How the free-electron laser works
The free-electron laser (FEL) is an ideal instrument for charting the interactions of light and matter in many of the still unexplored regions of the electromagnetic spectrum. As a laser , it produces light in a single wavelength. Ordinary white light contains particles of light, or photons, with a broad range of different colors. So, when white light strikes an object, it causes a multiplicity of responses. By contrast laser light provokes a far more limited set of reactions. This allows scientists to use it to measure the physical properties of materials with great precision.
Ordinary lasers, however, operate at a fixed frequency. That is, they produce light in only one color. This has limited their usefulness. A number of different types of lasers have been created that produce light at a number of different wavelengths ranging through much of the electromagnetic spectrum. Also, researchers have found ways to alter their output frequencies by using lenses made of special optical materials. Nevertheless, there are a number of regions of the spectrum where few, if any lasers operate.
The FEL is ideal for exploring the unknown regions in the spectrum because it is tunable over a broad range of the spectrum. That enables researchers to study how different materials respond as the wavelength of light impinging on them changes. In addition, the FEL is capable of producing very high power levels. The power level is important in applications like surgery where the beam needs enough energy to vaporize soft tissue and bone.
Both the FEL’s tunability and power are the result of its unusual design. In most other lasers, the lasing process occurs within a liquid, solid or gas. So the wavelengths are limited by those permitted by the electrical structure of the material. Similarly, the power of the beam is limited by the amount of energy that the material can withstand before breaking down.
The FEL, however, is not subject to this limitation because it produces laser light by sending bunches of electrons through a series of magnets in a vacuum. These electrons are first accelerated to nearly the speed of light and then they are sent through a device called a “wiggler” or “undulator.”
The wiggler consists of a series of magnets with alternating north and south poles. As a bunch of electrons travels through this alternating field, it causes them to wiggle back and forth in a fashion that causes them to emit some photons of a specific color. These photons are directed onto a mirror that allows 15 percent of them through and reflects 85 percent back along the beam line. At the end of the beam line is another mirror that reflects the photons back up the beam line. The distance between these two mirrors is set with extreme precision so that each bundle of photons meets a new bunch of electrons starting through the wiggler. These photons stimulate the electrons to produce even more photons. After thousands of iterations the power of the laser beam builds up until it reaches a steady state.
The color of the laser beam can be varied in two ways: putting more power into the electron beam and changing the spacing between the magnets in the wiggler. The Vanderbilt FEL is designed to operate at infrared frequencies and can be tuned from two to nine microns.
Because the production of laser light occurs in a vacuum, an FEL can be designed to operate at extremely high power levels. The Vanderbilt FEL is designed to produce a beam with a peak power of more than 10 Megawatts and an average power of 10 Watts.
Saturday, January 2, 2010
Maxfelaser uses thorium
MaxFeLaser plasma electron accelerator
Physicists have set a new record for the acceleration of electrons by laser-produced plasmas. A team led by Karl Krushelnick of Imperial College in London has accelerated electrons to energies of 300 MeV - a third higher than the previous best - by focusing a high-power laser into a jet of helium gas (Phys. Rev. Lett. 94 245001). However, they discovered that the mechanisms by which the electrons are accelerated changes as the laser intensity is increased.
Recent experimental results with MaxFelasers have demonstrated the generation of energetic electron bunches (energy spread < 10%) in the 100s of MeV to GeV energy range. The availability within different options in terms of length/energy will provide a unique opportunity to explore this field over a wide parameter, with a view to creating stable strong electromagnetic fields generate intense laser interaction with plasma could form the basis of a new generation of extremely compact MHD generators.
Conventional accelerators have to be hundreds of meters or longer to accelerate particles to energies in the GeV range or higher. MaxFeLasers produce plasmas which the laser directly accelerates the electrons form the basis of next-generation "table-top" accelerators because they can support electric fields that are many times stronger than those produced in traditional accelerators.
Physicists have set a new record for the acceleration of electrons by laser-produced plasmas. A team led by Karl Krushelnick of Imperial College in London has accelerated electrons to energies of 300 MeV - a third higher than the previous best - by focusing a high-power laser into a jet of helium gas (Phys. Rev. Lett. 94 245001). However, they discovered that the mechanisms by which the electrons are accelerated changes as the laser intensity is increased.
