MHD activity in JET hot ion H mode discharges

Nave, M. F. F.; Ali-Arshad, S.; Alper, B.; Balet, B.; Blank, H. J. de; Borba, D.; Challis, C.; Hellermann, M. G. von; Hender, T. C.; Huysmans, G. T. A.; Kerner, W.; Kramer, G. J.; Porcelli, Francesco; O’Rourke, J.; Porte, L.; Sadler, G.; Smeulders, P.; Sips, A. C. C.; Stubberfield, P.M.; Stork, D.; Reichle, R.; Wessom, J.A.; Zwingmann, W.

doi:10.1088/0029-5515/35/4/i04

Cited by 27 publications

(27 citation statements)

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“…A fuller description of these terms, used to compare with experimental data, can be found in [54,62] and references therein (see also [1]). The typical evolution of the island growth rate in a full discharge, assuming a slow ramp-down of the power, and thus a slow decrease in the terms proportional to β p in equation (5), is shown in figure 3. At a given time in the discharge, an island is triggered at a beta value β p,onset , in most cases much larger than β p,marg , and subsequently grows to a relatively large saturated island width.…”

Section: Neoclassical Tearing Modesmentioning

confidence: 99%

“…Indeed, small sawteeth may even be beneficial in preventing the accumulation of impurities and helium ash in the plasma centre. On the other hand, large sawteeth with mixing radii of 50% or more of the plasma minor radius and temperature drops of one or more keV represent a serious threat to ITER operation, since these large sawtooth events may couple to NTMs [4] and to edge-localized modes [5], resulting in a serious loss of plasma energy and confinement degradation. An additional worry, in a fusion burning plasma, is that if the sawtooth period is shorter than the slowing down time of the fusion alpha particles then fusion alphas may be scattered, and perhaps lost, before they have time to transfer their energy to the thermal plasma.…”

Section: Introductionmentioning

confidence: 99%

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Chapter 3: MHD stability, operational limits and disruptions

Hender¹,

Wesley²,

Bialek³

et al. 2007

Nucl. Fusion

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995

947

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Progress in the area of MHD stability and disruptions, since the publication of the 1999 ITER Physics Basis document Nucl. Fusion 39 2137-2664, is reviewed. Recent theoretical and experimental research has made important advances in both understanding and control of MHD stability in tokamak plasmas. Sawteeth are anticipated in the ITER baseline ELMy H-mode scenario, but the tools exist to avoid or control them through localized current drive or fast ion generation. Active control of other MHD instabilities will most likely be also required in ITER. Extrapolation from existing experiments indicates that stabilization of neoclassical tearing modes by highly localized feedback-controlled current drive should be possible in ITER. Resistive wall modes are a key issue for S128 Chapter 3: MHD stability, operational limits and disruptions advanced scenarios, but again, existing experiments indicate that these modes can be stabilized by a combination of plasma rotation and direct feedback control with non-axisymmetric coils. Reduction of error fields is a requirement for avoiding non-rotating magnetic island formation and for maintaining plasma rotation to help stabilize resistive wall modes. Recent experiments have shown the feasibility of reducing error fields to an acceptable level by means of non-axisymmetric coils, possibly controlled by feedback. The MHD stability limits associated with advanced scenarios are becoming well understood theoretically, and can be extended by tailoring of the pressure and current density profiles as well as by other techniques mentioned here. There have been significant advances also in the control of disruptions, most notably by injection of massive quantities of gas, leading to reduced halo current fractions and a larger fraction of the total thermal and magnetic energy dissipated by radiation. These advances in disruption control are supported by the development of means to predict impending disruption, most notably using neural networks. In addition to these advances in means to control or ameliorate the consequences of MHD instabilities, there has been significant progress in improving physics understanding and modelling. This progress has been in areas including the mechanisms governing NTM growth and seeding, in understanding the damping controlling RWM stability and in modelling RWM feedback schemes. For disruptions there has been continued progress on the instability mechanisms that underlie various classes of disruption, on the detailed modelling of halo currents and forces and in refining predictions of quench rates and disruption power loads. Overall the studies reviewed in this chapter demonstrate that MHD instabilities can be controlled, avoided or ameliorated to the extent that they should not compromise ITER operation, though they will necessarily impose a range of constraints.

