value in high B(POL) discharges may be due to a larger edge pressure gradient and wider H-mode transport barrier consistent with their higher edge ballooning mode limit. Deuterium puffing is found to reduce H consistent with the smaller pedestal pressure which results from the reduced barrier width and critical pressure gradient. Type I ELM energy loss is found to be proportional to the change in the pedestal energy

High brightness photonic band crystal semiconductor lasers in the passive mode locking regime

Energy Technology Data Exchange (ETDEWEB)

Rosales, R.; Kalosha, V. P.; Miah, M. J.; Bimberg, D. [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany); Posilović, K. [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany); PBC Lasers GmbH, Hardenbergstrasse 36, 10623 Berlin (Germany); Pohl, J.; Weyers, M. [Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, Berlin 12489 (Germany)

2014-10-20

High brightness photonic band crystal lasers in the passive mode locking regime are presented. Optical pulses with peak power of 3 W and peak brightness of about 180 MW cm{sup −2} sr{sup −1} are obtained on a 5 GHz device exhibiting 15 ps pulses and a very low beam divergence in both the vertical and horizontal directions.

Magnetic confinement

Energy Technology Data Exchange (ETDEWEB)

Batistoni, Paola; De Marco, Francesco; Pieroni, Leonardo (ed.)

2005-07-01

The Frascati Tokamak Upgrade (FTU) is a compact, high-magnetic-field tokamak capable of operating at density and magnetic field values similar to, or even encompassing, those of International Thermonuclear Experimental Reactor (ITER) and therefore provides a unique opportunity to explore physics issues that are directly relevant to ITER. During 2004 the experimental activities were focussed on fully exploiting the lower hybrid system (for generating and controlling the plasma current) and the electron cyclotron heating system (joint experiment with the Institute of Plasma Physics of the National Research Council, Milan). With all four gyrotrons in operation, full electron cyclotron power was achieved up to a record level of 1.5 MW. By simultaneously injecting lower hybrid waves, to tailor the plasma current radial profile, and electron cyclotron waves, to heat the plasma centre, good confinement regimes with internal transport barriers were obtained at the highest plasma density values ever achieved for this operation regime (n {approx}1.5X10{sup 20}m{sup -3}). Specific studies were devoted to optimising the coupling of lower hybrid waves to the plasma (by real-time control of the plasma position) and to generating current by electron cyclotron current drive. The new scanning CO{sub 2} interferometer (developed by the Reversed Field Experiment Consortium) for high spatial and time resolution (1 cm/50 {mu}s) density profile measurements was extensively used. The Thomson scattering diagnostic was upgraded and enabled observation of scattered signals associated with the Confinement background plasma dynamics. As for theoretical studies on the dynamics of turbulence in plasmas, the transition from Bohm-like scaling to gyro-Bohm scaling of the local plasma diffusivity was demonstrated on the basis of a generalised four wave model (joint collaboration with Princeton Plasma Physics Laboratory and the University of California at Irvine). The transition from weak to strong

Magnetic confinement

International Nuclear Information System (INIS)

Batistoni, Paola; De Marco, Francesco; Pieroni, Leonardo

2005-01-01

The Frascati Tokamak Upgrade (FTU) is a compact, high-magnetic-field tokamak capable of operating at density and magnetic field values similar to, or even encompassing, those of International Thermonuclear Experimental Reactor (ITER) and therefore provides a unique opportunity to explore physics issues that are directly relevant to ITER. During 2004 the experimental activities were focussed on fully exploiting the lower hybrid system (for generating and controlling the plasma current) and the electron cyclotron heating system (joint experiment with the Institute of Plasma Physics of the National Research Council, Milan). With all four gyrotrons in operation, full electron cyclotron power was achieved up to a record level of 1.5 MW. By simultaneously injecting lower hybrid waves, to tailor the plasma current radial profile, and electron cyclotron waves, to heat the plasma centre, good confinement regimes with internal transport barriers were obtained at the highest plasma density values ever achieved for this operation regime (n ∼1.5X10 20 m -3 ). Specific studies were devoted to optimising the coupling of lower hybrid waves to the plasma (by real-time control of the plasma position) and to generating current by electron cyclotron current drive. The new scanning CO 2 interferometer (developed by the Reversed Field Experiment Consortium) for high spatial and time resolution (1 cm/50 μs) density profile measurements was extensively used. The Thomson scattering diagnostic was upgraded and enabled observation of scattered signals associated with the Confinement background plasma dynamics. As for theoretical studies on the dynamics of turbulence in plasmas, the transition from Bohm-like scaling to gyro-Bohm scaling of the local plasma diffusivity was demonstrated on the basis of a generalised four wave model (joint collaboration with Princeton Plasma Physics Laboratory and the University of California at Irvine). The transition from weak to strong energetic particle

Ion thermal conductivity and convective energy transport in JET hot-ion regimes and H-modes

International Nuclear Information System (INIS)

Tibone, F.; Balet, B.; Cordey, J.G.

1989-01-01

Local transport in a recent series of JET experiments has been studied using interpretive codes. Auxiliary heating, mainly via neutral beam injection, was applied on low-density target plasmas confined in the double-null X-point configuration. This has produced two-component plasmas with high ion temperature and neutron yield and, above a threshold density, H-modes characterised by peak density and power deposition profiles. H-mode confinement was also obtained for the first time with 25 MW auxiliary power, of which 10 MW was from ion cyclotron resonance heating. We have used profile measurements of electron temperature T e from electron cyclotron emission and LIDAR Thomson scattering, ion temperature T i from charge-exchange recombination spectroscopy (during NBI), electron density n e from LIDAR and Abel-inverted interferometer measurements. Only sparse information is, however, available to date concerning radial profiles of effective ionic charge and radiation losses. Deuterium depletion due to high impurity levels is an important effect in these discharges, and our interpretation of thermal ion energy content, neutron yield and ion particle fluxes needs to be confirmed using measured Z eff -profiles. (author) 4 refs., 4 figs

Effect of ELMs on rotation and momentum confinement in H-mode discharges in JET

DEFF Research Database (Denmark)

Versloot, T.W.; de Vries, P.C.; Giroud, C.

2010-01-01

. An increase in profile peaking of ion temperature and angular frequency is observed. At the same time the plasma confinement is reduced while the ratio of confinement times (Rτ = τE/τ) increases noticeably with ELM frequency. This change could be explained by the relatively larger ELM induced losses......The loss of plasma toroidal angular momentum and thermal energy by edge localized modes (ELMs) has been studied in JET. The analysis shows a consistently larger drop in momentum in comparison with the energy loss associated with the ELMs. This difference originates from the large reduction...... in angular frequency at the plasma edge, observed to penetrate into the plasma up to r/a ~ 0.65 during large type-I ELMs. As a result, the time averaged angular frequency is lowered near the top of the pedestal with increasing ELM frequency, resulting in a significant drop in thermal Mach number at the edge...

Edge localized modes control: experiment and theory

International Nuclear Information System (INIS)

Bedoulet, M.; Huysmans, G.; Thomas, P.; Joffrin, E.; Rimini, F.; Monier-Garbet, P.; Grosman, A.; Ghendrih, P.; Parail, V.; Lomas, P.; Matthews, G.; Wilson, H.; Gryaznevich, M.; Gonsell, G.; Loarte, A.; Saibene, G.; Sartori, R.; Leonard, A.; Snyder, P.; Evans, T.; Gohil, P.; Burell, H.; Moyer, R.; Kamada, Y.; Oyama, N.; Hatae, T.; Degeling, A.; Martin, Y.; Lister, J.; Rapp, J.; Perez, C.; Lang, P.; Chankin, A.; Eich, T.; Sips, A.; Stober, J.; Horton, L.; Kallenbach, A.; Suttrop, W.; Saarelma, S.; Cowley, S.; Lonnroth, J.; Kamiya, K.; Shimada, M.; Polevoi, A.; Federici, G.

2004-01-01

The paper reviews recent theoretical and experimental results focusing on the identification of the key factors controlling ELM (energy localized mode) energy and particle losses both in natural ELMs and in the presence of external controlling mechanisms. The theoretical description of the most studied Type-I ELMs is progressing from linear MHD stability analysis for peeling and ballooning modes to the non-linear explosive models and transport codes. Present theories cannot predict the ELM size self-consistently, however they pointed out the benefit of the high plasma shaping, high q 95 and high pedestal density in reducing the ELM affected area. The experimental data also suggest that the conductive energy losses in Type-I ELM can be controlled by working in specific plasma conditions. In particular, the existence of purely convective small Type-I ELMs regimes at high q 95 (>4.5) with ΔW ELM /W ped <5% was demonstrated in high triangularity (δ ∼ 0.5) plasmas in JET. Small benign ELMs regimes in present machines (EDA, HRS, Type-II, grassy, QH, Type-III in impurity seeded discharges at high δ and their relevance for ITER parameters are reviewed briefly. The absence of already developed ITER relevant high confinement scenarios with acceptable ELMs has motivated recent intensive experimental and theoretical studies of active control of ELMs. The possibility of suppression of Type-I ELMs in H-mode scenarios at constant confinement was demonstrated in DIII-D experiments with a stochastic boundary created by external coils. It has been demonstrated in AUG that small pellets can trigger Type-I ELMs with a frequency imposed by the pellet injector. Pellet induced ELMs are similar to the intrinsic Type-I ELMs with the same frequency. At the same time the confinement degradation due to the fuelling can be minimized with pellets small as compared to the gas injection. Recent plasma current ramp experiments (JET, COMPASS-D) and modelling (JETTO) demonstrated that the edge

Edge localized modes control: experiment and theory

Energy Technology Data Exchange (ETDEWEB)

Bedoulet, M.; Huysmans, G.; Thomas, P.; Joffrin, E.; Rimini, F.; Monier-Garbet, P.; Grosman, A.; Ghendrih, P. [Association Euratom-CEA, Centre d' Etudes de Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee; Parail, V.; Lomas, P.; Matthews, G.; Wilson, H.; Gryaznevich, M.; Gonsell, G.; Loarte, A.; Saibene, G.; Sartori, R.; Leonard, A.; Snyder, P.; Evans, T.; Gohil, P.; Burell, H.; Moyer, R.; Kamada, Y.; Oyama, N.; Hatae, T.; Degeling, A.; Martin, Y.; Lister, J.; Rapp, J.; Perez, C.; Lang, P.; Chankin, A.; Eich, T.; Sips, A.; Stober, J.; Horton, L.; Kallenbach, A.; Suttrop, W.; Saarelma, S.; Cowley, S.; Lonnroth, J.; Kamiya, K.; Shimada, M.; Polevoi, A.; Federici, G

2004-07-01

The paper reviews recent theoretical and experimental results focusing on the identification of the key factors controlling ELM (energy localized mode) energy and particle losses both in natural ELMs and in the presence of external controlling mechanisms. The theoretical description of the most studied Type-I ELMs is progressing from linear MHD stability analysis for peeling and ballooning modes to the non-linear explosive models and transport codes. Present theories cannot predict the ELM size self-consistently, however they pointed out the benefit of the high plasma shaping, high q{sub 95} and high pedestal density in reducing the ELM affected area. The experimental data also suggest that the conductive energy losses in Type-I ELM can be controlled by working in specific plasma conditions. In particular, the existence of purely convective small Type-I ELMs regimes at high q{sub 95} (>4.5) with {delta}W{sub ELM}/W{sub ped}<5% was demonstrated in high triangularity ({delta} {approx} 0.5) plasmas in JET. Small benign ELMs regimes in present machines (EDA, HRS, Type-II, grassy, QH, Type-III in impurity seeded discharges at high {delta} and their relevance for ITER parameters are reviewed briefly. The absence of already developed ITER relevant high confinement scenarios with acceptable ELMs has motivated recent intensive experimental and theoretical studies of active control of ELMs. The possibility of suppression of Type-I ELMs in H-mode scenarios at constant confinement was demonstrated in DIII-D experiments with a stochastic boundary created by external coils. It has been demonstrated in AUG that small pellets can trigger Type-I ELMs with a frequency imposed by the pellet injector. Pellet induced ELMs are similar to the intrinsic Type-I ELMs with the same frequency. At the same time the confinement degradation due to the fuelling can be minimized with pellets small as compared to the gas injection. Recent plasma current ramp experiments (JET, COMPASS-D) and

In-plane confinement and waveguiding of surface acoustic waves through line defects in pillars-based phononic crystal

Directory of Open Access Journals (Sweden)

Abdelkrim Khelif

2011-12-01

Full Text Available We present a theoretical analysis of an in-plane confinement and a waveguiding of surface acoustic waves in pillars-based phononic crystal. The artificial crystal is made up of cylindrical pillars placed on a semi-infinite medium and arranged in a square array. With a well-chosen of the geometrical parameters, this pillars-based system can display two kinds of complete band gaps for guided waves propagating near the surface, a low frequency gap based on locally resonant mode of pillars as well as a higher frequency gap appearing at Bragg scattering regime. In addition, we demonstrate a waveguiding of surface acoustic wave inside an extended linear defect created by removing rows of pillars in the perfect crystal. We discuss the transmission and the polarization of such confined mode appearing in the higher frequency band gap. We highlight the strong similarity of such defect mode and the Rayleigh wave of free surface medium. An efficient finite element analysis is used to simulate the propagation of guided waves through silicon pillars on a silicon substrate.

Development of a tokamak plasma optimized for stability and confinement

International Nuclear Information System (INIS)

Politzer, P.A.

1995-02-01

Design of an economically attractive tokamak fusion reactor depends on producing steady-state plasma operation with simultaneous high energy density (β) and high energy confinement (τ E ); either of these, by itself, is insufficient. In operation of the DIII-D tokamak, both high confinement enhancement (H≡ τ E /τ ITER-89P = 4) and high normalized β (β N ≡ β/(I/aB) = 6%-m-T/MA) have been obtained. For the present, these conditions have been produced separately and in transient discharges. The DIII-D advanced tokamak development program is directed toward developing an understanding of the characteristics which lead to high stability and confinement, and to use that understanding to demonstrate stationary, high performance operation through active control of the plasma shape and profiles. The authors have identified some of the features of the operating modes in DIII-D that contribute to better performance. These are control of the plasma shape, control of both bulk plasma rotation and shear in the rotation and Er profiles, and particularly control of the toroidal current profiles. In order to guide their future experiments, they are developing optimized scenarios based on their anticipated plasma control capabilities, particularly using fast wave current drive (on-axis) and electron cyclotron current drive (off-axis). The most highly developed model is the second-stable core VH-mode, which has a reversed magnetic shear safety factor profile [q(O) = 3.9, q min = 2.6, and q 95 = 6]. This model plasma uses profiles which the authors expect to be realizable. At β N ≥ 6, it is stable to n=l kink modes and ideal ballooning modes, and is expected to reach H ≥ 3 with VH-mode-like confinement

Knotting dynamics of DNA chains of different length confined in nanochannels

International Nuclear Information System (INIS)

Suma, Antonio; Micheletti, Cristian; Orlandini, Enzo

2015-01-01

Langevin dynamics simulations are used to characterize the typical mechanisms governing the spontaneous tying, untying and the dynamical evolution of knots in coarse-grained models of DNA chains confined in nanochannels. In particular we focus on how these mechanisms depend on the chain contour length, L c , at a fixed channel width D = 56 nm corresponding to the onset of the Odijk scaling regime where chain backfoldings and hence knots are disfavoured but not suppressed altogether. We find that the lifetime of knots grows significantly with L c , while that of unknots varies to a lesser extent. The underlying kinetic mechanisms are clarified by analysing the evolution of the knot position along the chain. At the considered confinement, in fact, knots are typically tied by local backfoldings of the chain termini where they are eventually untied after a stochastic motion along the chain. Consequently, the lifetime of unknots is mostly controlled by backfoldings events at the chain ends, which is largely independent of L c . The lifetime of knots, instead, increases significantly with L c because knots can, on average, travel farther along the chain before being untied. The observed interplay of knots and unknots lifetimes underpins the growth of the equilibrium knotting probability of longer and longer chains at fixed channel confinement. (paper)

Characteristics of the TPE reversed-field pinch plasmas in conventional and improved confinement regimes

International Nuclear Information System (INIS)

Sakakita, H.; Asai, T.; Fiksel, G.; Yagi, Y.; Frassinetti, L.; Hayase, K.; Hirano, Y.; Kiyama, S.; Koguchi, H.; Shimada, T.; Innocente, P.; Spizzo, G.; Terranova, D.; Sato, Y.; Yoshikawa, M.

2005-01-01

We present the characteristics and experimental scaling laws of reversed-field pinch (RFP) plasmas, which are obtained from the recently established toroidal pinch experiment (TPE) database. The database contains information for approximately 1500 discharges consistently selected from four TPE RFP devices, and covers two decades of RFP experiments under conventional operating conditions at the National Institute of Advanced Industrial Science and Technology. We present the physics of the pulsed poloidal current drive (PPCD) discharges in the TPE-RX RFP device, and a comparison of the improved energy confinement time in PPCD, τ E P PCD , with τ E s caling as the reference scaling law (τ E s caling ∼ a 1.63 (I P 0.78 (I P /N) 0.33 Θ 2.97 ) in the TPE database, is attempted. The result shows that τ E P PCD agrees well with τ E s caling because of the strong pinch parameter dependence on the TPE scaling law. A potential improved confinement mode in the quasi-single-helicity (QSH) state is also investigated in TPE-RX, with respect to the operation conditions under which the QSH spontaneously appears in the core region, where a typical island structure is observed by means of soft Xray tomography. (author)

Fluctuating zonal flows in the I-mode regime in Alcator C-Mod

Energy Technology Data Exchange (ETDEWEB)

Cziegler, I.; Diamond, P. H.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M. [Center for Momentum Transport and Flow Organization, University of California, San Diego, La Jolla, California 92093 (United States); Churchill, R. M.; Hubbard, A. E.; Lipschultz, B.; Sierchio, J. M.; Terry, J. L.; Theiler, C. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02138 (United States)

2013-05-15

Velocity fields and density fluctuations of edge turbulence are studied in I-mode [F. Ryter et al., Plasma Phys. Controlled Fusion 40, 725 (1998)] plasmas of the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] tokamak, which are characterized by a strong thermal transport barrier in the edge while providing little or no barrier to the transport of both bulk and impurity particles. Although previous work showed no clear geodesic-acoustic modes (GAM) on C-Mod, using a newly implemented, gas-puff-imaging based time-delay-estimate velocity inference algorithm, GAM are now shown to be ubiquitous in all I-mode discharges examined to date, with the time histories of the GAM and the I-mode specific [D. Whyte et al., Nucl. Fusion 50, 105005 (2010)] Weakly Coherent Mode (WCM, f = 100–300 kHz, Δf/f≈0.5, and k{sub θ}≈1.3 cm{sup −1}) closely following each other through the entire duration of the regime. Thus, the I-mode presents an example of a plasma state in which zero frequency zonal flows and GAM continuously coexist. Using two-field (density-velocity and radial-poloidal velocity) bispectral methods, the GAM are shown to be coupled to the WCM and to be responsible for its broad frequency structure. The effective nonlinear growth rate of the GAM is estimated, and its comparison to the collisional damping rate seems to suggest a new view on I-mode threshold physics.

Investigation of equilibrium, global modes and microinstabilities in the stellarator W7-AS

International Nuclear Information System (INIS)

Weller, A.; Anton, M.; Brakel, R.

1999-01-01

Equilibrium and stability properties in the WENDELSTEIN 7-AS stellarator are investigated experimentally and compared with theoretical predictions for particular cases. The topology of equilibrium magnetic surfaces and of global MHD modes is inferred from X-ray tomography. The predicted effects of externally driven currents and internal currents on the equilibrium surfaces could be confirmed experimentally. In particular the reduced Shafranov shift due to reduced Pfirsch-Schlueter currents in W7-AS could be verified. Up to the maximum accessible β ((β) ∼ 2%) plasmas can be confined without significant deterioration by pressure driven MHD-activity. However, global modes in the stable MHD spectrum such as global and toroidal Alfven eigenmodes (GAE, TAE) can be destabilised by energetic ions from neutral beam heating. These instabilities appear as very coherent low frequency modes (≤ 40 kHz) in the lower β regime without significant impact on the global confinement. At medium β very strong particle driven MHD modes with frequencies up to the range of 500 kHz can be observed. These modes can show nonlinear behaviour including periodic bursting and frequency chirping in combination with significant plasma energy losses. With increasing β Alfven modes are widely stable, because under these conditions the damping relative to the particle drive is increased. Besides the global mode activity small scale turbulent structures have been investigated in the plasma core and at the edge. The measured data of electron temperature, density and magnetic fluctuations do not yet allow to assess turbulence driven transport fluxes. However, correlations with the global confinement have been found, and the measured amplitudes are in the range expected to be relevant for anomalous transport. The observed dependence of the confinement on the edge rotational transform and magnetic shear can be explained in terms of enhanced transport at rational surfaces, however, the underlying

Investigation of equilibrium, global modes and microinstabilities in the stellarator W7-AS

International Nuclear Information System (INIS)

Weller, A.; Anton, M.; Brakel, R.

2001-01-01

Equilibrium and stability properties in the WENDELSTEIN 7-AS stellarator are investigated experimentally and compared with theoretical predictions for particular cases. The topology of equilibrium magnetic surfaces and of global MHD modes is inferred from X-ray tomography. The predicted effects of externally driven currents and internal currents on the equilibrium surfaces could be confirmed experimentally. In particular the reduced Shafranov shift due to reduced Pfirsch-Schlueter currents in W7-AS could be verified. Up to the maximum accessible β ( ∼2%) plasmas can be confined without significant deterioration by pressure driven MHD-activity. However, global modes in the stable MHD spectrum such as global and toroidal Alfven eigenmodes (GAE, TAE) can be destabilised by energetic ions from neutral beam heating. These instabilities appear as very coherent low frequency modes (≤40 kHz) in the lower β regime without significant impact on the global confinement. At medium β very strong particle driven MHD modes with frequencies up to the range of 500 kHz can be observed. These modes can show nonlinear behaviour including periodic bursting and frequency chirping in combination with significant plasma energy losses. With increasing β Alfven modes are widely stable, because under these conditions the damping relative to the particle drive is increased. Besides the global mode activity small scale turbulent structures have been investigated in the plasma core and at the edge. The measured data of electron temperature, density and magnetic fluctuations do not yet allow to assess turbulence driven transport fluxes. However, correlations with the global confinement have been found, and the measured amplitudes are in the range expected to be relevant for anomalous transport. The observed dependence of the confinement on the edge rotational transform and magnetic shear can be explained in terms of enhanced transport at rational surfaces, however, the underlying

Decay of the diocotron rotation and transport in a new low-density asymmetry-dominated regime

International Nuclear Information System (INIS)

Sarid, Eli; Gilson, Erik; Fajans, Joel

2002-01-01

The decay of the diocotron rotation was studied in a new regime in which trap asymmetries dominate. The decay does not conserve angular momentum, and is strongest for small, low-density columns. For such columns decay of the diocotron mode within few diocotron periods was observed, orders of magnitude faster than the rotational pumping prediction. However, transition to decay dominated by rotational pumping was observed for larger and denser columns. The new regime is characterized by 'magnetron-like' rotation in the trap, dominated by the end confinement fields. The asymmetry-dominated transport was also studied, and found to depend linearly on the line density (and not the density) over nearly 4 orders of magnitude

Physics of the L-mode to H-mode transition in tokamaks

International Nuclear Information System (INIS)

Burrell, K.H.; Carlstrom, T.N.; Gohil, P.; Groebner, R.J.; Kim, J.; Osborne, T.H.; St. John, H.; Stambaugh, R.D.; Doyle, E.J.; Moyer, R.A.; Rettig, C.L.; Peebles, W.A.; Rhodes, T.L.; Finkenthal, D.; Hillis, D.L.; Wade, M.R.; Matsumoto, H.; Watkins, J.G.

1992-07-01

Combined theoretical and experimental work has resulted in the creation of a paradigm which has allowed semi-quantitative understanding of the edge confinement improvement that occurs in the H-mode. Shear in the E x B flow of the fluctuations in the plasma edge can lead to decorrelation of the fluctuations, decreased radial correlation lengths and reduced turbulent transport. Changes in the radial electric field, the density fluctuations and the edge transport consistent with shear stabilization of turbulence have been seen in several tokamaks. The purpose of this paper is to discuss the most recent data in the light of the basic paradigm of electric field shear stabilization and to critically compare the experimental results with various theories

Review of DIII-D H-Mode Density Limit Studies

International Nuclear Information System (INIS)

Maingi, R.; Mahdavi, M.A.

2005-01-01

Density limit studies over the past 10 yr on DIII-D have successfully identified several processes that limit plasma density in various operating modes. The recent focus of these studies has been on maintenance of the high-density operational window with good H-mode level energy confinement. We find that detachment and onset of multifaceted axisymmetric radiation from the edge (MARFE), fueling efficiency, particle confinement, and magnetohydrodynamic activity can impose density limits in certain regimes. By studying these processes, we have devised techniques with either pellets or gas fueling and divertor pumping to achieve line average density above Greenwald scaling, relying on increasing the ratio of pedestal to separatrix density, as well as density profile peaking. The scaling of several of these processes to next-step devices (e.g., the International Thermonuclear Experimental Reactor) has indicated that sufficiently high pedestal density can be achieved with conventional fueling techniques while ensuring divertor partial detachment needed for heat flux reduction. One density limit process requiring further study is neoclassical tearing mode (NTM) onset, and techniques for avoidance/mitigation of NTMs need additional development in present-day devices operated at high density

Collective modes across the soliton-droplet crossover in binary Bose mixtures

Science.gov (United States)

Cappellaro, Alberto; Macrı, Tommaso; Salasnich, Luca

2018-05-01

We study the collective modes of a binary Bose mixture across the soliton to droplet crossover in a quasi-one-dimensional waveguide with a beyond-mean-field equation of state and a variational Gaussian ansatz for the scalar bosonic field of the corresponding effective action. We observe a sharp difference in the collective modes in the two regimes. Within the soliton regime, modes vary smoothly upon the variation of particle number or interaction strength. On the droplet side, collective modes are inhibited by the emission of particles. This mechanism turns out to be dominant for a wide range of particle numbers and interactions. In a small window of particle number range and for intermediate interactions, we find that monopole frequency is likely to be observed. We focus on the spin-dipole modes for the case of equal intraspecies interactions and equal equilibrium particle numbers in the presence of a weak longitudinal confinement. We find that such modes might be unobservable in the real-time dynamics close to the equilibrium as their frequency is higher than the particle emission spectrum by at least one order of magnitude in the droplet phase. Our results are relevant for experiments with two-component Bose-Einstein condensates for which we provide realistic parameters.

Magnetic order and confinement improvement in high-current regimes of RFX-mod with MHD feedback control

International Nuclear Information System (INIS)

Piovesan, P.; Zuin, M.; Alfier, A.; Bonfiglio, D.; Bonomo, F.; Canton, A.; Cappello, S.; Carraro, L.; Cavazzana, R.; Fassina, A.; Gobbin, M.; Lorenzini, R.; Marrelli, L.; Martin, P.; Martines, E.; Pasqualotto, R.; Puiatti, M.E.; Spolaore, M.; Valisa, M.; Escande, D.F.

