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Journal Articles

Free boundary equilibrium in 3D tokamaks with toroidal rotation

Cooper, W. A.*; Brunetti, D.*; Faustin, J. M.*; Graves, J. P.*; Pfefferl$'e$, D.*; Raghunathan, M.*; Sauter, O.*; Tran, T. M.*; Chapman, I. T.*; Ham, C. J.*; et al.

Nuclear Fusion, 55(6), p.063032_1 - 063032_8, 2015/05

 Times Cited Count:1 Percentile:5.26(Physics, Fluids & Plasmas)

An approximate model for a single fluid 3D MHD equilibrium with pure isothermal toroidal flow with imposed nested magnetic flux surfaces is proposed. It recovers the rigorous toroidal rotation equilibrium description in the axisymmetric limit. The approximation is valid under conditions of nearly rigid or vanishing toroidal rotation in regions with 3D deformation of the equilibrium flux surfaces. Bifurcated helical core equilibrium simulations of long-lived modes in the MAST device demonstrate that the magnetic structure is only weakly affected by the flow but that the 3D pressure distortion is important. The pressure is displaced away from the major axis and therefore is not as noticeably helically deformed as the toroidal magnetic flux under the subsonic flow conditions. Fast particle confinement is investigated with the VENUS code. In the presence of toroidal flow, the drift orbit equations depend on the electrostatic potential associated with the rotation and quasineutrality at lowest order in Larmor radius. When the equilibrium has 3D deformations, geometrical terms appear from the evaluation of Ohm's Law that considerably complicates the description of fast particle confinement.

Journal Articles

An Approximate single fluid 3-dimensional magnetohydrodynamic equilibrium model with toroidal flow

Cooper, W. A.*; Hirshman, S. P.*; Chapman, I. T.*; Brunetti, D.*; Faustin, J. M.*; Graves, J. P.*; Pfefferl$'e$, D.*; Raghunathan, M.*; Sauter, O.*; Tran, T. M.*; et al.

Plasma Physics and Controlled Fusion, 56(9), p.094004_1 - 094004_8, 2014/09

 Times Cited Count:4 Percentile:22.69(Physics, Fluids & Plasmas)

An approximate model for a single fluid three-dimensional (3D) magnetohydrodynamic (MHD) equilibrium with pure isothermal toroidal flow with imposed nested magnetic flux surfaces is proposed. It recovers the rigorous toroidal rotation equilibrium description in the axisymmetric limit. The approximation is valid under conditions of nearly rigid or vanishing toroidal rotation in regions with significant 3D deformation of the equilibrium flux surfaces. Bifurcated helical core equilibrium simulations of long-lived modes in the MAST device demonstrate that the magnetic structure is only weakly affected by the flow but that the 3D pressure distortion is important. The pressure is displaced away from the major axis and therefore is not as noticeably helically deformed as the toroidal magnetic flux under the subsonic flow conditions measured in the experiment.

Journal Articles

Poly(ethylene-co-tetrafluoroethylene) (ETFE)-based graft-type polymer electrolyte membranes with different ion exchange capacities; Relative humidity dependence for fuel cell applications

Tran, D. T.; Sawada, Shinichi; Hasegawa, Shin; Katsumura, Yosuke*; Maekawa, Yasunari

Journal of Membrane Science, 447, p.19 - 25, 2013/11

 Times Cited Count:25 Percentile:68.19(Engineering, Chemical)

Relative humidity (RH) dependence of the proton conduction and mechanical properties of poly(ethylene-co-tetrafluoroethylene) (ETFE)-based radiation grafted polymer electrolyte membranes (PEMs) were investigated in a wide ion exchange capacity (IEC) range at 80 $$^{circ}$$C. The proton conductivities of the ETFE-based PEMs for IECs of 1.3-2.9 mmol/g were 0.001-0.013 S/cm at 30% RH. These PEMs have conductivities that are less dependent on RH than aromatic-hydrocarbon-polymer based PEMs. The ETFE PEM (IEC $$<$$ 2.4 mmol/g) showed higher tensile strength than Nafion at 100% RH. It was revealed that the mechanical strength and proton conductivity were clearly related to PEM crystallinities.

