18 results on '"Whyte, Dennis G"'
Search Results
2. Performance of demountable solder joints for no-insulation superconducting coils produced by vacuum pressure impregnation
- Author
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Mouratidis, Theodore, primary, Whyte, Dennis G, additional, LaBombard, Brian, additional, and Beck, William K, additional
- Published
- 2023
- Full Text
- View/download PDF
3. Modeling and analysis of the tritium fuel cycle for ARC- and STEP-class D-T fusion power plants
- Author
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Meschini, Samuele, primary, Ferry, Sara E., additional, Delaporte-Mathurin, Rémi, additional, and Whyte, Dennis G., additional
- Published
- 2023
- Full Text
- View/download PDF
4. Demountable Toroidal Field Magnets for Use in a Compact Modular Fusion Reactor
- Author
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Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Mangiarotti, Franco Julio, Goh, Jonathan Yanming, Takayasu, Makoto, Bromberg, Leslie, Minervini, Joseph V, Whyte, Dennis G, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Mangiarotti, Franco Julio, Goh, Jonathan Yanming, Takayasu, Makoto, Bromberg, Leslie, Minervini, Joseph V, and Whyte, Dennis G
- Abstract
A concept of demountable toroidal field magnets for a compact fusion reactor is discussed. The magnets generate a magnetic field of 9.2 T on axis, in a 3.3 m major radius tokamak. Subcooled YBCO conductors have a critical current density adequate to provide this large magnetic field, while operating at 20 K reduces thermodynamic cooling cost of the resistive electrical joints. Demountable magnets allow for vertical replacement and maintenance of internal components, potentially reducing cost and time of maintenance when compared to traditional sector maintenance. Preliminary measurements of contact resistance of a demountable YBCO electrical joint between are presented.
- Published
- 2018
5. Alcator C-Mod: research in support of ITER and steps beyond
- Author
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Candy, J., Canik, J., Churchill, R.M., Holland, C., Loarte, A., Reinke, M.L., Scott, S., Snyder, P., Theiler, C., Diallo, A., Edlund, E., LaBombard, B., Baek, Seung Gyou, Marmar, Earl S, Barnard, Harold Salvadore, Bonoli, Paul T, Brunner, Daniel Frederic, Ennever, Paul Chappell, Fiore, Catherine L, Gao, Chi, Golfinopoulos, Theodore, Greenwald, Martin J, Hartwig, Zachary Seth, Hubbard, Amanda E, Hughes Jr, Jerry, Hutchinson, Ian Horner, Irby, James Henderson, Labombard, Brian, Lin, Yijun, Mumgaard, Robert Thomas, Parker, Ronald R, Porkolab, Miklos, Rice, John E, Shiraiwa, Shunichi, Sorbom, Brandon Nils, Terry, David Rankin, Terry, James L, Vieira, Rui F, Walk Jr, John R, Wallace, Gregory Marriner, White, Anne E., Whyte, Dennis G, Wolfe, Stephen M, Wright, John C, Wright, Graham, Wukitch, Stephen James, Xu, Peng, Cziegler, Istvan, Dekow, Gary L, Delgado-Aparicio, Luis, Lipschultz, Bruce, Theiler, Christian, Diallo, Ahmed Y, Edlund, Eric Matthias, Faust, Ian Charles, Massachusetts Institute of Technology. Department of Biological Engineering, Massachusetts Institute of Technology. Department of Mathematics, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Department of Physics, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Hutchinson Ian, Baek, Seung Gyou, Marmar, Earl S, Barnard, Harold Salvadore, Bonoli, Paul T, Brunner, Daniel Frederic, Ennever, Paul Chappell, Fiore, Catherine L, Gao, Chi, Golfinopoulos, Theodore, Greenwald, Martin J, Hartwig, Zachary Seth, Hubbard, Amanda E, Hughes Jr, Jerry, Hutchinson, Ian Horner, Irby, James Henderson, Labombard, Brian, Lin, Yijun, Mumgaard, Robert Thomas, Parker, Ronald R, Porkolab, Miklos, Rice, John E, Shiraiwa, Shunichi, Sorbom, Brandon Nils, Terry, David Rankin, Terry, James L, Vieira, Rui F, Walk Jr, John R, Wallace, Gregory Marriner, White, Anne E., Whyte, Dennis G, Wolfe, Stephen M, Wright, John C, Wright, Graham, Wukitch, Stephen James, Xu, Peng, Cziegler, Istvan, Dekow, Gary L, Delgado-Aparicio, Luis, Lipschultz, Bruce, Theiler, Christian, Diallo, Ahmed Y, Edlund, Eric Matthias, and Faust, Ian Charles
- Subjects
Nuclear and High Energy Physics ,Materials science ,Tokamak ,Divertor ,Nuclear engineering ,Cyclotron ,FEC 2014 ,chemistry.chemical_element ,overview ,Electron ,Tungsten ,Condensed Matter Physics ,law.invention ,Pedestal ,Alcator C-Mod ,chemistry ,law ,Dielectric heating ,Atomic physics ,tokamak - Abstract
