fuel, having the “burning temperatures” compatible with many materials (such as
metals or ceramics).
Today, there are two major approaches to confining the fusion fuel at the fusionrelevant temperatures. The first one is the so-called “inertial confinement,” where the
hot fusion fuel is actually not really confined, but the fuel is burned down so fast that
it has not enough time to cool down. In a sense, this approach is analogous to what
happens during the explosion of an H-bomb, but on a much smaller scale tolerable
for the apparatus designed for the inertial confinement. The second one utilizes the
fundamental feature of the matter at high temperatures, where electrons are stripped
from neutral atoms, which results in the formation of plasma consisting of negatively
charged electrons and positively charged ions.
It should be noted that the plasma we consider in this book has virtually no net
charge since due to the different signs of the charge of electrons and ions, they attract
each other so that the plasma largely moves as a quasi-neutral “fluid” and its inertial
confinement lifetime is determined by the thermal speed of ions which are much
heavier than electrons. At the fusion temperatures ~10
8 K, the thermal speed of the
ions (nuclei) of hydrogen isotopes is about 10
6 m/s. Therefore, if one makes no effort
to confine such a quasi-neutral motion of plasma, the latter would be disintegrated
and cooled down within a short time (this is what actually happens in the inertial
confinement devices). The addition of an external magnetic field drastically changes
the plasma dynamics. Indeed, the charged particles, being subject to the Lorentz
force, cannot move freely across the magnetic field. Instead, they undergo gyromotion around the magnetic field lines. By applying a strong magnetic field, the
gyro-radii of both electrons and ions can be made much smaller than the size of the
apparatus (e.g., for the fusion-relevant temperatures and the strength of the magnetic
field ~1 T, the gyro-radii of the ions of hydrogen isotopes are ~10
À2 m). In addition,
to prevent the particle leakage along the magnetic field lines, one can utilize a closed
toroidal configuration of the external magnetic field so that the charged particles can
only escape across the magnetic field. This is the second major approach to confining
the hot fusion fuel, which is called “magnetic confinement,” Stellarator and tokamak
are two, the most known and advanced, fusion devices using the magnetic confinement. Stellarator, from “stellar,” suggests the device that produces energy like stars,
for example, the Sun. The “tokamak” is an acronym of Russian words “current,”
“chamber,” and “magnetic coils.”
The magnetic field in the magnetic confinement devices (e.g., tokamaks) does not
solve automatically all issues related to harnessing the fusion energy. The fusiongrade plasma is very “fragile” and sensitive to the presence of impurities
(non-hydrogenic species) since they open the plasma energy sink by strongly
enhancing the radiation losses and cooling down the plasma very efficiently (e.g.,
the relative concentration of a heavy impurity such as tungsten in a fusion-grade
plasma must be below 10
À4 ). Therefore, fusion plasma, embedded into a strong
magnetic field, must be insulated from the atmosphere in some vacuum chamber.
The plasma-facing material (PFM) of the vacuum chamber, however, can be eroded
by the impinging ions of even much smaller energy (~few tens of eV) than needed
for fusion. As a result of such erosion, individual atoms, clusters, and even
viii
Preface
metals or ceramics).
Today, there are two major approaches to confining the fusion fuel at the fusionrelevant temperatures. The first one is the so-called “inertial confinement,” where the
hot fusion fuel is actually not really confined, but the fuel is burned down so fast that
it has not enough time to cool down. In a sense, this approach is analogous to what
happens during the explosion of an H-bomb, but on a much smaller scale tolerable
for the apparatus designed for the inertial confinement. The second one utilizes the
fundamental feature of the matter at high temperatures, where electrons are stripped
from neutral atoms, which results in the formation of plasma consisting of negatively
charged electrons and positively charged ions.
It should be noted that the plasma we consider in this book has virtually no net
charge since due to the different signs of the charge of electrons and ions, they attract
each other so that the plasma largely moves as a quasi-neutral “fluid” and its inertial
confinement lifetime is determined by the thermal speed of ions which are much
heavier than electrons. At the fusion temperatures ~10
8 K, the thermal speed of the
ions (nuclei) of hydrogen isotopes is about 10
6 m/s. Therefore, if one makes no effort
to confine such a quasi-neutral motion of plasma, the latter would be disintegrated
and cooled down within a short time (this is what actually happens in the inertial
confinement devices). The addition of an external magnetic field drastically changes
the plasma dynamics. Indeed, the charged particles, being subject to the Lorentz
force, cannot move freely across the magnetic field. Instead, they undergo gyromotion around the magnetic field lines. By applying a strong magnetic field, the
gyro-radii of both electrons and ions can be made much smaller than the size of the
apparatus (e.g., for the fusion-relevant temperatures and the strength of the magnetic
field ~1 T, the gyro-radii of the ions of hydrogen isotopes are ~10
À2 m). In addition,
to prevent the particle leakage along the magnetic field lines, one can utilize a closed
toroidal configuration of the external magnetic field so that the charged particles can
only escape across the magnetic field. This is the second major approach to confining
the hot fusion fuel, which is called “magnetic confinement,” Stellarator and tokamak
are two, the most known and advanced, fusion devices using the magnetic confinement. Stellarator, from “stellar,” suggests the device that produces energy like stars,
for example, the Sun. The “tokamak” is an acronym of Russian words “current,”
“chamber,” and “magnetic coils.”
The magnetic field in the magnetic confinement devices (e.g., tokamaks) does not
solve automatically all issues related to harnessing the fusion energy. The fusiongrade plasma is very “fragile” and sensitive to the presence of impurities
(non-hydrogenic species) since they open the plasma energy sink by strongly
enhancing the radiation losses and cooling down the plasma very efficiently (e.g.,
the relative concentration of a heavy impurity such as tungsten in a fusion-grade
plasma must be below 10
À4 ). Therefore, fusion plasma, embedded into a strong
magnetic field, must be insulated from the atmosphere in some vacuum chamber.
The plasma-facing material (PFM) of the vacuum chamber, however, can be eroded
by the impinging ions of even much smaller energy (~few tens of eV) than needed
for fusion. As a result of such erosion, individual atoms, clusters, and even
viii
Preface