Page 375 - Fundamentals of Magnetic Thermonuclear Reactor Design

Mechanics of Magnetic Fusion Reactors Chapter | 12 353

12.2 TOKAMAK SUPERCONDUCTING MAGNET: LOAD
SCHEMES

12.2.1 System of Toroidal Field Coils
Each toroidal field coil (TFC) is exposed to ponderomotive forces acting in
its plane and those perpendicular to its plane (Fig. 12.1). Continuous body in-
plane forces arise from the toroidal magnetic field interaction with the coil cur-
rent. Forces along the coil circumference vary as the inverse of distance to the
machine centre and, in the general case, cause the TFC extension and in-plane
bending. Together, they represent an unbalanced radial force, F , directed to-
R
wards the tokamak central axis. Although often referred to as a centring force, it
has no relation to inertial forces. All coils have identical centring forces, which
makes the TFC system statically balanced. The centring forces are quite strong
in large tokamaks (e.g. a force of ∼400 MN acts of every TFC in ITER). These
forces are stationary in superconducting magnets and act cyclically following
current switching-on in ‘warm’ magnet machines.
Continuous body forces perpendicular to the TFC plane (out-of-plane) arise
from the poloidal magnetic field interaction with the coil current. These forces
tend to move the coil out of its plane. They act cyclically and vary in value ac-
cording to discharge scenario. These forces give rise to an overturn moment,
M , torque, M , and toroidal force, F , which are related by
T
Z’
R
M ′ Z = F R 0 . MZ’=FTR .
T
0

FIGURE 12.1 Magnetic force distribution along TFC circumference. (А) Forces in the coil
plane and (B) forces perpendicular to the coil plane.