Search

Your search keyword '"Francisquez, M."' showing total 36 results
Start Over Author "Francisquez, M."
36 results on '"Francisquez, M."'

1. Kinetic modeling of neutral transport for a continuum gyrokinetic code

Author

Bernard, T. N., Halpern, F. D., Francisquez, M., Mandell, N. R., Juno, J., Hammett, G. W., Hakim, A., Wilkie, G., and Guterl, J.

Subjects
Physics - Plasma Physics
Abstract

We present the first-of-its-kind coupling of a continuum full-f gyrokinetic turbulence model with a 6D continuum model for kinetic neutrals, carried out using the Gkeyll code. Our objective is to improve the first-principles understanding of the role of neutrals in plasma fueling, detachment, and their interaction with edge plasma profiles and turbulence statistics. Our model includes only atomic hydrogen and incorporates electron-impact ionization, charge exchange, and wall recycling. These features have been successfully verified with analytical predictions and benchmarked with the DEGAS2 Monte Carlo neutral code. We carry out simulations for a scrape-off layer (SOL) with simplified geometry and NSTX parameters. We compare these results to a baseline simulation without neutrals and find that neutral interactions reduce the normalized density fluctuation levels and associated skewness and kurtosis, while increasing auto-correlation times. A flatter density profile is also observed, similar to the SOL density shoulder formation in experimental scenarios with high fueling.

Published
2022
Full Text
View/download PDF

2. Reduction of transport due to magnetic shear in gyrokinetic simulations of the scrape-off layer

Author

Mandell, N. R., Hammett, G. W., Hakim, A., and Francisquez, M.

Subjects
Physics - Plasma Physics
Abstract

The effect of varying magnetic shear on scrape-off layer turbulence and profiles is studied via electromagnetic gyrokinetic simulations of a helical scrape-off layer model. We develop a model helical geometry with magnetic shear and a corresponding field-aligned coordinate system, which is used for simulations with the Gkeyll code. We find that perpendicular transport is reduced in cases with stronger shear, resulting in higher peak particle and heat fluxes to the endplates. Electromagnetic effects slightly increase transport in strong shear cases., Comment: 11 pages, 9 figures. arXiv admin note: text overlap with arXiv:2112.06880

Published
2021
Full Text
View/download PDF

3. Turbulent broadening of electron heat-flux width in electromagnetic gyrokinetic simulations of a helical scrape-off layer model

Author

Mandell, N. R., Hammett, G. W., Hakim, A., and Francisquez, M.

Subjects
Physics - Plasma Physics
Abstract

We demonstrate that cross-field transport in the scrape-off layer (SOL) can be moderately increased by electromagnetic effects in high-beta regimes, resulting in a broader electron heat-flux width on the endplates. This conclusion is taken from full-$f$ electromagnetic gyrokinetic simulations of a helical SOL model that roughly approximates the SOL of the National Spherical Torus Experiment (NSTX). The simulations have been performed with the Gkeyll code, which recently became the first code to demonstrate the capability to simulate electromagnetic gyrokinetic turbulence on open magnetic field lines with sheath boundary conditions. We scan the source rate and thus $\beta$ so that the normalized pressure gradient (the MHD ballooning parameter $\alpha \propto \partial \beta / \partial r \propto \beta / L_p$) is scanned over an experimentally-relevant range, $\alpha = 0.3-1.5$. While there is little change in the pressure gradient scale length $L_p$ near the midplane as beta is increased, a 10% increase in cross-field transport near the midplane results in an increase in the electron heat-flux width $\lambda_q$ and a 25% reduction of the peak electron heat flux to the endplates., Comment: 13 pages, 10 figures

Published
2021
Full Text
View/download PDF

4. Electromagnetic full-$f$ gyrokinetics in the tokamak edge with discontinuous Galerkin methods

Author

Mandell, N. R., Hakim, A., Hammett, G. W., and Francisquez, M.

