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Journal Articles

Edge pedestal characteristics in JET and JT-60U tokamaks under variable toroidal field ripple

Urano, Hajime; Saibene, G.*; Oyama, Naoyuki; Parail, V.*; de Vries, P.*; Sartori, R.*; Kamada, Yutaka; Kamiya, Kensaku; Loarte, A.*; L$"o$nnroth, J.*; et al.

Nuclear Fusion, 51(11), p.113004_1 - 113004_10, 2011/11

 Times Cited Count:7 Percentile:64.01(Physics, Fluids & Plasmas)

The effect of TF ripple on the edge pedestal characteristics are examined in JET and JT-60U. By the installation of ferritic inserts, TF ripple was reduced from $$1%$$ to $$0.6%$$ in JT-60U. In JET, TF ripple was varied from $$0.1%$$ to $$1%$$ by feeding different currents to TF coils. The pedestal pressure was similar with reduced ripple in JT-60U. In JET, no clear difference of the pedestal characteristics was also observed. The edge toroidal rotation clearly decreased in counter direction by increased TF ripple. However, in JT-60U, the ELM frequency decreased by $$sim 20%$$ and the increased ELM loss power by $$30%$$ with reduced ripple. In JET, ELM frequency increases only slightly with increased TF ripple. From this inter-machine experiment, TF ripple less than $$1%$$ does not strongly affect the pedestal pressure. The effect of TF ripple on pedestal characteristics at lower collisionality close to ITER should be investigated as a next step study.

Journal Articles

ITER test blanket module error field simulation experiments at DIII-D

Schaffer, M. J.*; Snipes, J. A.*; Gohil, P.*; de Vries, P.*; Evans, T. E.*; Fenstermacher, M. E.*; Gao, X.*; Garofalo, A. M.*; Gates, D. A.*; Greenfield, C. M.*; et al.

Nuclear Fusion, 51(10), p.103028_1 - 103028_11, 2011/10

 Times Cited Count:32 Percentile:15.51(Physics, Fluids & Plasmas)

Experiments at DIII-D investigated the effects of ferromagnetic error fields similar to those expected from proposed ITER Test Blanket Modules (TBMs). Studied were effects on: plasma rotation and locking; confinement; L-H transition; edge localized mode (ELM) suppression by resonant magnetic perturbations; ELMs and the H-mode pedestal; energetic particle losses; and more. The experiments used a 3-coil mock-up of 2 magnetized ITER TBMs in one ITER equatorial port. The experiments did not reveal any effect likely to preclude ITER operations with a TBM-like error field. The largest effect was slowed plasma toroidal rotation v across the entire radial profile by as much as $$Delta v/v_{0} sim 50%$$ via non-resonant braking. Changes to global $$Delta n/n_{0}$$, $$Delta v/v_{0}$$ and $$Delta H_{98}/H_{98,0}$$ were $$sim$$3 times smaller. These effects are stronger at higher $$beta$$ and lower $$v_{0}$$. Other effects were smaller.

Journal Articles

Overview of toroidal momentum transport

Peeters, A. G.*; Angioni, C.*; Bortolon, A.*; Camenen, Y.*; Casson, F. J.*; Duval, B.*; Fiederspiel, L.*; Hornsby, W. A.*; Idomura, Yasuhiro; Hein T.*; et al.

Nuclear Fusion, 51(9), p.094027_1 - 094027_13, 2011/09

 Times Cited Count:85 Percentile:2.11(Physics, Fluids & Plasmas)

Journal Articles

Core transport properties in JT-60U and JET identity plasmas

Litaudon, X.*; Sakamoto, Yoshiteru; de Vries, P. C.*; Salmi, A.*; Tala, T.*; Angioni, C.*; Benkadda, S.*; Beurskens, M. N. A.*; Bourdelle, C.*; Brix, M.*; et al.

Nuclear Fusion, 51(7), p.073020_1 - 073020_13, 2011/07

 Times Cited Count:8 Percentile:59.68(Physics, Fluids & Plasmas)

A variety of triggering mechanisms and structures of internal transport barrier (ITB) has been observed in various devices or depending on operation scenarios. Thus identity experiments on ITB in JT-60U and JET have been performed to shed light on the physics behind ITBs. Because of their similar size, the dimensionless parameters between both devices are the same. These experiments were performed with near identical magnetic configurations, heating waveforms and normalized quantities such as safety factor, magnetic shear, normalized Larmor radius, normalized collision frequency, beta, temperatures ratio. Similarities of the ITB triggering mechanism and the ITB strength have been observed when a proper match is achieved of the most relevant profiles of the normalized quantities. This paper will report on the detail comparison of transport properties of ITBs obtained in these JET/JT-60U identity experiments.

