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1. Title – Arial between 80 and 100pt Authors names Arial 50pt, A. N Other1, 1Associations Arial 28 pt 2EURATOM/Culham Fusion Association, Culham Science Centre, Oxon. OX14 3DB. 1Associations Arial 28 pt 2EURATOM/Culham Fusion Association, Culham Science Centre, Oxon. OX14 3DB • ABSTRACT • Neoclassical tearing modes (NTMs) are performance limiting instabilities likely to require control oavoidance strategies in ITER baseline scenarios. Inter-device identity experiments on the JET, ASDEX Upgrade and DIII-D tokamaks have explored the threshold for NTM metastability, and how it scales. Coupled with advances in numerical modelling, these allow the quantification of the underlying physics terms and extrapolation towards ITER. Detailed matches between theory and experiments can be obtained, constraining the key parameters governing NTM behaviour. Results suggest ITER baseline scenarios will operate well above the threshold for metastability of NTMs, and so highly susceptible to NTM triggering events. Further, to remove the modes, ECCD systems will have to drive islands sizes down to levels of a few cm, similar to those required for mode removal in present devices boxes and figures • HEADING • This template has been carefully matched to the standard drawing office output for official JET EPS posters • It is set up for single piece of A0 size – there is another template that print out to the full size 1m by 2m poster size on 2 sheets • Font sizes have been carefully matched to the JET standard poster template • Use guides installed in this template to align text boxes • Sub-Heading • Thresholds fall with • Good consistency between • three devices s and figures • Sub-Heading • Thresholds fall with • Good consistency between • three devices s and figures • HEADING • Conclusion 1 • Results indicate a clear trend of metastable b threshold falling with r*, that is carries over well between the machines • This indicates that the standard ELMy H-mode ITER baseline scenario will operate well above the NTM metastability threshold • Suitable seeds (comparable to those in present devices) will excite 3/2 NTMs in ITER • EXPERIMENTAL RESULTS • Most shots where a steady power ramp-down is applied exhibit a clear marginal b point • where island breaks b scaling and starts to decay more rapidly • be measured and plotted against underlyingplasma parameters at the marginal. • good range of parameters accessed: • Clear trend observed across devices: • Thresholds fall with • Good consistency between • three devices s and figures: • Good consistency between • three devices s and figures: • Clear trend observed across devices: • Good consistency between • three devices s and figuresNEXT STEPS... • Next step is to fold in ramp-down analyses for JET and ASDEX Upgrade • Explore ion polarisation model for small island size effects • Correct for slight variations in island size due to motions of q=3/2 surface • Finalise ITER extrapolations for marginal beta and marginal island size • Work is also progressing on use of similar techniques to explore: (1) ECCD stabilisation physics for NTMs, (2) the physics of the 2/1 NTM [10] • CONCLUSIONS and IMPLICATIONS FOR ITER • Conclusion 1 • Results indicate a clear trend of metastable b threshold falling with r*, that is carries over well between the machines • This indicates that the standard ELMy H-mode ITER baseline scenario will operate well above the NTM metastability threshold • Suitable seeds (comparable to those in present devices) will excite 3/2 NTMs in ITER • Preliminary results obtained for DIII-D alone indicate a weak dependence of small island size terms with r* • Suggests that for complete removal of an NTM by ECCD systems in ITER, islands sizes will have to be reduced to levels similar to those required on present devices (if borne out by JET and ASDEX Upgrad • ACKNOWLEDGEMENTS • "This work, carried out under the European Fusion Development Agreement, supported by the United Kingdom Engineering, Physical Sciences Research Counciland the European Communities,has been carried out within the contract of Association between EURATOM andUnited Kingdom Atomic Energy Authority.The views and opinions expressed herein do not necessarily reflect those of the European Commission." • *Association Specific • **General • REFERENCES • [1] R. Carrera, R. D. Hazeltine, and M. Kotschenreuther, Phys., Fluids 29, 899 (1986). • [2] O. Sauter et al., Phys. Plasmas 4, 1654 (1997). • [3] O. Sauter, C. Angioni, and Y. R. Lin-Liu, Phys. Plas. 6, 2834 (1999), & 9 5140 (2002).