Subjects
Physics - Plasma Physics, Physics - Computational Physics
Abstract

We present an energy-conserving discontinuous Galerkin scheme for the full-$f$ electromagnetic gyrokinetic system in the long-wavelength limit. We use the symplectic formulation and solve directly for $\partial A_\parallel/\partial t$, the inductive component of the parallel electric field, using a generalized Ohm's law derived directly from the gyrokinetic equation. Linear benchmarks are performed to verify the implementation and show that the scheme avoids the Amp\`ere cancellation problem. We perform a nonlinear electromagnetic simulation in a helical open-field-line system as a rough model of the tokamak scrape-off layer using parameters from the National Spherical Torus Experiment (NSTX). This is the first published nonlinear electromagnetic gyrokinetic simulation on open field lines. Comparisons are made to a corresponding electrostatic simulation., Comment: 38 pages, 11 figures

Published
2019
Full Text
View/download PDF

5. Global turbulence simulations of the tokamak edge region with GRILLIX

Author

Stegmeir, A., Ross, A., Body, T., Francisquez, M., Zholobenko, W., Coster, D., Maj, O., Manz, P., Jenko, F., Rogers, B. N., and Kang, K. S.

Subjects
Physics - Plasma Physics, Physics - Computational Physics
Abstract

Turbulent dynamics in the scrape-off layer (SOL) of magnetic fusion devices is intermittent with large fluctuations in density and pressure. Therefore, a model is required that allows perturbations of similar or even larger magnitude to the time-averaged background value. The fluid-turbulence code GRILLIX is extended to such a global model, which consistently accounts for large variation in plasma parameters. Derived from the drift reduced Braginskii equations, the new GRILLIX model includes electromagnetic and electron-thermal dynamics, retains global parametric dependencies and the Boussinesq approximation is not applied. The penalisation technique is combined with the flux-coordinate independent (FCI) approach [F. Hariri and M. Ottaviani, Comput.Phys.Commun. 184:2419, (2013); A. Stegmeir et al., Comput.Phys.Commun. 198:139, (2016)], which allows to study realistic diverted geometries with X-point(s) and general boundary contours. We characterise results from turbulence simulations and investigate the effect of geometry by comparing simulations in circular geometry with toroidal limiter against realistic diverted geometry at otherwise comparable parameters. Turbulence is found to be intermittent with relative fluctuation levels of up to 40% showing that a global description is indeed important. At the same time via direct comparison, we find that the Boussinesq approximation has only a small quantitative impact in a turbulent environment. In comparison to circular geometry the fluctuations are reduced in diverted geometry, which is related to a different zonal flow structure. Moreover, the fluctuation level has a more complex spatial distribution in diverted geometry. Due to local magnetic shear, which differs fundamentally in circular and diverted geometry, turbulent structures become strongly distorted in the perpendicular direction and are eventually damped away towards the X-point.

Published
2019
Full Text
View/download PDF

6. Conservative Discontinuous Galerkin Schemes for Nonlinear Fokker-Planck Collision Operators

Author

Hakim, Ammar, Francisquez, M., Juno, J., and Hammett, Greg W.

Subjects
Physics - Computational Physics, Physics - Plasma Physics
Abstract

We present a novel discontinuous Galerkin algorithm for the solution of a class of Fokker-Planck collision operators. These operators arise in many fields of physics, and our particular application is for kinetic plasma simulations. In particular, we focus on an operator often known as the `Lenard-Bernstein,' or `Dougherty,' operator. Several novel algorithmic innovations are reported. The concept of weak-equality is introduced and used to define weak-operators to compute primitive moments needed in the updates. Weak-equality is also used to determine a reconstruction procedure that allows an efficient and accurate discretization of the diffusion term. We show that when two integration by parts are used to construct the discrete weak-form, and finite velocity-space extents are accounted for, a scheme that conserves density, momentum and energy exactly is obtained. One novel feature is that the requirements of momentum and energy conservation lead to unique formulas to compute primitive moments. Careful definition of discretized moments also ensure that energy is conserved in the piecewise linear case, even though the $v^2$ term is not included in the basis-set used in the discretization. A series of benchmark problems are presented and show that the scheme conserves momentum and energy to machine precision. Empirical evidence also indicates that entropy is a non-decreasing function. The collision terms are combined with the Vlasov equation to study collisional Landau damping and plasma heating via magnetic pumping. We conclude with an outline of future work, in particular with some indications of how the algorithms presented here can be extended to use the Rosenbluth potentials to compute the drag and diffusion coefficients., Comment: Source code and input files available on bitbucket. See appendix