This paper presents an overview of recent highlights from research on Alcator C-Mod. Significant progress has been made across all research areas over the last two years, with particular emphasis on divertor physics and power handling, plasma–material interaction studies, edge localized mode-suppressed pedestal dynamics, core transport and turbulence, and RF heating and current drive utilizing ion cyclotron and lower hybrid tools. Specific results of particular relevance to ITER include: inner wall SOL transport studies that have led, together with results from other experiments, to the change of the detailed shape of the inner wall in ITER; runaway electron studies showing that the critical electric field required for runaway generation is much higher than predicted from collisional theory; core tungsten impurity transport studies reveal that tungsten accumulation is naturally avoided in typical C-Mod conditions., United States. Department of Energy (DE-FC02-99ER54512-CMOD), United States. Department of Energy (DE-AC02-09CH11466), United States. Department of Energy (DE-FG02-96ER-54373), United States. Department of Energy (DE-FG02-94ER54235)
- Published
- 2015
6. Multi-device studies of pedestal physics and confinement in the I-mode regime
- Author
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Massachusetts Institute of Technology. Plasma Science and Fusion Center, Whyte, Dennis, Hubbard, Amanda E, Hughes Jr, Jerry, Marinoni, Alessandro, Marmar, Earl S, Rice, John E, Walk Jr, John R, Whyte, Dennis G, Wolfe, Stephen M, Osborne, T., Ryter, F., Austin, M., Barrera Orte, L., Churchill, R. M., Cziegler, I., Fenstermacher, M., Fischer, R., Gerhardt, S., Groebner, R., Gohil, P., Happel, T., Loarte, A., Maingi, R., Manz, P., McDermott, R. M., McKee, G., Rhodes, T. L., Schmitz, L., Theiler, C., Viezzer, E., Walk, J. R., Wolfrum, E., Yan, Z., Massachusetts Institute of Technology. Plasma Science and Fusion Center, Whyte, Dennis, Hubbard, Amanda E, Hughes Jr, Jerry, Marinoni, Alessandro, Marmar, Earl S, Rice, John E, Walk Jr, John R, Whyte, Dennis G, Wolfe, Stephen M, Osborne, T., Ryter, F., Austin, M., Barrera Orte, L., Churchill, R. M., Cziegler, I., Fenstermacher, M., Fischer, R., Gerhardt, S., Groebner, R., Gohil, P., Happel, T., Loarte, A., Maingi, R., Manz, P., McDermott, R. M., McKee, G., Rhodes, T. L., Schmitz, L., Theiler, C., Viezzer, E., Walk, J. R., Wolfrum, E., and Yan, Z.
- Abstract
This paper describes joint ITPA studies of the I-mode regime, which features an edge thermal barrier together with L-mode-like particle and impurity transport and no edge localized modes (ELMs). The regime has been demonstrated on the Alcator C-Mod, ASDEX Upgrade and DIII-D tokamaks, over a wide range of device parameters and pedestal conditions. Dimensionless parameters at the pedestal show overlap across devices and extend to low collisionality. When they are matched, pedestal temperature profiles are also similar. Pedestals are stable to peeling–ballooning modes, consistent with lack of ELMs. Access to I-mode is independent of heating method (neutral beam injection, ion cyclotron and/or electron cyclotron resonance heating). Normalized energy confinement H 98,y2 ≥ 1 has been achieved for a range of 3 ≤ q 95 ≤ 4.9 and scales favourably with power. Changes in turbulence in the pedestal region accompany the transition from L-mode to I-mode. The L–I threshold increases with plasma density and current, and with device size, but has a weak dependence on toroidal magnetic field B T. The upper limit of power for I-modes, which is set by I–H transitions, increases with B T and the power range is largest on Alcator C-Mod at B > 5 T. Issues for extrapolation to ITER and other future fusion devices are discussed., United States. Department of Energy (DE-FC02-99ER54512-CMOD), United States. Department of Energy (DE-SC0012469), United States. Department of Energy (DE-FC02-04ER54698), United States. Department of Energy (DE-FG02-94ER54235), United States. Department of Energy (DE-AC52-07NA27344), United States. Department of Energy (DE-AC02-09CH11466), United States. Department of Energy (DE-FG02-89ER53296), United States. Department of Energy (DE-FG02-08ER54999), United States. Department of Energy (DE-FG02-08ER54984)
- Published
- 2017
7. High density LHRF experiments in Alcator C-Mod and implications for reactor scale devices
- Author
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Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Department of Physics, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Whyte, Dennis, Baek, Seung Gyou, Parker, Ronald R, Bonoli, Paul T, Shiraiwa, Shunichi, Wallace, Gregory Marriner, Labombard, Brian, Faust, Ian Charles, Porkolab, Miklos, Whyte, Dennis G, Parker, R., Bonoli, Paul T., Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Department of Physics, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Whyte, Dennis, Baek, Seung Gyou, Parker, Ronald R, Bonoli, Paul T, Shiraiwa, Shunichi, Wallace, Gregory Marriner, Labombard, Brian, Faust, Ian Charles, Porkolab, Miklos, Whyte, Dennis G, Parker, R., and Bonoli, Paul T.
