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[14] ITER Physics Basis: Nucl. Fusion 39, No.12, p2495 (1999)
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Ch.15 Development of Fusion Researches
The major research e\ufb00ort in the area of controlled nuclear fusion is focused on the con\ufb01nement of
hot plasmas by means of strong magnetic \ufb01elds. The magnetic con\ufb01nements are classi\ufb01ed to toroidal
and open end con\ufb01gurations. Con\ufb01nement in a linear mirror \ufb01eld (sec.17.3) may have advantages
over toroidal con\ufb01nement with respect to stability and anomalous di\ufb00usion across the magnetic
\ufb01eld. However, the end loss due to particles leaving along magnetic lines of force is determined
solely by di\ufb00usion in the velocity space; that is, the con\ufb01nement time cannot be improved by
increasing the intensity of the magnetic \ufb01eld or the plasma size. It is necessary to \ufb01nd ways to
suppress the end loss.
Toroidal magnetic con\ufb01nements have no open end. In the simple toroidal \ufb01eld, ions and electrons
drift in opposite directions due to the gradient of the magnetic \ufb01eld. This gradient B drift causes
the charge separation that induces the electric \ufb01eld E directed parallel to the major axis of the
torus. The subsequent E ×B drift tends to carry the plasma ring outward. In order to reduce the
E ×B drift, it is necessary to connect the upper and lower parts of the plasma by magnetic lines
of force and to short-circuit the separated charges along these \ufb01eld lines. Accordingly, a poloidal
component of the magnetic \ufb01eld is essential to the equilibrium of toroidal plasmas, and toroidal
devices may be classi\ufb01ed according to the method used to generate the poloidal \ufb01eld. The tokamak
(ch.16) and the reversed \ufb01eld (17.1) pinch devices use the plasma current along the toroid, whereas
the toroidal stellarator (sec.17.2) has helical conductors or equivalent winding outside the plasma
that produce appropriate rotational transform angles.
Besides the study of magnetic con\ufb01nement systems, inertial con\ufb01nement approaches are being
actively investigated. If a very dense and hot plasma could be produced within a very short time,
it might be possible to complete the nuclear fusion reaction before the plasma starts to expand.
An extreme example is a hydrogen bomb. This type of con\ufb01nement is called inertial con\ufb01nement.
In laboratory experiments, high-power laser beams or particle beams are focused onto small solid
deuterium and tritium targets, thereby producing very dense, hot plasma within a short time.
Because of the development of the technologies of high-power energy drivers, the approaches along
this line have some foundation in reality. Inertial con\ufb01nement will be discussed brie\ufb02y in ch.18.
The various kinds of approaches that are actively investigated in controlled thermonuclear fusion
are classi\ufb01ed as follows:
Reversed \ufb01eld pinch
Stellarator system
Bumpy torus
Open end
Mirror, Tandem mirror
Field Reversal Con\ufb01guration
Ion beam, Electron beam
From Secrecy to International Collaboration
Basic research into controlled thermonuclear fusion probably began right after World War II
in the United States, the Soviet Union, and the United Kingdom in strict secrecy. There are on
record many speculations about research into controlled thermonuclear fusion even in the 1940s.
The United States program, called Project Sherwood, has been described in detail by Bishop
(ref.[1]). Bishop states that Z pinch experiments for linear and toroidal con\ufb01gurations at the
Los Alamos Scienti\ufb01c Laboratory were carried out in an attempt to overcome sausage and kink
15 Development of Fusion Researches 187
instabilities. The astrophysicist L. Spitzer, Jr., started the \ufb01gure-eight toroidal stellarator project at
Princeton University in 1951. At the Lawrence Livermore National Laboratory, mirror con\ufb01nement
experiments were conducted. At the Atomic Energy Research Establishment in Harwell, United
Kingdom, the Zeta experiment was started (ref.[2]) and at the I.V. Kurchatov Institute of Atomic
Energy in the Soviet Union, experiments on a mirror called Ogra and on tokamaks were carried
out (ref.[3]).
The \ufb01rst United Nations International Conference on the Peaceful Uses of Atomic Energy was
held in Geneva in 1955. Although this conference was concerned with peaceful applications of
nuclear \ufb01ssion, the chairman, H.J. Bhabha, hazarded the prediction that ways of controlling fusion
energy that would render it industrially usable would be found in less than two decades. However,
as we have seen, the research into controlled nuclear fusion encountered serious and unexpected
di\ufb03culties. It was soon recognized that the realization of a practical fusion reactor was a long
way o\ufb00 and that basic research on plasma physics and the international exchange of scienti\ufb01c in-
formation were absolutely necessary. From around that time articles on controlled nuclear fusion
started appearing regularly in academic journals. Lawson\u2019s paper on the conditions for fusion was
published in January 1957 (ref.[4]), and several important theories on MHD instabilities had by
that time begun to appear (ref.[5],[6]). Experimental results of the Zeta (ref.[7]) (Zero Energy
Thermonuclear Assembly) and Stellarator (ref.[8]) projects were made public in January 1958. In
the fusion sessions of the second United Nations International Conference on the Peaceful Uses of
Atomic Energy, held in Geneva, September 1-13, 1958 (ref.[9],[10]), many results of research that
had proceeded in secrecy were revealed.
L.A.Artsimovich expressed his impression of this conference as \u201csomething that might be called a
display of ideas.\u201d The second UN conference marks that start of open rather than secret interna-
tional cooperation and competition in fusion research.
In Japan controlled fusion research started in Japan Atomic Energy Institute (JAERI) under the
ministry of science and technology and in Institute of Plasma Physics, Nagoya University under
the ministry of education and culture in early 1960\u2019s.
The First International Conference on Plasma Physics and Controlled Nuclear Fusion Research
was held in Salzburg in 1961 under the auspices of the International Atomic Energy Agency (IAEA).
At the Salzburg conference (ref.[11]) the big projects were fully discussed. Some of there were Zeta,
Alpha, StellaratorC, Ogra, and DCX. Theta pinch experiments (Scylla, Thetatron, etc.) appeared
to be more popular than linear pinches. The papers on the large scale experimental projects such as
Zeta or StellaratorC all reported struggles with various instabilities. L.A. Artsimovich said in the
summary on the experimental results: \u201cOur original beliefs that the doors into the desired regions
of ultra-high temperature would open smoothly...have proved as unfounded as the sinner\u2019s hope of
entering Paradise without passing through Purgatory.\u201d The importance of the PR-2 experiments of
M.S. Io\ufb00e and others was soon widely recognized (vol.3, p.1045). These experiments demonstrated
that the plasma con\ufb01ned in a minimum