Dependence of pedestal structure on collisionality at fixed beta in JT-60U

Urano, Hajime; Aiba, Nobuyuki; Kamiya, Kensaku; Kamada, Yutaka; JT-60 Team

Nuclear Fusion, 56(1), p.016005_1 - 016005_8, 2016/01

https://doi.org/10.1088/0029-5515/56/1/016005

Dependence of pedestal structure on collisionality at fixed beta has been investigated in JT-60U. In the ITER-relevant low collisionality regime, the pedestal width does not change with edge collisionality. In the high collisionality regime, the pedestal width broadens with increased edge collisionality. The pedestal pressure gradient and width are not significantly changed when the pedestal is close to an intermediate peeling-ballooning mode boundary at low collisionality. The experimental result indicates that conventional pedestal models where the pedestal width is independent of collisionality and is determined by at the pedestal is not a bad assumption in the ITER-relevant low collisionality regime. On the other hand, the pressure gradient decreases and the pedestal width increases at high collisionality. The pedestal broadening becomes significant when the pedestal is marginal to be unstable at high ballooning mode in high collisionality regime.

Development of operation scenarios for plasma breakdown and current ramp-up phases in JT-60SA tokamak

Urano, Hajime; Fujita, Takaaki*; Ide, Shunsuke; Miyata, Yoshiaki; Matsunaga, Go; Matsukawa, Makoto

Fusion Engineering and Design, 100, p.345 - 356, 2015/11

https://doi.org/10.1016/j.fusengdes.2015.06.138

The operation scenarios for plasma breakdown and current ramp-up phases in JT-60SA tokamak have been developed. The induced current in the in-vessel conducting elements such as vacuum vessel and stabilizing plate increases to the comparable level of plasma current of 600 kA during the breakdown phase and thus enhances the strength of error field. The optimized scenarios for half and full pre-magnetization cases satisfied the conditions required for the plasma initiation. At the initial plasma, the vertical magnetic field required to sustain the plasma position was controlled by the outer equilibrium field (EF) coil currents which compensate for a vertical field due to a large eddy current. The condition for the formation of divertor configurations given by the combination of the magnetic flux for plasma and the plasma current enables us to develop the operational scenarios with a smooth transition from a limiter to a divertor configuration.

Effects of toroidal rotation shear and magnetic shear on thermal and particle transport in plasmas with electron cyclotron heating on JT-60U

Yoshida, Maiko; Honda, Mitsuru; Narita, Emi*; Hayashi, Nobuhiko; Urano, Hajime; Nakata, Motoki; Miyato, Naoaki; Takenaga, Hidenobu; Ide, Shunsuke; Kamada, Yutaka

Nuclear Fusion, 55(7), p.073014_1 - 073014_9, 2015/07

https://doi.org/10.1088/0029-5515/55/7/073014

Conditions without the increases in the thermal and particle transport with ECH have been experimentally investigated in positive magnetic shear (PS), weak magnetic shear (WS) and reversed magnetic shear (RS) plasmas with internal transport barriers (ITBs) on JT-60U. The ion heat diffusivity around an internal transport barrier in the ion temperature (-ITB) remains constant with ECH when a large negative toroidal rotation shear is formed before the ECH. The condition does not depend on the electron to ion temperature ratio (/) and ECH power. The electron heat diffusivity around a -ITB stays constant with ECH when the magnetic shear is negative around the Te-ITB region. Effective particle transport remains constant or reduces during ECH under the condition of negative magnetic shear.

Assessment of the accuracy of plasma shape reconstruction by the Cauchy condition surface method in JT-60SA

Miyata, Yoshiaki; Suzuki, Takahiro; Takechi, Manabu; Urano, Hajime; Ide, Shunsuke

Review of Scientific Instruments, 86(7), p.073511_1 - 073511_13, 2015/07

https://doi.org/10.1063/1.4926997

It is essential for a stable plasma equilibrium control to reconstruct an accurate plasma boundary in tokamak devices. Cauchy Condition Surface (CCS) method is a numerical approach to calculate the spatial distribution of the magnetic flux outside a hypothetical plasma surface and reconstruct the plasma boundary from the magnetic measurements located outside the plasma. It is found that the optimum number of unknown parameters and shape of the CCS for minimizing errors in the reconstructed plasma shape increase in proportion to the plasma size. It is shown that the accuracy of the plasma shape reconstruction greatly improves by using the optimum number of unknown parameters. The assessment of accuracy of plasma shape reconstruction by CCS method in JT-60SA is reported.