- Abstract
Parametric decay instabilities (PDI) appear to be an ubiquitous feature of lower hybrid current drive (LHCD) experiments at high density. In density ramp experiments in Alcator C-Mod and other machines the onset of PDI activity has been well correlated with a decrease in current drive efficiency and production of fast electron bremsstrahlung. However whether PDI is the primary cause of the 'density limit', and if so by exactly what mechanism (beyond the obvious one of pump depletion) has not been clearly established. In order to further understand the connection, the frequency spectrum of PDI activity occurring during Alcator C-Mod LHCD experiments has been explored in detail by means of a number of RF probes distributed around the periphery of the C-Mod tokamak including a probe imbedded in the inner wall. The results show that (i) the excited spectra consists mainly of a few discrete ion cyclotron (IC) quasi-modes, which have higher growth than the ion sound branch; (ii) PDI activity can begin either at the inner or outer wall, depending on magnetic configuration; (iii) the frequencies of the IC quasi-modes correspond to the magnetic field strength close to the low-field side (LFS) or high-field side separatrix; and (iv) although PDI activity may initiate near the inner separatrix, the loss in fast electron bremsstrahlung is best correlated with the appearance of IC quasi-modes characteristic of the magnetic field strength near the LFS separatrix. These data, supported by growth rate calculations, point to the importance of the LFS scrape-off layer (SOL) density in determining PDI onset and degradation in current drive efficiency. By minimizing the SOL density it is possible to extend the core density regime over which PDI can be avoided, thus potentially maximizing the effectiveness of LHCD at high density. Increased current drive efficiency at high density has been achieved in FTU and EAST through lithium coating and special fuelling methods, and in recent C-Mod, United States. Department of Energy (DE-FC02-99ER54512)
- Published
- 2017
8. Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak
- Author
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Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Department of Physics, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Whyte, Dennis, Marinoni, Alessandro, Rost, Jon C, Porkolab, Miklos, Hubbard, Amanda E, Osborne, Thomas, White, Anne E., Whyte, Dennis G, Davis, Emily, Ernst, Darin R, Rhodes, T.L., Burrell, K.H., Rost, Jon C., Ernst, Darin R., Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Department of Physics, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Whyte, Dennis, Marinoni, Alessandro, Rost, Jon C, Porkolab, Miklos, Hubbard, Amanda E, Osborne, Thomas, White, Anne E., Whyte, Dennis G, Davis, Emily, Ernst, Darin R, Rhodes, T.L., Burrell, K.H., Rost, Jon C., and Ernst, Darin R.
- Abstract
The I-mode regime, routinely observed on the Alcator C-Mod tokamak, is characterized by an edge energy transport barrier without an accompanying particle barrier and with broadband instabilities, known as weakly coherent modes (WCM), believed to regulate particle transport at the edge. Recent experiments on the DIII-D tokamak exhibit I-mode characteristics in various physical quantities. These DIII-D plasmas evolve over long periods, lasting several energy confinement times, during which the edge electron temperature slowly evolves towards an H-mode-like profile, while maintaining a typical L-mode edge density profile. During these periods, referred to as I-mode phases, the radial electric field at the edge also gradually reaches values typically observed in H-mode. Density fluctuations measured with the phase contrast imaging diagnostic during I-mode phases exhibit three features typically observed in H-mode on DIII-D, although they develop progressively with time and without a sharp transition: the intensity of the fluctuations is reduced; the frequency spectrum is broadened and becomes non-monotonic; two dimensional space-time spectra appear to approach those in H-mode, showing phase velocities of density fluctuations at the edge increasing to about 10 km s−1. However, in DIII-D there is no clear evidence of the WCM. Preliminary linear gyro-kinetic simulations are performed in the pedestal region with the GS2 code and its recently upgraded model collision operator that conserves particles, energy and momentum. The increased bootstrap current and flow shear generated by the temperature pedestal are shown to decrease growth rates, thus possibly generating a feedback mechanism that progressively stabilizes fluctuations., United States. Department of Energy. Office of Fusion Energy Sciences (Award DE-FG02-94ER54235), United States. Department of Energy. Office of Fusion Energy Sciences (Award DE-FG02-94ER54084), United States. Department of Energy. Office of Fusion Energy Sciences (Award DE-FG02-08ER54984), United States. Department of Energy. Office of Fusion Energy Sciences (Award DE-FC02-04ER54698)
