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Colliding beam fusion
Colliding beam fusion (CBF), or colliding beam fusion reactor (CBFR), is a class of fusion power concepts that are based on two or more intersecting beams of fusion fuel ions that are independently accelerated to fusion energies using a variety of particle accelerator designs or other means. One of the beams may be replaced by a static target, in which case the approach is termed accelerator based fusion or beam-target fusion, but the physics is the same as colliding beams.
CBFR offers more efficient ways to provide the activation energy for fusion, by directly accelerating individual particles rather than heating a bulk fuel. The CBFR reactants are naturally non-thermal which gives them advantages, especially that they can directly carry enough energy to overcome the Coulomb barrier of aneutronic fusion fuels. This makes them attractive for use with alternative fuels like proton-boron, which cannot be used in traditional designs.
CBFRs face several problems that have limited their ability to be seriously considered as candidates for fusion power. When two ions collide, they are more likely to scatter than to fuse. Magnetic confinement fusion reactors overcome this problem using a bulk plasma and confining it for some time so that the ions have many thousands of chances to collide. Two beams colliding give ions little time to interact before the beams fly apart. This limits how much fusion power a beam-beam machine can make.
Several designs have sought to address the shortcomings of earlier CBFRs, including Migma, MARBLE, MIX, and other beam-based concepts. These attempt to overcome the fundamental challenges of CBFR by applying radio waves, bunching beams together, increasing recirculation, or applying some quantum effects. None of these approaches have succeeded yet.
Fusion takes place when atoms come into close proximity and the nuclear force pulls their nuclei together to form a single larger nucleus. Counteracting this process is the positive charge of the nuclei, which repel each other due to the electrostatic force. For fusion to occur, the nuclei must have enough energy to overcome this coulomb barrier. The barrier is lower for atoms with less positive charge: those with the fewest protons in the nucleus. The nuclear force increases with more nucleons: the total number of protons and neutrons. This means that a combination of deuterium and tritium has the lowest coulomb barrier, at about 100 keV (see requirements for fusion).
When the fuel is heated to high energies the electrons disassociate from the nuclei, which are left as individual ions and electrons mixed in a gas-like plasma. Particles in a gas are distributed across a wide range of energies in a spectrum known as the Maxwell–Boltzmann distribution. At any given temperature the majority of the particles are at lower energies, with a "long tail" containing smaller numbers of particles at much higher energies. So while 100 keV represents a temperature of over one billion degrees, to produce fusion events, the fuel does not need to be heated to this temperature as a whole: some reactions will occur even at lower temperatures due to the small number of high-energy particles in the mix.
As the fusion reactions give off large amounts of energy, and some of that energy will be deposited back in the fuel, these reactions heat the fuel. There is a critical temperature at which the rate of reactions, and thus the energy deposited, balances losses to the environment. At this point the reaction becomes self-sustaining, a point known as ignition. For D-T fuel, that temperature is between 50 and 100 million degrees. The overall rate of fusion and net energy release is dependent on the combination of temperature, density and energy confinement time, known as the fusion triple product.
Two primary approaches have developed to attack the fusion power problem. In the inertial confinement approach, the fuel is quickly squeezed to extremely high densities, which also increases the internal temperature through the adiabatic process. There is no attempt to maintain these conditions for any period of time, the fuel explodes outward as soon as the external force is released. The confinement time is on the order of microseconds, so the temperatures and density must be very high for any appreciable amount of the fuel to undergo fusion. This approach has been successful in producing fusion reactions, but to date, the devices that can provide the compression, typically lasers, require far more energy than the reactions produce.
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Colliding beam fusion
Colliding beam fusion (CBF), or colliding beam fusion reactor (CBFR), is a class of fusion power concepts that are based on two or more intersecting beams of fusion fuel ions that are independently accelerated to fusion energies using a variety of particle accelerator designs or other means. One of the beams may be replaced by a static target, in which case the approach is termed accelerator based fusion or beam-target fusion, but the physics is the same as colliding beams.
CBFR offers more efficient ways to provide the activation energy for fusion, by directly accelerating individual particles rather than heating a bulk fuel. The CBFR reactants are naturally non-thermal which gives them advantages, especially that they can directly carry enough energy to overcome the Coulomb barrier of aneutronic fusion fuels. This makes them attractive for use with alternative fuels like proton-boron, which cannot be used in traditional designs.
CBFRs face several problems that have limited their ability to be seriously considered as candidates for fusion power. When two ions collide, they are more likely to scatter than to fuse. Magnetic confinement fusion reactors overcome this problem using a bulk plasma and confining it for some time so that the ions have many thousands of chances to collide. Two beams colliding give ions little time to interact before the beams fly apart. This limits how much fusion power a beam-beam machine can make.
Several designs have sought to address the shortcomings of earlier CBFRs, including Migma, MARBLE, MIX, and other beam-based concepts. These attempt to overcome the fundamental challenges of CBFR by applying radio waves, bunching beams together, increasing recirculation, or applying some quantum effects. None of these approaches have succeeded yet.
Fusion takes place when atoms come into close proximity and the nuclear force pulls their nuclei together to form a single larger nucleus. Counteracting this process is the positive charge of the nuclei, which repel each other due to the electrostatic force. For fusion to occur, the nuclei must have enough energy to overcome this coulomb barrier. The barrier is lower for atoms with less positive charge: those with the fewest protons in the nucleus. The nuclear force increases with more nucleons: the total number of protons and neutrons. This means that a combination of deuterium and tritium has the lowest coulomb barrier, at about 100 keV (see requirements for fusion).
When the fuel is heated to high energies the electrons disassociate from the nuclei, which are left as individual ions and electrons mixed in a gas-like plasma. Particles in a gas are distributed across a wide range of energies in a spectrum known as the Maxwell–Boltzmann distribution. At any given temperature the majority of the particles are at lower energies, with a "long tail" containing smaller numbers of particles at much higher energies. So while 100 keV represents a temperature of over one billion degrees, to produce fusion events, the fuel does not need to be heated to this temperature as a whole: some reactions will occur even at lower temperatures due to the small number of high-energy particles in the mix.
As the fusion reactions give off large amounts of energy, and some of that energy will be deposited back in the fuel, these reactions heat the fuel. There is a critical temperature at which the rate of reactions, and thus the energy deposited, balances losses to the environment. At this point the reaction becomes self-sustaining, a point known as ignition. For D-T fuel, that temperature is between 50 and 100 million degrees. The overall rate of fusion and net energy release is dependent on the combination of temperature, density and energy confinement time, known as the fusion triple product.
Two primary approaches have developed to attack the fusion power problem. In the inertial confinement approach, the fuel is quickly squeezed to extremely high densities, which also increases the internal temperature through the adiabatic process. There is no attempt to maintain these conditions for any period of time, the fuel explodes outward as soon as the external force is released. The confinement time is on the order of microseconds, so the temperatures and density must be very high for any appreciable amount of the fuel to undergo fusion. This approach has been successful in producing fusion reactions, but to date, the devices that can provide the compression, typically lasers, require far more energy than the reactions produce.