Page 41 - Fundamentals of Magnetic Thermonuclear Reactor Design

Facilities With Magnetic Plasma Confinement Chapter | 2 23

l Physical parameters (T, k, Z , ∆t burn ) that can only be achieved if necessary
eff
technical solutions come up.
l Engineering parameters (such as the neutron fluence Fl and the ∆ PL–TF gap).
Let us review the status of fusion research. Although impressive normalised
beta values (β ≈ 6) and very good plasma confinement results (H ≈ 2) have
y,2
N
been achieved in some tokamak experiments, they cannot be sustained for an
extended time. Achievements reached with long facility operation are relatively
modest. According to Tomassen [17], the product β ·H falls when the ratio
N
y,2
∆t burn /τ increases.
E
The later investigations [18,19] allow to obtain the limitation for the combi-
nation β ·H /q 95 2 for the long-time pulses. Maximum values of H decreased
y,2
y,2
N
for high values of plasma density (near Greenwald limit) [19].
As one can see from Table 2.5, only ITER и DEMO-S can comply with the
β ·H ≤ 3.5–4 requirement. Hence, another requirement, β ·H > 4–6, be-
N
y,2
y,2
N
comes an objective, and searching for suitable operating modes should be one
of the ITER physicists’ priorities.
Different additional plasma heating systems are employed to heat plasma to
the required T ≥ 10 keV. A considerably elongated plasma (with k ≥ 1.7–1.9),
which modern fusion machines are designed to run, is vertically unstable, and a
computerised system is needed to control its steady burning, position and shape.
To reduce radiation losses, the plasma effective charge (Z ) must be kept as
eff
close to 1 as possible. Generally, Z is designed to be less than or equal to 1.7.
eff
To this end, special technologies are used to condition the walls of the discharge
and the divertor chambers.
In addition, oil-free vacuum pumping systems and engineering design meth-
ods for reducing the density of heat and corpuscular fluxes carried onto the first
wall are employed.
A quasi-steady state discharge mode can be obtained, if a poloidal magnetic
flux has sufficient margin. However, a radical way to move to a steady-state
mode is through a non-inductive discharge current drive.
2.5 ENGINEERING REQUIREMENTS TO MAIN FUNCTIONAL
SYSTEMS

2.5.1 Magnet System
The amplitude of the toroidal magnetic field on the coil (B ) is ∼12 Т in the
tc
ITER reactor and may reach 14–16 Т in the DEMO and FPP machines. Such
field magnitudes make resistive coils impracticable because of too large cooling
power values. As a result, superconducting coils are proposed for the discussed
projects. The same is true for the central solenoid with magnetic field amplitude
of ≤13 T. The magnetic field flux capacity ∆Ψ , required to maintain the induc-
cs
tive discharge scenario, is secured through the selection of the central solenoid’s
appropriate mean radius R and appropriate in-solenoid field B according to [3]
cs
cs