Download The Tokamak Fusion Test Reactor (TFTR) was first proposed in

The Tokamak Fusion Test Reactor (TFTR) was first proposed in 1973 and began
construction in 1976. The rector began its operation in 1982 and continued until 1997.
Through this time it operated first off of just DD reactions and then in 1993 it changed to
D-T fusion. TFTR operated with D-T for over 3 years, achieving a peak fusion power of
10.7 MW, producing over 1 GJ of fusion energy and providing a demonstration of the
feasibility of operating a fusion power plant. As a result of its overwhelming success it
demonstrated that “fusion research is ready to advance to the study of burning plasmas.”
From the above picture two types of fusion reactions are shown. The one two the left
is the reaction that TFTR utilizes in its chamber. For this process to occur the plasma
in the chamber must be heated to a sufficient temperature, which is a minimum of
20keV. Some of the methods used to reach this energy state are Electrical Resistance
(ohmic) heating, Neutral Beam Injection (NBI) heating, electron magnetic wave
heating, adiabatic compression of plasma and alpha particle heating in D-T plasma.
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Electrical Resistance heating or ohmic heating is a method that utilizes the
electrical conductivity of the plasma. This is done by passing a current through
the plasma, which is a similar heating process that an electric light bulb or an
electric heater experience. The heat produced by this process is dependent on the
amount of resistance that is generated by the plasma and the current. A problem
that develops with this method is that when the plasma is heated up the resistance
drops and the ohmic heating process becomes less effective. As a result of this
ohmic heating is not a suitable heating process by its self. The reason for this is
that the maximum plasma temperature attainable by this process is 20 to 30
million degrees Celsius which is far to less for fusion to be attained.
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The NBI is an acceleration of ions which are then neutralized and cross a
magnetic field to enter plasma (100keV in TFTR). ). "Neutral-beam injection
involves the introduction of high-energy (neutral) atoms into the ohmically
(heated, magnetically) confined plasma. The atoms are immediately ionized and
are trapped by the magnetic field. The high-energy ions then transfer part of their
energy to the plasma particles in repeated collisions, thus increasing the plasma
temperature."
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The electron magnetic wave process increases the heat in the chamber by
launching waves near the ion cyclotron frequency into plasma to heat ions. A
cyclotron is “a circular particle accelerator in which charged subatomic particles
generated at a central source are accelerated spirally outward in a plane
perpendicular to a fixed magnetic field by an alternating electric field.” A
cyclotron is capable of generating particle energies between a few million and
several tens of millions of electron volts. In radio frequency heating, high
frequency waves are generated by oscillators outside the torus. When the waves
produce a certain frequency or wavelength their energy can be transferred to
charged particles in the plasma. Theses charged particles then collide with other
plasma particles, which increases the temperature of the bulk plasma.
In an operating fusion reactor part of the energy needed to sustain the fusion process
well be provided by the energy generated by the rector itself. This is achieved by
introducing fresh deuterium and tritium into the chamber. For this to occur the
plasma needs to be heated to an initial temperature of 10 million degrees Celsius. The
TFTR didn’t produce sufficient fusion energy to maintain this plasma temperature
(nor has any other tokamak currently attained this level of efficiency). As a result of
this the fusion chamber operates in short pulses and the plasma must be heated afresh
for every pulse.
This image is a depiction of a plasma fusion chamber after an injection of frozen D2
pellets.
From the above pictures one can gain a perspective of what the future hold for
industrial tokamak energy providers. Though TFTR was not able to achieve a fusion
power output equal with the plasma heating power input, most scientist are very
confident that this will be accomplish do to how close they have come to attaining
this goal. From the results of the TFTR it suggest that D-T plasmas have better
confinement that their D-D counterparts. As a result of this understanding scientist
are becoming confident that they will be able to build a fusion reactor which will
generate gigawatts of surplus energy. One of the main challenges now is to do it in an
environmental and cost-effective manner.
For the future of plasma fusion reactors to progress one of the major challenges that
persist is sustaining the multi-megawatt power output for a second or longer. This
has become extremly crucial do to the known plasma instabilities which occur much
more quickly. These instabilities have been one of the most challenging advercities
to the program.