Publications (4)0 Total impact
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Article: Sawtooth, Neo-Classical Tearing Mode and Error Field Studies in JET
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ABSTRACT: A range of ITER relevant plasma stability issues have been studied in the JET tokamak; these include the effects of fast particles on sawteeth, control of NTMs via sawteeth seeds, scaling of (2,1) NTM thresholds and the effect of error fields on plasma rotation and vice-versa. The sawtooth studies have examined both the effects of ICRF and NBI fast particles, and models used for ITER predictions have been validated. Large sawteeth, due to fast particle stabilisation, have been shown to trigger m=3, n=2 NTMs at low beta. Conversely the use of ICCD to produce small short period sawteeth has been shown to raise the NTM beta-limit, suggesting the value of local current drive near q=1. The m=2, n=1 NTM, which when destabilised results in severe degradation of plasma performance, has been studied in a joint scaling experiment with the DIII-D tokamak. These experiments using closely matched non-dimensional parameters (plasma shape, R/a, q, gyro-radius and collisionality) on DIII-D and JET show similar NTM beta-limits and consistent scalings. The issue of error field thresholds and their variation with plasma rotation has also been studied, helping to clarify scalings to ITER. -
Article: Type-I ELM precursor modes in JET
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ABSTRACT: This version is available at the following URL: http://stacks.iop.org/0029-5515/44/609 -
Article: Observation of the palm tree mode, a new MHD mode excited by type-I ELMs on JET
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ABSTRACT: This version is available at the following URL: http://dx.doi.org/10.1088/0029-5515/45/3/006 -
Article: Observations of pre- and postcursor modes of type-I ELMs on JET
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ABSTRACT: Recent observations of MHD activity in type-I ELMy H-mode discharges on JET have revealed two phenomena: (i) the so-called palm tree mode, a new, snake-like MHD mode at the q=3 surface which is excited by type-I ELMs, and (ii) coherent MHD mode activity as a precursor to the ELM collapse. Both modes are detected by magnetic pick up coils and can also be seen on the edge ECE and SXR measurements. They are located a few cm inside the separatrix. Palm tree modes have been identified in a wide range of plasma conditions, which comprise standard ELMy H-modes, ITER-like plasma shapes, pellet fuelling, and even pure helium plasmas. The mode frequency increases in time and starts to saturate until the mode finally decays. A likely explanation of the palm tree mode is, that it is the remnant of an (3,1)-island created due to edge ergodisation by the ELM perturbation. Refined methods of data evaluation allowed to identified low frequency coherent type-I ELM precursor modes with toroidal mode numbers in the range 2 to 14. They seem to have a kink-like structure, and appear normally 0.5-1ms before the ELM, but in many cases even much earlier.Fusion Energy 2002, International Atomic Energy Agency (2003).
