The development of linear model of the present JET (Joint European Torus) electromagnetic system has allowed the design of an optimized Plasma Shape Controller. Quite extreme plasma boundaries (elongation k = 1.9 and triangularity <delta> = 0.6) are shown to be controllable also in the presence of large variations of the values of poloidal beta (0.1 < beta(p) < 0.6) and/or internal magnetic inductance (0.8 < l(i) < 1.4). The developed model gives also an excellent simulation of the growth rate of the experimental vertical disruptions. (C) 2003 Elsevier Science B.V. All rights reserved.