Page 356 - Fundamentals of Magnetic Thermonuclear Reactor Design

Power Supply Systems Chapter | 11 333

FIGURE 11.7 Pilot FDR element.

11.3 POLOIDAL FIELD COIL POWER SUPPLY
The poloidal magnetic field is produced by several coils. They can be divided
into two groups: (1) the central solenoid (CS) coils designed to generate a vor-
tex electric field, initiating the plasma and providing its ohmic heating, and (2)
the plasma control coils necessary to control the plasma shape and equilibrium.

11.3.1 Central Solenoid Coils
The electrical load of the CS power supply is peculiar in that its parameters
change non-linearly during the plasma current pulse due to variations in ac-
tive and inductive resistance of the plasma in the process of its heating and
compression. This is an important factor to be considered in the CS power
supply design. No less important is the fact that the PF coils are magnetically
intercoupled. Nevertheless, the PS sources of each coil may be considered in-
dependently. One exception is the calculation of actual parameters of the coils.
In tokamaks, the discharge current pulses have almost a trapezoidal form,
with the plateau duration much longer, as a rule, than that of the current ramp-
up and ramp-down. As the load is of an inductive nature, a higher voltage and,
hence, a higher power are required to quickly change the current than on the
current plateau. Meanwhile, the plateau phase accounts for the major part of
energy consumption due to its longer duration. It is therefore unreasonable, and
in most cases impracticable, to use power supplies rated for ultimate power and
for ultimate energy.
Even in early tokamaks with a relatively low power and energy consump-
tion the CS was powered by two PS sources operating into a common load.
One of them generated power necessary for the current ramp-up and had an en-
ergy store more or less consistent with the coil magnetic field energy. The other