Journal Articles

Actuator and diagnostic requirements of the ITER plasma control system

Snipes, J. A.*; Beltran, D.*; Casper, T.*; Gribov, Y.*; Isayama, Akihiko; Lister, J.*; Simrock, S.*; Vayakis, G.*; Winter, A.*; Yang, Y.*; et al.

Fusion Engineering and Design, 87(12), p.1900 - 1906, 2012/12

 Times Cited Count:22 Percentile:85.65(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Global nonlinear electromagnetic simulations of tokamak turbulence

Bottino, A.*; Scott, B. D.*; Brunner, S.*; McMillan, B. F.*; Tran, T. M.*; Vernay, T.*; Villard, L.*; Jolliet, S.; Hatzky, R.*; Peeters, A. G.*

IEEE Transactions on Plasma Science, 38(9), p.2129 - 2135, 2010/09

 Times Cited Count:24 Percentile:69.72(Physics, Fluids & Plasmas)

Journal Articles

Design of electron cyclotron heating and current drive system of ITER

Kobayashi, Noriyuki; Bigelow, T.*; Bonicelli, T.*; Cirant, S.*; Denisov, G.*; Heidinger, R.*; Henderson, M.*; Hogge, J.-P.*; Piosczyk, B.*; Ramponi, G.*; et al.

AIP Conference Proceedings 933, p.413 - 416, 2007/10

Since the EDA 2001, Design of Electron Cyclotron Heating and Current Drive (ECH&CD) System have been modified due to progress of physics understanding and change of interface. Nominal RF power 20 MW is injected by four upper launchers or one equatorial launcher. RF beams are steered by a front steering mirror. DCHV power supply will be composed of IGBT pulse step modulators because of high frequency modulation and design flexibility to three different types of 170 GHz gyrotrons from three parties. The RF power is transmitted by 63.5 mm dia corrugated waveguide and switched by a waveguide switch between the upper launcher and the equatorial launcher. A start-up system for initial discharge is composed of three 127.5 GHz gyrotrons and dedicated DCHV power supply. Three of transmission lines are shared between 170 GHz and 127.5 GHz gyrotrons to inject start-up RF beam through the equatorial launcher. R&Ds for high power long pulse have been on-going to obtain a reliable ITER ECH&CD system.

Oral presentation

Characterization of defects by the Helium and Hydrogen implantation using a slow positron beam

Maekawa, Masaki; Kawasuso, Atsuo; Tran, D. T.*

no journal, , 

The irradiation defect and induced structure which are formed by helium ion irradiation into silicon were observed by the positron annihilation method. The positron trapping to the helium bubbles has not been confirmed. Helium ions were implanted to the silicon (irradiation dose: 2$$times$$10$$^{17}$$/cm$$^2$$ at room temperature) with the energy of 50$$sim$$200 keV. The peak intensities of annihilation $$gamma$$ rays (S parameter) and its annealing behaviors were measured. S parameter decreased after 300 $$^{circ}$$C annealing. This means that positrons are trapped to the irradiation defects filled up with the helium atoms. S parameter slightly increased rapidly at 900 $$^{circ}$$C. This caused by the growth of helium bubbles and subsequent desorption of helium atoms. From the comparison with the experimental result and first principle calculation, positrons are trapped at the defect cluster of approximately 1 nm filled up with 36 helium atoms, which is considered the helium bubble.

