Showing papers by "T. C. Hender published in 1999"
TL;DR: In this article, the critical scalings of error field sensitivity and harmonic content effects were identified, enabling predictions to be made of the requirements for larger devices such as ITER Thresholds are lowest at low density, a regime proposed for H mode access on ITER.
Abstract: New experiments on JET, COMPASS-D and DIII-D have identified the critical scalings of error field sensitivity and harmonic content effects, enabling predictions to be made of the requirements for larger devices such as ITER Thresholds are lowest at low density, a regime proposed for H mode access on ITER Results suggest a moderate error field sensitivity (δB/B ≈ 10-4) for ITER, comparable with the size of its intrinsic error, although there are uncertainties in scaling behaviour Other studies on COMPASS-D and DIII-D show that sideband harmonics to the (2, 1) component play an important role Thus, a correction system for ITER will be important, with flexibility to correct sidebands desirable, possibly assisted by beam rotation Such a system has been designed and is capable of reducing multiple harmonic error levels to ~ 2 × 10-5
169 citations
TL;DR: In this article, the authors measured the structure of the MHD mode observed as a precursor to the disruption, as measured from SXR and ECE diagnostics, shows a global ideal MHD model.
Abstract: The main limitation to the performance of JET optimized shear (OS) discharges is due to MHD instabilities, mostly in the form of a disruptive limit. The structure of the MHD mode observed as a precursor to the disruption, as measured from SXR and ECE diagnostics, shows a global ideal MHD mode. The measured mode structure is in good agreement with the calculated mode structure of the pressure driven kink mode. The disruptions occur at relatively low normalized beta (1 < βN < 2), in good agreement with calculated ideal MHD stability limits for the n = 1 pressure driven kink mode. These low limits are mainly due to the extreme peaking factor of the pressure profiles. Other MHD instabilities observed in JET OS discharges include, usually benign, chirping modes. These modes, which occur in bursts during which the frequency changes, have the same mode structure as the disruption precursor but are driven unstable by fast particles.
74 citations
TL;DR: In this article, the ideal MHD β limit of reversed shear equilibria, due to n = 1, n = 2 and ballooning modes, was investigated for peaked pressure profiles, consistent with those occurring when the internal transport barrier is established in JET optimized shear discharges.
Abstract: The ideal MHD β limit of reversed shear equilibria, due to n = 1, n = 2 and ballooning modes, is investigated for peaked pressure profiles, consistent with those occurring when the internal transport barrier is established in JET optimized shear discharges. Higher βN can be reached with the control of the minimum q value, and a conducting wall can further improve the stable domain. The n = 2 mode plays an insignificant role, unless the conducting wall improves the n = 1 stability when the shear reversal is large. Increasing the amount of shear reversal generally improves MHD stability, and the effect is stronger for the n = 2 mode. β* ( = 2μ0 P2 1/2/B02) increases with normalized current (Ip/aB0) but βN is only weakly affected.
1 citations