Published
2019
Full Text
View/download PDF

8. Estimates of global recycling coefficients for LTX-β discharges

Author

Maan, A., primary, Boyle, D. P., additional, Majeski, R., additional, Wilkie, G. J., additional, Francisquez, M., additional, Banerjee, S., additional, Kaita, R., additional, Maingi, R., additional, LeBlanc, B. P., additional, Abe, S., additional, Jung, E., additional, Perez, E., additional, Capecchi, W., additional, Ostrowski, E. T., additional, Elliott, D. B., additional, Hansen, C., additional, Kubota, S., additional, Soukhanovskii, V., additional, and Zakharov, L., additional

Published
2024
Full Text
View/download PDF

15. NSTX-U theory, modeling and analysis results

Author

Guttenfelder, W., primary, Battaglia, D.J., additional, Belova, E., additional, Bertelli, N., additional, Boyer, M.D., additional, Chang, C.S., additional, Diallo, A., additional, Duarte, V.N., additional, Ebrahimi, F., additional, Emdee, E.D., additional, Ferraro, N., additional, Fredrickson, E., additional, Gorelenkov, N.N., additional, Heidbrink, W., additional, Ilhan, Z., additional, Kaye, S.M., additional, Kim, E.-H., additional, Kleiner, A., additional, Laggner, F., additional, Lampert, M., additional, Lestz, J.B., additional, Liu, C., additional, Liu, D., additional, Looby, T., additional, Mandell, N., additional, Maingi, R., additional, Myra, J.R., additional, Munaretto, S., additional, Podestà, M., additional, Rafiq, T., additional, Raman, R., additional, Reinke, M., additional, Ren, Y., additional, Ruiz, J. Ruiz, additional, Scotti, F., additional, Shiraiwa, S., additional, Soukhanovskii, V., additional, Vail, P., additional, Wang, Z.R., additional, Wehner, W., additional, White, A.E., additional, White, R.B., additional, Woods, B.J.Q., additional, Yang, J., additional, Zweben, S.J., additional, Banerjee, S., additional, Barchfeld, R., additional, Bell, R.E., additional, Berkery, J.W., additional, Bhattacharjee, A., additional, Bierwage, A., additional, Canal, G.P., additional, Chen, X., additional, Clauser, C., additional, Crocker, N., additional, Domier, C., additional, Evans, T., additional, Francisquez, M., additional, Gan, K., additional, Gerhardt, S., additional, Goldston, R.J., additional, Gray, T., additional, Hakim, A., additional, Hammett, G., additional, Jardin, S., additional, Kaita, R., additional, Koel, B., additional, Kolemen, E., additional, Ku, S.-H., additional, Kubota, S., additional, LeBlanc, B.P., additional, Levinton, F., additional, Lore, J.D., additional, Luhmann, N., additional, Lunsford, R., additional, Maqueda, R., additional, Menard, J.E., additional, Nichols, J.H., additional, Ono, M., additional, Park, J.-K., additional, Poli, F., additional, Rhodes, T., additional, Riquezes, J., additional, Russell, D., additional, Sabbagh, S.A., additional, Schuster, E., additional, Smith, D.R., additional, Stotler, D., additional, Stratton, B., additional, Tritz, K., additional, Wang, W., additional, and Wirth, B., additional

Published
2022
Full Text
View/download PDF

19. Pair plasma instability in homogeneous magnetic guide fields

Author

Pueschel, M. J., Sydora, R. D., Terry, P. W., Tyburska-Pueschel, B., Francisquez, M., Jenko, F., Zhu, B., Pueschel, M. J., Sydora, R. D., Terry, P. W., Tyburska-Pueschel, B., Francisquez, M., Jenko, F., and Zhu, B.

Abstract

Pair plasmas, collections of both matter and antimatter particles of equal mass, represent a paradigm for the study of basic plasma science, and many open questions exist regarding these unique systems. They are found in many astrophysical settings, such as gamma-ray bursts, and have recently also been produced in carefully designed laboratory experiments. A central research topic in plasma physics is instability; however, unlike their more common ion-electron siblings, pair plasmas are generally thought to be stable to cross field pressure gradients in homogeneous magnetic fields. It is shown here by means of kinetic full-f simulations that, when a pressure gradient is first established, the Gradient-driven Drift Coupling mode is destabilized and becomes turbulent. Force balance is eventually achieved by a combination of flattened pressure profiles due to turbulent transport and establishment of a magnetic field gradient, saturating the growth. During the unstable phase, key physics can be captured by a δf gyrokinetic description, where it is shown analytically and numerically that parallel particle motion results in a coupling of all electromagnetic field components. A fluid model derived therefrom accurately predicts linear eigenmodes and is used to resolve global profile effects. For laser-based electron-positron plasma experiments, prompt instability is predicted with growth times much shorter than plasma lifetimes. Similarly, growth rates are calculated for the planned APEX experiment as well as gamma-ray burst scenarios, suggesting that the instability may contribute to the early evolution of these systems.