Recent experimental results with MaxFelasers have demonstrated the generation of energetic electron bunches (energy spread < 10%) in the 100s of MeV to GeV energy range. The availability within different options in terms of length/energy will provide a unique opportunity to explore this field over a wide parameter, with a view to creating stable strong electromagnetic fields generate intense laser interaction with plasma could form the basis of a new generation of extremely compact MHD generators.
Conventional accelerators have to be hundreds of meters or longer to accelerate particles to energies in the GeV range or higher. MaxFeLasers produce plasmas which the laser directly accelerates the electrons form the basis of next-generation "table-top" accelerators because they can support electric fields that are many times stronger than those produced in traditional accelerators.
how much thorium would power the world
How much thorium would it take to power the whole world?
“Thorium, if efficiently utilized in a reactor, is an energy source of such magnitude that it is not difficult to conceive of an entire planet powered by thorium. It is worth considering for a moment that the thorium required to fuel the entire world's electrical needs would fit in a reasonably sized room, and the thorium required would only be about 2% of the mass of uranium mined today.
In a fission reaction, thorium-232 (having been transmuted to uranium-233) will release roughly 190 MeV of energy per fission reaction. Assuming that the original thorium had a mass of 232 atomic units (u), then that is equivalent to 190 MeV/232 u = 820 keV/u.
How much energy is that? If converted to electricity at 50% efficiency (which can be achieved through the use of a helium gas turbine power conversion system), 820 keV/u is equivalent to 11 billion kilowatt-hours per metric ton of thorium. (Note that a billion kilowatt-hours [BKWH] is equivalent to a terawatt-hour [TWH].)
In 2003, it was estimated that the world produced 16.5 trllion kilowatt-hours of electricity. If this had all been produced by liquid-fluoride thorium reactors, this would have required 1500 metric tonnes of thorium. Future energy projections foresee electrical production reaching 21.4 trillion kilowatt-hours by 2015. To bring the entire world's population up to the level of the average American's electrical consumption would require 80 trillion kilowatt-hours.
Is 1500 metric tonnes a lot? Thorium is a very dense material, and 1500 metric tonnes of thorium metal would only occupy 130 cubic meters of volume, or about the volume of a room 23 ft on a side and 9 feet high."
To put the above numbers in perspective a 2000 lb ton (a short ton) of the highest grade coal contains about 20,000,000 btu of energy; a kilowatt is equal to 3,410 btu/hr. This means that if coal could be converted to heat energy at 100% efficiency (the ‘real’ conversion efficiency in the production of electricity is at best about 39%) then it would take 2,000,000 short tons of coal to produce as much thermal energy as 1 metric ton of thorium! Keep in mind also that the thorium fueled reactor would produce NO greenhouse gases at all while the coal fired power stations produce nearly 8,000,000 short tons of carbon dioxide to produce the equivalent heat. Clearly the world needs to take a hard look at producing energy from thorium.
“Thorium, if efficiently utilized in a reactor, is an energy source of such magnitude that it is not difficult to conceive of an entire planet powered by thorium. It is worth considering for a moment that the thorium required to fuel the entire world's electrical needs would fit in a reasonably sized room, and the thorium required would only be about 2% of the mass of uranium mined today.
In a fission reaction, thorium-232 (having been transmuted to uranium-233) will release roughly 190 MeV of energy per fission reaction. Assuming that the original thorium had a mass of 232 atomic units (u), then that is equivalent to 190 MeV/232 u = 820 keV/u.
How much energy is that? If converted to electricity at 50% efficiency (which can be achieved through the use of a helium gas turbine power conversion system), 820 keV/u is equivalent to 11 billion kilowatt-hours per metric ton of thorium. (Note that a billion kilowatt-hours [BKWH] is equivalent to a terawatt-hour [TWH].)
In 2003, it was estimated that the world produced 16.5 trllion kilowatt-hours of electricity. If this had all been produced by liquid-fluoride thorium reactors, this would have required 1500 metric tonnes of thorium. Future energy projections foresee electrical production reaching 21.4 trillion kilowatt-hours by 2015. To bring the entire world's population up to the level of the average American's electrical consumption would require 80 trillion kilowatt-hours.
Is 1500 metric tonnes a lot? Thorium is a very dense material, and 1500 metric tonnes of thorium metal would only occupy 130 cubic meters of volume, or about the volume of a room 23 ft on a side and 9 feet high."