Journal Articles

Overview of anomalous toroidal momentum transport

Peeters, A. G.*; Angioni, C.*; Bortolon, A.*; Camenen, Y.*; Casson, F. J.*; Dubal, B.*; Fiederspiel, L.*; Hornsby, W. A.*; Idomura, Yasuhiro; Kluy, N.*; et al.

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 13 Pages, 2011/03

Journal Articles

Effect of toroidal field ripple on plasma rotation in JET

de Vries, P. C.*; Salmi, A.*; Parail, V.*; Giroud, C.*; Andrew, Y.*; Biewer, T. M.*; Cromb$'e$, K.*; Jenkins, I.*; Johnson, T.*; Kiptily, V.*; et al.

Nuclear Fusion, 48(3), p.035007_1 - 035007_6, 2008/03

 Times Cited Count:45 Percentile:11.5(Physics, Fluids & Plasmas)

Dedicated experiments on TF ripple effects on the performance of tokamak plasmas have been carried out at JET. The TF ripple was found to have a profound effect on the plasma rotation. The central Mach number, M, defined as the ratio of the rotation velocity and the thermal velocity, was found to drop as a function of TF ripple amplitude from an average value of M = 0.40-0.55 for operations at the standard JET ripple of 0.08% to M = 0.25-0.40 for 0.5% ripple and M = 0.1-0.3 for 1% ripple. With standard co-current injection of neutral beam injection (NBI), plasmas were found to rotate in the co-current direction. However, for higher TF ripple amplitudes ($$sim1%$$) an area of counter rotation developed at the edge of the plasma, while the core kept its co-rotation.

Journal Articles

Effect of toroidal field ripple and toroidal rotation on H-mode performance and ELM characteristics in JET/JT-60U similarity experiments

Oyama, Naoyuki; Saibene, G.*; Kamada, Yutaka; Kamiya, Kensaku; Loarte, A.*; L$"o$nnroth, J.*; Parail, V.*; Sakamoto, Yoshiteru; Salmi, A.*; Sartori, R.*; et al.

Journal of Physics; Conference Series, 123, p.012015_1 - 012015_13, 2008/00

 Times Cited Count:8 Percentile:8.57

The effect of the toroidal field ripple and the edge toroidal rotation on H-mode and pedestal performance as well as ELM characteristics are investigated both in JET and JT-60U. In JT-60U, the amplitude of TF ripple was reduced from 1.2 % to 0.5 % after the installation of ferritic steel tiles. In JET, the ripple amplitude can actively be varied. In both devices, edge rotation in the same direction to the plasma current was reduced with increasing the ripple amplitude. Even at the same amplitude of 0.5 %, the achievable edge rotation in JT-60U was still lower than that in JET. A series of power and density scans performed at several ripple amplitude indicated that plasmas with smaller ripple amplitude and/or larger co-rotation are favorable to achieve higher pedestal pressure and plasma confinement in both devices. As for ELM characteristics, larger co-rotation seems to increase the ELM energy loss together with the reduction of the ELM frequency.

Journal Articles

Effects of ripple-induced ion thermal transport on H-mode plasma performance

L$"o$nnroth, J.-S.*; Parail, V.*; Hyn$"o$nen, V.*; Johnson, T.*; Kiviniemi, T.*; Oyama, Naoyuki; Beurskens, M.*; Howell, D.*; Saibene, G.*; de Vries, P.*; et al.

Plasma Physics and Controlled Fusion, 49(3), p.273 - 295, 2007/03

 Times Cited Count:12 Percentile:55.27(Physics, Fluids & Plasmas)

It is investigated whether differences in the MHD stability of the pedestal, including effects of plasma rotation and aspect ratio, can explain the results of JET/JT-60U similarity experiments. As a result, these mechanisms fail to explain the experimental observations. Therefore, the effects of ripple losses on H-mode performance were investigated. The analysis shows that ripple losses of thermal ions can affect H-mode plasma performance very sensitively. Orbit-following simulations indicate that losses due to diffusive transport give rise to a wide radial distribution of enhanced ion thermal transport, whereas non-diffusive losses have a very edge-localized distribution. In predictive transport simulations with an energy sink term in the continuity equation for the ion pressure representing non-diffusive losses, reduced performance as well as an increase in the ELM frequency are demonstrated.