Published
2020

28. A two-dimensional numerical study of ion-acoustic turbulence – ERRATUM.

Author

Liu, Z., White, R., Francisquez, M., Milanese, L.M., and Loureiro, N.F.

Subjects
TURBULENCE, LASER plasma accelerators, PLASMA physics, PLASMA waves, PLASMA instabilities, PLASMA turbulence
Abstract

This document is a correction notice for an article titled "A two-dimensional numerical study of ion-acoustic turbulence." The original article contained an error in the acknowledgements section, which has now been updated. The article discusses a study on plasma instabilities, plasma waves, and plasma simulation. It was published in the Journal of Plasma Physics and is available as an Open Access article. The document provides the correct reference for the article and includes the DOI for further reference. [Extracted from the article]

Published
2024
Full Text
View/download PDF

30. Thermal dynamics in the flux‐coordinate independent turbulence code GRILLIX.

Author

Zholobenko, W., Stegmeir, A., Body, T., Ross, A., Manz, P., Maj, O., Coster, D., Jenko, F., Francisquez, M., Zhu, B., and Rogers, B.N.

Subjects
HEAT conduction, CONFORMAL geometry, TURBULENCE, GEODESIC flows, ELECTRIC fields, PLASMA turbulence, THERMAL hydraulics
Abstract

GRILLIX employs the flux‐coordinate independent approach (FCI), which allows us to study boundary plasma turbulence in realistic diverted configurations. Recently, the physical model in GRILLIX has been extended to a global drift‐reduced Braginskii model, without any separation between background and fluctuations. It includes electromagnetic and thermal dynamics with hot ions, relaxation of the Boussinesq approximation and non‐linear parametric dependencies. This contribution presents solutions to associated issues, that is, the ion diamagnetic polarization and the stiff parallel heat conduction. Simulations based on parameters characteristic for the Alcator C‐Mod tokamak were carried out. In circular geometry, the self‐consistent electric field contains zonal flows and geodesic acoustic modes in the confined region. In the scrape‐off layer, the electron parallel heat conduction and its boundary condition determine the temperature and electric field, leading to sheared flows at the last closed flux surface. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

31. Electromagnetic full- $f$ gyrokinetics in the tokamak edge with discontinuous Galerkin methods.

Author

Mandell, N. R., Hakim, A., Hammett, G. W., and Francisquez, M.

Subjects
GALERKIN methods, OHM'S law, ELECTRIC fields, TORUS, ROUGH sets, EDGES (Geometry)
Abstract

We present an energy-conserving discontinuous Galerkin scheme for the full- $f$ electromagnetic gyrokinetic system in the long-wavelength limit. We use the symplectic formulation and solve directly for $\unicode[STIX]{x2202}A_{\Vert }/\unicode[STIX]{x2202}t$ , the inductive component of the parallel electric field, using a generalized Ohm's law derived directly from the gyrokinetic equation. Linear benchmarks are performed to verify the implementation and show that the scheme avoids the Ampère cancellation problem. We perform a nonlinear electromagnetic simulation in a helical open-field-line system as a rough model of the tokamak scrape-off layer using parameters from the National Spherical Torus Experiment (NSTX). This is the first published nonlinear electromagnetic gyrokinetic simulation on open field lines. Comparisons are made to a corresponding electrostatic simulation. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

