Page 271 - Fundamentals of Magnetic Thermonuclear Reactor Design

250 Fundamentals of Magnetic Thermonuclear Reactor Design

l Developing linear models characterizing the dynamics of plasma position,
shape and current near a basic equilibrium.
l Synthesis of the plasma feedback control algorithms (selecting controllers
based on the linear models).
l Nonlinear modelling of plasma discharge scenarios, accounting for the pre-
programmed control and the synthesised feedback controllers. This analy-
sis is performed using codes describing the plasma parameter behaviour as
comprehensively as possible.
l Correction of the preprogrammed/feedback control where necessary.
A generally accepted method for calculating each of the basic equilibri-
ums is to find poloidal coil currents according to the given resistive losses at
the variations of the integral parameters I , l , R and the plasma shape. The
p
i
p
resistive losses are estimated (based either on physical scaling or phenomeno-
logical concepts). Simultaneously the poloidal coil voltages are determined
for the assessment of the requirements to the power supply system. Currents
induced in passive structures are neglected; therefore, every basic equilibrium
is calculated independently. The results of these calculations determine the
evolution of plasma parameters and current in the poloidal coils which, along
with the power supply system, is to be provided by the control system under
design.
An alternative approach to calculate the basic equilibriums is to use profiles
of the plasma poloidal current, stability margin q and plasma pressure profiles
(derived experimentally or theoretically) as input data, instead of the integral I ,
p
l , and R parameters. This method allows poloidal coil currents to be estimated
i
p
more reliably.
Numerical modelling is a centrepiece of the control system design. Linear
models are commonly used, as they enable the following:
l Evaluation of a passive plasma stabilisation effectiveness and optimisation
of conductive elements’ geometry, which is especially important for verti-
cally unstable plasmas.
l Determination of the requirements for good performance of poloidal field
coil power supplies in terms of power and operating speed.
l Synthesising of controllers providing feedback stabilisation of a plasma col-
umn. It should be noted that the modern theory of controller synthesis has
high development for the linear control objects.

Engineering practices have proved the adequacy of the linear numerical
models for the development of CLCSs. Such models have been extensively
used, among other things, in ITER design, assisting engineers in optimising
the geometry of the vacuum vessel and the in-vessel components to provide the
acceptable timescale of the control processes for plasmas with extreme elonga-
tion. They also laid the groundwork for the design of the interconnected plasma
control and PFC power supply systems.