Axisymmetric equilibrium and stability analysis in Alcator C-Mod, including effects of current profile, measurement noise and power supply saturation

The vertical position of elongated tokamak plasmas is unstable on the time scale of the eddy currents in the axisymmetric conducting structures. In the absence of feedback control, the plasma would drift vertically and quench on the wall, a situation known as Vertical Displacement Event (VDE), with serious consequences for machine integrity. As tokamaks approach reactor regimes, VDE's cannot be tolerated: vertical feedback control must be robust against system uncertainty and the occurrence of noise and disturbances. At the same time, adaptive routines should be in place to handle unexpected events. The problem of robust control of the vertical position can be formulated in terms of identifying which variables affect vertical stability and which ones are not directly controlled/controllable; identifying the physical region of these variables, and the corresponding most unstable equilibria; and designing the control system to stabilize all equilibria with sufficient margin. The margin should be enough to allow the system to tolerate realistic scenarios of noise and disturbances. A set of metrics is introduced to characterize the problem of vertical stability: the stability margin describes the plasma-wall interaction and the open-loop growth rate; the maximum controllable displacement looks at the vertical stabilization power supplies and their ability to handle noise and off-normal events; the gain and phase margins quantify the linear stability of the feedback control loop.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Nuclear Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Ferrara, Marco, Ph. D. Massachusetts Institute of Technology

Advisor dc:contributor.advisor

• Ian H. Hutchinson and Stephen M. Wolfe.

• Nuclear Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/53265

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/53265