34. Science and technology research and development in support to ITER and the Broader Approach at CEA

Author

Bécoulet, A., primary, Hoang, G.T., additional, Abiteboul, J., additional, Achard, J., additional, Alarcon, T., additional, Alba-Duran, J., additional, Allegretti, L., additional, Allfrey, S., additional, Amiel, S., additional, Ané, J.M., additional, Aniel, T., additional, Antar, G., additional, Argouarch, A., additional, Armitano, A., additional, Arnaud, J., additional, Arranger, D., additional, Artaud, J.F., additional, Audisio, D., additional, Aumeunier, M., additional, Autissier, E., additional, Azcona, L., additional, Back, A., additional, Bahat, A., additional, Bai, X., additional, Baiocchi, B., additional, Balaguer, D., additional, Balme, S., additional, Balorin, C., additional, Barana, O., additional, Barbier, D., additional, Barbuti, A., additional, Basiuk, V., additional, Baulaigue, O., additional, Bayetti, P., additional, Baylard, C., additional, Beaufils, S., additional, Beaute, A., additional, Bécoulet, M., additional, Bej, Z., additional, Benkadda, S., additional, Benoit, F., additional, Berger-By, G., additional, Bernard, J.M., additional, Berne, A., additional, Bertrand, B., additional, Bertrand, E., additional, Beyer, P., additional, Bigand, A., additional, Bonhomme, G., additional, Borel, G., additional, Boron, A., additional, Bottereau, C., additional, Bottollier-Curtet, H., additional, Bouchand, C., additional, Bouquey, F., additional, Bourdelle, C., additional, Bourg, J., additional, Bourmaud, S., additional, Brémond, S., additional, Bribiesca Argomedo, F., additional, Brieu, M., additional, Brun, C., additional, Bruno, V., additional, Bucalossi, J., additional, Bufferand, H., additional, Buravand, Y., additional, Cai, L., additional, Cantone, V., additional, Cantone, B., additional, Caprin, E., additional, Cartier-Michaud, T., additional, Castagliolo, A., additional, Belo, J., additional, Catherine-Dumont, V., additional, Caulier, G., additional, Chaix, J., additional, Chantant, M., additional, Chatelier, M., additional, Chauvin, D., additional, Chenevois, J., additional, Chouli, B., additional, Christin, L., additional, Ciazynski, D., additional, Ciraolo, G., additional, Clairet, F., additional, Clapier, R., additional, Cloez, H., additional, Coatanea-Gouachet, M., additional, Colas, L., additional, Colledani, G., additional, Commin, L., additional, Coquillat, P., additional, Corbel, E., additional, Corre, Y., additional, Cottet, J., additional, Cottier, P., additional, Courtois, X., additional, Crest, I., additional, Dachicourt, R., additional, Dapena Febrer, M., additional, Daumas, C., additional, de Esch, H.P.L., additional, De Gentile, B., additional, Dechelle, C., additional, Decker, J., additional, Decool, P., additional, Deghaye, V., additional, Delaplanche, J., additional, Delchambre-Demoncheaux, E., additional, Delpech, L., additional, Desgranges, C., additional, Devynck, P., additional, Dias Pereira Bernardo, J., additional, Dif-Pradalier, G., additional, Doceul, L., additional, Dong, Y., additional, Douai, D., additional, Dougnac, H., additional, Dubuit, N., additional, Duchateau, J.-L., additional, Ducobu, L., additional, Dugue, B., additional, Dumas, N., additional, Dumont, R., additional, Durocher, A., additional, Duthoit, F., additional, Ekedahl, A., additional, Elbeze, D., additional, Escarguel, A., additional, Escop, J., additional, Faïsse, F., additional, Falchetto, G., additional, Farjon, J., additional, Faury, M., additional, Fedorzack, N., additional, Féjoz, P., additional, Fenzi, C., additional, Ferlay, F., additional, Fiet, P., additional, Firdaouss, M., additional, Francisquez, M., additional, Franel, B., additional, Frauche, J., additional, Frauel, Y., additional, Futtersack, R., additional, Garbet, X., additional, Garcia, J., additional, Gardarein, J., additional, Gargiulo, L., additional, Garibaldi, P., additional, Garin, P., additional, Garnier, D., additional, Gauthier, E., additional, Gaye, O., additional, Geraud, A., additional, Gerome, M., additional, Gervaise, V., additional, Geynet, M., additional, Ghendrih, P., additional, Giacalone, I., additional, Gibert, S., additional, Gil, C., additional, Ginoux, S., additional, Giovannangelo, L., additional, Girard, S., additional, Giruzzi, G., additional, Goletto, C., additional, Goncalves, R., additional, Gonde, R., additional, Goniche, M., additional, Goswami, R., additional, Grand, C., additional, Grandgirard, V., additional, Gravil, B., additional, Grisolia, C., additional, Gros, G., additional, Grosman, A., additional, Guigue, J., additional, Guilhem, D., additional, Guillemaut, C., additional, Guillerminet, B., additional, Guimaraes Filho, Z., additional, Guirlet, R., additional, Gunn, J. P., additional, Gurcan, O., additional, Guzman, F., additional, Hacquin, S., additional, Hariri, F., additional, Hasenbeck, F., additional, Hatchressian, J.C., additional, Hennequin, P., additional, Hernandez, C., additional, Hertout, P., additional, Heuraux, S., additional, Hillairet, J., additional, Honore, C., additional, Hornung, G., additional, Houry, M., additional, Hunstad, I., additional, Hutter, T., additional, Huynh, P., additional, Icard, V., additional, Imbeaux, F., additional, Irishkin, M., additional, Isoardi, L., additional, Jacquinot, J., additional, Jacquot, J., additional, Jiolat, G., additional, Joanny, M., additional, Joffrin, E., additional, Johner, J., additional, Joubert, P., additional, Jourd'Heuil, L., additional, Jouve, M., additional, Junique, C., additional, Keller, D., additional, Klepper, C., additional, Kogut, D., additional, Kubič, M., additional, Labassé, F., additional, Lacroix, B., additional, Lallier, Y., additional, Lamaison, V., additional, Lambert, R., additional, Larroque, S., additional, Latu, G., additional, Lausenaz, Y., additional, Laviron, C., additional, Le, R., additional, Le