- Published
- 2017
9. Alcator C-Mod: research in support of ITER and steps beyond
- Author
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Massachusetts Institute of Technology. Department of Biological Engineering, Massachusetts Institute of Technology. Department of Mathematics, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Department of Physics, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Hutchinson Ian, Baek, Seung Gyou, Marmar, Earl S, Barnard, Harold Salvadore, Bonoli, Paul T, Brunner, Daniel Frederic, Ennever, Paul Chappell, Fiore, Catherine L, Gao, Chi, Golfinopoulos, Theodore, Greenwald, Martin J, Hartwig, Zachary Seth, Hubbard, Amanda E, Hughes Jr, Jerry, Hutchinson, Ian Horner, Irby, James Henderson, Labombard, Brian, Lin, Yijun, Mumgaard, Robert Thomas, Parker, Ronald R, Porkolab, Miklos, Rice, John E, Shiraiwa, Shunichi, Sorbom, Brandon Nils, Terry, David Rankin, Terry, James L, Vieira, Rui F, Walk Jr, John R, Wallace, Gregory Marriner, White, Anne E., Whyte, Dennis G, Wolfe, Stephen M, Wright, John C, Wright, Graham, Wukitch, Stephen James, Xu, Peng, Cziegler, Istvan, Dekow, Gary L, Delgado-Aparicio, Luis, Lipschultz, Bruce, Theiler, Christian, Diallo, Ahmed Y, Edlund, Eric Matthias, Faust, Ian Charles, Candy, J., Canik, J., Churchill, R.M., Holland, C., Loarte, A., Reinke, M.L., Scott, S., Snyder, P., Theiler, C., Diallo, A., Edlund, E., LaBombard, B., Marmar, Earl S., Bonoli, Paul T., Fiore, Catherine, Greenwald, Martin J., Parker, R., Rice, John E., Wright, John C., Massachusetts Institute of Technology. Department of Biological Engineering, Massachusetts Institute of Technology. Department of Mathematics, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Department of Physics, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Hutchinson Ian, Baek, Seung Gyou, Marmar, Earl S, Barnard, Harold Salvadore, Bonoli, Paul T, Brunner, Daniel Frederic, Ennever, Paul Chappell, Fiore, Catherine L, Gao, Chi, Golfinopoulos, Theodore, Greenwald, Martin J, Hartwig, Zachary Seth, Hubbard, Amanda E, Hughes Jr, Jerry, Hutchinson, Ian Horner, Irby, James Henderson, Labombard, Brian, Lin, Yijun, Mumgaard, Robert Thomas, Parker, Ronald R, Porkolab, Miklos, Rice, John E, Shiraiwa, Shunichi, Sorbom, Brandon Nils, Terry, David Rankin, Terry, James L, Vieira, Rui F, Walk Jr, John R, Wallace, Gregory Marriner, White, Anne E., Whyte, Dennis G, Wolfe, Stephen M, Wright, John C, Wright, Graham, Wukitch, Stephen James, Xu, Peng, Cziegler, Istvan, Dekow, Gary L, Delgado-Aparicio, Luis, Lipschultz, Bruce, Theiler, Christian, Diallo, Ahmed Y, Edlund, Eric Matthias, Faust, Ian Charles, Candy, J., Canik, J., Churchill, R.M., Holland, C., Loarte, A., Reinke, M.L., Scott, S., Snyder, P., Theiler, C., Diallo, A., Edlund, E., LaBombard, B., Marmar, Earl S., Bonoli, Paul T., Fiore, Catherine, Greenwald, Martin J., Parker, R., Rice, John E., and Wright, John C.
- Abstract
This paper presents an overview of recent highlights from research on Alcator C-Mod. Significant progress has been made across all research areas over the last two years, with particular emphasis on divertor physics and power handling, plasma–material interaction studies, edge localized mode-suppressed pedestal dynamics, core transport and turbulence, and RF heating and current drive utilizing ion cyclotron and lower hybrid tools. Specific results of particular relevance to ITER include: inner wall SOL transport studies that have led, together with results from other experiments, to the change of the detailed shape of the inner wall in ITER; runaway electron studies showing that the critical electric field required for runaway generation is much higher than predicted from collisional theory; core tungsten impurity transport studies reveal that tungsten accumulation is naturally avoided in typical C-Mod conditions., United States. Department of Energy (DE-FC02-99ER54512-CMOD), United States. Department of Energy (DE-AC02-09CH11466), United States. Department of Energy (DE-FG02-96ER-54373), United States. Department of Energy (DE-FG02-94ER54235)
- Published
- 2017
10. Electron temperature fluctuations associated with the weakly coherent mode in the edge of I-mode plasmas
- Author
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Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Plasma Science and Fusion Center, White, Anne E., Whyte, Dennis G., Hubbard, Amanda E., Sung, Choongki, Hughes, Jerry W., Dominguez, Arturo, Terry, James L., Cziegler, Istvan, Phillips, P., Whyte, Dennis G, Hubbard, Amanda E, Hughes Jr, Jerry, Terry, James L, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Plasma Science and Fusion Center, White, Anne E., Whyte, Dennis G., Hubbard, Amanda E., Sung, Choongki, Hughes, Jerry W., Dominguez, Arturo, Terry, James L., Cziegler, Istvan, Phillips, P., Whyte, Dennis G, Hubbard, Amanda E, Hughes Jr, Jerry, and Terry, James L
- Abstract
