Page 199 - Fundamentals of Magnetic Thermonuclear Reactor Design

Vacuum and Tritium System Chapter | 6 181

it is desirable to develop the algorithms and methodologies for their optimisa-
tion design.
The past few decades saw a radical modernisation of the vacuum equip-
ment as a response to the challenges presented by experimental physics.
Not only the in-line equipment and practices, but also the conventional con-
ceptual apparatus, based on the averaged state parameters of a rarefied gas,
were fundamentally updated [3]. This subject is treated in more detail in
Section 6.7.
Currently, the MFR vacuum system design ideology relies on the following
principles:

l Vacuum processes and equipment minimising the influx of impurities into
the plasma are given absolute priority [4].
l The design and parameter optimisation of the vacuum path should be based
on the analysis of gas flow spatial distribution.
l The heated chambers used in the design should be made of high-quality
non-magnetic steels and alloys and should be covered with special plasma-
resistant materials.
l Vacuum path integration using cryogenic sorption pumps [5].
l Implementation of electrochemical, thermal and ion-plasma techniques of
wall cleansing (conditioning) in addition to mechanical methods to bring
down carbon, oxide and water vapour surface concentrations and reduce the
influx of impurities.
l Establishing, based on these principles, an optimised flow chart of the vacu-
um chamber manufacture and operation process [6].

6.2 PHYSICAL PROCESSES IN THE VACUUM CHAMBER
In outline, the MFR operating cycle looks like this: a deuterium–tritium (D–T)
−5
fuel mix is injected at ∼1 mPa into a vacuum chamber evacuated to ∼10 Pa.
The mix is then ionised, and the plasma current is increased by vortex electric
field. This current heats the plasma to ∼1 keV and helps detach it from the wall,
giving rise to the formation of a plasma column. After that, additional heating
systems increase the plasma temperature to the level, at which a self-sustained
fusion reaction begins. It takes several tens of seconds to obtain a basic plasma
configuration [7].
The fusion reaction may take one of the following paths:
3
D (D, n) He, (a)
D (D, p) T, (b)
4
3
D ( He, p) He, (c)
4
D (T, n) He. (d)
Reaction (d) is a resonant reaction, and its cross-section is two orders of
magnitude larger than that of reactions (a) and (b). In practice, only the D–T
fuel, in which the two components are mixed in equal amounts, has significance