2009-01-01

The RFX-mod machine (Sonato et al 2003 Fusion Eng. Des. 66 161) recently achieved, for the first time in a reversed-field pinch, high plasma current up to 1.6 MA with good confinement. Magnetic feedback control of magnetohydrodynamic instabilities was essential to reach the goal. As the current is raised, the plasma spontaneously accesses a new helical state, starting from turbulent multi-helical conditions. Together with this raise, the ratio between the dominant and the secondary mode amplitudes increases in a continuous way. This brings a significant improvement in the magnetic field topology, with the formation of helical flux surfaces in the core. As a consequence, strong helical transport barriers with maximum electron temperature around 1 keV develop in this region. The energy confinement time increases by a factor of 4 with respect to the lower-current, multi-helical conditions. The properties of the new helical state scale favourably with the current, thus opening promising perspectives for the higher current experiments planned for the near future.

Effect of ripple-induced transport on H-mode performance in tokamaks

International Nuclear Information System (INIS)

Parail, V.; Vries, P. de; Lonnroth, J.; Kiviniemi, T.; Johnson, T.; Loarte, A.; Saibene, G.; Hatae, T.; Kamada, Y.; Konovalov, S.; Oyama, N.; Shinohara, K.; Tobita, K.; Urano, H.

2005-01-01

A number of experiments have shown that ripple-induced transport influences performance of ELMy H-modes in the tokamak. A noticeable difference in confinement, ELM frequency and amplitude was found between JET (with ripple amplitude δ∼0.1%) and JT-60U (with δ∼1%) in otherwise identical discharges. It was previously shown in JET experiments with enhanced ripple that a gradual increase in the ripple amplitude first leads to a modest improvement in plasma confinement, which is followed by the degradation of edge pedestal and further transition to the L-mode regime if δ increases further. The DIII-D team recently reported a marginal increase in confinement in experiments with an edge transport enhanced by the externally driven resonant magnetic perturbation. Numerical predictive modelling of the dynamics of ELMy H-mode JET plasma relevant to a JET/JT-60U similarity experiment has been conducted taking into account ripple-induced ion transport, which was computed using the orbit following code ASCOT. This predictive modelling reveals that, depending on plasma parameters, ripple amplitude and localisation (the latter depending on the toroidal coil design), this additional transport can either improve global plasma confinement or reduce it. These controlled ripple losses might be used as an effective tool for ELM mitigation and may provide an explanation for the difference between JET and JT-60U observed in the similarity experiments. A detailed comparison between ripple- induced transport and the alternative method of ELM mitigation by an externally driven edge magnetic perturbation is discussed. The fact that ripple losses mainly increase ion transport, while a stochastic magnetic layer increases electron transport indicates that it might be beneficial to use a combination of both methods in future experiments. This work was funded partly by the United Kingdom Engineering and Physical Sciences Research Council and by the European Communities under the contract of

Regimes of operation in the Princeton Large Torus

Energy Technology Data Exchange (ETDEWEB)

Hosea, J.C.

1979-10-01

In the quest for optimum discharge conditions in the Princeton Large Torus (PLT), a variety of discharge regimes have been produced. These separate broadly into two main categories - those regimes with m greater than or equal to 2 oscillatory MHD instabilities and often hollow electron profiles for tungsten limiters, and those regimes for which the electron temperature is sufficiently peaked to support the internal sawtooth or near-sawtooth (m = 1) instability. The internal sawtooth regime is found to be optimum for confinement but to be more difficult to select when low-Z impurity concentrations have been reduced with low power discharge cleaning or gettering to permit extension of the high density operation limit. Gas programming is used to cool the plasma periphery, thereby reducing the high-Z impurity concentrations and causing the current channel to constrict into the sawtooth regime, and then to attain the desired plasma density. With discharges selected in this manner, gross energetic confinement times up to approx. 100 msec have been obtained at densities of approx. 10/sup 14/ cm/sup -3/, and very high ion and electron temperatures have been produced with neutral beam injection heating at lower densities with no observable deleterious effect on energy confinement.

Electronic control of different generation regimes in mode-locked all-fibre F8 laser

Science.gov (United States)

Kobtsev, Sergey; Ivanenko, Aleksey; Kokhanovskiy, Alexey; Smirnov, Sergey

2018-04-01

We demonstrate for the first time an electronically controlled realisation of markedly different generation regimes in a mode-locked all-fibre figure-eight (F8) Yb-doped laser. Electronic adjustment of the ratio of pumping powers of two amplification stages in a nonlinear amplifying loop mirror enables the establishment of stable pulse generation regimes with different degrees of coherence and control over their parameters within relatively broad limits, with the pulse duration range exceeding a factor of two in the picosecond domain for coherent and incoherent pulses, the energy range exceeding an order of magnitude for incoherent pulses (2.2-24.8 nJ) and over a factor of 8 for coherent pulses (1.9-16.2 nJ). Adjustment of the pumping powers allows one to maintain the duration of the coherent pulses and to set their peak power in the range of 32.5-292.5 W. The proposed configuration of electronic control over the radiation parameters of a mode-locked all-fibre F8 laser enables reproducible generation of pulses of different types with specified parameters within a broad range of values.

The H-mode operational window as determined from the ITER H-mode database

International Nuclear Information System (INIS)

Ryter, F.; Kardaun, O.J.W.F.; Stroth, U.

1994-01-01

The H-mode is a promising regime for fusion reactors and it is essential to be able to predict its operational window in future devices. The 'H-Mode Database Working Group' started in 1992 to gather, analyze and compare H-mode threshold data from several divertor tokamaks so that predictions could be made. The database and first results were presented and the threshold database has been improved and extended since. The work has two objectives: 1) to predict the minimum heating power necessary to reach the H-mode in future devices, 2) to contribute to physics studies of the L-H transition. (author) 11 refs., 2 figs

Models for Predicting Boundary Conditions in L-Mode Tokamak Plasma

International Nuclear Information System (INIS)

Siriwitpreecha, A.; Onjun, T.; Suwanna, S.; Poolyarat, N.; Picha, R.

2009-07-01

Full text: The models for predicting temperature and density of ions and electrons at boundary conditions in L-mode tokamak plasma are developed using an empirical approach and optimized against the experimental data obtained from the latest public version of the International Pedestal Database (version 3.2). It is assumed that the temperature and density at boundary of L-mode plasma are functions of engineering parameters such as plasma current, toroidal magnetic field, total heating power, line averaged density, hydrogenic particle mass (A H ), major radius, minor radius, and elongation at the separatrix. Multiple regression analysis is carried out for these parameters with 86 data points in L-mode from Aug (61) and JT60U (25). The RMSE of temperature and density at boundary of L-mode plasma are found to be 24.41% and 18.81%, respectively. These boundary models are implemented in BALDUR code, which will be used to simulate the L-mode plasma in the tokamak

Confinement studies of helical-axis Heliotron plasmas

International Nuclear Information System (INIS)

Sano, F.; Mizuuchi, T.; Kondo, K.

2005-01-01

The L-H transition in the helical-axis heliotron, Heliotron J, was investigated. For ECH-only, NBI-only and ECH+NBI combination heating plasmas, the confinement quality of the H-mode was examined with special regard to the magnetic configuration, the vacuum edge iota value of which was chosen as a label of the configuration. The experimental iota dependence of the H ISS95 -factor (τ E exp /τ E ISS95 ) has revealed that there exist the specific configurations for which the high-quality H-modes (1.3 ISS95 p , was calculated and compared with the experiment. Edge plasma characteristics are also measured and discussed with regard to the E r -shear formation at the transition. (author)

Center-stabilized Yang-Mills Theory:Confinement and Large N Volume Independence

International Nuclear Information System (INIS)

Unsal, Mithat; Yaffe, Laurence G.

2008-01-01

We examine a double trace deformation of SU(N) Yang-Mills theory which, for large N and large volume, is equivalent to unmodified Yang-Mills theory up to O(1/N 2 ) corrections. In contrast to the unmodified theory, large N volume independence is valid in the deformed theory down to arbitrarily small volumes. The double trace deformation prevents the spontaneous breaking of center symmetry which would otherwise disrupt large N volume independence in small volumes. For small values of N, if the theory is formulated on R 3 x S 1 with a sufficiently small compactification size L, then an analytic treatment of the non-perturbative dynamics of the deformed theory is possible. In this regime, we show that the deformed Yang-Mills theory has a mass gap and exhibits linear confinement. Increasing the circumference L or number of colors N decreases the separation of scales on which the analytic treatment relies. However, there are no order parameters which distinguish the small and large radius regimes. Consequently, for small N the deformed theory provides a novel example of a locally four-dimensional pure gauge theory in which one has analytic control over confinement, while for large N it provides a simple fully reduced model for Yang-Mills theory. The construction is easily generalized to QCD and other QCD-like theories

Center-stabilized Yang-Mills theory: Confinement and large N volume independence

International Nuclear Information System (INIS)

Uensal, Mithat; Yaffe, Laurence G.

2008-01-01

We examine a double trace deformation of SU(N) Yang-Mills theory which, for large N and large volume, is equivalent to unmodified Yang-Mills theory up to O(1/N 2 ) corrections. In contrast to the unmodified theory, large N volume independence is valid in the deformed theory down to arbitrarily small volumes. The double trace deformation prevents the spontaneous breaking of center symmetry which would otherwise disrupt large N volume independence in small volumes. For small values of N, if the theory is formulated on R 3 xS 1 with a sufficiently small compactification size L, then an analytic treatment of the nonperturbative dynamics of the deformed theory is possible. In this regime, we show that the deformed Yang-Mills theory has a mass gap and exhibits linear confinement. Increasing the circumference L or number of colors N decreases the separation of scales on which the analytic treatment relies. However, there are no order parameters which distinguish the small and large radius regimes. Consequently, for small N the deformed theory provides a novel example of a locally four-dimensional pure-gauge theory in which one has analytic control over confinement, while for large N it provides a simple fully reduced model for Yang-Mills theory. The construction is easily generalized to QCD and other QCD-like theories.

Physics of high performance deuterium-tritium plasmas in TFTR

International Nuclear Information System (INIS)

McGuire, K.M.; Batha, S.

1996-11-01

During the past two years, deuterium-tritium (D-T) plasmas in the Tokamak Fusion Test Reactor (TFTR) have been used to study fusion power production, isotope effects associated with tritium fueling, and alpha-particle physics in several operational regimes. The peak fusion power has been increased to 10.7 MW in the supershot mode through the use of increased plasma current and toroidal magnetic field and extensive lithium wall conditioning. The high-internal-inductance (high-I i ) regime in TFTR has been extended in plasma current and has achieved 8.7 MW of fusion power. Studies of the effects of tritium on confinement have now been carried out in ohmic, NBI- and ICRF- heated L-mode and reversed-shear plasmas. In general, there is an enhancement in confinement time in D-T plasmas which is most pronounced in supershot and high-I i discharges, weaker in L-mode plasmas with NBI and ICRF heating and smaller still in ohmic plasmas. In reversed-shear discharges with sufficient deuterium-NBI heating power, internal transport barriers have been observed to form, leading to enhanced confinement. Large decreases in the ion heat conductivity and particle transport are inferred within the transport barrier. It appears that higher heating power is required to trigger the formation of a transport barrier with D-T NBI and the isotope effect on energy confinement is nearly absent in these enhanced reverse-shear plasmas. Many alpha-particle physics issues have been studied in the various operating regimes including confinement of the alpha particles, their redistribution by sawteeth, and their loss due to MHD instabilities with low toroidal mode numbers. In weak-shear plasmas, alpha-particle destabilization of a toroidal Alfven eigenmode has been observed

Observation of dynamic interactions between fundamental and second-harmonic modes in a high-power sub-terahertz gyrotron operating in regimes of soft and hard self-excitation.

Science.gov (United States)

Saito, Teruo; Tatematsu, Yoshinori; Yamaguchi, Yuusuke; Ikeuchi, Shinji; Ogasawara, Shinya; Yamada, Naoki; Ikeda, Ryosuke; Ogawa, Isamu; Idehara, Toshitaka

2012-10-12

Dynamic mode interaction between fundamental and second-harmonic modes has been observed in high-power sub-terahertz gyrotrons [T. Notake et al., Phys. Rev. Lett. 103, 225002 (2009); T. Saito et al. Phys. Plasmas 19, 063106 (2012)]. Interaction takes place between a parasitic fundamental or first-harmonic (FH) mode and an operating second-harmonic (SH) mode, as well as among SH modes. In particular, nonlinear excitation of the parasitic FH mode in the hard self-excitation regime with assistance of a SH mode in the soft self-excitation regime was clearly observed. Moreover, both cases of stable two-mode oscillation and oscillation of the FH mode only were observed. These observations and theoretical analyses of the dynamic behavior of the mode interaction verify the nonlinear hard self-excitation of the FH mode.

Preliminary study of energy confinement data with a statistical analysis system in HL-2A tokamak

International Nuclear Information System (INIS)

Xu Yuan; Cui Zhengying; Ji Xiaoquan; Dong Chunfeng; Yang Qingwei; O J W F Kardaun

2010-01-01

Taking advantage of the HL-2A experimental data,an energy confinement database facing ITERL DB2.0 version has been originally established. As for this database,a world widely used statistical analysis system (SAS) has been adopted for the first time to analyze and evaluate the confinement data from HL-2A and the research on scaling laws of energy confinement time corresponding to plasma density is developed, some preliminary results having been achieved. Finally, through comparing with both ITER scaling law and previous ASDEX database, the investigation about L-mode confinement quality on HL-2A and influence of temperature on Spitzer resistivity will be discussed. (authors)

Experimental studies of high-confinement mode plasma response to non-axisymmetric magnetic perturbations in ASDEX Upgrade

Science.gov (United States)

Suttrop, W.; Kirk, A.; Nazikian, R.; Leuthold, N.; Strumberger, E.; Willensdorfer, M.; Cavedon, M.; Dunne, M.; Fischer, R.; Fietz, S.; Fuchs, J. C.; Liu, Y. Q.; McDermott, R. M.; Orain, F.; Ryan, D. A.; Viezzer, E.; The ASDEX Upgrade Team; The DIII-D Team; The Eurofusion MST1 Team

2017-01-01

The interaction of externally applied small non-axisymmetric magnetic perturbations (MP) with tokamak high-confinement mode (H-mode) plasmas is reviewed and illustrated by recent experiments in ASDEX Upgrade. The plasma response to the vacuum MP field is amplified by stable ideal kink modes with low toroidal mode number n driven by the H-mode edge pressure gradient (and associated bootstrap current) which is experimentally evidenced by an observable shift of the poloidal mode number m away from field alignment (m  =  qn, with q being the safety factor) at the response maximum. A torque scan experiment demonstrates the importance of the perpendicular electron flow for shielding of the resonant magnetic perturbation, as expected from a two-fluid MHD picture. Two significant effects of MP occur in H-mode plasmas at low pedestal collisionality, ν \\text{ped}\\ast≤slant 0.4 : (a) a reduction of the global plasma density by up to 61 % and (b) a reduction of the energy loss associated with edge localised modes (ELMs) by a factor of up to 9. A comprehensive database of ELM mitigation pulses at low {ν\\ast} in ASDEX Upgrade shows that the degree of ELM mitigation correlates with the reduction of pedestal pressure which in turn is limited and defined by the onset of ELMs, i. e. a modification of the ELM stability limit by the magnetic perturbation.

Nanomechanical inverse electromagnetically induced transparency and confinement of light in normal modes

International Nuclear Information System (INIS)

Agarwal, G S; Huang, Sumei

2014-01-01

We demonstrate the existence of the phenomenon of the inverse electromagnetically induced transparency (IEIT) in an opto mechanical system consisting of a nanomechanical mirror placed in an optical cavity. We show that two weak counter-propagating identical classical probe fields can be completely absorbed by the system in the presence of a strong coupling field so that the output probe fields are zero. The light is completely confined inside the cavity and the energy of the incoming probe fields is shared between the cavity field and creation of a coherent phonon and resides primarily in one of the polariton modes. The energy can be extracted by a perturbation of the external fields or by suddenly changing the Q of the cavity. (paper)

Thermal electron transport in regimes with low and negative magnetic shear in Tore Supra

International Nuclear Information System (INIS)

Voitsekhovitch, I.; Litaudon, X.; Moreau, D.; Aniel, T.; Becoulet, A.; Erba, M.; Joffrin, E.; Kazarian-Vibert, F.; Peysson, Y.

1997-01-01

The magnetic shear effect on thermal electron transport is studied in a large variety of non-inductive plasmas in Tore Supra. An improved confinement in the region of low and negative shear was observed and quantified with an exponential dependence on the magnetic shear (Litaudon, et al., Fusion Energy 1996 (Proc. 16th Int. Conf. Montreal, 1996), Vol. 1, IAEA, Vienna (1997) 669). This is interpreted as a consequence of a decoupling of the global modes (Romanelli and Zonca, Phys. Fluids B 5 (1993) 4081) that are thought to be responsible for anomalous transport. This dependence is proposed in order to complete the Bohm-like L mode local electron thermal diffusivity so as to describe the transition from Bohm-like to gyroBohm transport in the plasma core. The good agreement between the predictive simulations of the different Tore Supra regimes (hot core lower hybrid enhanced performance, reversed shear plasmas and combined lower hybrid current drive and fast wave electron heating) and experimental data provides a basis for extrapolation of this magnetic shear dependence in the local transport coefficients to future machines. As an example, a scenario for non-inductive current profile optimization and control in ITER is presented. (author)

Continuous-wave to pulse regimes for a family of passively mode-locked lasers with saturable nonlinearity

Science.gov (United States)

Dikandé, Alain M.; Voma Titafan, J.; Essimbi, B. Z.

2017-10-01

The transition dynamics from continuous-wave to pulse regimes of operation for a generic model of passively mode-locked lasers with saturable absorbers, characterized by an active medium with non-Kerr nonlinearity, are investigated analytically and numerically. The system is described by a complex Ginzburg-Landau equation with a general m:n saturable nonlinearity (i.e {I}m/{(1+{{Γ }}I)}n, where I is the field intensity and m and n are two positive numbers), coupled to a two-level gain equation. An analysis of stability of continuous waves, following the modulational instability approach, provides a global picture of the self-starting dynamics in the system. The analysis reveals two distinct routes depending on values of the couple (m, n), and on the dispersion regime: in the normal dispersion regime, when m = 2 and n is arbitrary, the self-starting requires positive values of the fast saturable absorber and nonlinearity coefficients, but negative values of these two parameters for the family with m = 0. However, when the spectral filter is negative, the laser can self-start for certain values of the input field and the nonlinearity saturation coefficient Γ. The present work provides a general map for the self-starting mechanisms of rare-earth doped figure-eight fiber lasers, as well as Kerr-lens mode-locked solid-state lasers.

Overview of Tokamak Results

International Nuclear Information System (INIS)

Unterberg, Bernhard; Samm, Ulrich

2004-01-01

An overview is given of recent results obtained in tokamak devices. We introduce basic confinement scenarios as L-mode, H-mode and plasmas with an internal transport barrier and discuss methods for profile control. Important findings in DT-experiments at JET as α-particle heating are described. Methods for power exhaust like plasma regimes with a radiating mantle and radiative divertor scenarios are discussed. The overall impact of plasma edge conditions on the general plasma performance in tokamaks is illustrated by describing the impact of wall conditions on confinement and the edge operational diagram of H-mode plasmas

A thermal transport coefficient for ohmic and ICRF plasmas in alcator C-mode

International Nuclear Information System (INIS)

Daughton, W.; Coppi, B.; Greenwald, M.

1996-01-01

The energy confinement in plasmas produced by Alcator C-Mod machine is markedly different from that observed by previous high field compact machines such as Alcator A and C, FT, and more recently FTU. For ohmic plasmas at low and moderate densities, the confinement times routinely exceed those expected from the so-called open-quotes neo-Alcatorclose quotes scaling by a factor as high as three. For both ohmic and ICRF heated plasmas, the energy confinement time increases with the current and is approximately independent of the density. The similarity in the confinement between the ohmic and ICRF regimes opens the possibility that the thermal transport in Alcator C-Mod may be described by one transport coefficient for both regimes. We introduce a modified form of a transport coefficient previously used to describe ohmic plasmas in Alcator C-Mod. The coefficient is inspired by the properties of the so-called open-quotes ubiquitousclose quotes mode that can be excited in the presence of a significant fraction of trapped electrons and also includes the constraint of profile consistency. A detailed series of transport simulations are used to show that the proposed coefficient can reproduce the observed temperature profiles, loop voltage and energy confinement time for both ohmic and ICRF discharges. A total of nearly two dozen ohmic and ICRF Alcator C-Mod discharges have been fit over the range of parameter space available using this transport coefficient

Exploration of the Super H-mode regime on DIII-D and potential advantages for burning plasma devices

Energy Technology Data Exchange (ETDEWEB)

Solomon, W. M., E-mail: solomon@fusion.gat.com; Bortolon, A.; Grierson, B. A.; Nazikian, R.; Poli, F. [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Snyder, P. B.; Burrell, K. H.; Garofalo, A. M.; Groebner, R. J.; Leonard, A. W.; Meneghini, O.; Osborne, T. H.; Petty, C. C. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Loarte, A. [ITER Organization, Route de Vinon-sur-Verdon - CS 90 046, 13067 St Paul Lez Durance Cedex (France)

2016-05-15

A new high pedestal regime (“Super H-mode”) has been predicted and accessed on DIII-D. Super H-mode was first achieved on DIII-D using a quiescent H-mode edge, enabling a smooth trajectory through pedestal parameter space. By exploiting Super H-mode, it has been possible to access high pedestal pressures at high normalized densities. While elimination of Edge localized modes (ELMs) is beneficial for Super H-mode, it may not be a requirement, as recent experiments have maintained high pedestals with ELMs triggered by lithium granule injection. Simulations using TGLF for core transport and the EPED model for the pedestal find that ITER can benefit from the improved performance associated with Super H-mode, with increased values of fusion power and gain possible. Similar studies demonstrate that the Super H-mode pedestal can be advantageous for a steady-state power plant, by providing a path to increasing the bootstrap current while simultaneously reducing the demands on the core physics performance.

A new quasi-stationary, very high density plasma regime on the W7-AS stellarator

International Nuclear Information System (INIS)

Jaenicke, R; Baeumel, S; Baldzuhn, J; Brakel, R; Burhenn, R; Ehmler, H; Endler, M; Erckmann, V; Feng, Y; Gadelmeier, F; Geiger, J; Giannone, L; Grigull, P; Hartfuss, H J; Hartmann, D; Hildebrandt, D; Hirsch, M; Holzhauer, E; Kick, M; Kisslinger, J; Klinger, T; Klose, S; Knauer, J; Koenig, R; Kuehner, G; Laqua, H; Maassberg, H; McCormick, K; Narayanan, R; Niedermeyer, H; Pasch, E; Ruhs, N; Rust, N; Saffert, J; Sardei, F; Schneider, F; Schubert, M; Speth, E; Wagner, F; Weller, A; Wenzel, U; Werner, A; Wuersching, E

2002-01-01

Stellarators have the intrinsic property of steady state operation. However, on present-day stellarators the pulse length is usually not only limited due to technical reasons, but also by physical problems. Lack of density control and a subsequent radiation collapse terminate the discharges quite often at high densities. To improve the control of the plasma-wall interaction, the island divertor concept was developed for optimized stellarators. To test this divertor concept on W7-AS, all limiters were removed and replaced by ten divertor modules. In subsequent divertor experiments a promising new plasma operational regime has been discovered which is termed 'high density H-mode' (HDH-mode). During the transition into that regime a clear reduction of ELM-like events and turbulent fluctuations is observed. The HDH-mode combines good energy confinement with very low impurity confinement resulting in low core radiation, but high edge-localized radiation. Consequently, stationary discharges at densities of typically 2x10 20 m -3 can be performed within the accessible pulse length of about 1 s. At densities above 3x10 20 m -3 a controlled transition from attached to partially detached plasmas is observed. The still edge-localized radiation reaches 90% of the heating power so that the power load onto the divertor target plates is further reduced. At a lower toroidal field of 0.9 T average β-values could be raised from earlier 2% to more than 3% in magnetic field configurations with rather smooth flux surfaces at the plasma boundary. The recently obtained results render excellent prospects for W7-X, the larger superconducting successor experiment of W7-AS

Impact of plasma triangularity and collisionality on electron heat transport in TCV L-mode plasmas

International Nuclear Information System (INIS)

Camenen, Y.; Pochelon, A.; Behn, R.; Bottino, A.; Bortolon, A.; Coda, S.; Karpushov, A.; Sauter, O.; Zhuang, G.

2007-01-01

The impact of plasma shaping on electron heat transport is investigated in TCV L-mode plasmas. The study is motivated by the observation of an increase in the energy confinement time with decreasing plasma triangularity which may not be explained by a change in the temperature gradient induced by changes in the geometry of the flux surfaces. The plasma triangularity is varied over a wide range, from positive to negative values, and various plasmas conditions are explored by changing the total electron cyclotron (EC) heating power and the plasma density. The mid-radius electron heat diffusivity is shown to significantly decrease with decreasing triangularity and, for similar plasma conditions, only half of the EC power is required at a triangularity of -0.4 compared with +0.4 to obtain the same temperature profile. Besides, the observed dependence of the electron heat diffusivity on the electron temperature, electron density and effective charge can be grouped in a unique dependence on the plasma effective collisionality. In summary, the electron heat transport level exhibits a continuous decrease with decreasing triangularity and increasing collisionality. Local gyro-fluid and global gyro-kinetic simulations predict that trapped electron modes are the most unstable modes in these EC heated plasmas with an effective collisionality ranging from 0.2 to 1. The modes stability dependence on the plasma triangularity is investigated

Tokamak confinement scaling laws

International Nuclear Information System (INIS)

Connor, J.

1998-01-01

The scaling of energy confinement with engineering parameters, such as plasma current and major radius, is important for establishing the size of an ignited fusion device. Tokamaks exhibit a variety of modes of operation with different confinement properties. At present there is no adequate first principles theory to predict tokamak energy confinement and the empirical scaling method is the preferred approach to designing next step tokamaks. This paper reviews a number of robust theoretical concepts, such as dimensional analysis and stability boundaries, which provide a framework for characterising and understanding tokamak confinement and, therefore, generate more confidence in using empirical laws for extrapolation to future devices. (author)

Three novel tokamak plasma regimes in TFTR

International Nuclear Information System (INIS)

Furth, H.P.