Journal Articles

Theoretical analysis and predictive modelling of ELMs mitigation by enhanced toroidal ripple and ergodic magnetic field

Parail, V. V.*; Evans, T. E.*; Johnson, T.*; L$"o$nnroth, J.*; Oyama, Naoyuki; Saibene, G.*; Sartori, R.*; Salmi, A.*; de Vries, P.*; Becoulet, M.*; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

Ripple-induced transport and externally driven resonance magnetic perturbations (RMP) near the separatrix are considered as prospective methods of ELM mitigation in present day tokamaks and ITER. Although these methods rely on different physics to generate extra transport, the influence of this transport on plasma dynamics and ELM mitigation is either similar or supplementary. The results of extensive theoretical analysis of the underlying physics processes behind transport induced by ripple and RMP is presented together with predictive transport modelling. Comparison with experiments on present-day tokamaks is given.

Journal Articles

The "Hybrid" scenario in JET; Towards its validation for ITER

Joffrin, E.*; Sips, A. C. C.*; Artaud, J. F.*; Becoulet, A.*; Bertalot, L.*; Budny, R.*; Buratti, P.*; Belo, P.*; Challis, C. D.*; Crisanti, F.*; et al.

Nuclear Fusion, 45(7), p.626 - 634, 2005/07

 Times Cited Count:83 Percentile:6.29(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

The "hybrid" scenario in JET; Towards its validation for ITER

Joffrin, E.*; Sips, A. C. C.*; Artaud, J. F.*; Becoulet, A.*; Budny, R.*; Buratti, P.*; Belo, P.*; Challis, C. D.*; Crisanti, F.*; de Baar, M.*; et al.

Proceedings of 20th IAEA Fusion Energy Conference (FEC 2004) (CD-ROM), 8 Pages, 2004/11

no abstracts in English

Journal Articles

Edge localized mode physics and operational aspects in tokamaks

B$'e$coulet, M.*; Huysmans, G.*; Sarazin, Y.*; Garbet, X.*; Ghendrih, P.*; Rimini, F.*; Joffrin, E.*; Litaudon, X.*; Monier-Garbet, P.*; An$'e$, J.-M.*; et al.

Plasma Physics and Controlled Fusion, 45(12A), p.A93 - A113, 2003/12

 Times Cited Count:83 Percentile:6.96(Physics, Fluids & Plasmas)

no abstracts in English

Oral presentation

Results of the variable toroidal field ripple experiments in JET

Saibene, G.*; McDonald, D. C.*; Beurskens, M.*; Salmi, A.*; Lonnroth, J. S.*; Parail, V.*; de Vries, P.*; Andrew, Y.*; Budny, R.*; Boboc, A.*; et al.

no journal, , 

This paper describes the results of dedicated experiments carried out in JET, where H-mode plasmas properties were studied for varying levels of toroidal field ripple, in the range from 0.08% (natural $$delta$$$$_{rm BT}$$ for JET) up to $${sim}$$1%. The experiments were carried out in the ELMy H-mode regime with q$$_{95}$$ =3 to 3.6, to investigate the effect of $$delta$$$$_{rm BT}$$ on pedestal and core properties of the plasma. These experiments show that toroidal field ripple has a clear effect on H-mode properties, although the physics mechanisms at the root of the reduced energy confinement with $$delta$$$$_{rm BT}$$ have not been identified unambiguously. Plasma density pump out and reduction of the global energy confinement is found for $$delta$$$$_{rm BT}$$ $$sim$$ 0.5%, but the magnitude of this effect depends on plasma parameters. Ripple may also affect pedestal pressure, as well as size and frequency of ELMs. Plasma toroidal rotation was also strongly affected by ripple.

Oral presentation

Results of ITER test blanket module mock-up experiments on DIII-D

Snipes, J. A.*; Schaffer, M. J.*; Gohil, P.*; de Vries, P.*; Fenstermacher, M. E.*; Evans, T. E.*; Gao, X. M.*; Garofalo, A.*; Gates, D. A.*; Greenfield, C. M.*; et al.

no journal, , 

A series of experiments was performed on DIII-D to mock-up the field that will be induced in a pair of ferromagnetic Test Blanket Modules (TBMs) in ITER to determine the effects of such error fields on plasma operation and performance. A set of coils producing both poloidal and toroidal fields was placed inside a re-entrant horizontal port close to the plasma. The coils produce a localized ripple due to the toroidal field (TF) + TBM up to 5.7%, which is more than four times that expected from a pair of representative 1.3 ton TBMs in ITER. The experiments show that the reduction in the toroidal rotation is sensitive to the ripple. On the other hand, the confinement is reduced by up to 15-18% for local ripple $$ge$$ 3% but is hardly affected at 1.7% local ripple.

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