Nonlinear Local Control of the Safety-Factor-Profile Gradient at Moving Spatial Locations in Tokamak Plasmas
S.T. Paruchuri, A. Pajares and E. Schuster
American Control Conference (ACC)
San Diego, CA, USA, May 31 – June 2, 2023
|
Abstract
|
|
Tokamaks are toroidal devices that confine a very
hot plasma (hydrogenic ionized gas) by using strong magnetic
fields. When the kinetic energy is high, positively charged nuclei
in the plasma can overcome the Coulombic forces of repulsion
and fuse to form a heavier nucleus. A tremendous amount of energy
is released during this reaction. The pitch of the magnetic
field in a tokamak, measured by the safety factor profile q, plays
a crucial role in ensuring the magnetohydrodynamic (MHD)
stability of the tokamak plasma. MHD instabilities like the
Neoclassical Tearing Mode (NTM), which can deteriorate or
even terminate plasma confinement, can appear at regions in
the tokamak where the safety factor profile assumes a rational
value. Since the safety factor profile is a continuous function of
location in the tokamak, rational values at specific locations
are inevitable. Controlling the gradient of the safety factor
profile at these locations can prevent or mitigate the effect
of MHD instabilities. In this work, a one-dimensional model
that approximates the safety factor gradient dynamics at one
of the locations where the safety factor q achieves a rational
value is developed. A controller based on feedback linearization
of this model is designed to track a target gradient value in
the steady-state scenario. The effectiveness of this controller is
demonstrated in nonlinear numerical simulations powered by
the Control Oriented Transport SIMulator (COTSIM) for a
DIII-D tokamak scenario.