1985-10-01

Aside from extending ''standard'' ohmic and neutral beam heating studies to advanced plasma parameters, TFTR has encountered a number of special plasma regimes that have the potential to shed new light on the physics of tokamak confinement and the optimal design of future D-T facilities: (1) High-powered, neutral beam heating at low plasma densities can maintain a highly reactive hot-ion population (with quasi-steady-state beam fueling and current drive) in a tokamak configuration of modest bulk-plasma confinement requirements. (2) Plasma displacement away from limiter contact lends itself to clarification of the role of edge-plasma recycling and radiation cooling within the overall pattern of tokamak heat flow. (3) Noncentral auxiliary heating (with a ''hollow'' power-deposition profile) should serve to raise the central tokamak plasma temperature without deterioration of central region confinement, thus facilitating the study of alpha-heating effects in TFTR. The experimental results of regime (3) support the theory that tokamak profile consistency is related to resistive kink stability and that the global energy confinement time is determined by transport properties of the plasma edge region

Change of transport at L- and H-mode transition

International Nuclear Information System (INIS)

Itoh, Sanae-I; Itoh, Kimitaka.

1990-01-01

A new refined model of the L-mode and H-mode transition in tokamaks is presented based on the bifurcation of the radial electric field, E r , near edge. The radial gradient of E r is newly introduced to explain the sudden change of fluctuations as well as plasma fluxes at the onset of transition. This model predicts that the L-to H-mode transition is associated with the decrease of dE r /dr causing reduction of particle and energy fluxes at critical gradient. (author)

Analysis of a global energy confinement database for JET ohmic plasmas

International Nuclear Information System (INIS)

Bracco, G.; Thomsen, K.

1997-01-01

A database containing global energy confinement data for JET ohmic plasmas in the campaigns from 1984 to 1992 has been established. An analysis is presented of this database and the results are compared with data from other tokamaks, such as the Axially Symmetric Divertor Experiment (ASDEX), Frascati Tokamak Upgrade (FTU) and Tore Supra. The trends of JET ohmic confinement appear to be similar to those observed on other tokamaks: a linear dependence of the global energy confinement time on density is observed up to a density value where a saturation is attained; this density value defines the border between the linear and the saturated ohmic confinement regimes; this border is shifted towards higher density values if the q value of the discharge is decreased; the global confinement time in the saturated ohmic regime increases less than linearly with the value of the magnetic field. (author). 20 refs, 13 figs, 4 tabs

Active core profile and transport modification by application of ion Bernstein wave power in the Princeton Beta Experiment-Modification

Science.gov (United States)

LeBlanc, B.; Batha, S.; Bell, R.; Bernabei, S.; Blush, L.; de la Luna, E.; Doerner, R.; Dunlap, J.; England, A.; Garcia, I.; Ignat, D.; Isler, R.; Jones, S.; Kaita, R.; Kaye, S.; Kugel, H.; Levinton, F.; Luckhardt, S.; Mutoh, T.; Okabayashi, M.; Ono, M.; Paoletti, F.; Paul, S.; Petravich, G.; Post-Zwicker, A.; Sauthoff, N.; Schmitz, L.; Sesnic, S.; Takahashi, H.; Talvard, M.; Tighe, W.; Tynan, G.; von Goeler, S.; Woskov, P.; Zolfaghari, A.

1995-03-01

Application of Ion Bernstein Wave Heating (IBWH) into the Princeton Beta Experiment-Modification (PBX-M) [Phys. Fluids B 2, 1271 (1990)] tokamak stabilizes sawtooth oscillations and generates peaked density profiles. A transport barrier, spatially correlated with the IBWH power deposition profile, is observed in the core of IBWH-assisted neutral beam injection (NBI) discharges. A precursor to the fully developed barrier is seen in the soft x-ray data during edge localized mode (ELM) activity. Sustained IBWH operation is conducive to a regime where the barrier supports large ∇ne, ∇Te, ∇νφ, and ∇Ti, delimiting the confinement zone. This regime is reminiscent of the H(high) mode, but with a confinement zone moved inward. The core region has better than H-mode confinement while the peripheral region is L(low)-mode-like. The peaked profile enhances NBI core deposition and increases nuclear reactivity. An increase in central Ti results from χi reduction (compared to the H mode) and better beam penetration. Bootstrap current fractions of up to 0.32-0.35 locally and 0.28 overall were obtained when an additional NBI burst is applied to this plasma.

Active core profile and transport modification by application of ion Bernstein wave power in the Princeton Beta Experiment-Modification

International Nuclear Information System (INIS)

LeBlanc, B.; Batha, S.; Bell, R.; Bernabei, S.; Blush, L.; de la Luna, E.; Doerner, R.; Dunlap, J.; England, A.; Garcia, I.; Ignat, D.; Isler, R.; Jones, S.; Kaita, R.; Kaye, S.; Kugel, H.; Levinton, F.; Luckhardt, S.; Mutoh, T.; Okabayashi, M.; Ono, M.; Paoletti, F.; Paul, S.; Petravich, G.; Post-Zwicker, A.; Sauthoff, N.; Schmitz, L.; Sesnic, S.; Takahashi, H.; Talvard, M.; Tighe, W.; Tynan, G.; von Goeler, S.; Woskov, P.; Zolfaghari, A.

1995-01-01

Application of Ion Bernstein Wave Heating (IBWH) into the Princeton Beta Experiment-Modification (PBX-M) [Phys. Fluids B 2, 1271 (1990)] tokamak stabilizes sawtooth oscillations and generates peaked density profiles. A transport barrier, spatially correlated with the IBWH power deposition profile, is observed in the core of IBWH-assisted neutral beam injection (NBI) discharges. A precursor to the fully developed barrier is seen in the soft x-ray data during edge localized mode (ELM) activity. Sustained IBWH operation is conducive to a regime where the barrier supports large ∇n e , ∇T e , ∇ν φ , and ∇T i , delimiting the confinement zone. This regime is reminiscent of the H(high) mode, but with a confinement zone moved inward. The core region has better than H-mode confinement while the peripheral region is L(low)-mode-like. The peaked profile enhances NBI core deposition and increases nuclear reactivity. An increase in central T i results from χ i reduction (compared to the H mode) and better beam penetration. Bootstrap current fractions of up to 0.32--0.35 locally and 0.28 overall were obtained when an additional NBI burst is applied to this plasma

Active core profile and transport modification by application of Ion Bernstein Wave power in PBX-M

International Nuclear Information System (INIS)

LeBlanc, B.; Bell, R.

1995-01-01

Application of Ion Bernstein Wave Heating (IBWH) into the Princeton Beta Experiment-Modification (PBX-M) tokamak stabilizes sawtooth oscillations and generates peaked density profiles. A transport barrier, spatially correlated with the IBWH power deposition profile, is observed in the core of IBWH assisted neutral beam injection (NBI) discharges. A precursor to the fully developed barrier is seen in the soft x-ray data during edge localized mode (ELM) activity. Sustained IBWH operation is conducive to a regime where the barrier supports large triangledown n e , triangledown T e , triangledown v phi , and triangledown T i , delimiting the confinement zone. This regime is reminiscent of the H(high)-mode but with a confinement zone moved inwards. The core region has better than H-mode confinement while the peripheral region is L(low)-mode-like. The peaked profile enhanced NBI core deposition and increases nuclear reactivity. An increase in central T i results from χ i reduction (compared to H-mode) and better beam penetration. Bootstrap current fractions of up to 0.32--0.35 locally and 0.28 overall were obtained when an additional NBI burst is applied to this plasma

The role of edge physics and confinement issues in the fusion reactor

International Nuclear Information System (INIS)

Lackner, K.; Schneider, R.

1993-01-01

The compatibility of the power exhaust to the walls and target plates with an adequate survival time of these structures and a sufficiently low impurity concentration in the bulk plasma, on the one hand, and the scaling of the energy confinement time with the tokamak parameters, on the other, are presently seen as two of the most critical issues determining the viability and minimum size of a fusion reactor. Statistical analysis of the world-wide data base of divertor tokamaks and experimental progress in superposing different forms of confinement improvements instil confidence that tokamak devices with the dimensions of ITER can meet the energy confinement requirements for ignition when operating in the H-regime. The critical problem consists, however, in simultaneously satisfying both the impurity and energy confinement related requirements. Regimes of improved confinement also tend to show a reduced rate of outward flow of impurities, thus increasing (for a given production rate at the walls or - in the case of helium - in the interior) their expected concentration. The confinement improvement in the H-regime also extends beyond the separatrix, leading to a thinner scrape-off layer with enhanced power concentration at the target plate and an enhanced penetration of impurities into the bulk plasma. These issues have therefore become the focal point of divertor and H-regime studies. Experiments on ASDEX, DIII-D and JET have successfully demonstrated that the impurity concentration in the H-regime can be effectively limited by the spontaneous cyclic destruction of the transport barrier at the edge (through the so-called ELMs) with only partial sacrifice of the energy confinement improvement. Expectations of handling the power load issues hinge on the capability of the divertor solution to decouple plasma properties in the edge of the bulk plasma from those near the target plates and the possibility of converting the energy flux arriving in the divertor into

Transport and confinement in the Mega Ampere Spherical Tokamak (MAST) plasma

Energy Technology Data Exchange (ETDEWEB)

Akers, R J; Ahn, J W; Appel, L C; Brickley, C; Bunting, C; Carolan, P G; Challis, C D; Conway, N J; Counsell, G F; Dendy, R O; Dudson, B; Field, A R; Kirk, A; Lloyd, B; Meyer, H F; Morris, A W; Patel, A; Roach, C M; Sykes, A; Taylor, D; Tournianski, M R; Valovic, M; Wilson, H R; Axon, K B; Buttery, R J; Ciric, D; Cunningham, G; Dowling J; Dunstan, M R; Gee, S J; Gryaznevich, M P; Helander, P; Keeling, D L; Knight, P J; Lott, F; Loughlin, M J; Manhood, S J; Martin, R; McArdle, G J; Price, M N; Stammers, K; Storrs, J [EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Antar, G Y [Fusion Energy Research Program, University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0417 (United States); Applegate, D [Imperial College of Science, Technology and Medicine, University of London, London SW7 2BZ (United Kingdom); Rohzansky, V [St. Petersburg State Politechnical University, Polytechnicheskaya 29, 195251 St. Petersburg (Russian Federation); Walsh, M J [Walsh Scientific Ltd., Abingdon, Oxon OX14 3EB (United Kingdom)

2003-12-01

A combination of recently installed state-of-the-art imaging and profile diagnostics, together with established plasma simulation codes, are providing for the first time on Mega Ampere Spherical Tokamak (MAST) the tools required for studying confinement and transport, from the core through to the plasma edge and scrape-off-layer (SOL). The H-mode edge transport barrier is now routinely turned on and off using a combination of poloidally localized fuelling and fine balancing of the X-points. Theory, supported by experiment, indicates that the edge radial electric field and toroidal flow velocity (thought to play an important role in H-mode access) are largest if gas fuelling is concentrated at the inboard side. H-mode plasmas show predominantly type III ELM characteristics, with confinement H{sub H} factor (w.r.t. scaling law IPB98[y, 2]) around approx. 1.0. Combining MAST H-mode data with the International Tokamak Physics Activities (ITPA) analyses, results in an L-H power threshold scaling proportional to plasma surface area (rather than P{sub LH} approx. R{sup 2}). In addition, MAST favours an inverse aspect ratio scaling P{sub LH} approx. epsilon 0.5. Similarly, the introduction of type III ELMing H-mode data to the pedestal energy regression analysis introduces a scaling W{sub ped} approx. epsilon -2.13 and modifies the exponents on R, B{sub T} and Kappa. Preliminary TRANSP simulations indicate that ion and electron thermal diffusivities in ELMing H-mode approach the ion-neoclassical level in the half-radius region of the plasma with momentum diffusivity a few times lower. Linear flux-tube ITG and ETG microstability calculations using GS2 offer explanations for the near-neoclassical ion diffusivity and significantly anomalous electron diffusivity seen on MAST. To complement the baseline quasi-steady-state H-mode, newly developed advanced regimes are being explored. In particular, 'broad' internal transport barriers (ITBs) have been formed using

Transport and confinement in the Mega Ampere Spherical Tokamak (MAST) plasma

International Nuclear Information System (INIS)

Akers, R J; Ahn, J W; Antar, G Y; Appel, L C; Applegate, D; Brickley, C; Bunting, C; Carolan, P G; Challis, C D; Conway, N J; Counsell, G F; Dendy, R O; Dudson, B; Field, A R; Kirk, A; Lloyd, B; Meyer, H F; Morris, A W; Patel, A; Roach, C M; Rohzansky, V; Sykes, A; Taylor, D; Tournianski, M R; Valovic, M; Wilson, H R; Axon, K B; Buttery, R J; Ciric, D; Cunningham, G; Dowling, J; Dunstan, M R; Gee, S J; Gryaznevich, M P; Helander, P; Keeling, D L; Knight, P J; Lott, F; Loughlin, M J; Manhood, S J; Martin, R; McArdle, G J; Price, M N; Stammers, K; Storrs, J; Walsh, M J

2003-01-01

A combination of recently installed state-of-the-art imaging and profile diagnostics, together with established plasma simulation codes, are providing for the first time on Mega Ampere Spherical Tokamak (MAST) the tools required for studying confinement and transport, from the core through to the plasma edge and scrape-off-layer (SOL). The H-mode edge transport barrier is now routinely turned on and off using a combination of poloidally localized fuelling and fine balancing of the X-points. Theory, supported by experiment, indicates that the edge radial electric field and toroidal flow velocity (thought to play an important role in H-mode access) are largest if gas fuelling is concentrated at the inboard side. H-mode plasmas show predominantly type III ELM characteristics, with confinement H H factor (w.r.t. scaling law IPB98[y, 2]) around approx. 1.0. Combining MAST H-mode data with the International Tokamak Physics Activities (ITPA) analyses, results in an L-H power threshold scaling proportional to plasma surface area (rather than P LH approx. R 2 ). In addition, MAST favours an inverse aspect ratio scaling P LH approx. epsilon 0.5. Similarly, the introduction of type III ELMing H-mode data to the pedestal energy regression analysis introduces a scaling W ped approx. epsilon -2.13 and modifies the exponents on R, B T and Kappa. Preliminary TRANSP simulations indicate that ion and electron thermal diffusivities in ELMing H-mode approach the ion-neoclassical level in the half-radius region of the plasma with momentum diffusivity a few times lower. Linear flux-tube ITG and ETG microstability calculations using GS2 offer explanations for the near-neoclassical ion diffusivity and significantly anomalous electron diffusivity seen on MAST. To complement the baseline quasi-steady-state H-mode, newly developed advanced regimes are being explored. In particular, 'broad' internal transport barriers (ITBs) have been formed using techniques developed at conventional aspect

Demonstration of high performance negative central magnetic shear discharges on the DIII-D tokamak

International Nuclear Information System (INIS)

Rice, B.W.; Burrell, K.H.; Lao, L.L.

1996-01-01

Reliable operation of discharges with negative central magnetic shear has led to significant increases in plasma performance and reactivity in both low confinement, L-mode, and high confinement, H-mode, regimes in the DIII-D tokamak. Using neutral beam injection early in the initial current ramp, a large range of negative shear discharges have been produced with durations lasting up to 3.2 s. The total non- inductive current (beam plus bootstrap) ranges from 50% to 80% in these discharges. In the region of shear reversal, significant peaking of the toroidal rotation [f φ ∼ 30-60 kHz] and ion temperature [T i (0) ∼ 15-22 keV] profiles are observed. In high power discharges with an L-mode edge, peaked density profiles are also observed. Confinement enhancement factors up to H ≡ τ E /τ ITER-89P ∼ 2.5 with an L-mode edge, and H ∼ 3.3 in an Edge Localized Mode (ELM)-free H-mode, are obtained. Transport analysis shows both ion thermal diffusivity and particle diffusivity to be near or below standard neoclassical values in the core. Large pressure peaking in L- mode leads to high disruptivity with Β N ≡ Β T /(I/aB) ≤ 2.3, while broader pressure profiles in H- mode gives low disruptivity with Β N ≤ 4.2

Confinement and βsub(p)-studies in neutral injection heated ASDEX plasmas

International Nuclear Information System (INIS)

Wagner, F.; Becker, G.; Behringer, K.; Campbell, D.; Eberhagen, A.; Engelhardt, W.; Fussmann, G.; Gehre, O.; Gernhardt, J.; Gierke, G. von; Haas, G.; Huang, M.; Karger, F.; Keilhacker, M.; Klueber, O.; Kornherr, M.; Lackner, K.; Lisitano, G.; Lister, G.G.; Mayer, H.M.; Meisel, D.; Mueller, E.R.; Murmann, H.; Niedermeyer, H.; Poschenrieder, W.; Rapp, H.; Roehr, H; Schneider, F.; Siller, G.; Speth, E.; Staebler, A.; Steuer, K.H.; Succi, S.; Venus, G.; Vollmer, O.

1983-03-01

Neutral injection experiments into limiter and divertor discharges in ASDEX are described with hydrogen and deuterium as working gas. Two operational regimes have been observed in neutral injection heated divertor discharges. One regime is characterized by deteriorated energy and particle confinement. The global energy confinement times are comparable to those of neutral injection heated limited discharges. Tthe other regime has particle and energy confinement times comparable to those of ohmic discharges with tausub(E) = 40 - 60 msec at beam powers up to 3.1 MW. This regime is further characterized by high βsub(p)-values comparable to the aspect ratio A (βsub(p) proportional 0.65 A), by good electron heating (etasub(e) proportional 2.5 x 10 13 eV cm -3 kW -1 ) and ion heating (etasub(i) proportional 4.2 x 10 13 eV cm -3 kW -1 ). In both regimes, tausub(E) increases with plasma current but there is hardly any variation with density. The differences in confinement and scaling to ohmic discharges seem to be caused by modifications of the electron loss channel. The high βsub(p)-regime develops at an injection power >=1.8 MW, anti nsub(e) >= 3 x 10 13 cm -3 and q >= 2.45, and is so far only observed in divertor discharges. There are indications that this may be due to the broad profiles with high edge temperatures which can develop in divertor discharges. An indication of broad current density profiles is given by the lack of sawtooth activity in these discharges. (orig.)

Threshold for the destabilisation of the ion-temperature-gradient mode in magnetically confined toroidal plasmas

Science.gov (United States)

Zocco, A.; Xanthopoulos, P.; Doerk, H.; Connor, J. W.; Helander, P.

2018-02-01

The threshold for the resonant destabilisation of ion-temperature-gradient (ITG) driven instabilities that render the modes ubiquitous in both tokamaks and stellarators is investigated. We discover remarkably similar results for both confinement concepts if care is taken in the analysis of the effect of the global shear . We revisit, analytically and by means of gyrokinetic simulations, accepted tokamak results and discover inadequacies of some aspects of their theoretical interpretation. In particular, for standard tokamak configurations, we find that global shear effects on the critical gradient cannot be attributed to the wave-particle resonance destabilising mechanism of Hahm & Tang (Phys. Plasmas, vol. 1, 1989, pp. 1185-1192), but are consistent with a stabilising contribution predicted by Biglari et al. (Phys. Plasmas, vol. 1, 1989, pp. 109-118). Extensive analytical and numerical investigations show that virtually no previous tokamak theoretical predictions capture the temperature dependence of the mode frequency at marginality, thus leading to incorrect instability thresholds. In the asymptotic limit , where is the rotational transform, and such a threshold should be solely determined by the resonant toroidal branch of the ITG mode, we discover a family of unstable solutions below the previously known threshold of instability. This is true for a tokamak case described by a local local equilibrium, and for the stellarator Wendelstein 7-X, where these unstable solutions are present even for configurations with a small trapped-particle population. We conjecture they are of the Floquet type and derive their properties from the Fourier analysis of toroidal drift modes of Connor & Taylor (Phys. Fluids, vol. 30, 1987, pp. 3180-3185), and to Hill's theory of the motion of the lunar perigee (Acta Math., vol. 8, 1886, pp. 1-36). The temperature dependence of the newly determined threshold is given for both confinement concepts. In the first case, the new temperature

Interaction of Fast Ions with Global Plasma Modes in the C-2 Field Reversed Configuration Experiment

Science.gov (United States)

Smirnov, Artem; Dettrick, Sean; Clary, Ryan; Korepanov, Sergey; Thompson, Matthew; Trask, Erik; Tuszewski, Michel

2012-10-01

A high-confinement operating regime [1] with plasma lifetimes significantly exceeding past empirical scaling laws was recently obtained by combining plasma gun edge biasing and tangential Neutral Beam Injection (NBI) in the C-2 field-reversed configuration (FRC) experiment [2, 3]. We present experimental and computational results on the interaction of fast ions with the n=2 rotational and n=1 wobble modes in the C-2 FRC. It is found that the n=2 mode is similar to quadrupole magnetic fields in its detrimental effect on the fast ion transport due to symmetry breaking. The plasma gun generates an inward radial electric field, thus stabilizing the n=2 rotational instability without applying the quadrupole magnetic fields. The resultant FRCs are nearly axisymmetric, which enables fast ion confinement. The NBI further suppresses the n=2 mode, improves the plasma confinement characteristics, and increases the plasma configuration lifetime [4]. The n=1 wobble mode has relatively little effect on the fast ion transport, likely due to the approximate axisymmetry about the displaced plasma column. [4pt] [1] M. Tuszewski et al., Phys. Rev. Lett. 108, 255008 (2012).[0pt] [2] M. Binderbauer et al., Phys. Rev. Lett. 105, 045003 (2010).[0pt] [3] H.Y. Guo et al., Phys. Plasmas 18, 056110 (2011).[0pt] [4] M. Tuszewski et al., Phys. Plasmas 19, 056108 (2012)

Quiescent double barrier regime in the DIII-D tokamak.

Science.gov (United States)

Greenfield, C M; Burrell, K H; DeBoo, J C; Doyle, E J; Stallard, B W; Synakowski, E J; Fenzi, C; Gohil, P; Groebner, R J; Lao, L L; Makowski, M A; McKee, G R; Moyer, R A; Rettig, C L; Rhodes, T L; Pinsker, R I; Staebler, G M; West, W P

2001-05-14

A new sustained high-performance regime, combining discrete edge and core transport barriers, has been discovered in the DIII-D tokamak. Edge localized modes (ELMs) are replaced by a steady oscillation that increases edge particle transport, thereby allowing particle control with no ELM-induced pulsed divertor heat load. The core barrier resembles those usually seen with a low (L) mode edge, without the degradation often associated with ELMs. The barriers are separated by a narrow region of high transport associated with a zero crossing in the E x B shearing rate.

Extending the collisional fluid equations into the long mean-free-path regime in toroidal plasmas. IV. Banana regime

International Nuclear Information System (INIS)

Shaing, K. C.

2007-01-01

In Part I [Phys. Fluids B 2, 1190 (1990)] and Part II [Phys. Plasmas 12, 082508 (2005)], it was emphasized that the equilibrium plasma viscous forces when applied for the magnetohydrodynamic (MHD) modes are only rigorously valid at the mode rational surface where m-nq=0. Here, m is the poloidal mode number, n is the toroidal mode number, and q is the safety factor. This important fact has been demonstrated explicitly by calculating the viscous forces in the plateau regime in Parts I and II. Here, the effective viscous forces in the banana regime are calculated for MHD modes by solving the linear drift kinetic equation that is driven by the plasma flows first derived in Part I. At the mode rational surface, the equilibrium plasma viscous forces are reproduced. However, it is found that away from the mode rational surface, the viscous forces for MHD modes decrease, a behavior similar to that observed in the viscous forces for the plateau regime. The proper form of the momentum equation that is appropriate for the modeling of the MHD modes is also discussed

Pedestal characteristics and MHD stability of H-mode plasmas in TCV

International Nuclear Information System (INIS)

Pitzschke, A.

2011-01-01

The tokamak à configuration variable (TCV) is unique in its ability to create a variety of plasma shapes and to heat the electron population in high density regimes using microwave power at the third harmonic of the electron cyclotron frequency. In the frame of this thesis, the impact of plasma shaping and heating on the properties of the edge transport barrier (ETB) in the high confinement mode (H-mode) was studied. This mode of operation is foreseen as one of the reference scenarios for ITER, the International Tokamak Experimental Reactor, which is being built to demonstrate the feasibility of thermonuclear fusion using magnetic confinement. A feature of H-mode regime operation are edge localized modes (ELMs), instabilities driven by the steep pressure gradients that form in the plasma edge region due to a transport barrier. During an ELM event, energy and particles are expelled from the plasma in a short burst. This will cause serious problems with respect to the heat load on plasma facing components in a tokamak of the size of ITER. Understanding of the phenomena associated with ELMs is thus required and dedicated investigations of their theory and experimental observations are carried out in many laboratories worldwide. This thesis presents several experimental and numerical investigations of tokamak behavior for configurations where the plasma edge plays an important role. From the experimental viewpoint, studies of transport barriers are challenging, as plasma parameters change strongly within a narrow spatial region. As part of the work presented here, the TCV Thomson scattering system was upgraded to meet the requirements for diagnosing electron temperature and density with high spatial resolution in the region of internal and external transport barriers. Simultaneously, the data analysis was significantly improved to cope with statistical uncertainties and alleviate possible systematic errors. For measurements of the time evolution of density and

Field reversal experiments (FRX). [Equilibrium, confinement, and stability

Energy Technology Data Exchange (ETDEWEB)

Linford, R.K.; Armstrong, W.T.; Platts, D.A.; Sherwood, E.G.

1978-01-01

The equilibrium, confinement, and stability properties of the reversed-field configuration (RFC) are being studied in two theta-pinch facilities. The RFC is an elongated toroidal plasma confined in a purely poloidal field geometry. The open field lines of the linear theta pinch support the closed-field RFC much like the vertical field centers the toroidal plasma in a tokamak. Depending on stability and confinement properties, the RFC might be used to greatly reduce the axial losses in linear fusion devices such as mirrors, theta pinches, and liners. The FRX systems produce RFC's with a major radius R = 2-6 cm, minor radius a approximately 2 cm, and a total length l approximately 35 cm. The observed temperatures are T/sub e/ approximately 100 eV and T/sub i/ = 150-350 eV with a peak density n approximately 2 x 10/sup 15/ cm/sup -3/. After the plasma reaches equilibrium, the RFC remains stable for up to 30 ..mu..s followed by the rapid growth of the rotational m = 2 instability, which terminates the confinement. During the stable equilibrium, the particle and energy confinement times are more than 10 times longer than in an open-field system. The behavior of the m = 2 mode qualitatively agrees with the theoretically predicted instability for rotational velocities exceeding some critical value.