Oral presentation

Structural analysis of ETFE-based graft-type polymer electrolyte membranes by small angle X-ray / neutron scattering method

Tran, D. T.; Sawada, Shinichi; Hasegawa, Shin; Putra, A.; Yamaguchi, Daisuke; Oba, Yojiro*; Koizumi, Satoshi; Onuma, Masato*; Maekawa, Yasunari; Katsumura, Yosuke*

no journal, , 

We investigated the structure of the ethylene-co-tetrafluoroethylene (ETFE) based radiation-grafted polymer electrolyte membranes (PEMs) by the small-angle X-ray scattering (SAXS) method. From SAXS profile for the base ETFE film, a lamellar structure with spacing of 23 nm was observed. For the styrene-grafted film and PEM, the lamellar spacing measured by SAXS profiles were 30 and 33 nm, respectively. This can be explained by that the grafted regions were introduced into the amorphous phases in the lamellar structures, thereby extending the lamellar spacing.

Oral presentation

Analysis of hierarchical structure of ETFE-based graft-type polymer electrolyte membranes by small angle X-ray scattering

Tran, D. T.; Sawada, Shinichi; Hasegawa, Shin; Oba, Yojiro*; Onuma, Masato*; Katsumura, Yosuke*; Maekawa, Yasunari

no journal, , 

We investigated the hierarchical structures of poly(ethylene-co-tetrafluoroethylene) (ETFE) based polymer electrolyte membranes (ETFE-PEMs) by comparison with those of precursor original ETFE and styrene-grafted (grafted ETFE) films using small-angle X-ray scattering (SAXS). The ETFE substrate has a lamellar structure with d-spacing of 23.1 nm, while grafted ETFE and ETFE-PEMs showed shoulder peaks at lower Q values, corresponding to d-spacing of 32.7 and 36.1 nm. The grafted ETFE and ETFE-PEM showed new peaks at larger Q value regions, corresponding to d-spacing of 0.94 and 1.48 nm, respectively. These peaks should be ascribed to internal structures of grafted polymers and ion channels.

Oral presentation

Hierarchical structure / property analysis of ETFE-based graft-type polymer electrolyte membranes

Tran, D. T.; Sawada, Shinichi; Hasegawa, Shin; Yoshimura, Kimio; Oba, Yojiro*; Onuma, Masato*; Katsumura, Yosuke*; Maekawa, Yasunari

no journal, , 

Fundamental understanding of the structure-property relationship of PEM is prerequisite for proper material design to improve PEM performance. In this work, we studied hierarchical structures of ETFE-based graft-type polymer electrolyte membranes using small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), and field emission scanning electron microscopy (FE-SEM). Then the relationship between hierarchical structures and fuel cell properties of ETFE-PEM was explained. The membrane possesses a shoulder peak at low q range with d-spacing of 36.1 nm and new peak at high q range with d-spacing of 1.48 nm. Such peaks should be originated from lamellar structure and correlation distance of the sulfo groups in poly(styrene sulfonic acid) grafts, respectively. In FE-SEM images, the clear phase separation between hydrophobic and hydrophilic domains was observed.

Oral presentation

Hierarchical structure analysis of poly(ethylene-co-tetraflouroethylene)-based graft-type polymer electrolyte membranes by small angle X-ray scattering

Tran, D. T.; Sawada, Shinichi; Hasegawa, Shin; Yoshimura, Kimio; Oba, Yojiro*; Onuma, Masato*; Katsumura, Yosuke*; Maekawa, Yasunari

no journal, , 

Fundamental understanding of the structure-property relationship of PEM is prerequisite for a material design satisfying PEM performance requirement. Therefore, the hierarchical structures of ETFE-PEMs were characterized using wide q observation in small angle X-ray scattering (SAXS) by comparing those of precursor original ETFE and polystyrene-grafted film (grafted ETFE). ETFE-PEM possesses three distinct structures: (1) Graft polymer domains with d-spacing of 390 nm, which should act as ion conducting layer; (2) Lamellar structures with d-spacing of 29 nm; (3) An inner structure of graft domains with d-spacing of 1.5 nm correspond to correlation distances of sulfonic acid group. The ion-conducting layers and lamellar structures with d-spacing of 390 nm and 29 nm in ETFE-PEM can be confirmed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM), respectively.

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