To put the above numbers in perspective a 2000 lb ton (a short ton) of the highest grade coal contains about 20,000,000 btu of energy; a kilowatt is equal to 3,410 btu/hr. This means that if coal could be converted to heat energy at 100% efficiency (the ‘real’ conversion efficiency in the production of electricity is at best about 39%) then it would take 2,000,000 short tons of coal to produce as much thermal energy as 1 metric ton of thorium! Keep in mind also that the thorium fueled reactor would produce NO greenhouse gases at all while the coal fired power stations produce nearly 8,000,000 short tons of carbon dioxide to produce the equivalent heat. Clearly the world needs to take a hard look at producing energy from thorium.
china and thorium
China extended its space ambitions this week with the launch of its third manned mission. The Long-March II-F rocket was launched from the Jiuquan spaceport in Gansu province on Thursday. The flight will last for approximately 70 hours and include China's first spacewalk, which is set to take place on Saturday. The Shenzhou-VII capsule is currently orbiting Earth at a height of 300 kilometers, where astronaut Zhai Zhigang will conduct extra-vehicular activity to oversee the release of a satellite.
China became the third nation after the United States and Russia to independently put a man in space when Yang Liwei went into orbit on the Shenzhou V mission in October 2003. The nation also launched a lunar probe, Chang'e-1, last year to orbit the moon and gather data.
Chinese media stated that this is a critical step in the country's three-step program, which consists of sending a human into orbit, docking spacecraft together to form a small laboratory and finally building a large space station. The Shenzhou VIII and IX missions planned for 2010 will start the development of China's space laboratory. Its long term goals include landing on the moon.
Not all is going according to plan. Chinese state media Xinhua ran a story on the spacewalk, including quotes from the astronauts as if they were in space, on Thursday before the launch had taken place. Xinhua has since pulled the gaffe from its website.
India also has its lunar ambitions in full swing, with plans to launch a flight next month. The Chandrayaan probe has a two-year mission, during which it will orbit the moon and digitally map the lunar surface and scan for minerals such as thorium and uranium.
China became the third nation after the United States and Russia to independently put a man in space when Yang Liwei went into orbit on the Shenzhou V mission in October 2003. The nation also launched a lunar probe, Chang'e-1, last year to orbit the moon and gather data.
Chinese media stated that this is a critical step in the country's three-step program, which consists of sending a human into orbit, docking spacecraft together to form a small laboratory and finally building a large space station. The Shenzhou VIII and IX missions planned for 2010 will start the development of China's space laboratory. Its long term goals include landing on the moon.
Not all is going according to plan. Chinese state media Xinhua ran a story on the spacewalk, including quotes from the astronauts as if they were in space, on Thursday before the launch had taken place. Xinhua has since pulled the gaffe from its website.
India also has its lunar ambitions in full swing, with plans to launch a flight next month. The Chandrayaan probe has a two-year mission, during which it will orbit the moon and digitally map the lunar surface and scan for minerals such as thorium and uranium.
Green Technologies & Alternative Fuels
Introduction to Thorium the fuel of the future.
This is intended to be a location for discussion and education about the value of thorium as a future energy source. Despite the fact that our world is desperately searching for new sources of energy, the value of thorium is not well-understood, even in the "nuclear engineering" community.
The fundamental basis for considering nuclear energy over chemical energy is the binding energy released in each case. Chemical energy is released when the electron configuration of atoms is rearranged through a chemical process (combustion, digestion, etc.) Electrons are bound to nuclei with binding energies measured in electron volts (eV).
The protons and neutrons in an atomic nucleus, on the other hand, are bound with energies measured in millions of electron volts (MeV). Thus, rearranging the nucleus of an atom releases roughly a million times more energy than chemical energy release.
This is intended to be a location for discussion and education about the value of thorium as a future energy source. Despite the fact that our world is desperately searching for new sources of energy, the value of thorium is not well-understood, even in the "nuclear engineering" community.
The fundamental basis for considering nuclear energy over chemical energy is the binding energy released in each case. Chemical energy is released when the electron configuration of atoms is rearranged through a chemical process (combustion, digestion, etc.) Electrons are bound to nuclei with binding energies measured in electron volts (eV).
The protons and neutrons in an atomic nucleus, on the other hand, are bound with energies measured in millions of electron volts (MeV). Thus, rearranging the nucleus of an atom releases roughly a million times more energy than chemical energy release.
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