This annual workshop on MHD Stability Control has been held since 1996 with a focus on understanding and developing control of MHD instabilities for future fusion reactors. The workshop generally covers a wide range of stability topics: from disruptions, to tearing modes, error fields, ELMs, resistive wall modes (RWMs) and ideal MHD. It spans many device types, particularly tokamaks, stellarators and reversed field pinches, to pull out commonalities in the physics and improve understanding.In 2010 the workshop was held on 15–17 November at the University of Wisconsin in Madison and was combined with the annual US–Japan MHD Workshop. The theme was `3D Magnetic Field Effects in MHD Control', with a focus on multidisciplinary sessions exploring issues of plasma response to 3D fields, the manifestation of such fields in the plasma, and how they influence stability. This has been a topic of renewed interest, with utilisation of 3D fields for ELM control now planned in ITER, and a focus on the application of such fields for error field correction, disruption avoidance, and RWM control. Key issues included the physics of the interaction, types of coils and harmonic spectra needed to control instabilities, and subsidiary effects such as braking (or rotating) the plasma. More generally, a wider range of issues were discussed including RWM physics, tearing mode physics, disruption mitigation, ballooning stability, the snowflake divertor concept, and the line tied pinch! A novel innovation to the meeting was a panel discussion session, this year on Neoclassical Toroidal Viscosity, which ran well; more will be tried next year.In this special section of Plasma Physics and Controlled Fusion we present several of the invited and contributed papers from the 2010 workshop, which have been subject to the normal refereeing procedures of the journal. These papers give a sense of the exceptional quality of the presentations at this workshop, all of which may be found at http://fusion.gat.com/conferences/mhd10/.The Program Committee deeply appreciates the participation and support our community continues to show in this workshop. This year's meeting attracted a record number of talks, and we feel the workshop provides an unparalleled opportunity for in-depth discussion amongst the stability community. We would also like to thank our hosts this year—the University of Wisconsin, and in particular Professor Francesco Volpe—for the outstanding support and facilities. Finally, the opportunity was taken to rotate the membership of the Program Committee; we would like to thank outgoing members Professors Gerald Navratil, John Sarff and François Waelbroeck for their many years of excellent advice and service. Their contributions have helped make the workshop a stimulating and friendly environment, which will no doubt continue to press forward on the critical questions of plasma stability for fusion energy.
Chapter 3: MHD stability, operational limits and disruptions