New measurements of electron temperature fluctuations associated with the weakly coherent mode (WCM) during improved mode, or I-mode plasmas (Whyte et al 2010 Nucl. Fusion. 50 105005) at Alcator C-Mod (Marmar et al 2007 Fusion. Sci. Technol. 51 3261) are presented in this paper. The measurements are made with a 32-channel, high-resolution profile electron cyclotron emission radiometer. The WCM electron temperature fluctuations are localized to a 1 cm region inside the last closed flux surface. The WCM electron temperature fluctuation level is measured in several different I-mode discharges and is in the range 1% [~ over T][subscript e/T[subscript e] < 2%, which is an order of magnitude smaller than the WCM density fluctuation level. The WCM edge fluctuations observed in I-mode are believed to play a role in increasing particle transport but not energy transport in the edge of I-mode plasmas. The large difference between normalized density and electron temperature fluctuation amplitudes provides new evidence that the WCM fluctuations can separately affect energy and particle transport., United States. Dept. of Energy (DE-FC02-99-ER54512-CMOD)
- Published
- 2013
11. Tungsten nano-tendril growth in the Alcator C-Mod divertor
- Author
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Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Wright, Graham, Brunner, Daniel Frederic, Labombard, Brian, Lipschultz, Bruce, Terry, James L., Whyte, Dennis G., Baldwin, M. J., Doerner, R. P., Terry, James L, Whyte, Dennis G, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Wright, Graham, Brunner, Daniel Frederic, Labombard, Brian, Lipschultz, Bruce, Terry, James L., Whyte, Dennis G., Baldwin, M. J., Doerner, R. P., Terry, James L, and Whyte, Dennis G
- Abstract
Growth of tungsten nano-tendrils ('fuzz') has been observed for the first time in the divertor region of a high-power density tokamak experiment. After 14 consecutive helium L-mode discharges in Alcator C-Mod, the tip of a tungsten Langmuir probe at the outer strike point was fully covered with a layer of nano-tendrils. The thickness of the individual nano-tendrils (50–100 nm) and the depth of the layer (600 ± 150 nm) are consistent with observations from experiments on linear plasma devices. The observation of tungsten fuzz in a tokamak may have important implications for material erosion, dust formation, divertor lifetime and tokamak operations in next-step devices., National Science Foundation (U.S.) (Award DMR-08-19762), United States. Dept. of Energy (Award DE-SC00-02060), United States. Dept. of Energy (Contract DE-FC02-99ER54512)
- Published
- 2013
12. Multi-device studies of pedestal physics and confinement in the I-mode regime
- Author
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Jerry Hughes, A. Loarte, T.H. Osborne, L. W. Schmitz, George McKee, Alessandro Marinoni, D.G. Whyte, E. Wolfrum, E. Viezzer, Istvan Cziegler, R. M. McDermott, S.P. Gerhardt, Zheng Yan, M.E. Fenstermacher, L. Barrera Orte, Amanda Hubbard, F. Ryter, J. E. Rice, R. Maingi, P. Gohil, T. L. Rhodes, R. Fischer, Randy Michael Churchill, J.R. Walk, S.M. Wolfe, Max E Austin, P. Manz, T. Happel, Anne White, Earl Marmar, R. J. Groebner, Christian Theiler, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Whyte, Dennis, Hubbard, Amanda E, Hughes Jr, Jerry, Marinoni, Alessandro, Marmar, Earl S, Rice, John E, Walk Jr, John R, Whyte, Dennis G, Wolfe, Stephen M, Alcator C-Mod Team, ASDEX Upgrade Team, Max Planck Institute for Plasma Physics, Max Planck Society, and DIII-D Team
- Subjects
Physics ,Nuclear and High Energy Physics ,Tokamak ,Cyclotron ,Collisionality ,Condensed Matter Physics ,01 natural sciences ,Neutral beam injection ,Electron cyclotron resonance ,010305 fluids & plasmas ,law.invention ,Pedestal ,ASDEX Upgrade ,law ,Physics::Plasma Physics ,0103 physical sciences ,Atomic physics ,010306 general physics ,Dimensionless quantity - Abstract
This paper describes joint ITPA studies of the I-mode regime, which features an edge thermal barrier together with L-mode-like particle and impurity transport and no edge localized modes (ELMs). The regime has been demonstrated on the Alcator C-Mod, ASDEX Upgrade and DIII-D tokamaks, over a wide range of device parameters and pedestal conditions. Dimensionless parameters at the pedestal show overlap across devices and extend to low collisionality. When they are matched, pedestal temperature profiles are also similar. Pedestals are stable to peeling–ballooning modes, consistent with lack of ELMs. Access to I-mode is independent of heating method (neutral beam injection, ion cyclotron and/or electron cyclotron resonance heating). Normalized energy confinement H 98,y2 ≥ 1 has been achieved for a range of 3 ≤ q 95 ≤ 4.9 and scales favourably with power. Changes in turbulence in the pedestal region accompany the transition from L-mode to I-mode. The L–I threshold increases with plasma density and current, and with device size, but has a weak dependence on toroidal magnetic field B T. The upper limit of power for I-modes, which is set by I–H transitions, increases with B T and the power range is largest on Alcator C-Mod at B > 5 T. Issues for extrapolation to ITER and other future fusion devices are discussed., United States. Department of Energy (DE-FC02-99ER54512-CMOD), United States. Department of Energy (DE-SC0012469), United States. Department of Energy (DE-FC02-04ER54698), United States. Department of Energy (DE-FG02-94ER54235), United States. Department of Energy (DE-AC52-07NA27344), United States. Department of Energy (DE-AC02-09CH11466), United States. Department of Energy (DE-FG02-89ER53296), United States. Department of Energy (DE-FG02-08ER54999), United States. Department of Energy (DE-FG02-08ER54984)