Nonlinear Plasma Response to Resonant Magnetic Perturbation in Rutherford Regime

Science.gov (United States)

Zhu, Ping; Yan, Xingting; Huang, Wenlong

2017-10-01

Recently a common analytic relation for both the locked mode and the nonlinear plasma response in the Rutherford regime has been developed based on the steady-state solution to the coupled dynamic system of magnetic island evolution and torque balance equations. The analytic relation predicts the threshold and the island size for the full penetration of resonant magnetic perturbation (RMP). It also rigorously proves a screening effect of the equilibrium toroidal flow. In this work, we test the theory by solving for the nonlinear plasma response to a single-helicity RMP of a circular-shaped limiter tokamak equilibrium with a constant toroidal flow, using the initial-value, full MHD simulation code NIMROD. Time evolution of the parallel flow or ``slip frequency'' profile and its asymptotic approach to steady state obtained from the NIMROD simulations qualitatively agree with the theory predictions. Further comparisons are carried out for the saturated island size, the threshold for full mode penetration, as well as the screening effects of equilibrium toroidal flow in order to understand the physics of nonlinear plasma response in the Rutherford regime. Supported by National Magnetic Confinement Fusion Science Program of China Grants 2014GB124002 and 2015GB101004, the 100 Talent Program of the Chinese Academy of Sciences, and U.S. Department of Energy Grants DE-FG02-86ER53218 and DE-FC02-08ER54975.

Limiter H-mode experiments on TFTR

Energy Technology Data Exchange (ETDEWEB)

Bush, C [Oak Ridge National Lab., TN (USA); Bretz, N L; Fredrickson, E D; McGuire, K M; Nazikian, R; Park, H K; Schivell, J; Taylor, G; Bitter, B; Budny, R; Cohen, S A; Kilpatrick, S J; LeBlanc, B; Manos, D M; Meade, D; Paul, S F; Scott, S D; Stratton, B C; Synakowski, E J; Towner, H H; Weiland, R M; Arunasalam, V; Bateman, G; Bell, M G; Bell, R; Boivin, R; Cavallo, A; Cheng, C Z; Chu, T K; Cowl,

1990-12-15

Limiter H-modes with centrally peaked density profiles have been obtained in TFTR using a highly conditioned graphite limiter. The transition to these centrally peaked H-modes takes place from the supershot to the H-mode rather than the usual L- to H-mode transition observed on other tokamaks. Bi-directional beam heating is required to induce the transition. Density peaking factors, n{sub e}(0)/{l angle}n{sub e}{r angle}, >2.3 are obtained and at the same time the H-mode characteristics are similar to those of limiter H-modes on other tokamaks and the global confinement, {tau}{sub E}, can be >2.5 times L-mode scaling. The TRANSP analysis shows that transport in these H-modes is similar to that of supershots within the inner 60 cm of the plasma, but the stored electron energy (calculated using measured values of T{sub e} and n{sub e}) is higher for the H-mode at the plasma edge. Microwave scattering near the edge shows broad spectra at k = 5.5 cm{sup {minus}1} which begin at the drop in D{sub {alpha}} radiation and are strongly shifted in the electron diamagnetic drift direction. At the same time beam emission spectroscopy shows a coherent mode near the boundary with m = 15--20 at 20--30 kHz which is propagating in the ion direction. During an ELM event these apparent rotations cease and Mirnov fluctuations in the 50--500 kHz increase in intensity.

Scattering resonances of ultracold atoms in confined geometries

International Nuclear Information System (INIS)

Saeidian, Shahpoor

2008-01-01

Subject of this thesis is the investigation of the quantum dynamics of ultracold atoms in confined geometries. We discuss the behavior of ground state atoms inside a 3D magnetic quadrupole field. Such atoms in enough weak magnetic fields can be approximately treated as neutral point-like particles. Complementary to the well-known positive energy resonances, we point out the existence of short-lived negative energy resonances. The latter originate from a fundamental symmetry of the underlying Hamiltonian. We drive a mapping of the two branches of the spectrum. Moreover, we analyze atomic hyperfine resonances in a magnetic quadrupole field. This corresponds to the case for which both the hyperfine and Zeeman interaction, are comparable, and should be taken into account. Finally, we develop a general grid method for multichannel scattering of two atoms in a two-dimensional harmonic confinement. With our approach we analyze transverse excitations/deexcitations in the course of the collisional process (distinguishable or identical atoms) including all important partial waves and their couplings due to the broken spherical symmetry. Special attention is paid to suggest a non-trivial extension of the CIRs theory developed so far only for the single-mode regime and zero-energy limit. (orig.)

Scattering resonances of ultracold atoms in confined geometries

Energy Technology Data Exchange (ETDEWEB)

Saeidian, Shahpoor

2008-06-18

Subject of this thesis is the investigation of the quantum dynamics of ultracold atoms in confined geometries. We discuss the behavior of ground state atoms inside a 3D magnetic quadrupole field. Such atoms in enough weak magnetic fields can be approximately treated as neutral point-like particles. Complementary to the well-known positive energy resonances, we point out the existence of short-lived negative energy resonances. The latter originate from a fundamental symmetry of the underlying Hamiltonian. We drive a mapping of the two branches of the spectrum. Moreover, we analyze atomic hyperfine resonances in a magnetic quadrupole field. This corresponds to the case for which both the hyperfine and Zeeman interaction, are comparable, and should be taken into account. Finally, we develop a general grid method for multichannel scattering of two atoms in a two-dimensional harmonic confinement. With our approach we analyze transverse excitations/deexcitations in the course of the collisional process (distinguishable or identical atoms) including all important partial waves and their couplings due to the broken spherical symmetry. Special attention is paid to suggest a non-trivial extension of the CIRs theory developed so far only for the single-mode regime and zero-energy limit. (orig.)

Radial electric field at the plasma edge on the FT-2 Tokamak in regimes with large gradients

International Nuclear Information System (INIS)

Lashkul, S.; Popov, A.

2001-01-01

The transport barrier formation is widely believed to be the fundamental element of transition into improved confinement regimes (H-mode). Experiments on many tokamaks demonstrate that transport barrier formation is connected with the suppression of turbulent transport by shear of E x B drift. Therefore, the calculation of radial electric field is of great importance. Our work is devoted to progress the neoclassical theory by taking into account electron viscosity and non-linear effects (ion inertia), presented results being valuable for interpretation transition into H-mode at the plasma edge in small tokamaks. Calculations of the electric field profile for FT-2 tokamak (a=8cm, R 0 =55cm, Ioffe Institute, Russia) according found expressions are in the good agreement with experimental results obtained. (orig.)

Numerical modeling of the transition from low to high confinement in magnetically confined plasma

International Nuclear Information System (INIS)

Rasmussen, J Juul; Nielsen, A H; Madsen, J; Naulin, V; Xu, G S

2016-01-01

The transition dynamics from low (L) to high (H) mode confinement in magnetically confined plasmas is investigated using a four-field drift fluid model—HESEL (Hot Edge-Sol-Electrostatic). The model includes profile evolution and is solved in a 2D domain at the out-board mid-plane of a tokamak including both open and closed field lines. The results reveal different types of L–H-like transitions in response to ramping up the input power by increasing the ion temperature in the edge region. For a fast rising input power we obtain an abrupt transition, and for a slow rising power we obtain a L–I–H transition with an intermediate I-phase displaying limit-cycle oscillations (LCO). The model recovers the power threshold for the L–H transition, the scaling of the threshold with the density and with the loss-rate in the SOL, indicating a decrease in power threshold when switching from single to double null configuration. The results hold promises for developing full predictive modeling of the L–H transition, which is an essential step in understanding and optimizing fusion devices. (paper)

Combined confinement system applied to tokamaks

International Nuclear Information System (INIS)

Ohkawa, Tihiro

1986-01-01

From particle orbit point of view, a tokamak is a combined confinement configuration where a closed toroidal volume is surrounded by an open confinement system like a magnetic mirror. By eliminating a cold halo plasma, the energy loss from the plasma becomes convective. The H-mode in diverted tokamaks is an example. Because of the favorable scaling of the energy confinement time with temperature, the performance of the tokamak may be significantly improved by taking advantage of this effect. (author)

Feasibility of a dual regime gyrotron

International Nuclear Information System (INIS)

Sawant, Ashwini; Jain, Prerit; Kartikeyan, M.V.

2012-01-01

The design concept of a 42/84 GHz, 500 kW, CW, dual-regime gyrotron for ECRH of plasma in an experimental Tokamak will be presented in this paper. Operation at 42 GHz is fundamental where as that in 84 GHz will be second harmonic so that a similar guidance system will be retained for dual regime operation. In this paper, the mode competition and mode selection procedures are presented for such a dual regime operation. Cold cavity design and self-consistent calculations will be carried out for power and efficiencies. (author)

Trapped ion mode in toroidally rotating plasmas

International Nuclear Information System (INIS)

Artun, M.; Tang, W.M.; Rewoldt, G.

1995-04-01

The influence of radially sheared toroidal flows on the Trapped Ion Mode (TIM) is investigated using a two-dimensional eigenmode code. These radially extended toroidal microinstabilities could significantly influence the interpretation of confinement scaling trends and associated fluctuation properties observed in recent tokamak experiments. In the present analysis, the electrostatic drift kinetic equation is obtained from the general nonlinear gyrokinetic equation in rotating plasmas. In the long perpendicular wavelength limit k τ ρ bi much-lt 1, where ρ bi is the average trapped-ion banana width, the resulting eigenmode equation becomes a coupled system of second order differential equations nmo for the poloidal harmonics. These equations are solved using finite element methods. Numerical results from the analysis of low and medium toroidal mode number instabilities are presented using representative TFTR L-mode input parameters. To illustrate the effects of mode coupling, a case is presented where the poloidal mode coupling is suppressed. The influence of toroidal rotation on a TFTR L-mode shot is also analyzed by including a beam species with considerable larger temperature. A discussion of the numerical results is presented

Method for determining the optimum mode of operation of the chemical water regime in the water-steam-circuit of power plants

International Nuclear Information System (INIS)

Sommerfeldt, P.; Reisner, H.; Hartmann, G.; Kulicke, P.

1988-01-01

The method aims at increasing the lifetime of secondary coolant circuit components in nuclear power plants through the determination of the optimum mode of operation of the chemical water regime by help of radioisotopes

Magnetic confinement in plasmas in nuclear devices

International Nuclear Information System (INIS)

Tull, C.G.

1979-01-01

The main emphasis of the magnetic fusion energy research program today lies in the development of two types of confinement schemes: magnetic mirrors and tokamaks. Experimental programs for both of these confinement schemes have shown steady progress toward achieving fusion power breakeven. The scaling of the current machines to a reactor operating regime and newly developed methods for plasma heating will very likely produce power breakeven within the next decade. Predictions are that the efficiency in a fusion power plant should exceed 32%

Comparison of a low- to high-confinement transition theory with experimental data from DIII-D.

Science.gov (United States)

Guzdar, P N; Kleva, R G; Groebner, R J; Gohil, P

2002-12-23

From our recent theory based on the generation of shear flow and field in finite beta plasmas, the criterion for bifurcation from low to high confinement mode yields a critical parameter proportional to T(e)/square root (L(n)), where T(e) is the electron temperature and L(n) is the density scale length. The predicted threshold shows very good agreement with edge measurements on discharges undergoing low-to-high transitions in DIII-D. The observed differences in the transitions with the reversal of the toroidal magnetic field are reconciled in terms of this critical parameter. The theory also provides an explanation for pellet injection H modes in DIII-D, thereby unifying unconnected methods for accomplishing the transition.

Z/sub N/ topology and charge confinement in SU(N) Higgs models

International Nuclear Information System (INIS)

Ezawa, Z.F.; Iwazaki, A.

1981-01-01

We analyze topological effects in frozen SU(N) Higgs models in continuous space-time, where topological excitations are Z/sub N/ vortices together with associated Z/sub N/ monopoles. The space dimension is either two or three. We show that vortex condensation generates magnetic gauge symmetry and that monopole condensation leads to a spontaneous breakdown of this symmetry. By summing up all possible excitation modes of Z/sub N/ vortices and Z/sub N/ monopoles, we derive an effective Lagrangian in the strong-coupling regime. We obtain the following conclusions: (i) if external charges are introduced in the fundamental representation, they are confined by electric vortex strings, and (ii) if external charges are introduced in the adjoint representation, they are screened completely

Plasma confinement in a magnetic dipole

International Nuclear Information System (INIS)

Kesner, J.; Bromberg, L.; Garnier, D.; Mauel, M.

1999-01-01

A dipole fusion confinement device is stable to MHD interchange and ballooning modes when the pressure profile is sufficiently gentle. The plasma can be confined at high beta, is steady state and disruption free. Theory indicates that when the pressure gradient is sufficiently gentle to satisfy MHD requirements drift waves will also be stable. The dipole approach is particularly applicable for advanced fuels. A new experimental facility is presently being built to test the stability and transport properties of a dipole-confined plasma. (author)

Plasma confinement in a magnetic dipole

International Nuclear Information System (INIS)

Kesner, J.; Bromberg, L.; Garnier, D.; Mauel, M.

2001-01-01

A dipole fusion confinement device is stable to MHD interchange and ballooning modes when the pressure profile is sufficiently gentle. The plasma can be confined at high beta, is steady state and disruption free. Theory indicates that when the pressure gradient is sufficiently gentle to satisfy MHD requirements drift waves will also be stable. The dipole approach is particularly applicable for advanced fuels. A new experimental facility is presently being built to test the stability and transport properties of a dipole-confined plasma. (author)

On global H-mode scaling laws for JET

International Nuclear Information System (INIS)

Kardaun, O.; Lackner, K.; Thomsen, K.; Christiansen, J.; Cordey, J.; Gottardi, N.; Keilhacker, M.; Smeulders, P.

1989-01-01

Investigation of the scaling of the energy confinement time τ E with various plasma parameters has since long been an interesting, albeit not uncontroversial topic in plasma physics. Various global scaling laws have been derived for ohmic as well as (NBI and/or RF heated) L-mode discharges. Due to the scarce availability of computerised, extensive and validated H-mode datasets, systematic statistical analysis of H-mode scaling behaviour has hitherto been limited. A common approach is to fit the available H-mode data by an L-mode scaling law (e.g., Kaye-Goldston, Rebut-Lallia) with one or two adjustable constant terms. In this contribution we will consider the alternative approach of fitting all free parameters of various simple scaling models to two recently compiled datasets consisting of about 140 ELM-free and 40 ELMy H-mode discharges, measured at JET in the period 1986-1988. From this period, approximately all known H-mode shots have been included that satisfy the following criteria: D-injected D + discharges with no RF heating, a sufficiently long (≥300 ms) and regular P NBI flat-top, and validated main diagnostics. (author) 13 refs., 1 tab

Atom-atom scattering under cylindrical harmonic confinement: Numerical and analytic studies of the confinement induced resonance

International Nuclear Information System (INIS)

Bergeman, T.; Moore, M.G.; Olshanii, M.

2003-01-01

It was recently predicted [Phys. Rev. Lett. 81, 938 (1998)10.1103/PhysRevLett.81.938] that atom-atom scattering under transverse harmonic confinement is subject to a 'confinement-induced resonance' where the effective one-dimensional coupling strength diverges at a particular ratio of the confinement and scattering lengths. As the initial prediction made use of the zero-range pseudopotential approximation, we now report numerical results for finite-range interaction potentials that corroborate this resonance. In addition, we now present a physical interpretation of this effect as a novel type of Feshbach resonance in which the transverse modes of the confining potential assume the roles of 'open' and 'closed' scattering channels

Bifurcated equilibria in centrifugally confined plasma

International Nuclear Information System (INIS)

Shamim, I.; Teodorescu, C.; Guzdar, P. N.; Hassam, A. B.; Clary, R.; Ellis, R.; Lunsford, R.

2008-01-01

A bifurcation theory and associated computational model are developed to account for abrupt transitions observed recently on the Maryland Centrifugal eXperiment (MCX) [R. F. Ellis et al. Phys. Plasmas 8, 2057 (2001)], a supersonically rotating magnetized plasma that relies on centrifugal forces to prevent thermal expansion of plasma along the magnetic field. The observed transitions are from a well-confined, high-rotation state (HR-mode) to a lower-rotation, lesser-confined state (O-mode). A two-dimensional time-dependent magnetohydrodynamics code is used to simulate the dynamical equilibrium states of the MCX configuration. In addition to the expected viscous drag on the core plasma rotation, a momentum loss term is added that models the friction of plasma on the enhanced level of neutrals expected in the vicinity of the insulators at the throats of the magnetic mirror geometry. At small values of the external rotation drive, the plasma is not well-centrifugally confined and hence experiences the drag from near the insulators. Beyond a critical value of the external drive, the system makes an abrupt transition to a well-centrifugally confined state in which the plasma has pulled away from the end insulator plates; more effective centrifugal confinement lowers the plasma mass near the insulators allowing runaway increases in the rotation speed. The well-confined steady state is reached when the external drive is balanced by only the viscosity of the core plasma. A clear hysteresis phenomenon is shown.

Stationary high confinement plasmas with large bootstrap current fraction in JT-60U

International Nuclear Information System (INIS)

Sakamoto, Y.; Fujita, T.; Ide, S.; Isayama, A.; Takechi, M.; Suzuki, T.; Takenaga, H.; Oyama, N.; Kamada, Y.

2005-01-01

This paper reports the results of the progress in stationary discharges with a large bootstrap current fraction in JT-60U towards steady-state tokamak operation. In the weak shear plasma regime, high-β p ELMy H-mode discharges have been optimized under nearly full non-inductive current drive conditions by the large bootstrap current fraction (f BS ∼ 45%) and the beam driven current fraction (f BD ∼ 50%), which was sustained for 5.8 s in the stationary condition. This duration corresponds to ∼26τ E and ∼2.8τ R , which was limited by the pulse length of negative-ion-based neutral beams. The high confinement enhancement factor H 89 ∼ 2.2 (HH 98y2 ∼ 1.0) was obtained and the profiles of current and pressure reached the stationary condition. In the reversed shear plasma regime, a large bootstrap current fraction (f BS ∼ 75%) has been sustained for 7.4 s under nearly full non-inductive current drive conditions. This duration corresponds to ∼16τ E and ∼2.7τ R . The high confinement enhancement factor H 89 ∼ 3.0 (HH 98y2 ∼ 1.7) was also sustained, and the profiles of current and pressure reached the stationary condition. The large bootstrap current and the off-axis beam driven current sustained this reversed q profile. This duration was limited only by the duration of the neutral beam injection

Energy confinement in the T-10 tokamak and canonic profile models

International Nuclear Information System (INIS)

Dnestrovskii, Yu.N.; Pereverzev, G.V.

1988-01-01

A classification of experimental results on electron cyclotron resonance heating (ECRH) is that T-10 tokamak is presented. Analysis of the experiments is consistent with two energy balance models. The first is based on the idea of profile consistency of the plasma current and pressure. The on-axis and off-axis ECRH as well as the heat wave propagation in T-10 can be reasonably represented in this way. In addition, this model allows the L to H mode transition to be described as the bifurcation of the solutions of a set of non-linear equations. The second model is based on the idea of a thermal pinch produced by a toroidal electric field. The electron temperature profiles under ohmic heating as well as under ECRH can be described by this model. Furthermore, this approach explains the cause of the confinement degradation under non-ohmic plasma heating (L-mode). (Author)

Recent results on confinement in JET

International Nuclear Information System (INIS)

Campbell, D.J.

1992-01-01

The JET device is the world's largest tokamak and has been utilized in plasma heating experiments at total powers of up to 35MW using both neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH). At the highest performance, JET plasmas have achieved conditions equivalent to energy ''breakeven''. A principal aim of the JET experiment is the investigation of plasma heating and confinement in plasma regimes relevant to thermonuclear ignition. The central issues in confinement physics involved in these advances are briefly reviewed and the most recent investigations of transport in high performance plasmas are summarized. (Author)

Controlled fusion and plasma physics

International Nuclear Information System (INIS)

Bickerton, R.J.

1991-01-01

On JET results were presented on additional heating power, on a recently discovered regime of enhanced pellet performance (PEP), on low-density H-mode plasma confinement with hot ions, bounds on very high electric currents by material limiters, the first experiments on lower hybrid current drive, on the L-H transition threshold dependence on the direction of the gradient-B drift, and on alpha-particle physics issues. The TFTR presentations focused on transport. Particle loss ramifications of the toroidal Alfven eigenmodes were found to be small, while their threshold of excitation is lower than theoretically predicted. On DIII-D a scaling study of transport with gyroradius as the only variable was reported, with approximately Bohm scaling emerging; but the effective heat diffusivity scaling could not be established due to profile consistency effects. While beta-limit investigations with DIII-D generally confirm the ideal, MHD limit found by Troyon, evidence of a reduction of the accessible range for the internal inductance with the safety factor seems to favour current-density control in a steady-state D-T burner. Onset of strongly sheared poloidal rotation in a thin layer during the L-H mode transition was experimentally shown, while a new, so-called VH (''very high'') confinement mode was discovered by boronization of the wall. The JT-90 tokamak has recently been upgraded to JT-60-U. Presentations by the ASDEX team summarized the lack of agreement with theory of L-mode confinement. With TEXTOR, an improved mode (I-mode) of confinement was found by boronization. Finally, reviews are included on the status of impurity transport and helium removal in tokamaks, on stellarators, alternative magnetic confinement systems, inertial confinement, and non-fusion plasma physics. 2 tabs

High Confinement and High Density with Stationary Plasma Energy and Strong Edge Radiation Cooling in Textor-94

Science.gov (United States)

Messiaen, A. M.

1996-11-01

A new discharge regime has been observed on the pumped limiter tokamak TEXTOR-94 in the presence of strong radiation cooling and for different scenarii of additional hearing. The radiated power fraction (up to 90%) is feedback controlled by the amount of Ne seeded in the edge. This regime meets many of the necessary conditions for a future fusion reactor. Energy confinement increases with increasing densities (reminiscent of the Z-mode obtained at ISX-B) and as good as ELM-free H-mode confinement (enhancement factor verus ITERH93-P up to 1.2) is obtained at high densities (up to 1.2 times the Greenwald limit) with peaked density profiles showing a peaking factor of about 2 and central density values around 10^14cm-3. In experiments where the energy content of the discharges is kept constant with an energy feedback loop acting on the amount of ICRH power, stable and stationary discharges are obtained for intervals of more than 5s, i.e. 100 times the energy confinement time or about equal to the skin resistive time, even with the cylindrical q_α as low as 2.8 β-values up to the β-limits of TEXTOR-94 are achieved (i.e. β n ≈ 2 of and β p ≈ 1.5) and the figure of merit for ignition margin f_Hqa in these discharges can be as high as 0.7. No detrimental effects of the seeded impurity on the reactivity of the plasma are observed. He removal in these discharges has also been investigated. [1] Laboratoire de Physique des Plasmas-Laboratorium voor Plasmafysica, Association "EURATOM-Belgian State", Ecole Royale Militaire-Koninklijke Militaire School, Brussels, Belgium [2] Institut für Plasmaphysik, Forschungszentrum Jülich, GmbH, Association "EURATOM-KFA", Jülich, Germany [3] Fusion Energy Research Program, Mechanical Engineering Division, University of California at San Diego, La Jolla, USA [4] FOM Institüt voor Plasmafysica Rijnhuizen, Associatie "FOM-EURATOM", Nieuwegein, The Netherlands [*] Researcher at NFSR, Belgium itemize

Passively mode-locked 4.6 and 10.5 GHz quantum dot laser diodes around 1.55 μm with large operating regime

NARCIS (Netherlands)

Heck, M.J.R.; Renault, A.; Bente, E.A.J.M.; Oei, Y.S.; Smit, M.K.; Eikema, K.S.E.; Ubachs, W.; Anantathanasarn, S.; Nötzel, R.

2009-01-01

Passive mode-locking in two-section InAs/InP quantum dot laser diodes operating at wavelengths around 1.55 µm is reported. For a 4.6-GHz laser, a large operating regime of stable mode-locking, with RF-peak heights of over 40 dB, is found for injection currents of 750 mA up to 1.0 A and for values of

Flow regimes and heat transfer modes identification in ANGRA 2 core, during small break in the primary loop with area of 100 cm2, simulated with RELAP5 code

International Nuclear Information System (INIS)

Borges, Eduardo M.; Sabundjian, Gaiane

2015-01-01

Identifying the flow regimes and the heat transfer modes is important for the analysis of accidents such as the Loss-of-Coolant Accident (LOCA). The aim of this paper is to identify the flow regimes, the heat transfer modes, and the correlations used in the RELAP5/MOD3.2.gama code in ANGRA 2 during the Small-Break Loss-of-Coolant Accident (SBLOCA) with a 100cm 2 -rupture area in the cold leg of primary loop. The Chapter 15 of the Final Safety Analysis Report of ANGRA 2 (FSAR - A2) reports this specific kind of accident. The results from this work demonstrated the several flow regimes and heat transfer modes that can be present in the core of ANGRA 2 during the postulated accident. (author)

Bi-fluid and neoclassical effect on a Double-Tearing mode in Tore Supra

Energy Technology Data Exchange (ETDEWEB)

Maget, Patrick, E-mail: patrick.maget@cea.fr; Garbet, Xavier; Février, Olivier; Ségui, Jean-Luc [CEA, IRFM, F-13108 Saint Paul-lez-Durance (France); Lütjens, Hinrich; Luciani, Jean-François [Centre de Physique Théorique, Ecole Polytechnique, CNRS (France)

2014-06-15

Tearing modes associated to hollow current profiles are prone to grow in moderate performance plasmas and often constrain the realization of non-inductive discharges in the Tore Supra tokamak, where long pulse duration is performed using Lower Hybrid waves for providing most of the plasma current. The prediction of MHD boundaries in such scenarios is complicated by the importance of diamagnetic effects, combined with curvature stabilization, which determine the stability of these modes. We show that diamagnetic effects, as well as neoclassical forces, are playing a key role in the linear and nonlinear regimes of Double-Tearing Modes on q = 5/3 and q = 2 in these experimental conditions. Detailed comparison with experimental measurements, combined with a scaling in plasma resistivity, give constraints about the experimental equilibrium. Resistive-Interchange Modes destabilized by diamagnetic rotation could also play a role in degrading the energy confinement in the negative magnetic shear region.

One-dimensional Tamm plasmons: Spatial confinement, propagation, and polarization properties

Science.gov (United States)

Chestnov, I. Yu.; Sedov, E. S.; Kutrovskaya, S. V.; Kucherik, A. O.; Arakelian, S. M.; Kavokin, A. V.

2017-12-01

Tamm plasmons are confined optical states at the interface of a metal and a dielectric Bragg mirror. Unlike conventional surface plasmons, Tamm plasmons may be directly excited by an external light source in both TE and TM polarizations. Here we consider the one-dimensional propagation of Tamm plasmons under long and narrow metallic stripes deposited on top of a semiconductor Bragg mirror. The spatial confinement of the field imposed by the stripe and its impact on the structure and energy of Tamm modes are investigated. We show that the Tamm modes are coupled to surface plasmons arising at the stripe edges. These plasmons form an interference pattern close to the bottom surface of the stripe that involves modification of both the energy and loss rate for the Tamm mode. This phenomenon is pronounced only in the case of TE polarization of the Tamm mode. These findings pave the way to application of laterally confined Tamm plasmons in optical integrated circuits as well as to engineering potential traps for both Tamm modes and hybrid modes of Tamm plasmons and exciton polaritons with meV depth.