Luyer, A., additional, Le Niliot, C., additional, Le Tonqueze, Y., additional, Lebourg, P., additional, Lefevre, T., additional, Leroux, F., additional, Letellier, L., additional, Li, Y., additional, Lipa, M., additional, Lister, J., additional, Litaudon, X., additional, Liu, F., additional, Loarer, T., additional, Lombard, G., additional, Lotte, P., additional, Lozano, M., additional, Lucas, J., additional, Lütjens, H., additional, Magaud, P., additional, Maget, P., additional, Magne, R., additional, Mahieu, J.-F., additional, Maini, P., additional, Malard, P., additional, Manenc, L., additional, Marandet, Y., additional, Marbach, G., additional, Marechal, J.-L., additional, Marfisi, L., additional, Marle, M., additional, Martin, C., additional, Martin, V., additional, Martin, G., additional, Martinez, A., additional, Martino, P., additional, Masset, R., additional, Mazon, D., additional, Mellet, N., additional, Mercadier, L., additional, Merle, A., additional, Meshcheriakov, D., additional, Messina, P., additional, Meyer, O., additional, Millon, L., additional, Missirlian, M., additional, Moerel, J., additional, Molina, D., additional, Mollard, P., additional, Moncada, V., additional, Monier-Garbet, P., additional, Moreau, D., additional, Moreau, M., additional, Moreau, P., additional, Morel, P., additional, Moriyama, T., additional, Motassim, Y., additional, Mougeolle, G., additional, Moulton, D., additional, Moureau, G., additional, Mouyon, D., additional, Naim Habib, M., additional, Nardon, E., additional, Négrier, V., additional, Nemeth, J., additional, Nguyen, C., additional, Nguyen, M., additional, Nicolas, L., additional, Nicolas, T., additional, Nicollet, S., additional, Nilsson, E., additional, N'Konga, B., additional, Noel, F., additional, Nooman, A., additional, Norscini, C., additional, Nouailletas, R., additional, Oddon, P., additional, Ohsako, T., additional, Orain, F., additional, Ottaviani, M., additional, Pagano, M., additional, Palermo, F., additional, Panayotis, S., additional, Parrat, H., additional, Pascal, J.-Y., additional, Passeron, C., additional, Pastor, P., additional, Patterlini, J., additional, Pavy, K., additional, Pecquet, A.-L., additional, Pégourié, B., additional, Peinturier, C., additional, Pelletier, T., additional, Peluso, B., additional, Petrzilka, V., additional, Peysson, Y., additional, Pignoly, E., additional, Pirola, R., additional, Pocheau, C., additional, Poitevin, E., additional, Poli, V., additional, Poli, S., additional, Pompon, F., additional, Porchy, I., additional, Portafaix, C., additional, Preynas, M., additional, Prochet, P., additional, Prou, M., additional, Ratnani, A., additional, Raulin, D., additional, Ravenel, N., additional, Renard, S., additional, Ricaud, B., additional, Richou, M., additional, Ritz, G., additional, Roche, H., additional, Roubin, P., additional, Roux, C., additional, Ruiz, K., additional, Sabathier, F., additional, Sabot, R., additional, Saille, A., additional, Saint-Laurent, F., additional, Sakamoto, R., additional, Salasca, S., additional, Salmon, T., additional, Samaille, F., additional, Sanchez, S., additional, Santagiustina, A., additional, Saoutic, B., additional, Sarazin, Y., additional, Sardain, P., additional, Schlosser, J., additional, Schneider, M., additional, Schwob, J., additional, Segui, J., additional, Seguin, N., additional, Selig, G., additional, Serret, D., additional, Signoret, J., additional, Simonin, A., additional, Soldaini, M., additional, Soler, B., additional, Soltane, C., additional, Song, S., additional, Sourbier, F., additional, Sparagna, J., additional, Spitz, P., additional, Spuig, P., additional, Storelli, A., additional, Strugarek, A., additional, Tamain, P., additional, Tena, M., additional, Theis, J., additional, Thomine, O., additional, Thouvenin, D., additional, Torre, A., additional, Toulouse, L., additional, Travère, J., additional, Tsitrone, E., additional, Turck, B., additional, Urban, J., additional, Vallet, J.-C., additional, Vallory, J., additional, Valognes, A., additional, Van Helvoirt, J., additional, Vartanian, S., additional, Verger, J.-M., additional, Vermare, L., additional, Vermare, C., additional, Vezinet, D., additional, Vicente, K., additional, Vidal, J., additional, Vignal, N., additional, Vigne, T., additional, Villecroze, F., additional, Villedieu, E., additional, Vincent, B., additional, Volpe, B., additional, Volpe, D., additional, Volpe, R., additional, Wagrez, J., additional, Wang, H., additional, Wauters, T., additional, Wintersdorff, O., additional, Wittebol, E., additional, Zago, B., additional, Zani, L., additional, Zarzoso, D., additional, Zhang, Y., additional, Zhong, W., additional, and Zou, X.L., additional

