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Exploring H-mode Transition Thresholds and ELM Dynamics in Fusion Plasmas

This document discusses the latest findings on H-mode threshold power requirements and the characteristics of density thresholds in nuclear fusion plasmas. It reviews scaling factors related to magnetic fields and the impact of rotation on plasma confinement. Key topics include hysteresis effects, experiments from various nuclear fusion devices, and the necessary conditions for transitioning between Type III and Type I ELMs. Insights from joint experiments and recommendations for further studies are provided for optimizing plasma performance and stability.

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Exploring H-mode Transition Thresholds and ELM Dynamics in Fusion Plasmas

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  1. ITPA – CDBMH-mode threshold databaseDiscussionOctober 2007 - Naka Yves Martin Centre de Recherches en Physique des Plasmas Association Euratom - Confédération Suisse Ecole Polytechnique Fédérale de Lausanne (EPFL) CH - 1015 Lausanne, Switzerland

  2. Outline • Mukhovatov's note • Joint experiments (CDB-10, ...) • Density threshold • Rotation • Hysteresis • Transitions between type III and type I ELMs

  3. Vladimir Mukhovatov's note • H-mode Threshold Power: ITER needs • Scaling with toroidal magnetic field of plasma density (nmin) at minimum L-H threshold power • L-H threshold power as a function of magnetic ripple amplitude at the same n and B (Task for JET) • Scaling for power threshold PTypeI for transition from Type III to Type I ELMy H-mode at high triangularity (~0.4-0.5) • Scaling for power threshold for back transition from Type I ELMs to Type III ELMy H-mode at high triangularity (~0.4-0.5)

  4. Density threshold • After C-Mod contribution ... • Following paper content ... • Characterisation of density threshold • Dependence on magnetic field, divertor geometry, plasma geometry, neutrals, plasma current, ... • New experiments ?

  5. Rotation data in threshold DB • JT-60U data – Edge toroidal rotation

  6. Rotation • What can we do ? • DIII-D data ? • Send data to DB ? • Other devices ? • Presentations from individual devices ? • Who ? • New data (new time slices or rotation data) in the DB ? • Continue with VTO95 and VPO95 or add other vars ?

  7. Hysteresis from DB • Extract plasma characteristics for time slices data with good confinement at power ratio close to 1. • Compare characteristics to average operational conditions

  8. Hysteresis foreseen in ITER • Entering H-mode at low density (0.5 x 1020m-3) • Maintain input power above H-L transition threshold while increasing the density up to nominal value (1.0 x 1020m-3) • Increase the power until good confinement (H=1) is obtained

  9. Hysteresis experiments in present day devices • Obtain H-mode at low density (tbd) with minimum required power • Characterise H-mode quality (ELM type) during 'natural' density increase/excursion while maintaining the power constant (close to threshold) • With power ramps or single steps • Power maintained at Pthresh * 1.0 (ideally) or 1.1 or 1.2 • Increase the density while maintaining the power constant

  10. Threshold power between ELM types • JET results for ELM type transition (and sustainment) • PIII-I = Y x Pth where 1.5<Y<2.5 • In the literature • Provide some info • In the DB • Correlation between small / big ELMs and type III / I ELMs • New experiments • Threshold studies similar to those for L-H transition • who?

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