Page 347 - Fundamentals of Magnetic Thermonuclear Reactor Design

324 Fundamentals of Magnetic Thermonuclear Reactor Design

projects, but also to the specificity and complexity of the technical problems to
be addressed. These problems include the following:

l Generation of a magnetic field varying in time in a wide induction range
combined with its high change rate at the discharge start.
l Simultaneous operation of several PS sources, when there is a magnetic cou-
pling between magnet system coils.
l Need for special methods and means for protecting the superconducting coils.
l Unusual set of requirements for the electrical equipment, including switch-
ing devices. This limits the applicability of commercial products and requires
a highly tailored approach to technology.
Tokamaks usually need a PS system to power
l toroidal field (TF) coils.
l poloidal field (PF) coils.
l correction coils (CCs).
The PS system for the TF coils operates in a quasistationary mode, with pa-
rameters unchanged throughout the cycle. The PF coils are powered in a pulsed
mode. The correction coils used to compensate for magnetic field distortions
caused by current leads, coil displacements or imperfections consume a rela-
tively low power. Their PS system is based on commercial equipment and will
not be discussed here [1].
The sections that follow deal with the design concepts for PS and protection
systems of large-scale tokamak magnet systems, including the ITER reactor, as
well as with the main problems arising in the course of their development and the
approaches to the solutions of these problems. Along with other sources the author
used the detailed review of tokamak PS systems [1], performed by A.M. Stolov
and F.M. Spevakova, the pioneers of works in this field at the Efremov Institute.

11.2 POWER SUPPLY FOR TOROIDAL FIELD COILS

11.2.1 Resistive Coils
The important parameters of resistive coil power supplies are the generated
power and electric energy delivered to load. They depend on the coil character-
istics, such as current, inductance and resistance, and the operating cycle length.
Since the early days of tokamak research, the consumption of energy supplied
by power sources has increased by an order of four (Table 11.1).
The first tokamaks, such as MT-1, TM-4M and ‘Tuman’, employed capaci-
tor banks as PS sources (Fig. 11.1). A pre-charged capacitor bank was dis-
charged to the coil by a connected-in-series ignitron or a controlled spark-gap.
The plasma discharge was initiated at the moment when the current attained
its amplitude values. A diode connected in parallel to the coil was used to
extend the time interval, in which current changes were within the tolerance
range.