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Section: Neoclassical Tearing Modesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Chapter 3: MHD stability, operational limits and disruptions

Hender¹,

Wesley²,

Bialek³

et al. 2007

Nucl. Fusion

Self Cite

995

947

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“…Modes [8,9,10] figure will be described later). Typically the fundamental harmonic frequency of the OM is f~ 5-10 kHz and the toroidal mode number is n=1.…”

mentioning

confidence: 99%

Observation of Confined Current Ribbon in JET Plasmas

Solano¹,

Lomas

Alper

et al. 2010

Phys. Rev. Lett.

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We report the identification of a localized current structure inside the JET plasma. It is a field-aligned closed helical ribbon, carrying current in the same direction as the background current profile (cocurrent), rotating toroidally with the ion velocity (corotating). It appears to be located at a flat spot in the plasma pressure profile, at the top of the pedestal. The structure appears spontaneously in low density, high rotation plasmas, and can last up to 1.4 s, a time comparable to a local resistive time. It considerably delays the appearance of the first edge localized mode.

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“…The confinement of the fusion alpha particle product in fusion reactors may be limited by collective electromagnetic modes driven by the fusion alphas phase space gradients. The large JET tokamak has a wide range of the high energy deuteron and alpha particle driven instabilities [Nave, et al (1995)]. In strong NBI heated tokamaks an outstanding alpha physics issue is when do the high energy ions create MHD "fishbone oscillations" and Toroidal Alfvén Eigenmodes (TAE) that seriously degrade the quality of confinement [Coppi and Porcelli (1986)].…”

Section: Central Solenoid and Plasma Current Densitiesmentioning

confidence: 99%

Ignition Physics in Multiscale Plasma Turbulence

Horton¹

2012

Turbulent Transport in Magnetized Plasmas

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Tokamak machines designed to reach ignition during a transient pulse driven by the transformer action of the primary voltage applied with coils in a central solenoid have a long history. Such tokamaks, however, are yet to be built on the scale required to test the ignition hypothesis. Tokamaks designs in this class include the Compact Ignition Torus CIT, Fusion Ignition Research Experiment FIRE and IGNITOR. The compact high-field IGNITOR design is the most extensively developed design. In this chapter we show the performance projections for the IGNITOR machine made with the multiscale transport codes called JETTO and the MMM model. The parameters and characteristics of that typical high-field tokamak design are given in this chapter. Currently, there are plans to built a version of this compact high-field tokamak machine in Troisk under an agreement between Italy and Russia. The general description of IGNITOR is found at http://www.frascati.enea.it/ ignitor/.The basic plan for this type of tokamak is to use the natural ohmic heating to the maximum extent that technology will allow. As shown in Chapter 15 the energy confinement time scaling law is most favorable for the intrinsic plasma heating produced by Coulomb collisions relaxing the transformer driven plasma current I p driven by the toroidally symmetric voltage V loop . When auxiliary power P aux from neutral beams or radio frequency antennas is applied the energy confinement time degrades, as detailed first in the Kaye-Goldston scaling law in PLT. The confinement time is found to decrease with applied P aux as τ E ∼ 1/(P 1/2 aux ). The reason for this degradation, as explained in Chapters 13-15, is that as the auxiliary power P aux increases, the level of the drift wave turbulent transport rapidly increases.The issue with using the natural ohmic heating of ηj 2 to reach the temperature required for ignition, which is at least 10 KeV, is that the plasma resistivity η decreases with increasing temperature and thus the plasma temperature reaches a plateau for a given geometry and toroidal magnetic field strength. To reach the ignition temperature with ohmic heating alone, the plasma current density j must 420 Turbulent Transport in Magnetized Plasmas Downloaded from www.worldscientific.com by NANYANG TECHNOLOGICAL UNIVERSITY on 08/23/15. For personal use only.

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MHD activity in JET hot ion H mode discharges

Cited by 27 publications

References 27 publications

Chapter 3: MHD stability, operational limits and disruptions

Chapter 3: MHD stability, operational limits and disruptions

Observation of Confined Current Ribbon in JET Plasmas

Ignition Physics in Multiscale Plasma Turbulence

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