- Published
- 2016
13. High density LHRF experiments in Alcator C-Mod and implications for reactor scale devices
- Author
-
Brian LaBombard, Seung Gyou Baek, Paul Bonoli, Miklos Porkolab, S. Shiraiwa, Gregory Wallace, Ian Faust, Dennis Whyte, Ronald R. Parker, Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Department of Physics, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Whyte, Dennis, Baek, Seung Gyou, Parker, Ronald R, Bonoli, Paul T, Shiraiwa, Shunichi, Wallace, Gregory Marriner, Labombard, Brian, Faust, Ian Charles, Porkolab, Miklos, and Whyte, Dennis G
- Subjects
Nuclear and High Energy Physics ,Materials science ,Tokamak ,Cyclotron ,Bremsstrahlung ,Electron ,Condensed Matter Physics ,law.invention ,Ion ,Magnetic field ,Nuclear magnetic resonance ,Alcator C-Mod ,law ,Atomic physics ,Order of magnitude - Abstract
Parametric decay instabilities (PDI) appear to be an ubiquitous feature of lower hybrid current drive (LHCD) experiments at high density. In density ramp experiments in Alcator C-Mod and other machines the onset of PDI activity has been well correlated with a decrease in current drive efficiency and production of fast electron bremsstrahlung. However whether PDI is the primary cause of the 'density limit', and if so by exactly what mechanism (beyond the obvious one of pump depletion) has not been clearly established. In order to further understand the connection, the frequency spectrum of PDI activity occurring during Alcator C-Mod LHCD experiments has been explored in detail by means of a number of RF probes distributed around the periphery of the C-Mod tokamak including a probe imbedded in the inner wall. The results show that (i) the excited spectra consists mainly of a few discrete ion cyclotron (IC) quasi-modes, which have higher growth than the ion sound branch; (ii) PDI activity can begin either at the inner or outer wall, depending on magnetic configuration; (iii) the frequencies of the IC quasi-modes correspond to the magnetic field strength close to the low-field side (LFS) or high-field side separatrix; and (iv) although PDI activity may initiate near the inner separatrix, the loss in fast electron bremsstrahlung is best correlated with the appearance of IC quasi-modes characteristic of the magnetic field strength near the LFS separatrix. These data, supported by growth rate calculations, point to the importance of the LFS scrape-off layer (SOL) density in determining PDI onset and degradation in current drive efficiency. By minimizing the SOL density it is possible to extend the core density regime over which PDI can be avoided, thus potentially maximizing the effectiveness of LHCD at high density. Increased current drive efficiency at high density has been achieved in FTU and EAST through lithium coating and special fuelling methods, and in recent C-Mod experiments by operating at higher plasma current. Another approach would be to locate the launcher in the inner wall with double null operation. This would reduce the SOL density by an order of magnitude or more and greatly mitigate the effects of PDI as well as other parasitic losses., United States. Department of Energy (DE-FC02-99ER54512)
- Published
- 2015
14. Core impurity transport in Alcator C-Mod L-, I- and H-mode plasmas
- Author
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Martin Greenwald, Robert Mumgaard, Amanda Hubbard, S.M. Wolfe, S.J. Wukitch, J.L. Terry, Anne White, Nathan Howard, L. F. Delgado-Aparicio, C. Gao, Earl Marmar, D.G. Whyte, J. H. Irby, M. Chilenski, Yu-Ming Lin, S. D. Scott, Jerry Hughes, J.R. Walk, John Rice, Matthew Reinke, Robert Granetz, Massachusetts Institute of Technology. Department of Physics, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Whyte Dennis, Rice, John E, Gao, Chi, Howard, Nathaniel Thomas, Chilenski, Mark Alan, Granetz, Robert S, Greenwald, Martin J, Hubbard, Amanda E, Hughes Jr, Jerry, Irby, James Henderson, Lin, Yijun, Marmar, Earl S, Mumgaard, Robert Thomas, Terry, James L, Walk Jr, John R, White, Anne E., Whyte, Dennis G, Wolfe, Stephen M, and Wukitch, Stephen James
- Subjects
Convection ,Nuclear and High Energy Physics ,Materials science ,Cyclotron ,Plasma ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,law.invention ,Ion ,Amplitude ,Alcator C-Mod ,law ,Impurity ,Physics::Plasma Physics ,Electron temperature ,Atomic physics - Abstract
