Neutral Beam Injection
Encyclopedia
To initiate a sustained fusion
reaction, it is usually necessary to use many methods to heat the plasma, including RF
heating, electron
cyclotron
resonance
heating (ECRH), ion
cyclotron
resonance
heating (ICRH), and neutral beam injection.
Neutral Beam Injection (NBI) involves injecting a high-energy beam of neutral atom
s, typically a hydrogen
isotope
such as deuterium
, into the core of the plasma
. These energetic atoms transfer their energy to the plasma, raising the overall temperature.
Although the atoms are injected with no net electrostatic charge, as the beam passes through the plasma, the atoms are ionized as they bounce off the ions already in the plasma. Because the magnetic field inside the torus is circular, these fast ions are confined to the background plasma.
The confined fast ions mentioned above are slowed down by the background plasma, in a similar way to how air resistance
slows down a baseball. The energy transfer from the fast ions to the plasma increases the overall plasma temperature.
It is very important that the fast ions are confined within the plasma long enough for them to deposit their energy. Magnetic fluctuations are a big problem for plasma confinement in this type of device (see plasma stability
) by scrambling what were initially well-ordered magnetic fields. If the fast ions are susceptible to this type of behavior they can escape very quickly. But there is evidence to suggest that they aren't.
The text in this article is derived from the Madison Symmetric Torus
page.
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
reaction, it is usually necessary to use many methods to heat the plasma, including RF
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
heating, electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
heating (ECRH), ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
heating (ICRH), and neutral beam injection.
Neutral Beam Injection (NBI) involves injecting a high-energy beam of neutral atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s, typically a hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
such as deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...
, into the core of the plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
. These energetic atoms transfer their energy to the plasma, raising the overall temperature.
Although the atoms are injected with no net electrostatic charge, as the beam passes through the plasma, the atoms are ionized as they bounce off the ions already in the plasma. Because the magnetic field inside the torus is circular, these fast ions are confined to the background plasma.
The confined fast ions mentioned above are slowed down by the background plasma, in a similar way to how air resistance
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
slows down a baseball. The energy transfer from the fast ions to the plasma increases the overall plasma temperature.
It is very important that the fast ions are confined within the plasma long enough for them to deposit their energy. Magnetic fluctuations are a big problem for plasma confinement in this type of device (see plasma stability
Plasma stability
An important field of plasma physics is the stability of the plasma. It usually only makes sense to analyze the stability of a plasma once it has been established that the plasma is in equilibrium. "Equilibrium" asks whether there are net forces that will accelerate any part of the plasma...
) by scrambling what were initially well-ordered magnetic fields. If the fast ions are susceptible to this type of behavior they can escape very quickly. But there is evidence to suggest that they aren't.
The text in this article is derived from the Madison Symmetric Torus
Madison Symmetric Torus
The Madison Symmetric Torus is a reversed field pinch physics experiment with applications to both fusion energy research and astrophysical plasmas located at University of Wisconsin-Madison...
page.