GRAVITATIONAL INSTABILITY OF ROTATING, PRESSURE-CONFINED, POLYTROPIC GAS DISKS WITH VERTICAL STRATIFICATION

International Nuclear Information System (INIS)

Kim, Jeong-Gyu; Kim, Woong-Tae; Seo, Young Min; Hong, Seung Soo

2012-01-01

We investigate the gravitational instability (GI) of rotating, vertically stratified, pressure-confined, polytropic gas disks using a linear stability analysis as well as analytic approximations. The disks are initially in vertical hydrostatic equilibrium and bounded by a constant external pressure. We find that the GI of a pressure-confined disk is in general a mixed mode of the conventional Jeans and distortional instabilities, and is thus an unstable version of acoustic-surface-gravity waves. The Jeans mode dominates in weakly confined disks or disks with rigid boundaries. On the other hand, when the disk has free boundaries and is strongly pressure confined, the mixed GI is dominated by the distortional mode that is surface-gravity waves driven unstable under their own gravity and thus incompressible. We demonstrate that the Jeans mode is gravity-modified acoustic waves rather than inertial waves and that inertial waves are almost unaffected by self-gravity. We derive an analytic expression for the effective sound speed c eff of acoustic-surface-gravity waves. We also find expressions for the gravity reduction factors relative to a razor-thin counterpart that are appropriate for the Jeans and distortional modes. The usual razor-thin dispersion relation, after correcting for c eff and the reduction factors, closely matches the numerical results obtained by solving a full set of linearized equations. The effective sound speed generalizes the Toomre stability parameter of the Jeans mode to allow for the mixed GI of vertically stratified, pressure-confined disks.

Slide-away distributions and relevant collective modes in high-temperature plasmas

International Nuclear Information System (INIS)

Coppi, B.; Pegoraro, F.; Pozzoli, R.; Rewoldt, G.

1976-01-01

The evolution of the electron distribution function, when an electric field that is not too small in comparison with the critical electron runaway field is applied along the confining magnetic field of a high temperature plasma, is analysed. In the regimes considered, a finite fraction of the electron population has magnetically trapped orbits, and is not appreciably affected by the applied electric field, while the distribution of circulating electrons tends to ''slide away'' as a whole. Then the Spitzer-Haerm model for the current-carrying electron distribution is inadequate, and the role that collective modes, in particular current-driven microinstabilities, and collisions can play in producing a stationary electron distribution is analysed. Modes at the ion plasma frequency, ωsub(pi), that are driven by the positive slope of the current-carrying electron distribution, can be excited, when the average electron drift velocity is a finite fraction of the electron thermal velocity, and transfer transverse energy to the main body of the electron distribution. These features are consistent with the experimental observations performed on the Alcator device. Modes at the ''reduced'' electron plasma frequency (ksub(parallel)/k)ωsub(pe) can also be excited both in connection with the modes at wsub(pi) and independently. Modes at the electron gyrofrequency Ωsub(e) associated with the loss-cone feature that the electron distribution tends to develop are considered, among others, as a factor for the strongly enhanced electron cyclotron emission experimentally observed in regimes where non-thermal electron distributions have been realized. (author)

Transport of impurities during H-mode pulses in JET

International Nuclear Information System (INIS)

Giannella, R.; Gottardi, N.; Mompean, F.; Mori, H.; Pasini, D.; Stork, D.; Barnsley, R.; Hawkes, N.C.; Lawson, K.

1990-01-01

The transport of impurities during the H-mode is very different from that observed in the other regimes. This is clearly evident in the quiescent discharges where the confinement time of impurities τ I are measured in all the quiescent H-mode discharges in spite of the variety of impurity behavior observed corresponding to different plasma parameters and operating scenarios. The condition of the machine has an influence on the role played by the various impurities, but this does not seem to affect the flow patterns of these ions substantially. In particular oxygen, which was often detected as the dominant radiator, can be reduced to a negligible fraction by He conditioning of the carbon X-point tiles or limiters or by evaporating beryllium in the vacuum vessel. Nevertheless the behaviour of the residual impurities in otherwise similar discharges remains substantially unchanged. The transport patterns appear in fact to be affected by the plasma parameters and their profiles. In particular, two extreme transport regimes are presented in the following. These discharges have been modelled with the aid of a recently developed fully time-dependent impurity transport code using heuristic profiles for the impurity diffusion D and the convection velocity v. (author) 4 refs., 5 figs

Formation of discrete solitons as a function of waveguide array geometry under the well-confined mode condition

International Nuclear Information System (INIS)

Vergara-Betancourt, A; Martí-Panameño, E; Luis-Ramos, A; Parada-Alfonso, R

2013-01-01

Based on numerical techniques, in this paper, we study light propagation in two types of waveguide arrays. One array contains hexagonal cells, and the second contains honeycomb cells. The waveguides demonstrate the well-confined mode condition and possess Kerr nonlinearity. The mathematical model is based on the modified discrete nonlinear Schrödinger equation, which allows us to evaluate the influence of the array geometry on nonlinear light propagation, primarily the process of discrete soliton formation. The main conclusion involves the role of the coupling length; the greater the coupling length, the lower the power threshold required for discrete soliton formation. (paper)

Peeling-off of the external kink modes at tokamak plasma edge

International Nuclear Information System (INIS)

Zheng, L. J.; Furukawa, M.

2014-01-01

It is pointed out that there is a current jump between the edge plasma inside the last closed flux surface and the scrape-off layer and that the current jump can lead the external kink modes to convert to the tearing modes, due to the current interchange effects [L. J. Zheng and M. Furukawa, Phys. Plasmas 17, 052508 (2010)]. The magnetic reconnection in the presence of tearing modes subsequently causes the tokamak edge plasma to be peeled off to link to the divertors. In particular, the peeling or peeling-ballooning modes can become the “peeling-off” modes in this sense. This phenomenon indicates that the tokamak edge confinement can be worse than the expectation based on the conventional kink mode picture

Peeling-off of the external kink modes at tokamak plasma edge

Energy Technology Data Exchange (ETDEWEB)

Zheng, L. J. [Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States); Furukawa, M. [Graduate School of Engineering, Tottori University, Tottori 680-8552 (Japan)

2014-08-15

It is pointed out that there is a current jump between the edge plasma inside the last closed flux surface and the scrape-off layer and that the current jump can lead the external kink modes to convert to the tearing modes, due to the current interchange effects [L. J. Zheng and M. Furukawa, Phys. Plasmas 17, 052508 (2010)]. The magnetic reconnection in the presence of tearing modes subsequently causes the tokamak edge plasma to be peeled off to link to the divertors. In particular, the peeling or peeling-ballooning modes can become the “peeling-off” modes in this sense. This phenomenon indicates that the tokamak edge confinement can be worse than the expectation based on the conventional kink mode picture.

Amplification of 12 OAM Modes in an air-core erbium doped fiber.

Science.gov (United States)

Kang, Qiongyue; Gregg, Patrick; Jung, Yongmin; Lim, Ee Leong; Alam, Shaif-ul; Ramachandran, Siddharth; Richardson, David J

2015-11-02

We theoretically propose an air-core erbium doped fiber amplifier capable of providing relatively uniform gain for 12 orbital angular momentum (OAM) modes (|L| = 5, 6 and 7, where |L| is the OAM mode order) over the C-band. Amplifier performance under core pumping conditions for a uniformly doped core for each of the supported pump modes (110 in total) was separately assessed. The differential modal gain (DMG) was found to vary significantly depending on the pump mode used, and the minimum DMG was found to be 0.25 dB at 1550 nm provided by the OAM (8,1) pump mode. A tailored confined doping profile can help to reduce the pump mode dependency for core pumped operation and help to increase the number of pump modes that can support a DMG below 1 dB. For the more practical case of cladding-pumped operation, where the pump mode dependency is almost removed, a DMG of 0.25 dB and a small signal gain of >20 dB can be achieved for the 12 OAM modes across the full C-band.

Ball-Pen Probe Measurements in L-Mode and H-Mode on ASDEX Upgrade

Czech Academy of Sciences Publication Activity Database

Adámek, Jiří; Horáček, Jan; Müller, H. W.; Rohde, V.; Ionita, C.; Schrittwieser, R.; Mehlmann, F.; Kurzan, B.; Stöckel, Jan; Dejarnac, Renaud; Weinzettl, Vladimír; Seidl, Jakub; Peterka, M.

2010-01-01

Roč. 50, č. 9 (2010), s. 854-859 ISSN 0863-1042. [International Workshop on Electric Probes in Magnetized Plasmas/8th./. Innsbruck, 21.09.2009-24.09.2009] R&D Projects: GA AV ČR KJB100430901; GA ČR GA202/09/1467 Institutional research plan: CEZ:AV0Z20430508 Keywords : Tokamak * ball- pen probe * electron temperature * L-mode * H-mode * ELMs Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.006, year: 2010 http://onlinelibrary.wiley.com/doi/10.1002/ctpp.201010145/pdf

Energy confinement in the tokamak devices pulsator and ASDEX

International Nuclear Information System (INIS)

Klueber, O.; Murmann, H.

1982-04-01

The energy confinement of ohmically heated hydrogen plasmas obtained in the ASDEX and Pulsator tokamaks is investigated. In both devices, the confinement time does not follow a simple scaling law of the type tausub(E) approx. equal to nsub(e)a 2 . In the case of Pulsator, a regime is identified in which the transport is governed by electron heat conduction. The experimental data are compared with an analytic solution of the energy balance equation from which a heat diffusivity chisub(e) approx. equal to Zsub(eff)sup(1/3)/nsub(e)(r)Tsub(e)sup(1/2)(r)q(r) is inferred. chisub(i) is supposed to be neoclassical (plateau regime). Heat conduction following these laws is shown to lead to a consistent description of the full data set. (orig.)

Modeling cavities exhibiting strong lateral confinement using open geometry Fourier modal method

Science.gov (United States)

Häyrynen, Teppo; Gregersen, Niels

2016-04-01

We have developed a computationally efficient Fourier-Bessel expansion based open geometry formalism for modeling the optical properties of rotationally symmetric photonic nanostructures. The lateral computation domain is assumed infinite so that no artificial boundary conditions are needed. Instead, the leakage of the modes due to an imperfect field confinement is taken into account by using a basis functions that expand the whole infinite space. The computational efficiency is obtained by using a non-uniform discretization in the frequency space in which the lateral expansion modes are more densely sampled around a geometry specific dominant transverse wavenumber region. We will use the developed approach to investigate the Q factor and mode confinement in cavities where top DBR mirror has small rectangular defect confining the modes laterally on the defect region.

Extrap mode operation on Extrap T1-U

International Nuclear Information System (INIS)

Scheffel, J.; Brzozowski, J.; Hellblom, G.; Hoerling, P.; Welander, A.

1995-02-01

An extensive series of experiments in the Extrap mode has been carried out on Extrap T1-U in an attempt to obtain hot, collisionless discharges. Performance has, however, been limited to low temperatures (≤15 eV) and low currents (≤20 kA) at high loop voltages ≤1.4 kV, leading to energy confinement times of only a few μs or Alfven times. The discharge length is typically of order >100 Alfven times. The poor confinement is attributed to the absence of an axial magnetic field, generating strong instability- induced fluctuations and related transport in the core plasma. A turbulence core plasma transport model is suggested, based on theoretical evidence of linear instability in the kinetic regime. Experiments show that nonlinear saturation prevents the discharge from quenching on a time scale of a few Alfven times. Relaxation to RFP-like states is prevented from by a sufficiently strong octupole magnetic field. Edge transport appears to be strongly influenced by particle diffusion and heat conduction along open field lines (X-points) to the wall. 43 refs, 11 figs

Energy confinement in the torsatron URAGAN-3M during the rf-heating mode

International Nuclear Information System (INIS)

Pashnev, V.K.; Burchenko, P.Ya.; Lozin, A.V. and others

2008-01-01

Energy confinement time of plasma in torsatron U-3M was measured both during quasi-stationary study of RF-discharge and after RF-power cut-off. Power absorbed by plasma in the confinement region was estimated. A mechanism which explain the plasma density behavior in the confinement region is proposed

Flow regimes and heat transfer modes identification in ANGRA 2 core, during small break in the primary loop with area of 100 cm{sup 2}, simulated with RELAP5 code

Energy Technology Data Exchange (ETDEWEB)

Borges, Eduardo M.; Sabundjian, Gaiane, E-mail: gdgian@ipen.br, E-mail: borges.em@hotmail.com [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

2015-07-01

Identifying the flow regimes and the heat transfer modes is important for the analysis of accidents such as the Loss-of-Coolant Accident (LOCA). The aim of this paper is to identify the flow regimes, the heat transfer modes, and the correlations used in the RELAP5/MOD3.2.gama code in ANGRA 2 during the Small-Break Loss-of-Coolant Accident (SBLOCA) with a 100cm{sup 2}-rupture area in the cold leg of primary loop. The Chapter 15 of the Final Safety Analysis Report of ANGRA 2 (FSAR - A2) reports this specific kind of accident. The results from this work demonstrated the several flow regimes and heat transfer modes that can be present in the core of ANGRA 2 during the postulated accident. (author)

The Impact of Different Water Regime on Chlorophyll Fluorescence of Pyrus pyraster L. and Sorbus domestica L

Directory of Open Access Journals (Sweden)

Viera Šajbidorová

2015-01-01

Full Text Available The water deficit is considered to be significant cause of photosynthesis defects. Measuring of chlorophyll fluorescence is one of the methods revealing defects in the photosynthetic apparatus. The experiment was established with two woody plant (Pyrus pyraster L. and Sorbus domestica L. cultivated in two different regimes of the substrate saturation. The measurement of the modulated fluorescence of chlorophyll a was done by FMS1 fluorometer during three-week period between June and September (2012 and 2013. There were analysed selected parameters of chlorophyll fluorescence: Fv/Fm – maximum quantum efficiency of PSII, ΦPSII – effective quantum yield of PSII and RFD – chlorophyll fluorescence decrease ratio. According to the obtained results, Pyrus pyraster has probably higher potential for adaptation to water deficiency. There were recorded the significant decreases mainly in the values of parameter RFD and ΦPSII for Sorbus domestica within duration of experiment with different water regime in both growing seasons 2012 and 2013. The results document a weak sensitivity of the parameter Fv/Fm on changes in the amount of available water in the substrate in both taxa.

Repetitive 'snakes' and their damping effect on core toroidal rotation in EAST plasmas with multiple H-L-H transitions

International Nuclear Information System (INIS)

Xu Liqing; Hu Liqun

2015-01-01

Repetitive impurity snake-modes have been observed after H-L mode transitions (high to low confinement modes) in EAST plasmas exhibiting multiple H-L-H transitions. Such snake-modes have been observed to lower the core plasma toroidal rotation. A critical impurity strength factor associated with snake-mode formation has been estimated to be as high as α_Z_,_c =n_Z_,_cZ"2 / n_e ∼0.75. These observations have implications for ITER H-mode sustainability when the heating power is only slightly above the H-mode power threshold. (author)

Comparison of L- and H-mode plasma edge fluctuations in MAST

International Nuclear Information System (INIS)

Dudson, B D; Dendy, R O; Kirk, A; Meyer, H; Counsell, G F

2005-01-01

Edge turbulence measurements from a reciprocating Langmuir probe in MAST are presented. A comparison of the range/standard deviation (R/S), growth of range, first moment and differencing and rescaling methods for calculating the Hurst exponent is made. The differencing and rescaling method is found to be the most useful for identifying scaling over long time-periods. A comparison is made between L-mode, dithering H-mode and H-mode plasma edge turbulence and evidence for self-similarity is found. Tests are performed and it is demonstrated that the results are due to properties of the data, and are not artefacts of the methods. A comparison of Hurst exponent methods with the autocorrelation function and power spectrum is used to demonstrate the presence of long-time correlation in L-mode data, and the absence of long-time correlation in the case of dithering H-mode

Helical Confinement Concepts

Energy Technology Data Exchange (ETDEWEB)

Beidler, C; Brakel, R; Burhenn, R; Dinklage, A; Erckmann, V; Feng, Y; Geiger, J; Hartmann, D; Hirsch, M; Jaenicke, R; Koenig, R; Laqua, H P; Maassberg, H; Wagner, F; Weller, A; Wobig, H [Max-Planck Institut fuer Plasmaphysik, EURATOM Association, Greifswald (Germany)

2012-09-15

Stellarators, conceived 1951 by Lyman Spitzer in Princeton, are toroidal devices that confine a plasma in a magnetic field which originates from currents in coils outside the plasma. A plasma current driven by external means, for example by an ohmic transformer, is not required for confinement. Supplying the desired poloidal field component by external coils leads to a helically structured plasma topology. Thus stellarators - or helical confinement devices - are fully three-dimensional in contrast to the toroidal (rotational) symmetry of tokamaks. As stellarators can be free of an inductive current, whose radial distribution depends on the plasma parameters, their equilibrium must not be established via the evolving plasma itself, but to a first order already given by the vacuum magnetic field. They do not need an active control (like positional feedback) and therefore cannot suffer from its failure. The outstanding conceptual advantage of stellarators is the potential of steady state plasma operation without current drive. As there is no need for current drive, the recirculating power is expected to be smaller than in equivalent tokamaks. The lack of a net current avoids current driven instabilities; specifically, no disruptions, no resistive wall modes and no conventional or neoclassical tearing modes appear. Second order pressure-driven currents (Pfirsch-Schlueter, bootstrap) exist but they can be modified and even minimized by the magnetic design. The magnetic configuration of helical devices naturally possesses a separatrix, which allows the implementation of a helically structured divertor for exhaust and impurity control. (author)

Thermalization in a holographic confining gauge theory

Science.gov (United States)

Ishii, Takaaki; Kiritsis, Elias; Rosen, Christopher

2015-08-01

Time dependent perturbations of states in the holographic dual of a 3+1 dimensional confining theory are considered. The perturbations are induced by varying the coupling to the theory's most relevant operator. The dual gravitational theory belongs to a class of Einstein-dilaton theories which exhibit a mass gap at zero temperature and a first order deconfining phase transition at finite temperature. The perturbation is realized in various thermal bulk solutions by specifying time dependent boundary conditions on the scalar, and we solve the fully backreacted Einstein-dilaton equations of motion subject to these boundary conditions. We compute the characteristic time scale of many thermalization processes, noting that in every case we examine, this time scale is determined by the imaginary part of the lowest lying quasi-normal mode of the final state black brane. We quantify the dependence of this final state on parameters of the quench, and construct a dynamical phase diagram. Further support for a universal scaling regime in the abrupt quench limit is provided.

Thermalization in a holographic confining gauge theory

International Nuclear Information System (INIS)

Ishii, Takaaki; Kiritsis, Elias; Rosen, Christopher

2015-01-01

Time dependent perturbations of states in the holographic dual of a 3+1 dimensional confining theory are considered. The perturbations are induced by varying the coupling to the theory’s most relevant operator. The dual gravitational theory belongs to a class of Einstein-dilaton theories which exhibit a mass gap at zero temperature and a first order deconfining phase transition at finite temperature. The perturbation is realized in various thermal bulk solutions by specifying time dependent boundary conditions on the scalar, and we solve the fully backreacted Einstein-dilaton equations of motion subject to these boundary conditions. We compute the characteristic time scale of many thermalization processes, noting that in every case we examine, this time scale is determined by the imaginary part of the lowest lying quasi-normal mode of the final state black brane. We quantify the dependence of this final state on parameters of the quench, and construct a dynamical phase diagram. Further support for a universal scaling regime in the abrupt quench limit is provided.

L-H transition in the mega-Amp spherical tokamak

DEFF Research Database (Denmark)

Akers, R.J.; Counsell, G.F.; Sykes, A.

2002-01-01

H-mode plasmas have been achieved on the MAST spherical tokamak at input power considerably higher than predicted by conventional threshold scalings. Following L-H transition, a clear improvement in energy confinement is obtained, exceeding recent international scalings even at densities approach...

L-mode and inter-ELM divertor particle and heat flux width scaling on MAST

Energy Technology Data Exchange (ETDEWEB)

Harrison, J.R., E-mail: james.harrison@ccfe.ac.uk [EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Fishpool, G.M.; Kirk, A. [EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom)

2013-07-15

The distribution of particles and power to plasma-facing components is of key importance in the design of next-generation fusion devices. Power and particle decay lengths have been measured in a number of MAST L-mode and H-mode discharges in order to determine their parametric dependencies, by fitting power and particle flux profiles measured by divertor Langmuir probes, to a convolution of an exponential decay and a Gaussian function. In all discharges analysed, it is found that exponential decay lengths mapped to the midplane are mostly dependent on separatrix electron density (n{sub e,sep}{sup 0.65±0.15}) L-mode, (n{sub e,sep}{sup 0.76±0.19}) H-mode) and plasma current (I{sub p}{sup -0.36±0.11}) L-mode, I{sub p}{sup -1.05±0.18} H-mode) (or parallel connection length). The widths of the convolved Gaussian functions have been used to derive an approximate diffusion coefficient, which is found to vary from 1 m{sup 2}/s to 7 m{sup 2}/s, and is systematically lower in H-mode compared with L-mode.

Cross-correlated imaging of single-mode photonic crystal rod fiber with distributed mode filtering

DEFF Research Database (Denmark)

Laurila, Marko; Barankov, Roman; Jørgensen, Mette Marie

2013-01-01

Photonic crystal bandgap fibers employing distributed mode filtering design provide near diffraction-limited light outputs, a critical property of fiber-based high-power lasers. Microstructure of the fibers is tailored to achieve single-mode operation at specific wavelength by resonant mode...... identify regimes of resonant coupling between higher-order core modes and cladding band. We demonstrate a passive fiber design in which the higher-order modal content inside the single-mode guiding regime is suppressed by at least 20 dB even for significantly misaligned input-coupling configurations....

Stability and control of resistive wall modes in high beta, low rotation DIII-D plasmas

International Nuclear Information System (INIS)

Garofalo, A.M.; Jackson, G.L.; Haye, R.J. La; Okabayashi, M.; Reimerdes, H.; Strait, E.J.; Ferron, J.R.; Groebner, R.J.; In, Y.; Lanctot, M.J.; Matsunaga, G.; Navratil, G.A.; Solomon, W.M.; Takahashi, H.; Takechi, M.; Turnbull, A.D.

2007-01-01

Recent high-β DIII-D (Luxon J.L. 2002 Nucl. Fusion 42 64) experiments with the new capability of balanced neutral beam injection show that the resistive wall mode (RWM) remains stable when the plasma rotation is lowered to a fraction of a per cent of the Alfven frequency by reducing the injection of angular momentum in discharges with minimized magnetic field errors. Previous DIII-D experiments yielded a high plasma rotation threshold (of order a few per cent of the Alfven frequency) for RWM stabilization when resonant magnetic braking was applied to lower the plasma rotation. We propose that the previously observed rotation threshold can be explained as the entrance into a forbidden band of rotation that results from torque balance including the resonant field amplification by the stable RWM. Resonant braking can also occur naturally in a plasma subject to magnetic instabilities with a zero frequency component, such as edge localized modes. In DIII-D, robust RWM stabilization can be achieved using simultaneous feedback control of the two sets of non-axisymmetric coils. Slow feedback control of the external coils is used for dynamic error field correction; fast feedback control of the internal non-axisymmetric coils provides RWM stabilization during transient periods of low rotation. This method of active control of the n = 1 RWM has opened access to new regimes of high performance in DIII-D. Very high plasma pressure combined with elevated q min for high bootstrap current fraction, and internal transport barriers for high energy confinement, are sustained for almost 2 s, or 10 energy confinement times, suggesting a possible path to high fusion performance, steady-state tokamak scenarios

Ultrashort Generation Regimes in the All-Fiber Kerr Mode-Locked Erbium-Doped Fiber Ring Laser for Terahertz Pulsed Spectroscopy

Directory of Open Access Journals (Sweden)

V. S. Voropaev

2015-01-01

Full Text Available Many femtosecond engineering applications require for a stable generation of ultrashort pulses. Thus, in the terahertz pulsed spectroscopy a measurement error in the refractive index is strongly dependent on the pulse duration stability with allowable variation of few femtoseconds. The aim of this work is to study the ultrashort pulses (USP regimes stability in the all – fiber erbium doped ring laser with Kerr mode-locking. The study was conducted at several different values of the total resonator intra-cavity dispersion. Three laser schemes with the intra-cavity dispersion values from -1.232 ps2 to +0.008 ps2 have been studied. In the experiment there were two regimes of generation observed: the stretched pulse generation and ordinary soliton generation. Main attention is focused on the stability of regimes under study. The most stable regime was that of the stretched pulse generation with a spectrum form of sech2 , possible pulse duration of 490 fs at least, repetition rate of 2.9 MHz, and average output power of 17 mW. It is worth noting, that obtained regimes had characteristics suitable for the successful use in the terahertz pulsed spectroscopy. The results may be useful in the following areas of science and technology: a high-precision spectroscopy, optical frequency standards, super-continuum generation, and terahertz pulsed spectroscopy. The future system development is expected to stabilize duration and repetition rate of the obtained regime of ultra-short pulse generation.

Evidence of L-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith

Directory of Open Access Journals (Sweden)

T. B. Leyser

2018-02-01

Full Text Available The response of ionospheric plasma to pumping by powerful HF (high frequency electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association Heating facility in magnetic zenith. The CASSIOPE (CAScade, Smallsat and IOnospheric Polar Explorer spacecraft in the topside ionosphere above the F-region density peak detected transionospheric pump radiation, although the pump frequency was below the maximum ionospheric plasma frequency. The pump wave is deduced to arrive at CASSIOPE through L-mode propagation and associated double (O to Z, Z to O conversion in pump-induced radio windows. L-mode propagation allows the pump wave to reach higher plasma densities and higher ionospheric altitudes than O-mode propagation so that a pump wave in the L-mode can facilitate excitation of upper hybrid phenomena localized in density depletions in a larger altitude range. L-mode propagation is therefore suggested to be important in explaining the magnetic zenith effect.

Kinetic transport in a magnetically confined and flux-constrained fusion plasma

International Nuclear Information System (INIS)

Darmet, G.

2007-11-01

This work deals with the kinetic transport in a fusion plasma magnetically confined and flux-constrained. The author proposes a new interpretation of the dynamics of zonal flows. The model that has been studied is a gyrokinetic model reduced to the transport of trapped ions. The inter-change stability that is generated allows the study of the kinetic transport of trapped ions. This model has a threshold instability and can be simulated over a few tens confining time for either thermal bath constraint or flux constraint. For thermal baths constraint, the simulation shows a metastable state where zonal flows are prevailing while turbulence is non-existent. In the case of a flux-constraint, zonal flows appear and relax by exchanging energy with system's kinetic energy and turbulence energy. The competition between zonal flows and turbulence can be then simulated by a predator-prey model. 2 regimes can be featured out: an improved confining regime where zonal flows dominate transport and a turbulent regime where zonal flows and turbulent transport are of the same magnitude order. We show that flux as well as the Reynolds tensor play an important role in the dynamics of the zonal flows and that the gyrokinetic description is relevant for all plasma regions. (A.C.)