Core impurity transport has been investigated for a variety of confinement regimes in Alcator C-Mod plasmas from x-ray emission following injection of medium and high Z materials. In ohmic L-mode discharges, impurity transport is anomalous (D[subscript eff] ≫ D[subscript nc]) and changes very little across the LOC/SOC boundary. In ion cyclotron range of frequencies (ICRF) heated L-mode plasmas, the core impurity confinement time decreases with increasing ICRF input power (and subsequent increasing electron temperature) and increases with plasma current. Nearly identical impurity confinement characteristics are observed in I-mode plasmas. In enhanced D[subscript α] H-mode discharges the core impurity confinement times are much longer. There is a strong connection between core impurity confinement time and the edge density gradient across all confinement regimes studied here. Deduced central impurity density profiles in stationary plasmas are generally flat, in spite of large amplitude sawtooth oscillations, and there is little evidence of impurity convection inside of r/a = 0.3 when averaged over sawteeth., United States. Department of Energy (Contract DE-FC02-99ER54512), United States. Dept. of Energy. Fusion Energy Postdoctoral Research Program (Oak Ridge Institute for Science and Education)
- Published
- 2014
15. Demountable Toroidal Field Magnets for Use in a Compact Modular Fusion Reactor
- Author
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D.G. Whyte, Leslie Bromberg, F. J. Mangiarotti, J. Goh, Makoto Takayasu, Joseph Minervini, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Mangiarotti, Franco Julio, Goh, Jonathan Yanming, Takayasu, Makoto, Bromberg, Leslie, Minervini, Joseph V, and Whyte, Dennis G
- Subjects
History ,Engineering ,Resistive touchscreen ,Tokamak ,business.industry ,Nuclear engineering ,Contact resistance ,Electrical engineering ,Fusion power ,Computer Science Applications ,Education ,law.invention ,Magnetic field ,Subcooling ,law ,Magnet ,business ,Electrical conductor - Abstract
A concept of demountable toroidal field magnets for a compact fusion reactor is discussed. The magnets generate a magnetic field of 9.2 T on axis, in a 3.3 m major radius tokamak. Subcooled YBCO conductors have a critical current density adequate to provide this large magnetic field, while operating at 20 K reduces thermodynamic cooling cost of the resistive electrical joints. Demountable magnets allow for vertical replacement and maintenance of internal components, potentially reducing cost and time of maintenance when compared to traditional sector maintenance. Preliminary measurements of contact resistance of a demountable YBCO electrical joint between are presented.
- Published
- 2013
16. Tungsten nano-tendril growth in the Alcator C-Mod divertor
- Author
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D. G. Whyte, Bruce Lipschultz, M.J. Baldwin, Brian LaBombard, Dan Brunner, J.L. Terry, G.M. Wright, R.P. Doerner, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Wright, Graham, Brunner, Daniel Frederic, Labombard, Brian, Lipschultz, Bruce, Terry, James L., and Whyte, Dennis G.
- Subjects
Nuclear and High Energy Physics ,Materials science ,Tokamak ,Divertor ,chemistry.chemical_element ,Plasma ,Tungsten ,Condensed Matter Physics ,law.invention ,symbols.namesake ,Alcator C-Mod ,chemistry ,law ,Nano ,symbols ,Langmuir probe ,Atomic physics ,Helium - Abstract
Growth of tungsten nano-tendrils ('fuzz') has been observed for the first time in the divertor region of a high-power density tokamak experiment. After 14 consecutive helium L-mode discharges in Alcator C-Mod, the tip of a tungsten Langmuir probe at the outer strike point was fully covered with a layer of nano-tendrils. The thickness of the individual nano-tendrils (50–100 nm) and the depth of the layer (600 ± 150 nm) are consistent with observations from experiments on linear plasma devices. The observation of tungsten fuzz in a tokamak may have important implications for material erosion, dust formation, divertor lifetime and tokamak operations in next-step devices., National Science Foundation (U.S.) (Award DMR-08-19762), United States. Dept. of Energy (Award DE-SC00-02060), United States. Dept. of Energy (Contract DE-FC02-99ER54512)
- Published
- 2011
17. Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak
- Author
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D.G. Whyte, T. L. Rhodes, K. H. Burrell, Amanda Hubbard, Miklos Porkolab, D.R. Ernst, T.H. Osborne, Alessandro Marinoni, Anne White, J.C. Rost, E. M. Davis, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Department of Physics, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Whyte, Dennis, Marinoni, Alessandro, Rost, Jon C, Porkolab, Miklos, Hubbard, Amanda E, Osborne, Thomas, White, Anne E., Whyte, Dennis G, Davis, Emily, Ernst, Darin R, and White, Anne
- Subjects
