M. Gospodarczyk

On the measurement of the threshold electric field for runaway electron generation in the Frascati Tokamak Upgrade

Experiments have been carried out to evaluate the threshold electric field for runaway generation during the flat-top phase of ohmic discharges in the Frascati Tokamak Upgrade tokamak. An investigation of the conditions for runaway electron generation and suppression has been performed for a wide range of plasma parameter values. The measured threshold electric field is found to be significantly larger ( ∼2−5 times) than predicted by the relativistic collissional theory of runaway generation, ER=ne e3 lnΛ/4π e02 me c2, and can be explained to a great extent by an increase of the critical electric field due to the effect of the electron synchrotron radiation losses. These findings are consistent with the results of an ITPA joint experiment to study the onset, growth, and decay of relativistic runaway electrons [Granetz et al., Phys. Plasmas 21, 072506 (2014)]. Confirmation of these results for disruptions with high electric field might imply significantly lower requirements on electron densities for suppre...

Optimization of two-controller switchings for LTI plants

In this paper we propose procedures to evaluate switching times, controller resets and vanishing feedforward terms when two linear controllers can be switched in order to optimize a quadratic cost function of the closed-loop system response in case of linear plants. Numerical and closed-form solutions are provided. Simulation results are presented to show the effectiveness of the proposed strategies.

Performance-based controller switching: An application to plasma current control at FTU

In this paper we derive state-dependent switching conditions to optimize closed-loop (transient) performance of switching controllers for linear time invariant plants. The methodology is applied to plasma current control at Frascati Tokamak Upgrade (FTU) facility to improve steady-state and transient response. Further simulation results are presented to show the effectiveness of the proposed switching controller.