Page 215 - Fundamentals of Magnetic Thermonuclear Reactor Design

Vacuum and Tritium System Chapter | 6 197

l Solution 3: Not only the blanket, but also radiation-shielded magnetic field
coils are placed inside the chamber cavity. The entire reactor becomes encased
in a ‘vacuum jacket,’ which seriously impedes access to the blanket and the
magnet. At the same time, the chamber operating conditions become easier.

Combinations of the three solutions are possible. For example, the cryostat
for superconducting magnets acts as a ‘vacuum jacket’ in the ITER design (the
discharge and divertor chambers, using a shared pumping system and shared
vacuum-tight shell, are placed inside the cryostat).
The magnetic field topology requirements are an important design and struc-
tural material issue for the reactor FW, blanket and vacuum chamber. Only very
small deviations from the prescribed magnetic field parameters – due to structural
material magnetic properties and eddy current fields – are allowable. The first
potential cause of deviations constrains the use of ferrites; the second imposes
limitations on the electric conductivity of closed circuits in the structural elements.

6.6.3 Vacuum Pumping Duct Design
Let us consider the practical aspects of the ‘design/materials/processes’ triad
implementation. The vacuum pumping duct design relies on a careful elaboration
of the key elements, particularly the vacuum vessel and in-vessel components. It
is built on a number of design principles, the most important being the following:
l focusing on the highest possible reliability of operation under cyclic heat
and mechanical loads as a key criterion controlling the technical decision-
making process;
l providing for structural sophistication of design elements – where this is
instrumental in achieving reproductivity and removing subjectivity from the
fabrication process;
l unconditional compliance with the vacuum hygiene requirements;
l attention to proper treatment of equipment employed for cleaning surfaces,
surface microrelief optimisation and reduction of desorption flows, which
may include procedures involving ultrasonic cleaning, electrochemical and
electrophysical technologies to aid in those processes;
l intermediate degreasing and washing in the course of installation and adjust-
ment of key units;
l high-temperature conditioning and degassing of parts in vacuum furnaces
using oil-free pumping systems;
l intermediate and finishing vacuum testing of parts and assemblies using
mass spectrometry methods;
l thermal cycling and resource testing, including intermediate tightness con-
trol, of parts exposed to high and cryogenic temperatures;
l heat conditioning of ultra-high vacuum equipment parts combined with oil-
free pumping (Table 6.4). For sizable chambers, allowable heating temperature
is determined through joint thermal/physical and durability modelling [4, 14].