Nuclear physics ,Physics ,Nuclear and High Energy Physics ,Tokamak ,DIII-D ,Physics::Plasma Physics ,law ,Statistical physics ,Fusion power ,Condensed Matter Physics ,Energy (signal processing) ,law.invention ,Characterization (materials science) - Abstract
The I-mode regime, routinely observed on the Alcator C-Mod tokamak, is characterized by an edge energy transport barrier without an accompanying particle barrier and with broadband instabilities, known as weakly coherent modes (WCM), believed to regulate particle transport at the edge. Recent experiments on the DIII-D tokamak exhibit I-mode characteristics in various physical quantities. These DIII-D plasmas evolve over long periods, lasting several energy confinement times, during which the edge electron temperature slowly evolves towards an H-mode-like profile, while maintaining a typical L-mode edge density profile. During these periods, referred to as I-mode phases, the radial electric field at the edge also gradually reaches values typically observed in H-mode. Density fluctuations measured with the phase contrast imaging diagnostic during I-mode phases exhibit three features typically observed in H-mode on DIII-D, although they develop progressively with time and without a sharp transition: the intensity of the fluctuations is reduced; the frequency spectrum is broadened and becomes non-monotonic; two dimensional space-time spectra appear to approach those in H-mode, showing phase velocities of density fluctuations at the edge increasing to about 10 km s−1. However, in DIII-D there is no clear evidence of the WCM. Preliminary linear gyro-kinetic simulations are performed in the pedestal region with the GS2 code and its recently upgraded model collision operator that conserves particles, energy and momentum. The increased bootstrap current and flow shear generated by the temperature pedestal are shown to decrease growth rates, thus possibly generating a feedback mechanism that progressively stabilizes fluctuations., United States. Department of Energy. Office of Fusion Energy Sciences (Award DE-FG02- 94ER54235), United States. Department of Energy. Office of Fusion Energy Sciences (Award DE-FG02-94ER54084), United States. Department of Energy. Office of Fusion Energy Sciences (Award DE-FG02-08ER54984), United States. Department of Energy. Office of Fusion Energy Sciences (Award DE-FC02-04ER54698)
- Published
- 2015
18. Lower hybrid current drive at high density in Alcator C-Mod
- Author
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S. Shiraiwa, Ian Faust, Amanda Hubbard, R.R. Parker, Stephen Wukitch, Gregory Wallace, R. W. Harvey, James R. Wilson, Brian LaBombard, D.G. Whyte, Jerry Hughes, Andrea Schmidt, John Wright, Alexander Smirnov, Orso Meneghini, Paul Bonoli, Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology. Plasma Science and Fusion Center, Wallace, Gregory Marriner, Hubbard, Amanda E., Bonoli, Paul T., Faust, Ian Charles, Hughes, Jerry W., Labombard, Brian, Meneghini, Orso-Maria Cornelio, Parker, Ronald R., Schmidt, A. E., Shiraiwa, Shunichi, Whyte, Dennis G., Wright, John C., and Wukitch, Stephen James
- Subjects
Physics ,Nuclear and High Energy Physics ,education.field_of_study ,Tokamak ,Population ,Bremsstrahlung ,Electron ,Plasma ,Condensed Matter Physics ,law.invention ,Alcator C-Mod ,law ,Electron temperature ,Atomic physics ,Absorption (electromagnetic radiation) ,education - Abstract
Experimental observations of lower hybrid current drive (LHCD) at high density on the Alcator C-Mod tokamak are presented in this paper. Bremsstrahlung emission from relativistic fast electrons in the core plasma drops suddenly above line-averaged densities of 10[superscript 20] m[superscript −3] (ω/ω[subscript LH] ~ 3) in single null discharges with large (≥8 mm) inner gaps, well below the density limit previously observed on limited tokamaks (ω/ω[subscript LH] ~ 2). Modelling and experimental evidence suggest that the absence of LHCD driven fast electrons at high density may be due to parasitic collisional absorption in the scrape-off layer (SOL). Experiments show that the population of fast electrons produced by LHCD at high density ([bar over n][subscript e] > 10[superscript 20] m[superscript -3]) can be increased by operating with an inner gap of less than ~5 mm with the strongest non-thermal emission in inner wall limited plasmas. A change in plasma topology from single to double null produces a modest increase in non-thermal emission at high density. Increasing the electron temperature in the periphery of the plasma (0.8 > r/a > 1.0) also results in a modest increase in non-thermal electron emission above the density limit. Ray tracing/Fokker–Planck simulations of these discharges predict the observed sensitivity to plasma position when the effects of collisional absorption in the SOL are included in the model., United States. Dept. of Energy (Award DE-FC02-99ER54512), United States. Dept. of Energy (Award DE-AC02-76CH03073)
- Published
- 2011
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