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2011
The effect of momentum injection on the temperature gradient in tokamak plasmas is studied. A plausible scenario for transitions to reduced transport regimes is proposed. The transition happens when there is sufficient momentum input so that the velocity shear can suppress or reduce the turbulence. However, it is possible to drive too much velocity…
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2011
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2011
The kinetic effects, due to the mode resonance with thermal particle drift motions in the reversed field pinch (RFP) plasmas, are numerically investigated for the stability of the resistive wall mode, using a non-perturbative MHD-kinetic hybrid formulation. The kinetic effects are generally found too weak to substantially change the mode growth rat…
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2011
Magnetohydrodynamic equilibrium states with a three-dimensional helical core are computed to model the MAST spherical tokamak and the RFX-mod reversed field pinch. The boundary is fixed as axisymmetric. The MAST equilibrium state has the appearance of an internal kink mode and is obtained under conditions of weak reversed central shear. The RFX-mod…
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2011
The low-temperature plastic yield of a -Fe single crystals is known to display a strong temperature dependence and to be controlled by the thermally activated motion of screw dislocations. In this paper, we present molecular dynamics simulations of 1 2 111{112} screw dislocation motion as a function of temperature and stress in order to extract mob…
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2011
Nonlinear gyrokinetic simulations are conducted to investigate turbulent transport in tokamak plasmas with rotational shear. At sufficiently large flow shears, linear instabilities are suppressed, but transiently growing modes drive subcritical turbulence whose amplitude increases with flow shear. This leads to a local minimum in the heat flux, ind…
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2011
Access into H-mode is studied in the MAST tokamak when plasma is fuelled by cryogenic pellets. It is shown that pellet fuelling from the high field side allows access to Hmode in plasmas heated by neutral beams. Simple and two-stage L-H transitions are identified. The results of comparison of the L-H transitions with pellet injection with transitio…
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2011
The non-active operation phase of ITER will be done in H|4 He plasmas at half the nominal magnetic field, B 0 =2.65T. At this field|for the given frequency range of the ICRF system (f=40-55MHz), three ICRF heating scenarios are available a priori : (i) Fundamental ICRH of majority H plasmas at f?40MHz, (ii) second harmonic (N=2) 3 He ICRH in H plas…
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2011
We examine a possible mechanism for the formation of protrusions on a metallic surface held in a sufficiently high electric field in the presence of a near-surface void. By means of molecular dynamics simulations we show that the high tensile stress exerted on a Cu f110g surface with a near-surface void can promote the nucleation of dislocations on…
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2009
Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks. Using the increased heating capabilities PNBI ≤ 3.8 MWH-mode at Ip = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with Ip and more strong…
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