Identification of trapped electron modes in frequency fluctuation spectra of fusion plasmas

International Nuclear Information System (INIS)

Arnichand, Hugo

2015-01-01

This thesis shows that the analysis of frequency fluctuation spectra can provide an additional experimental indication of the dominant mode. Depending on the plasma scenario, fluctuation spectra can display different frequency components: Broadband spectra (Δf ∼ hundreds of kHz) which are always observed. Their amplitude is maximum at the zero frequency and they are attributed to turbulence. Coherent modes (Δf ∼ 1 kHz) which oscillate at a very well defined frequency. They can for example be due to geodesic acoustic or magnetohydrodynamic (MHD) modes; Quasi-Coherent (QC) modes (Δf ∼ tens of kHz) which oscillate at a rather well defined frequency but which are reminiscent of broadband fluctuations. The fluctuation study performed in the plasma core region shows that the fluctuation spectra in TEM-dominated regimes can be noticeably different from the ones in ITG-dominated regimes, as only TEM can induce QC modes. Such a finding has been achieved by comparing fluctuations measurements with simulations Measurements are made with a reflectometry diagnostic, a radar-like technique able to provide local indications of the density fluctuations occurring in the vicinity of the reflection layer. Frequency fluctuation spectra are inferred from a Fourier analysis of the reflectometry signal. First, the main properties of QC modes are characterized experimentally. Their normalized scale is estimated to k(perpendicular)ρ i ≤1, their amplitude is ballooned on the low field side mid-plane and they can be observed at many different radii. These indications are in agreement with what could be expected for ITG/TEM instabilities. Then reflectometry measurements are analyzed in Ohmic plasmas. QC modes are observed in the Linear Ohmic Confinement (LOC) regime dominated by TEM whereas only broadband spectra are seen in the Saturated Ohmic Confinement (SOC) regime dominated by ITG. Frequency spectra from nonlinear gyrokinetic simulations show that TEM induce a narrow

L-mode radiative plasma edge studies for model validation in ASDEX Upgrade and JET

Energy Technology Data Exchange (ETDEWEB)

Aho-Mantila, L., E-mail: leena.aho-mantila@vtt.fi [VTT Technical Research Centre of Finland, FI-02044 VTT (Finland); Bernert, M. [Max-Planck Institut für Plasmaphysik, D-85748 Garching (Germany); Coenen, J.W. [Energie- und Klimaforschung IEK-4, FZJ, EURATOM Association, TEC, 52425 Jülich (Germany); Fischer, R. [Max-Planck Institut für Plasmaphysik, D-85748 Garching (Germany); Lehnen, M. [Energie- und Klimaforschung IEK-4, FZJ, EURATOM Association, TEC, 52425 Jülich (Germany); Lowry, C. [EFDA JET CSU, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Marsen, S. [Max-Planck-Institut für Plasmaphysik, Teilinsitut Greifswald, D-17491 Greifswald (Germany); McCormick, K.; Müller, H.W.; Sieglin, B. [Max-Planck Institut für Plasmaphysik, D-85748 Garching (Germany); Stamp, M.F. [Culham Centre for Fusion Energy, EURATOM-CCFE Association, Abingdon (United Kingdom); Wischmeier, M. [Max-Planck Institut für Plasmaphysik, D-85748 Garching (Germany); Bonnin, X. [LSPM, CNRS, Université Paris 13, F-93430 Villetaneuse (France); Coster, D.P. [Max-Planck Institut für Plasmaphysik, D-85748 Garching (Germany); Reiter, D.; Brezinsek, S. [Energie- und Klimaforschung IEK-4, FZJ, EURATOM Association, TEC, 52425 Jülich (Germany)

2013-07-15

The presently favoured option for reactor power handling combines metallic plasma-facing components and impurity seeding to achieve highly radiative scrape-off layer and divertor plasmas. It is uncertain whether tolerable divertor power loads will be obtained in this scenario, necessitating the development of predictive modelling tools. L-mode experiments with N{sub 2} seeding have been conducted at both ASDEX Upgrade and JET for benchmarking the critically important impurity radiation models in edge fluid codes. In both machines, particle and power loads are observed to first reduce at the inner target, and only then at the outer target. The outer divertor cools down with increasing N seeding rate, evolving from low-recycling conditions to a regime with peak temperature of 8–10 eV in both devices. First SOLPS5.0 simulations of N{sub 2} seeding in ASDEX Upgrade geometry show a similar in–out asymmetry in the effect of impurity radiation when drifts are activated in the simulations.

Plasma confinement using biased electrode in the TCABR tokamak

International Nuclear Information System (INIS)

Nascimento, I.C.; Kuznetsov, Y.K.; Severo, J.H.F.; Fonseca, A.M.M.; Elfimov, A.; Bellintani, V.; Heller, M.V.A.P.; Galvao, R.M.O.; Sanada, E.K.; Elizondo, J.I.; Machida, M.

2005-01-01

Experimental data obtained on the TCABR tokamak (R = 0.61 m, r = 0.18 m) with an electrally polarized electrode, placed at r = 0.16 m, is reported in this paper. The experiment was performed with plasma current of 90 kA (q 3.1), and hydrogen gas injection adjusted for keeping the electron density at 1.0x10(19) m(-3) without bias. Temporal and radial profiles of plasma parameters with and without bias were measured. The comparison of the profiles shows an increase of the density, up to a maximum factor of 2.6, while H-alpha hydrogen spectral line intensity decreases, and the CIII impurity stays on the same level. The analysis of temporal and radial profiles of plasma parameters indicates that the confined plasma entered in the H-mode regime. The data analysis shows a maximum enhanced confinement factor of 1.95, decaying to 1.5 at the maximum of the density, in comparison with predicted Neo-Alcator scaling law values. Indications of transient increase of the density gradient near the plasma edge were obtained with measurements of density profiles. Calculations of turbulence and transport at the plasma edge, using measured floating potentials and ion saturation currents, show strong decrease in the power spectra and transport. Bifurcation was not observed, and the decrease in the saturation current occurs in 50 microseconds. (author)

International workshop of the Confinement Database and Modelling Expert Group in collaboration with the Edge and Pedestal Physics Expert Group

International Nuclear Information System (INIS)

Cordey, J.; Kardaun, O.

2001-01-01

A Workshop of the Confinement Database and Modelling Expert Group (EG) was held on 2-6 April at the Plasma Physics Research Center of Lausanne (CRPP), Switzerland. Presentations were held on the present status of the plasma pedestal (temperature and energy) scalings from an empirical and theoretical perspective. An integrated approach to modelling tokamaks incorporating core transport, edge pedestal and SOL, together with a model for ELMs was presented by JCT. New experimental data on on global H-mode confinement were discussed and presentations on L-H threshold power were made

From stripe to slab confinement for DNA linearization in nanochannels

Science.gov (United States)

Cifra, Peter; Benkova, Zuzana; Namer, Pavol

We investigate suggested advantageous analysis in the linearization experiments with macromolecules confined in a stripe-like channel using Monte Carlo simulations. The enhanced chain extension in a stripe that is due to significant excluded volume interactions between monomers in two dimensions weakens on transition to experimentally feasible slit-like channel. Based on the chain extension-confinement strength dependence and the structure factor behavior for the chain in stripe we infer the excluded volume regime typical for two-dimensional systems. On transition to the slab geometry, the advantageous chain extension decreases and the Gaussian regime is observed for not very long semiflexible chains. The evidence for pseudo-ideality in confined chains is based on indicators such as the extension curves, variation of the extension with the persistence length or the structure factor. The slab behavior is observed when the stripe (originally of monomer thickness) reaches the thickness larger than cca 10nm in the third dimension. This maximum height of the slab to retain the advantage of the stripe is very low and this have implication for DNA linearization experiments. The presented analysis, however, has a broader relevance for confined polymers. Support from Slovak R&D Agency (SRDA-0451-11) is acknowledged.

Isotope effect on confinement in DT plasmas

International Nuclear Information System (INIS)

Fukuyama, A.; Itoh, K.; Itoh, S.; Yagi, M.; Azumi, M.

1994-03-01

Isotope effect on the energy confinement time is discussed for the DT plasma. The transport theory which is based on the ballooning mode turbulence is applied. When the DT plasma is produced under the condition of β p >1, the energy confinement time of DT plasma (50% mixture) is expected to be about 1.2 times better than the D plasma with the same operation condition. (author)

Overview of H-mode studies in DIII-D

International Nuclear Information System (INIS)

Groebner, R.J.; Baker, D.R,; Allen, S.L.

1994-01-01

A major portion of the DIII-D program includes studies of the L-H transition, of the VH-mode, of particle transport and control and of the power-handling capability of a diverter. Significant progress has been made in all of these areas and the purpose of this paper is to summarize the major results obtained during the last two years. An increased understanding of the origin of improved confinement in H-mode and in VH-mode discharges has been obtained, good impurity control has been achieved in several operating scenarios, studies of helium transport provide encouraging results from the point of view of reactor design, an actively pumped diverter chamber has controlled the density in H-mode discharges and a radiative diverter is a promising technique for controlling the heat flux from the main plasma

Studies on Ytterbium-doped Fibre Laser Operating in Different Regimes

International Nuclear Information System (INIS)

Gan, Y; Xiang, W H; Zhang, G Z

2006-01-01

An ytterbium-doped fibre laser with a unidirectional ring cavity containing a polarizer placed between two in-line polarization controllers is presented. Depending on an equivalent saturable absorber, this laser operates in continuous, Q-switched mode-locked or CW mode-locked regimes. The passive method described here allowed us to choose the operating regime of the fibre laser by rotating the two polarization controllers and adjusting the pump power. Results of numerical simulations of pulse propagation in such a mode-locked fibre ring laser are presented, which reveals that the Q-switched mode-locked or CW modelocked regimes can be achieved by aligning the polarizer near the slow or the fast axes of the fibre

Study of the dynamical approach to the interface localization-delocalization transition of the confined Ising model

International Nuclear Information System (INIS)

Albano, Ezequiel V; Virgiliis, Andres de; Mueller, Marcus; Binder, Kurt

2004-01-01

Confined magnetic Ising films in a L x D geometry (L w (h). For T w (h) (T>T w (h)) such an interface is bounded (unbounded) to the walls, while right at T w (h) the interface is freely fluctuating around the centre of the film. Starting from disordered configurations, corresponding to T → ∞, we quench to the wetting critical temperature and study the dynamics of the approach to the stationary regime by means of extensive Monte Carlo simulations. It is found that for all layers parallel to the wall (rows), the row magnetizations exhibit a peak at a time τ max ∝ L 2 and subsequently relax to the stationary, equilibrium behaviour. The characteristic time for such a relaxation scales as τ R ∝ L 4 , as expected from theoretical arguments, that are discussed in detail

The Role of an Electric Field in the Formation of a Detached Regime in Tokamak Plasma

Science.gov (United States)

Senichenkov, I.; Kaveeva, E.; Rozhansky, V.; Sytova, E.; Veselova, I.; Voskoboynikov, S.; Coster, D.

2018-03-01

Modeling of the transition to the detachment of ASDEX Upgrade tokamak plasma with increasing density is performed using the SOLPS-ITER numerical code with a self-consistent account of drifts and currents. Their role in plasma redistribution both in the confinement region and in the scrape-off layer (SOL) is investigated. The mechanism of high field side high-density formation in the SOL in the course of detachment is suggested. In the full detachment regime, when the cold plasma region expands above the X-point and reaches closed magnetic-flux surfaces, plasma perturbation in a confined region may lead to a change in the confinement regime.

Regimes of the magnetized Rayleigh endash Taylor instability

International Nuclear Information System (INIS)

Winske, D.

1996-01-01

Hybrid simulations with kinetic ions and massless fluid electrons are used to investigate the linear and nonlinear behavior of the magnetized Rayleigh endash Taylor instability in slab geometry with the plasma subject to a constant gravity. Three regimes are found, which are determined by the magnitude of the complex frequency ω=ω r +iγ. For |ω| i (Ω i = ion gyrofrequency), one finds the typical behavior of the usual fluid regime, namely the development of open-quote open-quote mushroom-head close-quote close-quote spikes and bubbles in the density and a strongly convoluted boundary between the plasma and magnetic field, where the initial gradient is not relaxed much. A second regime, where |ω|∼0.1Ω i , is characterized by the importance of the Hall term. Linearly, the developing flute modes are more finger-like and tilted along the interface; nonlinearly, clump-like structures form, leading to a significant broadening of the interface. The third regime is characterized by unmagnetized ion behavior, with |ω|∼Ω i . Density clumps, rather than flutes, form in the linear stage, while nonlinearly, longer-wavelength modes that resemble those in fluid regime dominate. Finite Larmor radius stabilization of short-wavelength modes is observed in each regime. copyright 1996 American Institute of Physics

Physics of turbulence control and transport barrier formation in DIII-D

International Nuclear Information System (INIS)

Doyle, E.J.; Burrell, K.H.; Carlstrom, T.N.

1996-10-01

This paper describes the physical mechanisms responsible for turbulence control and transport barrier formation on DIII-D as determined from a synthesis of results from different enhanced confinement regimes, including quantitative and qualitative comparisons to theory. A wide range of DIII-D data support the hypothesis that a single underlying physical mechanism, turbulence suppression via E x B shear flow is playing an essential, though not necessarily unique, role in reducing turbulence and transport in all of the following improved confinement regimes: H-mode, VH-mode, high-ell i modes, improved performance counter-injection L-mode discharges and high performance negative central shear (NCS) discharges. DIII-D data also indicate that synergistic effects are important in some cases, as in NCS discharges where negative magnetic shear also plays a role in transport barrier formation. This work indicates that in order to control turbulence and transport it is important to focus on understanding physical mechanisms, such as E x B shear, which can regulate and control entire classes of turbulent modes, and thus control transport. In the highest performance DIII-D discharges, NCS plasmas with a VH-mode like edge, turbulence is suppressed at all radii, resulting in neoclassical levels of ion transport over most of the plasma volume

Results from deuterium-tritium tokamak confinement experiments

International Nuclear Information System (INIS)

Hawryluk, R.J.

1997-02-01

Recent scientific and technical progress in magnetic fusion experiments has resulted in the achievement of plasma parameters (density and temperature) which enabled the production of significant bursts of fusion power from deuterium-tritium fuels and the first studies of the physics of burning plasmas. The key scientific issues in the reacting plasma core are plasma confinement, magnetohydrodynamic (MHD) stability, and the confinement and loss of energetic fusion products from the reacting fuel ions. Progress in the development of regimes of operation which have both good confinement and are MHD stable have enabled a broad study of burning plasma physics issues. A review of the technical and scientific results from the deuterium-tritium experiments on the Joint European Torus (JET) and the Tokamak Fusion Test Reactor (TFTR) is given with particular emphasis on alpha-particle physics issues

Issues in tokamak/stellarator transport and confinement enhancement mechanisms

International Nuclear Information System (INIS)

Perkins, F.W.

1990-08-01

At present, the mechanism for anomalous energy transport in low-β toroidal plasmas -- tokamaks and stellarators -- remains unclear, although transport by turbulent E x B velocities associated with nonlinear, fine-scale microinstabilities is a leading candidate. This article discusses basic theoretical concepts of various transport and confinement enhancement mechanisms as well as experimental ramifications which would enable one to distinguish among them and hence identify a dominant transport mechanism. While many of the predictions of fine-scale turbulence are born out by experiment, notable contradictions exist. Projections of ignition margin rest both on the scaling properties of the confinement mechanism and on the criteria for entering enhanced confinement regimes. At present, the greatest uncertainties lie with the basis for scaling confinement enhancement criteria. A series of questions, to be answered by new experimental/theoretical work, is posed to resolve these outstanding contradictions (or refute the fine-scale turbulence model) and to establish confinement enhancement criteria. 73 refs., 4 figs., 5 tabs

Enhancement of confinement in tokamaks

International Nuclear Information System (INIS)

Furth, H.P.

1986-01-01

The analysis begins by identifying a hypothetical model of tokamak confinement that is designed to take into account the conflict between Tsub(e)(r)-profile shapes arising from microscopic transport and J(r)-profile shapes required for gross stability. On the basis of this model, a number of hypothetical lines of advance are developed. Some TFTR experiments that may point the way to a particularly attractive type of tokamak reactor regime are discussed. (author)

Predictive modelling of edge transport phenomena in ELMy H-mode tokamak fusion plasmas

International Nuclear Information System (INIS)

Loennroth, J.-S.

2009-01-01

This thesis discusses a range of work dealing with edge plasma transport in magnetically confined fusion plasmas by means of predictive transport modelling, a technique in which qualitative predictions and explanations are sought by running transport codes equipped with models for plasma transport and other relevant phenomena. The focus is on high confinement mode (H-mode) tokamak plasmas, which feature improved performance thanks to the formation of an edge transport barrier. H-mode plasmas are generally characterized by the occurrence of edge localized modes (ELMs), periodic eruptions of particles and energy, which limit confinement and may turn out to be seriously damaging in future tokamaks. The thesis introduces schemes and models for qualitative study of the ELM phenomenon in predictive transport modelling. It aims to shed new light on the dynamics of ELMs using these models. It tries to explain various experimental observations related to the performance and ELM-behaviour of H-mode plasmas. Finally, it also tries to establish more generally the potential effects of ripple-induced thermal ion losses on H-mode plasma performance and ELMs. It is demonstrated that the proposed ELM modelling schemes can qualitatively reproduce the experimental dynamics of a number of ELM regimes. Using a theory-motivated ELM model based on a linear instability model, the dynamics of combined ballooning-peeling mode ELMs is studied. It is shown that the ELMs are most often triggered by a ballooning mode instability, which renders the plasma peeling mode unstable, causing the ELM to continue in a peeling mode phase. Understanding the dynamics of ELMs will be a key issue when it comes to controlling and mitigating the ELMs in future large tokamaks. By means of integrated modelling, it is shown that an experimentally observed increase in the ELM frequency and deterioration of plasma confinement triggered by external neutral gas puffing might be due to a transition from the second to

Improved confinement and related physics study in Compact Helical System

International Nuclear Information System (INIS)

Okamura, S.; Akiyama, T.; Fujisawa, A.; Ida, K.; Iguchi, H.; Isobe, M.; Minami, T.; Nagaoka, K.; Nakamura, K.; Nishimura, S.; Matsuoka, K.; Matsushita, H.; Nakano, H.; Ohshima, S.; Shimizu, A.; Suzuki, C.; Takahashi, C.; Toi, K.; Yoshimura, Y.; Yoshinuma, M.; Oishi, T.; Kado, S.

2005-01-01

Recent experimental results in Compact Helical System (CHS) will be presented focusing on the improved confinement and physics study of electric field and turbulence in helical plasmas. Among various improved confinement modes found in CHS experiments, the edge transport barrier (ETB) formation is an important topic, which we have been studying intensively for these years. The discharges of CHS with ETB have characteristics very similar to H-mode discharges in tokamaks and W7-AS stellarator. We observe a sharp drop of Hα emission signal, increase of plasma density together with an increase of local density gradient at the plasma edge, so we call our ETB discharges as H-mode. The power threshold for the transition is clearly observed which is again similar to standard H-mode discharges, i.e., the threshold increases with the density and magnetic field. Unique feature of CHS H-mode is the dependence on the magnetic field configuration. We examined H-mode discharges for the configurations with magnetic axis shift and the magnetic quadrupole control. The transition appeared for a wide range of configurations with the rotational transform at the plasma edge (iota(a)) below and above unity. There is a general dependence of power threshold: higher power needed for the inward shifted configuration (with lower value of iota(a)) and lower power for outward shift. The absolute power threshold of CHS H-mode for the outward shifted configuration is very close to the tokamak H-mode with a divertor configuration. Other topics of confinement studies in CHS will be also presented. We have a unique diagnostic system of two heavy ion beam probes. It is unique in stellarator research and also for all toroidal confinement research including many tokamaks in the world. As well as fruitful result of electric field measurements, that is one of key elements for stellarator physics, this diagnostic measures turbulence in the plasma, which gives essential information for the study of

Unusual large-pitch banding in poly(L-lactic acid): Effects of composition and geometry confinement

International Nuclear Information System (INIS)

Woo, Eamor M.; Lugito, Graecia; Hsieh, Ya-Ting; Nurkhamidah, Siti

2014-01-01

Lamellar patterns and orientations in blends of two crystalline polymers: poly(ethylene oxide) (PEO) and low-molecular-weight poly(L-lactic acid) (PLLA) were investigated using polarizing light optical microscopy (POM), and atomic and scanning electron microscopy (AFM, SEM). Specific etching off of PEO was used to reveal the complex earlier-grown PLLA lamellae patterns with various PEO content in blends. Banding of extremely long pitch (50 μm) in crystallized PLLA spherulites was induced by two kinetic factors: geometry confinement by top cover and introduction of diluent such as PEO. The mechanisms and correlation among the lamellar assembly, ring bands, and cracks are exemplified. Lamellar patterns and ring-band types in blends were found to vary with respect to not only blend compositions, but also confinement of top-cover

Experimental studies of tearing mode and resistive wall mode dynamics in the reversed field pinch configuration

International Nuclear Information System (INIS)

Malmberg, Jenny-Ann

2003-06-01

It is relatively straightforward to establish equilibrium in magnetically confined plasmas, but the plasma is frequently susceptible to a variety of instabilities that are driven by the free energy in the magnetic field or in the pressure gradient. These unstable modes exhibit effects that affect the particle, momentum and heat confinement properties of the configuration. Studies of the dynamics of several of the most important modes are the subject of this thesis. The studies are carried out on plasmas in the reversed field pinch (RFP) configuration. One phenomenon commonly observed in RFPs is mode wall locking. The localized nature of these phase- and wall locked structures results in localized power loads on the wall which are detrimental for confinement. A detailed study of the wall locked mode phenomenon is performed based on magnetic measurements from three RFP devices. The two possible mechanisms for wall locking are investigated. Locking as a result of tearing modes interacting with a static field error and locking due to the presence of a non-ideal boundary. The characteristics of the wall locked mode are qualitatively similar in a device with a conducting shell system (TPE-RX) compared to a device with a resistive shell (Extrap T2). A theoretical model is used for evaluating the threshold values for wall locking due to eddy currents in the vacuum vessel in these devices. A good correlation with experiment is observed for the conducting shell device. The possibility of successfully sustaining discharges in a resistive shell RFP is introduced in the recently rebuilt device Extrap T2R. Fast spontaneous mode rotation is observed, resulting in low magnetic fluctuations, low loop voltage and improved confinement. Wall locking is rarely observed. The low tearing mode amplitudes allow for the theoretically predicted internal non-resonant on-axis resistive wall modes to be observed. These modes have not previously been distinguished due to the formation of wall

Equilibrium partitioning of macromolecules in confining geometries: Improved universality with a new molecular size parameter

DEFF Research Database (Denmark)

Wang, Yanwei; Peters, Günther H.J.; Hansen, Flemming Yssing

2008-01-01

structures (CABS), allows the computation of equilibrium partition coefficients as a function of confinement size solely based on a single sampling of the configuration space of a macromolecule in bulk. Superior in computational speed to previous computational methods, CABS is capable of handling slits...... parameter for characterization of spatial confinement effects on macromolecules. Results for the equilibrium partition coefficient in the weak confinement regime depend only on the ratio ofR-s to the confinement size regardless of molecular details....

NSTX Plasma Response to Lithium Coated Divertor

Energy Technology Data Exchange (ETDEWEB)

H.W. Kugel, M.G. Bell, J.P. Allain, R.E. Bell, S. Ding, S.P. Gerhardt, M.A. Jaworski, R. Kaita, J. Kallman, S.M. Kaye, B.P. LeBlanc, R. Maingi, R. Majeski, R. Maqueda, D.K. Mansfield, D. Mueller, R. Nygren, S.F. Paul, R. Raman, A.L. Roquemore, S.A. Sabbagh, H. Schneider, C.H. Skinner, V.A. Soukhanovskii, C.N. Taylor, J.R. Timberlak, W.R. Wampler, L.E. Zakharov, S.J. Zweben, and the NSTX Research Team

2011-01-21

NSTX experiments have explored lithium evaporated on a graphite divertor and other plasma facing components in both L- and H- mode confinement regimes heated by high-power neutral beams. Improvements in plasma performance have followed these lithium depositions, including a reduction and eventual elimination of the HeGDC time between discharges, reduced edge neutral density, reduced plasma density, particularly in the edge and the SOL, increased pedestal electron and ion temperature, improved energy confinement and the suppression of ELMs in the H-mode. However, with improvements in confinement and suppression of ELMs, there was a significant secular increase in the effective ion charge Zeff and the radiated power in H-mode plasmas as a result of increases in the carbon and medium-Z metallic impurities. Lithium itself remained at a very low level in the plasma core, <0.1%. Initial results are reported from operation with a Liquid Lithium Divertor (LLD) recently installed.

NSTX plasma response to lithium coated divertor

International Nuclear Information System (INIS)

Kugel, H.W.; Bell, M.G.; Allain, J.P.; Bell, R.E.; Ding, S.; Gerhardt, S.P.; Jaworski, M.A.; Kaita, R.; Kallman, J.; Kaye, S.M.; LeBlanc, B.P.; Maingi, Rajesh; Majeski, R.; Maqueda, R.J.; Mansfield, D.K.; Mueller, D.; Nygren, R.E.; Paul, S.F.; Raman, R.; Roquemore, A.L.; Sabbagh, S.A.; Schneider, H.; Skinner, C.H.; Soukhanovskii, V.A.; Taylor, C.N.; Timberlake, J.; Wampler, W.R.; Zakharov, L.E.; Zweben, S.J.

2011-01-01

NSTX experiments have explored lithium evaporated on a graphite divertor and other plasma-facing components in both L- and H- mode confinement regimes heated by high-power neutral beams. Improvements in plasma performance have followed these lithium depositions, including a reduction and eventual elimination of the HeGDC time between discharges, reduced edge neutral density, reduced plasma density, particularly in the edge and the SOL, increased pedestal electron and ion temperature, improved energy confinement and the suppression of ELMs in the H-mode. However, with improvements in confinement and suppression of ELMs, there was a significant secular increase in the effective ion charge Z(eff) and the radiated power in H-mode plasmas as a result of increases in the carbon and medium-Z metallic impurities. Lithium itself remained at a very low level in the plasma core, < 0.1%. Initial results are reported from operation with a Liquid Lithium Divertor (LLD) recently installed.

Single-mode regime in large-mode-area rare-earth-doped rod-type PCFs

DEFF Research Database (Denmark)

Poli, F.; Cucinotta, A.; Passaro, D.

2009-01-01

In this paper, large-mode-area, double-cladding, rare-earth-doped photonic crystal fibers are investigated in order to understand how the refractive index distribution and the mode competition given by the amplification can assure single-mode propagation. Fibers with different core diameters, i...