Published
2013
Full Text
View/download PDF

35. Modelling of power limit in RF antenna waveguides operated in the lower hybrid range of frequency.

Author

Goniche, M., Mhari, C. El, Francisquez, M., Anza, S., Belo, J.H., Hertout, P., and Hillairet, J.

Subjects
NUCLEAR energy, RADIO frequency, ANTENNAS (Electronics), PLASMA hybrid waves, ELECTRIC fields, TOKAMAKS
Abstract

Multipactor, the well-known electron avalanche phenomena occurring in waveguides when the amplitude of the RF electric field exceeds a threshold, is modelled for lower hybrid current drive (LHCD) antennas. The electric field threshold departures significantly from the expected linear scaling with the frequency when the width of the waveguide along the electric field increases. For 5 GHz waveguides, the multipactor does not occur when this width exceeds 26 mm, in very good agreement with analytical formulation. Effect of static magnetic field with typical values of tokamak environment is examined. It is found that the threshold is weakly reduced (−6%) for the front face of the antenna featuring the rows of narrow waveguides. Strong reduction in the threshold is found where the wave frequency equals the electron cyclotron frequency (0.178 T at 5 GHz) but this condition will not be met on ITER. After baking at 240 °C, wide waveguides at the antenna input (29 mm on ITER) have a threshold of ∼7 kV cm−1, assuming a homogeneous magnetic field. However, preliminary results indicate higher threshold when the gradient of the magnetic field along the waveguide is taken into account and no limitation, from this section, is expected for the ITER LHCD antenna. [ABSTRACT FROM AUTHOR]

Published
2014
Full Text
View/download PDF

36. Dynamo in Weakly Collisional Nonmagnetized Plasmas Impeded by Landau Damping of Magnetic Fields.

Author

Pusztai I, Juno J, Brandenburg A, TenBarge JM, Hakim A, Francisquez M, and Sundström A

Abstract

We perform fully kinetic simulations of flows known to produce dynamo in magnetohydrodynamics (MHD), considering scenarios with low Reynolds number and high magnetic Prandtl number, relevant for galaxy cluster scale fluctuation dynamos. We find that Landau damping on the electrons leads to a rapid decay of magnetic perturbations, impeding the dynamo. This collisionless damping process operates on spatial scales where electrons are nonmagnetized, reducing the range of scales where the magnetic field grows in high magnetic Prandtl number fluctuation dynamos. When electrons are not magnetized down to the resistive scale, the magnetic energy spectrum is expected to be limited by the scale corresponding to magnetic Landau damping or, if smaller, the electron gyroradius scale, instead of the resistive scale. In simulations we thus observe decaying magnetic fields where resistive MHD would predict a dynamo.

Published
2020
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results