On the L to H mode transition and instabilities on the H mode barrier in tokamak plasmas

Moestam, Robert; Weiland, Jan

doi:10.1088/0029-5515/42/6/304

Cited by 5 publications

(4 citation statements)

References 14 publications

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“…This mode has several features in common with our drift wave model and, in fact, the systems can be combined by using a complex trapped fraction i.e. an adiabaticity index 14 . All these systems 11-14 include a possibility for diamagnetic stabilization of a strong instability in L-mode which could correspond to a L-H transition.…”

Section: Edge Barriermentioning

confidence: 99%

Comparison of Edge and Internal Transport Barriers in Drift Wave Predictive Simulations

Crombé¹,

Mantica²,

Naulin³

et al. 2011

AIP Conference Proceedings

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Abstract.We have simulated the formation of an internal transport barrier on JET including a self-consistent treatment of ion and electron temperatures and poloidal and toroidal momentum. Similar simulations of edge transport barriers, including the L-H transition have also been made. However, here only polodal momentum and the temperatures were simulated. The internal barrier included an anomalous spinup of poloidal momentum similar to that in the experiment. Also the edge barrier was accompanied by a spinup of poloidal momentum. The experimental density (with no barrier) was used and kept fixed for the internal barrier. For the edge barrier the edge density was varied and it turned out that a lower edge density gave a stronger barrier. Electromagnetic and nonlocal effects were important for both types of barriers.

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Section: Edge Barriermentioning

confidence: 99%

Comparison of Edge and Internal Transport Barriers in Drift Wave Predictive Simulations

Crombé¹,

Mantica²,

Naulin³

et al. 2011

AIP Conference Proceedings

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“…A lot of theory work has been devoted to this problem. [14][15][16][17][18][19][20][21] A useful review of both experimental background and theoretical models was given in Ref. 14.…”

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confidence: 99%

Simulations of the L-H transition on experimental advanced superconducting Tokamak

Weiland

2014

Physics of Plasmas

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We have simulated the L-H transition on the EAST tokamak [Baonian Wan, EAST and HT-7 Teams, and International Collaborators, "Recent experiments in the EAST and HT-7 superconducting tokamaks," Nucl. Fusion 49, 104011 (2009)] using a predictive transport code where ion and electron temperatures, electron density, and poloidal and toroidal momenta are simulated self consistently. This is, as far as we know, the first theory based simulation of an L-H transition including the whole radius and not making any assumptions about where the barrier should be formed. Another remarkable feature is that we get H-mode gradients in agreement with the a -a d diagram of Rogers et al. [Phys. Rev. Lett. 81, 4396 (1998)]. Then, the feedback loop emerging from the simulations means that the L-H power threshold increases with the temperature at the separatrix. This is a main feature of the C-mod experiments [Hubbard et al., Phys. Plasmas 14, 056109 (2007)]. This is also why the power threshold depends on the direction of the grad B drift in the scrape off layer and also why the power threshold increases with the magnetic field. A further significant general H-mode feature is that the density is much flatter in H-mode than in L-mode. V C 2014 AIP Publishing LLC. [http://dx.The understanding of the L-H transition in tokamaks is still one of the outstanding issues in fusion transport research. We have here used data from the EAST tokamak 1-3 which we have recently studied with our transport code 4 to improve our general understanding of the L-H transition. 5-12 A main reason is that the performance of the projected ITER depends strongly on the height of the edge temperature pedestal. 13 In the present design, a pedestal temperature of about 4 keV is needed. The achievement of this temperature may be critical, i.e., some but not all theories predict such a high temperature. Thus, we need to understand both the H-mode power threshold and the height of the pedestal. A lot of theory work has been devoted to this problem. 14-21 A useful review of both experimental background and theoretical models was given in Ref. 14. The most ambitious models have been derived through nonlinear simulations of edge turbulence. 16,17 In particular, the dimensionless parameters a ¼ Àq 2 Rdb/dr, where b is the usual plasma beta (ideal MHD parameter) and a d ¼ v d t ib /L, where v d is the ion diamagnetic velocity, t ib is the ideal toroidal ITG growth time, and L is a characteristic turbulence scale length prop to q(Rq s ei /X ce ) 0.5 were successfully used to characterize the edge. 17 In an a -a d plane, regions of H-mode as well as density limit instability and ideal MHD instability could be identified. 17 Their H-mode region is actually in fairly good agreement with the H-mode in C-mod as seen in Ref. 10. Actually, several measurement points in C-mode were just below the H-mode regime in Ref. 17 so clearly we can also accept results just below this region as H-modes in our simulations. In recent more detailed studies of the pedestal, it has been found that...

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“…This mode gives a small transport compatible with H-mode and also gives a particle pinch. Later a generalized formalism with a complex trapped fraction was shown to be able to make the transition from the drift wave system to the collision-dominated system [11]. Later a generalized formalism with a complex trapped fraction was shown to be able to make the transition from the drift wave system to the collision-dominated system [11].…”

Section: Introductionmentioning

confidence: 99%

“…Both the ITG-TE system and the collision-dominated system were reviewed in [10], including a comparison of H-mode thresholds due to stabilization by FLR and shear flows. Later a generalized formalism with a complex trapped fraction was shown to be able to make the transition from the drift wave system to the collision-dominated system [11]. In this transition, the typical separation in two modes remained for the whole transition.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear condensation modes

Weiland¹

2010

J. Plasma Phys.

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In the far edge, in L-mode plasmas and the outer parts of the H-mode barrier, tokamak plasmas may be so collisional that parallel electron motion can be neglected or included as a perturbation. Thus we have a regime that is basically two dimensional. We will here consider the outer part of the H-mode barrier where transport is small. Recently a condensation mode was found for this regime. We have extended the theory to the nonlinear regime.

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On the L to H mode transition and instabilities on the H mode barrier in tokamak plasmas

Cited by 5 publications

References 14 publications

Comparison of Edge and Internal Transport Barriers in Drift Wave Predictive Simulations

Comparison of Edge and Internal Transport Barriers in Drift Wave Predictive Simulations

Simulations of the L-H transition on experimental advanced superconducting Tokamak

Nonlinear condensation modes

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