Effect of shear in the radial electric field on confinement in JET

Energy Technology Data Exchange (ETDEWEB)

O` Brien, D P; Balet, B; Deliyanakis, N; Cordey, J G; Stubberfield, P M [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking

1994-07-01

The role of the radial electric field during enhanced confinement of JET discharges is studied. Results from two series of experiments are presented: beam dominated with the addition of a small amount of ICRH, and ICRH dominated discharges, showing that for high performance ICRH heated discharges which obtain the high confinement regime, there is evidence against the E x B flow stabilisation. 4 refs., 4 figs.

Comments on experimental results of energy confinement of tokamak plasmas

International Nuclear Information System (INIS)

Chu, T.K.

1989-04-01

The results of energy-confinement experiments on steady-state tokamak plasmas are examined. For plasmas with auxiliary heating, an analysis based on the heat diffusion equation is used to define heat confinement time (the incremental energy confinement time). For ohmically sustained plasmas, experiments show that the onset of the saturation regime of energy confinement, marfeing, detachment, and disruption are marked by distinct values of the parameter /bar n//sub e///bar j/. The confinement results of the two types of experiments can be described by a single surface in 3-dimensional space spanned by the plasma energy, the heating power, and the plasma density: the incremental energy confinement time /tau//sub inc/ = ΔW/ΔP is the correct concept for describing results of heat confinement in a heating experiment; the commonly used energy confinement time defined by /tau//sub E/ = W/P is not. A further examination shows that the change of edge parameters, as characterized by the change of the effective collision frequency ν/sub e/*, governs the change of confinement properties. The totality of the results of tokamak experiments on energy confinement appears to support a hypothesis that energy transport is determined by the preservation of the pressure gradient scale length. 70 refs., 6 figs., 1 tab

Pedestal formation during L-H transitions in H-1 heliac

International Nuclear Information System (INIS)

Punzmann, H.; Shats, M.G.

2003-01-01

In this work we present experimental results on the spatial structure of the particle transport during spontaneous confinement bifurcations in H-1 heliac. We performed parameter scans in both L- and H-modes to investigate the relation between the particle flux and the density gradient. (orig.)

Reciprocating Probe Measurements of L-H Transition in LHCD H-mode on EAST

DEFF Research Database (Denmark)

Peng, Liu; Guosheng, Xu; Huiqian, Wang

2013-01-01

that the power loss P loss was comparable during the L-H transition, by comparing the adjacent L-mode and H-mode discharge. The Dα emission, Te and ne decreased rapidly in the time scale of about 1 ms, and the radial electric field Er turned positive in this process near the last closed flux surface. Multiple L......-H-L transitions were observed during a single shot when the applied LHW power was marginal to the threshold. The floating potential (Vf) had negative spikes corresponding with the Dα signal, and Er oscillation evolved into several intermittent negative spikes just before the L-H transition. In some shots......, dithering was observed just before the L-H transition....

Impact of Te and ne on edge current density profiles in ELM mitigated regimes on ASDEX Upgrade

Science.gov (United States)

Dunne, M. G.; Rathgeber, S.; Burckhart, A.; Fischer, R.; Giannone, L.; McCarthy, P. J.; Schneider, P. A.; Wolfrum, E.; the ASDEX Upgrade Team

2015-01-01

ELM resolved edge current density profiles are reconstructed using the CLISTE equilibrium code. As input, highly spatially and temporally resolved edge electron temperature and density profiles are used in addition to data from the extensive set of external poloidal field measurements available at ASDEX Upgrade, flux loop difference measurements, and current measurements in the scrape-off layer. Both the local and flux surface averaged current density profiles are analysed for several ELM mitigation regimes. The focus throughout is on the impact of altered temperature and density profiles on the current density. In particular, many ELM mitigation regimes rely on operation at high density. Two reference plasmas with type-I ELMs are analysed, one with a deuterium gas puff and one without, in order to provide a reference for the behaviour in type-II ELMy regimes and high density ELM mitigation with external magnetic perturbations at ASDEX Upgrade. For type-II ELMs it is found that while a similar pedestal top pressure is sustained at the higher density, the temperature gradient decreases in the pedestal. This results in lower local and flux surface averaged current densities in these phases, which reduces the drive for the peeling mode. No significant differences between the current density measured in the type-I phase and ELM mitigated phase is seen when external perturbations are applied, though the pedestal top density was increased. Finally, ELMs during the nitrogen seeded phase of a high performance discharge are analysed and compared to ELMs in the reference phase. An increased pedestal pressure gradient, which is the source of confinement improvement in impurity seeded discharges, causes a local current density increase. However, the increased Zeff in the pedestal acts to reduce the flux surface averaged current density. This dichotomy, which is not observed in other mitigation regimes, could act to stabilize both the ballooning mode and the peeling mode at the

Entanglement as a probe of confinement

International Nuclear Information System (INIS)

Klebanov, Igor R.; Kutasov, David; Murugan, Arvind

2008-01-01

We investigate the entanglement entropy in gravity duals of confining large N c gauge theories using the proposal of [S. Ryu, T. Takayanagi, Phys. Rev. Lett. 96 (2006) 181602, (hep-th/0603001); S. Ryu, T. Takayanagi, JHEP 0608 (2006) 045, (hep-th/0605073)]. Dividing one of the directions of space into a line segment of length l and its complement, the entanglement entropy between the two subspaces is given by the classical action of the minimal bulk hypersurface which approaches the endpoints of the line segment at the boundary. We find that in confining backgrounds there are generally two such surfaces. One consists of two disconnected components localized at the endpoints of the line segment. The other contains a tube connecting the two components. The disconnected surface dominates the entropy for l above a certain critical value l crit while the connected one dominates below that value. The change of behavior at l=l crit is reminiscent of the finite temperature deconfinement transition: for l crit the entropy scales as N c 2 , while for l>l crit as N c 0 . We argue that a similar transition should occur in any field theory with a Hagedorn spectrum of non-interacting bound states. The requirement that the entanglement entropy has a phase transition may be useful in constraining gravity duals of confining theories

Millimeter wave absorption by confined acoustic modes in CdSe/CdTe core-shell quantum dots

International Nuclear Information System (INIS)

Liu, T-M; Lu, J-Y; Kuo, C-C; Wen, Y-C; Lai, C-W; Yang, M-J; Chou, P-T; Murray, D B; Saviot, L; Sun, C-Kuang

2007-01-01

Taking advantage of the specific core-shell charge separation structure in the CdSe/CdTe core-shell Type-II quantum dots (QDs), we experimentally observed the resonant-enhanced dipolar interaction between millimeter-wave (MMW) photons and their corresponding (l = 1) confined acoustic phonons. With proper choice of size, the absorption band can be tuned to desired frequency of MMW imaging. Exploiting this characteristic absorption, in a fiber-scanned MMW imaging system, we demonstrated the feasibility of CdSe/CdTe QDs as the contrast agents of MMW imaging

Understanding and Control of Transport in Advanced Tokamak Regimes in DIII-D

International Nuclear Information System (INIS)

C.M. Greenfield; J.C. DeBoo; T.C. Luce; B.W. Stallard; E.J. Synakowski; L.R. Baylor; K.H. Burrell; T.A. Casper; E.J. Doyle; D.R. Ernst; J.R. Ferron; P. Gohil; R.J. Groebner; L.L. Lao; M. Makowski; G.R. McKee; M. Murakami; C.C. Petty; R.I. Pinsker; P.A. Politzer; R. Prater; C.L. Rettig; T.L. Rhodes; B.W. Rice; G.L. Schmidt; G.M. Staebler; E.J. Strait; D.M. Thomas; M.R. Wade

1999-01-01

Transport phenomena are studied in Advanced Tokamak (AT) regimes in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomics Energy Agency, Vienna, 1987), Vol. I, p. 159], with the goal of developing understanding and control during each of three phases: Formation of the internal transport barrier (ITB) with counter neutral beam injection takes place when the heating power exceeds a threshold value of about 9 MW, contrasting to CO-NBI injection, where P threshold N H 89 = 9 for 16 confinement times has been accomplished in a discharge combining an ELMing H-mode edge and an ITB, and exhibiting ion thermal transport down to 2-3 times neoclassical. The microinstabilities usually associated with ion thermal transport are predicted stable, implying that another mechanism limits performance. High frequency MHD activity is identified as the probable cause

Strong coupling of two interacting excitons confined in a nanocavity-quantum dot system

International Nuclear Information System (INIS)

Cardenas, Paulo C; RodrIguez, Boris A; Quesada, Nicolas; Vinck-Posada, Herbert

2011-01-01

We present a study of the strong coupling between radiation and matter, considering a system of two quantum dots, which are in mutual interaction and interact with a single mode of light confined in a semiconductor nanocavity. We take into account dissipative mechanisms such as the escape of the cavity photons, decay of the quantum dot excitons by spontaneous emission, and independent exciton pumping. It is shown that the mutual interaction between the dots can be measured off-resonance only if the strong coupling condition is reached. Using the quantum regression theorem, a reasonable definition of the dynamical coupling regimes is introduced in terms of the complex Rabi frequency. Finally, the emission spectrum for relevant conditions is presented and compared with the above definition, demonstrating that the interaction between the excitons does not affect the strong coupling.

Confinement bifurcation by current density profile perturbation in TUMAN-3M tokamak

International Nuclear Information System (INIS)

Lebedev, S.V.; Andreiko, M.V.; Askinazi, L.G.

2001-01-01

In the recent experiments performed on TUMAN-3M the possibility to switch on/off the H-mode by current density profile perturbations has been shown. The j(r) perturbations were created by fast Current Ramp Up/Down or by Magnetic Compression produced by a fast increase of the toroidal magnetic field. It was found that the Current Ramp Up (CRU) and Magnetic Compression (MC) are useful means for H-mode triggering. The Current Ramp Down (CRD) triggers H-L transition. The difference in the j(r) behavior in these experiments suggests the peripheral current density may not be the critical parameter controlling L-H and H-L transitions. Confinement bifurcation in the above experiments could be explained by the unified mechanism: variation of a turbulent transport resulting from radial electric field emerging near the edge in the conditions of alternating toroidal electric field Ej and different electron and ion collisionalities. According to the suggested model the toroidal field E φ arising in the periphery during the CRU and MC processes amplifies Ware drift, which mainly influences electron component. As a result the favorable for the transition negative (inward directed) E r emerges. In the CRD scenario, when E φ is opposite to the total plasma current direction, the mechanism should generate positive E r , which is thought to be unfavorable for the H-mode. The experimental data on L-H and H-L transitions in various scenarios and the results of the modeling of E r emerging in the CRU experiment are presented in the paper. (author)

Plasma confinement using biased electrode in the TCABR tokamak

International Nuclear Information System (INIS)

Nascimento, I.C.; Kuznetsov, Y.K.; Severo, J.H.F.; Fonseca, A.M.M.; Elfimov, A.; Bellintani, V.; Machida, M.; Heller, M.V.A.P.; Galvao, R.M.O.; Sanada, E.K.; Elizondo, J.I.

2005-01-01

Experimental data obtained on the TCABR tokamak (R = 0.61 m, a = 0.18 m) with an electrically polarized electrode, placed at r = 0.16 m, is reported in this paper. The experiment was performed with plasma current of 90 kA (q 3.1) and hydrogen gas injection adjusted for keeping the electron density at 1.0 x 10 19 m -3 without bias. Time evolution and radial profiles of plasma parameters with and without bias were measured. The comparison of the profiles shows an increase of the central line-averaged density, up to a maximum factor of 2.6, while H α hydrogen spectral line intensity decreases and the C III impurity stays on the same level. The analysis of temporal behaviour and radial profiles of plasma parameters indicates that the confined plasma enters the H-mode regime. The data analysis shows a maximum enhanced energy confinement factor of 1.95, decaying to 1.5 at the maximum of the density, in comparison with predicted Neo-Alcator scaling law values. Indications of transient increase of the density gradient near the plasma edge were obtained with measurements of density profiles. Calculations of turbulence and transport at the Scrape-Off-Layer, using measured floating potentials and ion saturation currents, show a strong decrease in the power spectra and transport. Bifurcation was not observed and the decrease in the saturation current occurs in 50 μs

Experimental studies of edge turbulence and confinement in Alcator C-Moda)

Science.gov (United States)

Cziegler, I.; Terry, J. L.; Hughes, J. W.; LaBombard, B.

2010-05-01

The steep gradient edge region and scrape-off-layer (SOL) on the low-field-side of Alcator C-Mod [I. H. Hutchinson, R. Boivin, F. Bombarda et al., Phys. Plasmas 1, 1511 (1994)] tokamak plasmas are studied using gas-puff-imaging diagnostics. In L-mode plasmas, the region extending ˜2 cm inside the magnetic separatrix has fluctuations showing a broad, turbulent spectrum, propagating in the electron diamagnetic drift direction, whereas features in the open field line region propagate in the ion diamagnetic drift direction. This structure is robust against toroidal field strength, poloidal null-point geometry, plasma current, and plasma density. Global parameter dependence of spectral and spatial structure of the turbulence inside the separatrix is explored and characterized, and both the intensity and spectral distributions are found to depend strongly on the plasma density normalized to the tokamak density limit. In H-mode discharges the fluctuations at and inside the magnetic separatrix show fundamentally different trends compared to L-mode, with the electron diamagnetic direction propagating turbulence greatly reduced in ELM-free [F. Wagner et al., Proceedings of the Thirteenth Conference on Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1982), Vol. I, p. 277], and completely dominated by the modelike structure of the quasicoherent mode in enhanced D-alpha regimes [A. E. Hubbard, R. L. Boivin, R. S. Granetz et al., Phys. Plasmas 8, 2033 (2001)], while the normalized SOL turbulence is largely unaffected.

Three mode Er3+ ring-doped fiber amplifier for mode-division multiplexed transmission

NARCIS (Netherlands)

Jung, Y.; Kang, Q.; Sleiffer, V.A.J.M.; Inan, B.; Kuschnerov, M.; Veljanovski, V.; Corbett, B.; Winfield, R.; Li, Z.; Teh, P.S.; Dhar, A.; Sahu, J.K.; Poletti, F.; Alam, S.U.; Richardson, D.J.

2013-01-01

We successfully fabricate three-mode erbium doped fiber with a confined Er3+ doped ring structure and experimentally characterize the amplifier performance with a view to mode-division multiplexed (MDM) transmission. The differential modal gain was effectively mitigated by controlling the relative

Resolving Fast, Confined Diffusion in Bacteria with Image Correlation Spectroscopy.

Science.gov (United States)

Rowland, David J; Tuson, Hannah H; Biteen, Julie S

2016-05-24

By following single fluorescent molecules in a microscope, single-particle tracking (SPT) can measure diffusion and binding on the nanometer and millisecond scales. Still, although SPT can at its limits characterize the fastest biomolecules as they interact with subcellular environments, this measurement may require advanced illumination techniques such as stroboscopic illumination. Here, we address the challenge of measuring fast subcellular motion by instead analyzing single-molecule data with spatiotemporal image correlation spectroscopy (STICS) with a focus on measurements of confined motion. Our SPT and STICS analysis of simulations of the fast diffusion of confined molecules shows that image blur affects both STICS and SPT, and we find biased diffusion rate measurements for STICS analysis in the limits of fast diffusion and tight confinement due to fitting STICS correlation functions to a Gaussian approximation. However, we determine that with STICS, it is possible to correctly interpret the motion that blurs single-molecule images without advanced illumination techniques or fast cameras. In particular, we present a method to overcome the bias due to image blur by properly estimating the width of the correlation function by directly calculating the correlation function variance instead of using the typical Gaussian fitting procedure. Our simulation results are validated by applying the STICS method to experimental measurements of fast, confined motion: we measure the diffusion of cytosolic mMaple3 in living Escherichia coli cells at 25 frames/s under continuous illumination to illustrate the utility of STICS in an experimental parameter regime for which in-frame motion prevents SPT and tight confinement of fast diffusion precludes stroboscopic illumination. Overall, our application of STICS to freely diffusing cytosolic protein in small cells extends the utility of single-molecule experiments to the regime of fast confined diffusion without requiring advanced

L-H transition dynamics in fluid turbulence simulations with neoclassical force balance

Energy Technology Data Exchange (ETDEWEB)

Chôné, L. [Aix–Marseille Université, CNRS, PIIM UMR 7345, 13397 Marseille Cedex 20 (France); CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Beyer, P.; Fuhr, G.; Benkadda, S. [Aix–Marseille Université, CNRS, PIIM UMR 7345, 13397 Marseille Cedex 20 (France); Sarazin, Y.; Bourdelle, C. [CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France)

2014-07-15

Spontaneous transport barrier generation at the edge of a magnetically confined plasma is reproduced in flux-driven three-dimensional fluid simulations of electrostatic turbulence. Here, the role on the radial electric field of collisional friction between trapped and passing particles is shown to be the key ingredient. Especially, accounting for the self-consistent and precise dependence of the friction term on the actual plasma temperature allows for the triggering of a transport barrier, provided that the input power exceeds some threshold. In addition, the barrier is found to experience quasi-periodic relaxation events, reminiscent of edge localised modes. These results put forward a possible key player, namely, neoclassical physics via radial force balance, for the low- to high-confinement regime transition observed in most of controlled fusion devices.

Photosynthetic plasticity of populations of Heliotropium curassavicum L. originating from differing thermal regimes.

Science.gov (United States)

Mooney, H A

1980-01-01

Plants of the widely distributed species Heliotropium curassavicum L. have a large photosynthetic acclimation potential to temperature. There are, however, some differences among the acclimation potentials of populations occupying dissimilar thermal regimes. Plants of populations originating from a cool maritime climate have a greater acclimation potential than plants of populations originating from a desert habitat, which is characterized by large seasonal changes in temperature.

Correlation of the tokamak H-mode density limit with ballooning stability at the separatrix

Science.gov (United States)

Eich, T.; Goldston, R. J.; Kallenbach, A.; Sieglin, B.; Sun, H. J.; ASDEX Upgrade Team; Contributors, JET

2018-03-01

We show for JET and ASDEX Upgrade, based on Thomson-scattering measurements, a clear correlation of the density limit of the tokamak H-mode high-confinement regime with the approach to the ideal ballooning instability threshold at the periphery of the plasma. It is shown that the MHD ballooning parameter at the separatrix position α_sep increases about linearly with the separatrix density normalized to Greenwald density, n_e, sep/n_GW for a wide range of discharge parameters in both devices. The observed operational space is found to reach at maximum n_e, sep/n_GW≈ 0.4 -0.5 at values for α_sep≈ 2 -2.5, in the range of theoretical predictions for ballooning instability. This work supports the hypothesis that the H-mode density limit may be set by ballooning stability at the separatrix.

Theoretical studies of turbulence and anomalous transport in toroidal confinement devices

International Nuclear Information System (INIS)

Terry, P.W.

1993-01-01

The research performed under this grant has focused on key issues with respect to turbulence and transport in toroidal confinement devices. Progress and publications in these areas are summarized in this report. This work includes analytical and numerical studies of spectral energy transfer and the saturation dynamics and transport of dissipative and collisionless trapped electron turbulence, the role of flow curvature in L-H mode transition physics, fully nonlinear calculations of the anomalous particle transport from the ion mixing mode, and the development of a theory for the drift wave frequency spectrum. Novel aspects of this work include an elucidation of the role of nonlinear frequency shifts in producing nonstationary saturated states, an identification of reverse and non-conserved flows in Hasegawa-Mima turbulence, and a description of the way incoherent emission affects the frequency of turbulent fluctuations

Formation of edge transport barrier in the ergodic field layer of helical divertor configuration on the Large Helical Device

International Nuclear Information System (INIS)

Toi, K; Ohdachi, S; Watanabe, F; Narihara, K; Morisaki, T; Sakakibara, S; Morita, S; Goto, M; Ida, K; Masuzaki, S; Miyazawa, K; Tanaka, K; Tokuzawa, T; Watanabe, K W; Yoshinuma, M

2006-01-01

On the Large Helical Device (LHD), low to high confinement (L-H) transition and edge transport barrier (ETB) formation were observed in the low beta regime ((β dia ) dia ): volume-averaged beta derived from diamagnetic measurement) as well as in relatively high beta regime (>1.5%). In most of ETB plasmas electron density preferentially increases in the edge region without a substantial rise of the edge electron temperature. The ETB zone develops inside the ergodic field layer calculated in the vacuum field. The ETB formation strongly destabilizes edge coherent modes such as m/n = 2/3 or 1/2 (m, n: poloidal and toroidal mode numbers), because the plasma edge region is in the magnetic hill. The ETB is partially destroyed by the combination of these edge MHD modes and ELM-like activities. For a particular experimental condition, the forced generation of a sizable m/n = 1/1 magnetic island near the edge by application of external field perturbations facilitates the L-H transition at a lower electron density and suppresses edge MHD modes and ELM-like activities to lower levels

Dependence of the L-Mode scrape-off layer power fall-off length on the upper triangularity in TCV

Science.gov (United States)

Faitsch, M.; Maurizio, R.; Gallo, A.; Coda, S.; Eich, T.; Labit, B.; Merle, A.; Reimerdes, H.; Sieglin, B.; Theiler, C.; the Eurofusion MST1 Team; the TCV Team

2018-04-01

This paper reports on experimental observations on TCV with a scan in upper triangularity {δ }up}, including negative triangularity, focusing on the power fall-off length {λ }{{q}} in L-Mode. The upper triangularity is scanned from -0.28 to 0.47. Smaller {λ }{{q}}out} is measured at the outer divertor target for decreasing {δ }up} together with higher edge temperature {T}{{e},{edge}} leading to increased confinement. This effect is observed for both magnetic drift directions for discharges in deuterium and helium. In helium larger {λ }{{q}} values are observed compared to deuterium. The power fall-off length at the inner divertor target {λ }{{q}}in} has a non-monotonic behaviour with changing triangularity. The largest values are around {δ }up}=0. The ratio {λ }{{q}}in}/{λ }{{q}}out} increases for decreasing {δ }up} for positive triangularity and is approximately constant for negative triangularity. {λ }{{q}}out} is compared to available scaling laws. Partial agreement is only observed for a scaling law containing a proxy for {T}{{e},{edge}} at ASDEX Upgrade (Sieglin 2016 Plasma Phys. Control. Fusion 58 055015). Extending this scaling to TCV and using {T}{{e},{edge}} at {ρ }pol}=0.95 suggests that {λ }{{q}}out} is independent of machine size {λ }{{q}}{{L} - {Mode}} ({mm}) = 165\\cdot {B}pol}{({{T}})}-0.66\\cdot A{({{u}})}-0.15\\cdot {T}{{e},{edge}}{({eV})}-0.93\\cdot R{({{m}})}-0.03. Possible explanations for smaller {λ }{{q}}out} for decreasing {δ }up} is a reduction in turbulence or a direct effect of increasing {T}{{e},{edge}}.

H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Moda)

Science.gov (United States)

Hubbard, A. E.; Hughes, J. W.; Bespamyatnov, I. O.; Biewer, T.; Cziegler, I.; LaBombard, B.; Lin, Y.; McDermott, R.; Rice, J. E.; Rowan, W. L.; Snipes, J. A.; Terry, J. L.; Wolfe, S. M.; Wukitch, S.

2007-05-01

This paper reports on studies of the edge transport barrier and transition threshold of the high confinement (H) mode of operation on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)], over a wide range of toroidal field (2.6-7.86T) and plasma current (0.4-1.7MA). The H-mode power threshold and edge temperature at the transition increase with field. Barrier widths, pressure limits, and confinement are nearly independent of field at constant current, but the operational space at high B shifts toward higher temperature and lower density and collisionality. Experiments with reversed field and current show that scrape-off-layer flows in the high-field side depend primarily on configuration. In configurations with the B ×∇B drift away from the active X-point, these flows lead to more countercurrent core rotation, which apparently contributes to higher H-mode thresholds. In the unfavorable case, edge temperature thresholds are higher, and slow evolution of profiles indicates a reduction in thermal transport prior to the transition in particle confinement. Pedestal temperatures in this case are also higher than in the favorable configuration. Both high-field and reversed-field results suggest that parameters at the L-H transition are influencing the evolution and parameters of the H-mode pedestal.

New features of L-H transition in limiter H-modes of JIPP T-IIU

International Nuclear Information System (INIS)

Toi, K.; Morita, S.; Kawahata, K.

1992-09-01

In limiter H-modes of JIPP T-IIU, a new type of L-H transition preceded by an ELM is observed. The preceding ELM (pre-ELM) appears just prior to the L-H transition. This type of transition is usually observed in H-modes of JIPP T-IIU. The L-H transition without the pre-ELM is triggered only in the case when a sufficiently large rapid current ramp down is emploied. In H-modes with constant q(a)∼3.5-4.5, coherent magnetic oscillations with m=3/n=1 destabilized during L-phase are further enhanced at the pre-ELM, and suppressed suddenly at the transition. This mode is situated in the region of the transport barrier. Propagation frequency of the m=3/n=1 mode, which may be affected by plasma mass rotation, rises appreciably (by ∼ 10 %) during H-phase with frequent ELMs, but remains unchanged for at least 200 μs after the transition. Behaviours of the m=3/n=1 and m=2/n=1 modes are well explained by quasi-linear resistive tearing mode analysis for modelled toroidal current density profiles slightly detached from the limiter. These experimental results suggest that the transition is controlled by the change of a magnetic field structure relating to the modification of a toroidal current density profile near the edge. The possibility for the development of edge radial electric field as a consequence of the transition is discussed. (author)

Observation of a High Performance Operating Regime with Small Edge-Localized Modes in the National Spherical Torus Experiment

International Nuclear Information System (INIS)

Maingi, R.; Tritz, K.; Fredrickson, E.D.; Menard, J.E.; Sabbagh, S.A.; Stutman, D.; Bell, M.G.; Bell, R.E.; Bush, C.E.; Gates, D.A.; Johnson, D.W.; Kaita, R.; Kaye, S.M.; Kugel, H.W.; LeBlanc, B.P.; Mueller, D.; Raman, R.; Roquemore, A.L.; Soukhanovskii, V.A.

2004-01-01

We report observation of a high performance scenario in the National Spherical Torus Experiment with very small edge-localized modes (ELMs). These ELMs have no measurable impact on stored energy and are consistent with high bootstrap current operation with line average density approaching Greenwald scaling. The ELM perturbation is observed to typically originate near the lower divertor region, as opposed to the outer midplane for ELMs described in the literature. If extrapolable, this scenario would provide an attractive operating regime for next step fusion experiments

H-Mode Turbulence, Power Threshold, ELM, and Pedestal Studies in NSTX

International Nuclear Information System (INIS)

Maingi, R.; Bush, C.E.; Fredrickson, E.D.; Gates, D.A.; Kaye, S.M.; LeBlanc, B.P.; Menard, J.E.; Meyer, H.; Mueller, D.; Nishino, N.; Roquemore, A.L.; Sabbagh, S.A.; Tritz, K.; Zweben, S.J.; Bell, M.G.; Bell, R.E.; Biewer, T.; Boedo, J.A.; Johnson, D.W.; Kaita, R.; Kugel, H.W.; Maqueda, R.J.; Munsat, T.; Raman, R.; Soukhanovskii, V.A.; Stevenson, T.; Stutman, D.