Dependence of pedestal structure on collisionality in JT-60U

Urano, Hajime; Aiba, Nobuyuki; Kamiya, Kensaku; Kamada, Yutaka; JT-60 Team

Europhysics Conference Abstracts (Internet), 39E, p.P5.146_1 - P5.146_4, 2015/06

http://ocs.ciemat.es/EPS2015PAP/pdf/P5.146.pdf

no abstracts in English

Progress at JET in integrating ITER-relevant core and edge plasmas within the constraints of an ITER-like wall

Giroud, C.*; Jachmich, S.*; Jacquet, P.*; Jrvinen, A.*; Lerche, E.*; Rimini, F.*; Aho-Mantila, L.*; Aiba, Nobuyuki; Balboa, I.*; Belo, P.*; et al.

Plasma Physics and Controlled Fusion, 57(3), p.035004_1 - 035004_20, 2015/03

https://doi.org/10.1088/0741-3335/57/3/035004

This paper reports the progress made at JET-ILW on integrating the requirements of the reference ITER baseline scenario with normalized confinement factor of 1, at a normalized pressure of 1.8 together with partially detached divertor whilst maintaining these conditions over many energy confinement times. The 2.5 MA high triangularity ELMy H-modes are studied with two different divertor configurations with D-gas injection and nitrogen seeding. The power load reduction with N seeding is reported. The relationship between an increase in energy confinement and pedestal pressure with triangularity is investigated. The operational space of both plasma configurations is studied together with the ELM energy losses and stability of the pedestal of unseeded and seeded plasmas.

The Experiments with tungsten divertor in tokamak devices

Urano, Hajime

Purazuma, Kaku Yugo Gakkai-Shi, 91(3), p.183 - 190, 2015/03

http://ci.nii.ac.jp/naid/110009930915

The experiments with tungsten divertor in tokamak devices are described in this article.

Boundary condition for toroidal plasma flow imposed at the separatrix in high confinement JT-60U plasmas with edge localized modes and the physics process in pedestal structure formation

Kamiya, Kensaku; Honda, Mitsuru; Urano, Hajime; Yoshida, Maiko; Kamada, Yutaka; Ito, Kimitaka*; JT-60 Team

Physics of Plasmas, 21(12), p.122517_1 - 122517_8, 2014/12

https://doi.org/10.1063/1.4904815

Modulation Charge eXchange Recombination Spectroscopy (MCXRS) measurements with high spatial and temporal resolution have made the evaluation of the toroidal plasma flow of fully stripped carbon impurity ions in the JT-60U tokamak peripheral region (including in particular separatrix) possible with a better signal-to-noise ratio. Boundary condition of Vt imposed at the separatrix in ELMy H-mode plasmas has been identified, comparing between co- and counter-NBI discharges. The Vt value at the separatrix is not held fixed at the zero, varying with momentum input direction, but being not strongly affected by the ELM event. A non-zero Vt value at the separatrix might be connected to fast ion losses due to toroidal field ripple that results in formation of a negative radial electric field (Er) layer having almost zero (or very weak positive) Er-shear value at the separatrix. Improved understanding of physics process in pedestal structure formation for the Vt and Er is also discussed.

Experimental analyses and predictive simulations of toroidal rotation driven by the neoclassical toroidal viscosity in rippled tokamaks

Honda, Mitsuru; Satake, Shinsuke*; Suzuki, Yasuhiro*; Matsunaga, Go; Shinohara, Koji; Yoshida, Maiko; Matsuyama, Akinobu; Ide, Shunsuke; Urano, Hajime

Nuclear Fusion, 54(11), p.114005_1 - 114005_14, 2014/11

https://doi.org/10.1088/0029-5515/54/11/114005

Impact of plasma core profiles on MHD stability at tokamak edge pedestal

Aiba, Nobuyuki; Urano, Hajime

Nuclear Fusion, 54(11), p.114007_1 - 114007_9, 2014/11

https://doi.org/10.1088/0029-5515/54/11/114007

no abstracts in English