2004-01-01

High-confinement mode (H-mode) operation plays a crucial role in NSTX [National Spherical Torus Experiment] research, allowing higher beta limits due to reduced plasma pressure peaking, and long-pulse operation due to high bootstrap current fraction. Here, new results are presented in the areas of edge localized modes (ELMs), H-mode pedestal physics, L-H turbulence, and power threshold studies. ELMs of several other types (as observed in conventional aspect ratio tokamaks) are often observed: (1) large, Type I ELMs, (2) ''medium'' Type II/III ELMs, and (3) giant ELMs which can reduce stored energy by up to 30% in certain conditions. In addition, many high-performance discharges in NSTX have tiny ELMs (newly termed Type V), which have some differences as compared with ELM types in the published literature. The H-mode pedestal typically contains between 25-33% of the total stored energy, and the NSTX pedestal energy agrees reasonably well with a recent international multi-machine scaling. We find that the L-H transition occurs on a ∼100 (micro)sec timescale as viewed by a gas puff imaging diagnostic, and that intermittent quiescent periods precede the final transition. A power threshold identity experiment between NSTX and MAST shows comparable loss power at the L-H transition in balanced double-null discharges. Both machines require more power for the L-H transition as the balance is shifted toward lower single null. High field side gas fueling enables more reliable H-mode access, but does not always lead to a lower power threshold e.g., with a reduction of the duration of early heating. Finally the edge plasma parameters just before the L-H transition were compared with theories of the transition. It was found that while some theories can separate well-developed L- and H-mode data, they have little predictive value

Extremes of 2d Coulomb gas: universal intermediate deviation regime

Science.gov (United States)

Lacroix-A-Chez-Toine, Bertrand; Grabsch, Aurélien; Majumdar, Satya N.; Schehr, Grégory

2018-01-01

In this paper, we study the extreme statistics in the complex Ginibre ensemble of N × N random matrices with complex Gaussian entries, but with no other symmetries. All the N eigenvalues are complex random variables and their joint distribution can be interpreted as a 2d Coulomb gas with a logarithmic repulsion between any pair of particles and in presence of a confining harmonic potential v(r) \\propto r2 . We study the statistics of the eigenvalue with the largest modulus r\\max in the complex plane. The typical and large fluctuations of r\\max around its mean had been studied before, and they match smoothly to the right of the mean. However, it remained a puzzle to understand why the large and typical fluctuations to the left of the mean did not match. In this paper, we show that there is indeed an intermediate fluctuation regime that interpolates smoothly between the large and the typical fluctuations to the left of the mean. Moreover, we compute explicitly this ‘intermediate deviation function’ (IDF) and show that it is universal, i.e. independent of the confining potential v(r) as long as it is spherically symmetric and increases faster than \\ln r2 for large r with an unbounded support. If the confining potential v(r) has a finite support, i.e. becomes infinite beyond a finite radius, we show via explicit computation that the corresponding IDF is different. Interestingly, in the borderline case where the confining potential grows very slowly as v(r) ∼ \\ln r2 for r \\gg 1 with an unbounded support, the intermediate regime disappears and there is a smooth matching between the central part and the left large deviation regime.

Momentum confinement at low torque

Energy Technology Data Exchange (ETDEWEB)

Solomon, W M [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Burrell, K H [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); De Grassie, J S [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Budny, R [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Groebner, R J [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Kinsey, J E [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Kramer, G J [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Luce, T C [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Makowski, M A [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Mikkelsen, D [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Nazikian, R [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Petty, C C [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Politzer, P A [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Scott, S D [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Zeeland, M A Van [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Zarnstorff, M C [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States)

2007-12-15

Momentum confinement was investigated on DIII-D as a function of applied neutral beam torque at constant normalized beta {beta}{sub N}, by varying the mix of co (parallel to the plasma current) and counter neutral beams. Under balanced neutral beam injection (i.e. zero total torque to the plasma), the plasma maintains a significant rotation in the co-direction. This 'intrinsic' rotation can be modeled as being due to an offset in the applied torque (i.e. an 'anomalous torque'). This anomalous torque appears to have a magnitude comparable to one co neutral beam source. The presence of such an anomalous torque source must be taken into account to obtain meaningful quantities describing momentum transport, such as the global momentum confinement time and local diffusivities. Studies of the mechanical angular momentum in ELMing H-mode plasmas with elevated q{sub min} show that the momentum confinement time improves as the torque is reduced. In hybrid plasmas, the opposite effect is observed, namely that momentum confinement improves at high torque/rotation. GLF23 modeling suggests that the role of E x B shearing is quite different between the two plasmas, which may help to explain the different dependence of the momentum confinement on torque.

Engineered valley-orbit splittings in quantum-confined nanostructures in silicon

NARCIS (Netherlands)

Rahman, R.; Verduijn, J.; Kharche, N.; Lansbergen, G.P.; Klimeck, G.; Hollenberg, L.C.L.; Rogge, S.

2011-01-01

An important challenge in silicon quantum electronics in the few electron regime is the potentially small energy gap between the ground and excited orbital states in 3D quantum confined nanostructures due to the multiple valley degeneracies of the conduction band present in silicon. Understanding

Numerical Analysis of Index-Guiding Photonic Crystal Fibers with Low Confinement Loss and Ultra-Flattened Dispersion by FDFD Method

Directory of Open Access Journals (Sweden)

M. Pourmahyabadi

2009-09-01

Full Text Available In this article, perfectly matched layer (PML for the boundary treatment and an efficient compact two dimensional finite-difference frequency-domain (2-D FDFD method were combined to model photonic crystal fibers (PCF. For photonic crystal fibers, if we assume that the propagation constant along the propagation direction is fixed, three-dimensional hybrid guided modes can be calculated by using only a two-dimensional mesh. An index-guiding PCF with an array of air-holes surrounding the silica core region has special characteristics compared with conventional single-mode fibers (SMFs. Using this model, the fundamental characteristics of single mode photonic crystal fibers (SMPCFs such as confinement loss, bending loss, effective mode area and chromatic dispersion are numerically investigated. The results revealed that low confinement loss and zero-flattened chromatic dispersion can be obtained by varying the air-holes diameter of each ring along the PCF radius. In this work, an especial PCF with nearly zero-flattened dispersion (1.3 ps/nm/km over a wide wavelength range which covers O, E, S, C, L and U telecommunication wavelength bands and low confinement loss (0.06 dB/km at 1.55μm is designed. Macro-bending loss performance of the designed PCF is also studied and it is found that the fiber shows low bending losses for the smallest feasible bending radius of 5 mm. Also, it is revealed that the temperature sensitivity of PCFs is very low in compared with the conventional fibers.

Confinement of a non cylindrical z discharge by a cusp geometry

International Nuclear Information System (INIS)

Watteau, J.H.

1968-03-01

The plasma of a non-cylindrical z discharge is accumulated in the centre of a cusp geometry and then captured and confined by the rising cusp magnetic field. The cusp geometry is produced by two identical coaxial coils the currents of which are equal but in opposite directions. Stability and confinement properties of this zero minimum B geometry are recalled; in particular it is shown (the coils cross section being supposed punctual) that the magnetic well depth of the configuration without plasma is maximum for an optimum coils distance. Two modes of confinement are observed experimentally : - a collisional mode for which the plasma confinement is limited to 10 μsec (temperature 5 eV, density 7 x 10 16 cm -3 ) as a result of the gradual interpenetration of the plasma and of the magnetic field. - a collisionless mode (temperature 40 eV) where the radial leak thickness is of the order of the ion cyclotron radius. Plasma accumulation occurs even without confinement and is due to the non-cylindrical shape of the discharge chamber. The two-dimensional snow-plough model gives good account of the discharge dynamics. A comparison is made with plasma focus experiments: in particular experimental conditions (deuterium, pressure 1 torr,energy 3 kJ, current 100 kA) a 10 7 neutron yield is detected which appears to be connected with the unstable behavior of the discharge. (authors) [fr

Small ELM regimes with good confinement on JET and comparison to those on ASDEX Upgrade, Alcator C-mod, and JT-60U

International Nuclear Information System (INIS)

Stober, J.; Lomas, P.; Saibene, G.

2005-01-01

Since it is uncertain if ITER operation is compatible with type-I ELMs, the study of alternative H-mode pedestals is an urgent issue. This paper reports on experiments on JET aiming to find scenarios with small ELMs and good confinement, such as the type-II ELMs in ASDEX Upgrade, the enhanced D-alpha H-mode in Alcator C-mod or the grassy ELMs in JT-60U. The study includes shape variations, especially the closeness to a double-null configuration, variations of q 95 , density and beta poloidal. H-mode pedestals without type-I ELMs have been observed only at the lowest currents (≤ 1.2 MA), showing similarities to the observations in the devices mentioned above. These are discussed in detail on the basis of edge fluctuation analysis. For higher currents, only the mixed type-I/II scenario is observed. Although the increased inter-ELM transport reduces the type-I ELM frequency, a single type-I ELM is not significantly reduced in size. Obviously, these results do question the accessibility of such small ELM scenarios on ITER, except perhaps the high beta-poloidal scenario at higher q 95 , which could not be tested at higher currents at JET due to limitations in heating power. (author)

Emergent patterns of collective cell migration under tubular confinement.

Science.gov (United States)

Xi, Wang; Sonam, Surabhi; Beng Saw, Thuan; Ladoux, Benoit; Teck Lim, Chwee

2017-11-15

Collective epithelial behaviors are essential for the development of lumens in organs. However, conventional assays of planar systems fail to replicate cell cohorts of tubular structures that advance in concerted ways on out-of-plane curved and confined surfaces, such as ductal elongation in vivo. Here, we mimic such coordinated tissue migration by forming lumens of epithelial cell sheets inside microtubes of 1-10 cell lengths in diameter. We show that these cell tubes reproduce the physiological apical-basal polarity, and have actin alignment, cell orientation, tissue organization, and migration modes that depend on the extent of tubular confinement and/or curvature. In contrast to flat constraint, the cell sheets in a highly constricted smaller microtube demonstrate slow motion with periodic relaxation, but fast overall movement in large microtubes. Altogether, our findings provide insights into the emerging migratory modes for epithelial migration and growth under tubular confinement, which are reminiscent of the in vivo scenario.

Divertor and scoop limiter experiments on PDX

International Nuclear Information System (INIS)

McGuire, K.; Beirsdorfer, P.; Bell, M.

1985-01-01

Routine operation in the enhanced-energy-confinement (or H-mode) regime during neutral-beam injection was achieved by modifying the PDX divertor hardware to inhibit the influx of neutral gas from the divertor region to the main plasma chamber. A particle scoop limiter has been studied as a mechanical means of controlling particles at the plasma edge, and neutral-beam-heated discharges with this limiter show similar confinement times (normalized to tausub(E)/Isub(p)) to average H-mode plasma. Two new instabilities are observed near the plasma edge in PDX during H-mode operation. The first, a quasi-coherent fluctuation, occurred in bursts at well-defined frequencies (Δω/ω<=0.1) in the range 50 to 180 kHz, and had no obvious effects on confinement. The second instability, the edge relaxation phenomena (ERP), did cause deterioration in the global confinement time. The ERPs are characterized by sharp spikes in the divertor plasma density, Hsub(α) emission, and on the X-ray signals they appear as sawtooth-like relaxations at the plasma edge with an inversion radius near the separatrix. Attempts to obtain high βsub(T) in the H-mode discharges were hampered by a deterioration in the H-mode confinement and major disruptions which limited the achievable βsub(T). A study of the stability of both the limiter L-mode and divertor H-mode discharge close to the theoretical β boundary showed that the major disruptions observed there are sometimes caused by a fast growing m/n=1/1 mode with no observable external precursor oscillations. (author)

JET Radiative Mantle Experiments in ELMy H-Mode

International Nuclear Information System (INIS)

Budny, R.; Coffey, I.; Dumortier, P.; Grisolia, C.; Strachan, J.D.

1999-01-01

Radiative mantle experiments were performed on JET ELMy H-mode plasmas. The Septum configuration was used where the X-point is embedded into the top of the Septum. Argon radiated 50% of the input power from the bulk plasma while Z eff rose from an intrinsic level of 1.5 to about 1.7 due to the injected Argon. The total energy content and global energy confinement time decreased 15% when the impurities were introduced. In contrast, the effective thermal diffusivity in the core confinement region (r/a = .4--.8) decreased by 30%. Usually, JET ELMy H-mode plasmas have confinement that is correlated to the edge pedestal pressure. The radiation lowered the edge pedestal and consequently lowered the global confinement. Thus the confinement was changed by a competition between the edge pedestal reduction lowering the confinement and the weaker RI effect upon the core transport coefficients raising the confinement. The ELM frequency increased from 10 Hz Type I ELMs, to 200 Hz type III ELMs. The energy lost by each ELM reduced to 0.5% of the plasma energy content

A consistency analysis on the tokamak reactor plasmas

International Nuclear Information System (INIS)

Fukuyama, A.; Itoh, S.-I.; Itoh, K.

1990-12-01

The parameter regime which simultaneously fulfills the various physics constraints are looked for in the case of ITER grade tokamaks. The consistency analysis code is applied. It is found that, if the energy confinement time reaches 1.6 times of the prediction of the L-mode scaling law, the Q-value of about 4 is possible for the full current drive operation at the input power P in of 100MW (Q is the ratio of fusion output and P in ). In the ignition mode, where half of the current is inductively sustained, Q approaches to 15 for this circulating power. If only the L-mode is realized, Q is about 1.5 for P in ≅100 MW. (author)

Effects of the New Island Divertor on the Plasma Performance in the W7-AS Stellarator

International Nuclear Information System (INIS)

Grigull, P.; McCormick, K.; Baldzuhn, J.; Burhenn, R.; Brakel, R.; Ehmler, H.; Feng, Y.; Gadelmeier, F.; Giannone, L.; Hartmann, D.; Hildebrandt, D.; Hirsch, M.; Jaenicke, R.; Kisslinger, J.; Klinger, T.; Knauer, J.; Koenig, R.; Naujoks, D.; Niedermeyer, H.; Pasch, E.

2003-01-01

The island divertor in the W7-AS stellarator enables access to a new NBI-heated, high density operating regime with promising confinement properties. This regime -- the High Density H-Mode -- displays no evident mode activity, is extant above a threshold density and characterized by flat density profiles, high energy- and low impurity-confinement times and edge localized radiation. Impurity accumulation, normally associated with ELM-free H-modes, is avoided. Quasi steady-state discharges with n e up to 4 1020 m-3, edge radiation levels up to 90%, and partial plasma detachment at the divertor targets can be simultaneously realized

Role of Density Gradient Driven Trapped Electron Modes in the H-Mode Inner Core with Electron Heating

Science.gov (United States)

Ernst, D.

2015-11-01

We present new experiments and nonlinear gyrokinetic simulations showing that density gradient driven TEM (DGTEM) turbulence dominates the inner core of H-Mode plasmas during strong electron heating. Thus α-heating may degrade inner core confinement in H-Mode plasmas with moderate density peaking. These DIII-D low torque quiescent H-mode experiments were designed to study DGTEM turbulence. Gyrokinetic simulations using GYRO (and GENE) closely match not only particle, energy, and momentum fluxes, but also density fluctuation spectra, with and without ECH. Adding 3.4 MW ECH doubles Te /Ti from 0.5 to 1.0, which halves the linear TEM critical density gradient, locally flattening the density profile. Density fluctuations from Doppler backscattering (DBS) intensify near ρ = 0.3 during ECH, displaying a band of coherent fluctuations with adjacent toroidal mode numbers. GYRO closely reproduces the DBS spectrum and its change in shape and intensity with ECH, identifying these as coherent TEMs. Prior to ECH, parallel flow shear lowers the effective nonlinear DGTEM critical density gradient 50%, but is negligible during ECH, when transport displays extreme stiffness in the density gradient. GS2 predictions show the DGTEM can be suppressed, to avoid degradation with electron heating, by broadening the current density profile to attain q0 >qmin > 1 . A related experiment in the same regime varied the electron temperature gradient in the outer half-radius (ρ ~ 0 . 65) using ECH, revealing spatially coherent 2D mode structures in the Te fluctuations measured by ECE imaging. Fourier analysis with modulated ECH finds a threshold in Te profile stiffness. Supported by the US DOE under DE-FC02-08ER54966 and DE-FC02-04ER54698.

Effect of surface hydrophobicity on the dynamics of water at the nanoscale confinement: A molecular dynamics simulation study

International Nuclear Information System (INIS)

Choudhury, Niharendu

2013-01-01

Highlights: • We present atomistic MD simulation of water confined between two paraffin-like plates. • Effect of plate hydrophobicity on the confined water dynamics is investigated. • Diffusivity of confined water is calculated from mean squared displacements. • Rotational dynamics of the confined water has bimodal nature of relaxation. • Monotonic dependence of translational and rotational dynamics on hydrophobicity. - Abstract: We present detailed molecular dynamics simulations of water in and around a pair of plates immersed in water to investigate the effect of degree of hydrophobicity or hydrophilicity of the plates on dynamics of water confined between the two plates. The nature of the plate has been tuned from hydrophobic to hydrophilic and vice versa by varying plate-water dispersion interaction. Analyses of the translational dynamics as performed by calculating mean squared displacements of the confined water reveal a monotonically decreasing trend of the diffusivity with increasing hydrophilicity of the plates. Orientational dynamics of the confined water also follows the same monotonic trend. Although orientational time constant almost does not change with the increase of plate-water dispersion interaction in the hydrophobic regime corresponding to the smaller plate-water attraction, it changes considerably in the hydrophilic regime corresponding to larger plate-water dispersion interactions

2D heat flux pattern in ASDEX upgrade L-mode with magnetic perturbation

Energy Technology Data Exchange (ETDEWEB)

Faitsch, Michael; Sieglin, Bernhard; Eich, Thomas; Herrmann, Albrecht; Suttrop, Wolfgang [Max-Planck-Institute for Plasma Physics, Boltzmannstr. 2, D-85748 Garching (Germany); Collaboration: the ASDEDX Upgrade Team

2016-07-01

A future fusion reactor is likely to operate in high confinement mode (H-mode). This mode is associated with a periodic instability at the plasma edge that expels particles and energy. This instability is called edge localized mode (ELM). External magnetic perturbation (MP) is one technique that is thought to be able to mitigate or even suppress large ELMs in next step fusion devices such as ITER, where the ELM induced heat load for unmitigated ELMs might limit the lifetime of the divertor. Applying an external magnetic perturbation breaks the axisymmetry and leads to a 2D steady state heat flux pattern at the divertor. The ASDEX Upgrade tokamak is equipped with 16 perturbation coils, 8 above (upper row) and 8 below (lower row) the outer mid plane, toroidal equally distributed. A high resolution infra red system is measuring the heat flux at the outer target at a fixed toroidal position with a resolution of around 0.6 mm. In order to measure the 2D structure a slow rotation of the MP field was applied (1 Hz) with a toroidal mode number n=2. The differential phase between the upper and lower row was changed to investigate the effect of the alignment with the field lines at the edge. The density was varied to study the density dependence of the heat transport with applied external MP and compare it to the axisymmetric scenario.

Momentum Confinement at Low Torque

International Nuclear Information System (INIS)

Solomon, W.M.; Burrell, K.H.; deGrassie, J.S.; Budny, R.; Groebner, R.J.; Heidbrink, W.W.; Kinsey, J.E.; Kramer, G.J.; Makowski, M.A.; Mikkelsen, D.; Nazikian, R.; Petty, C.C.; Politzer, P.A.; Scott, S.D.; Van Zeeland, M.A.; Zarnstorff, M.C.

2007-01-01

Momentum confinement was investigated on DIII-D as a function of applied neutral beam torque at constant normalized β N , by varying the mix of co (parallel to the plasma current) and counter neutral beams. Under balanced neutral beam injection (i.e. zero total torque to the plasma), the plasma maintains a significant rotation in the co-direction. This 'intrinsic' rotation can be modeled as being due to an offset in the applied torque (i.e. an 'anomalous torque'). This anomalous torque appears to have a magnitude comparable to one co-neutral beam source. The presence of such an anomalous torque source must be taken into account to obtain meaningful quantities describing momentum transport, such as the global momentum confinement time and local diffusivities. Studies of the mechanical angular momentum in ELMing H-mode plasmas with elevated q min show that the momentum confinement time improves as the torque is reduced. In hybrid plasmas, the opposite effect is observed, namely that momentum confinement improves at high torque/rotation. The relative importance of E x B shearing between the two is modeled using GLF23 and may suggest a possible explanation.

Enhancement of confinement in tokamaks

International Nuclear Information System (INIS)

Furth, H.P.

1986-05-01

A plausible interpretation of the experimental evidence is that energy confinement in tokamaks is governed by two separate considerations: (1) the need for resistive MHD kink-stability, which limits the permissible range of current profiles - and therefore normally also the range of temperature profiles; and (2) the presence of strongly anomalous microscopic energy transport near the plasma edge, which calibrates the amplitude of the global temperature profile, thus determining the energy confinement time tau/sub E/. Correspondingly, there are two main paths towards the enhancement of tokamak confinement: (1) Configurational optimization, to increase the MHD-stable energy content of the plasma core, can evidently be pursued by varying the cross-sectional shape of the plasma and/or finding stable radial profiles with central q-values substantially below unity - but crossing from ''first'' to ''second'' stability within the peak-pressure region would have the greatest ultimate potential. (2) Suppression of edge turbulence, so as to improve the heat insulation in the outer plasma shell, can be pursued by various local stabilizing techniques, such as use of a poloidal divertor. The present confinement model and initial TFTR pellet-injection results suggest that the introduction of a super-high-density region within the plasma core should be particularly valuable for enhancing ntau/subE/. In D-T operation, a centrally peaked plasma pressure profile could possibly lend itself to alpha-particle-driven entry into the second-stability regime

Resistive MHD studies of TFTR discharges

International Nuclear Information System (INIS)

Hughes, M.H.; Phillips, M.W.; Sabbagh, S.A.; Budny, R.V.

1991-01-01

MHD instabilities, thought to be resistive in character, are frequently observed in the supershot operating regime of TFTR (var-epsilon β p ≤ 0.7). These instabilities are always accompanied by substantial degradation of the confinement. Similarly of interest are recent experiments at much larger β p (var-epsilon β p ≤ 1.6), achieved through ramping the current during the beam heating phase of the discharge. In this latter regime the confinement can exceed three times the corresponding L-mode value and the β value normalized to I/aB can be as large as 4.7. Representative discharges from each of these operating regimes have been analyzed using a linear resistive MHD stability code with equilibrium pressure and q profiles obtained initially from the TRANSP analysis code. The main difference between the two types of discharge, as far as stability is concerned is shown to be the shape of the current density profile. The sensitivity to the assumed parameters is discussed. 1 ref

Fluctuations and confinement in ATF

International Nuclear Information System (INIS)

Isler, R.C.; Harris, J.H.; Murakami, M.

1993-01-01

In the period immediately prior to the suspension of ATF operation in November, 1991, a great deal of emphasis was palced on investigations of the fundamental mechanisms controlling confinement in this device. At that time, measurements of the density fluctuations throughout the plasma volume indicated the existence of theoretically predicted dissipative trapped electron and resistive interchange instabilities. These identifications were supported by results of dynamic configuration scans of the magnetic fields during which the extent of the magnetic well, shear, and fraction of confined trapped particles were changed continuously. Interpretation of the data from these experiments has been an ongoing exercise. Most recently, analysis of discharges employing strong gas puffing to change density gradients and fluctuation levels have strengthened the view that dissipative trapped electron modes may be present but do not play a significant direct role in energy transport. The present paper summarizes the current understanding concerning the identification of instabilities and their relationship to confinement in ATF

Are low-dimensional dynamics typical in magnetically confined plasmas?

International Nuclear Information System (INIS)

Ball, R.; Dewar, R.L.

2000-01-01

Full text: Since 1988 there have been many serious attempts to construct low-dimensional dynamical systems that model L-H transitions and associated oscillatory phenomena in magnetically confined plasmas. Such models usually consist of coupled ordinary differential equations in a few dynamical state variables and several parameters that represent physical properties or external controls. The advantages of a unified, low-dimensional approach to modelling plasma behaviour are multifold. Most importantly, the qualitative analysis of nonlinear ODE and algebraic systems is supported by a substantial body of theory. The toolkits of singularity and stability theory are well-developed and accessible, and contain the right tools for the job of charting the state and parameter space. One of the driving forces behind the development of low-dimensional dynamical models is the predictive potential of a parameter map. For example, a model that talks of the shape and extent of hysteresis in the L-H transition would help engineers who are interested in controlling access to H-mode. We can express this problem another way: given the enormous number of variables and parameters that could be varied around a hysteretic regime, it would be cheaper to know in advance which ones actually do influence the quality and quantity of the hysteresis. The quest for a low-dimensional state space that contains the qualitative dynamics of L-H transitions also introduces other problems. We need to identify the essential (few) dynamical variables and the essential (few) independent parameter groups, clarify the mechanisms for the feedback that is modelled by nonlinear terms, and identify symmetries in the physics. Before jumping the gun on these questions the fundamental issue should be addressed of whether a confined plasma, having many important length and time scales, steep gradients, strong anisotropy, and an uncountable multiplicity of states, can indeed exhibit low-dimensional dynamics. In this

Far SOL transport and main wall plasma interaction in DIII-D

International Nuclear Information System (INIS)

Rudakov, D.L.; Boedo, J.A.; Moyer, R.A.; Doerner, R.P.; Hollmann, E.M.; Krasheninnikov, S.I.; Pigarov, A.Yu.; Stangeby, P.C.; McLean, A.G.; Watkins, J.G.; Wampler, W.R.; Whyte, D.G.; McKee, G.R.; Zeng, L.; Wang, G.; Brooks, N.H.; Evans, T.E.; Leonard, A.W.; Mahdavi, M.A.; West, W.P.; Wong, C.P.C.; Fenstermacher, M.E.; Groth, M.; Lasnier, C.J.

2005-01-01

Far scrape-off layer (SOL) and near-wall plasma parameters in DIII-D depend strongly on the discharge parameters and confinement regime. In L-mode discharges cross-field transport increases with the average discharge density and flattens far SOL profiles, thus increasing plasma-wall contact. In H-mode between edge localized modes (ELMs), plasma-wall contact is generally weaker than in L-mode. During ELMs plasma fluxes to the wall increase to, or above the L-mode levels. Depending on the discharge conditions ELMs are responsible for 30-90% of the ion flux to the outboard chamber wall. Cross-field fluxes in far SOL are dominated by large amplitude intermittent transport events that may propagate all the way to the outer wall and cause sputtering. A Divertor Material Evaluation System (DiMES) probe containing samples of several ITER-relevant materials including carbon, beryllium and tungsten was exposed to a series of upper single null (USN) discharges as a proxy to measure the first wall erosion. (author)

Optimized confinement discharges in the stellarator W7-AS