Principles of Fusion Energy Generation
The fusion reaction between deuterium and tritium releases huge amounts of energy. Fusion of a fraction of a gram of material (about 1/30th of a gram) releases the amount of energy contained in two barrels of oil. This is one essential aspect of an ideal energy source. There is no possibility of more fusion energy being released than planned, because only the desired amount of fuel is injected and subjected to the demanding technical processes that will bring the fuel to the very special conditions that will initiate the reaction. These special conditions, and the processes to bring the fuel to them, are described in summary form below.
The essential challenge of fusion is that the fuel nuclei are electrically charged with
the same “sign”. The electrostatic (Coulombic) force pushes the nuclei apart,
opposing their coming close enough together for the nuclear force to take over and
cause fusion to occur. To get past this “Coulomb barrier”, the nuclei must be on a
collision course at very high speed. This means the fuel must be raised to extreme temperatures.
Figure T-2. Ignition and burn parameter space
Accelerator technology, under development for most of a century, has been
essential to mankind’s deepening understanding of nature. By the early 1970's, the storied development of “atom smashers” had achieved the ability to accelerate
electrons, protons and heavy ions to very high energy – much higher than the
energy per “particle” required in the accelerator drivers needed to initiate fusion.
(See Figure T-3.) It is important for practical fusion power, as planned by FPC,
that accelerator technology is a mature technology. Once the desired ion source is
identified and the desired particle energy is specified, engineers can design and
build a machine to supply the needed number of particles (ionized heavy ions in
HIF) in the desired (very short) time window. In our case, this requires a linear
accelerator that is several miles long.
Linear accelerators are a known technology, similar to that used in hundreds of
accelerator facilities around the world. The short stopping distance of heavy ions
(i.e., comparable to dimension of the fuel pellet) allows each ion to be high-energy,
many billions of “electron-Volts, or eV.” (Note the eV units on the vertical axis in
Figure T-3. M is for mega or millions, G for giga or billions, etc.)
Since Power = Volts x Amps, raising the particle energy translates to reducing the
particle current (beam current). While the technology to attain high energy per
particle was well established by 1975, the big discovery of that year was that
rearrangement of the known accelerator hardware could provide the robust ignition
beams needed to get into the high gain regime that is shown in Figure T-2. The
same spirit of innovation and creativity that led to the steady advances shown in
Figure T-3 would achieve the total beam current needed for the beam to have
Power = Energy x Current ~ 1 PW (a petaWatt is one million billion Watts); this is
the canonical instantaneous power requirement for igniting inertial confinement
Heavy ion accelerator drivers have another special advantage for reliable ignition.
This is the ability to achieve the two-step process called “fast ignition”. More
efficient than using the same process that compresses the fuel to ignite a central
“hot spot”, in fast ignition a separate, very sharp pulse (high peak-power and less
than 1/10 the duration of the compression process) is used to ignite only the
desired mass of fuel after it has been compressed. The “fast ignited” fuel sets off
the rest of the fuel much like a blasting cap sets off a stick of dynamite. The great
importance of this feature of FPC’s driver (also a feature of the Russian design) is
that the required fuel compression has been within the state of the art for some
years already, as noted previously.
The space in which the fusion reactions take place is called a reaction chamber.
which has been crucial in achieving new discoveries by the steadily increased capabilities. The
capabilities needed for HIF accelerator-drivers have been present since 1975
Three factors influence its design. First, the chamber needs to hold a good vacuum
to enable the heavy ions from the accelerator system to reach the fuel pellet and to
provide a secure containment vessel for the capture of the tritium that is generated after the reaction takes place. Second, the chamber must be able to withstand the
pressure generated by the fusion reaction. And third, the reaction chamber must
contain a liquid that can be heated to a high temperature as part of the energy
extraction process. All of this has been designed on paper, and unique hardware
has been demonstrated, but an integrated fusion system has, of course, never been
built. Reaction chambers for ICF experiments have been built at numerous
installations worldwide, the largest of which is part of the National Ignition
Facility at the Lawrence Livermore National Laboratory.
There is a fourth factor that must also be considered in the design of the reaction
chamber. As stated earlier, the neutrons produced by the fusion reaction carry 80%
of the reaction’s energy. The energy must be captured as thermal energy, for
downstream conversion to electricity and other energy products, and the neutrons
must be prevented from degrading the structural properties of the chamber
materials. FPC’s chamber concept accomplishes all the required missions, and
much more. The numerous advantages of the chamber’s configuration include a unique combination of long chamber life and the high temperatures in working fluid that are needed for efficient energy conversion. Ultimately, the set of advantages results in very large economic benefits. (Also see chamber summary .)
Figure T-4.1 StarPower Reaction Chamber ready for ignition
Figure T-4.2 Microseconds after ignition
Nanoseconds after the fusion reactions take place, the lithium sphere has vaporized and an expanding sphere of lithium plasma (ionized gas) is now present. As this plasma expands, it cools by radiation (photon flow), expansion, and by interaction with lithium droplets and sprays throughout the chamber. (Figure T-4.2)
We generally think that fusion power plants will be sources of electricity. FPC's
Figure T-5 Schematic of the Heat Exchange Process, illustrating use for electricity generation
StarPower System (SPS) will also produce electricity, but electricity will not be the
only product, and may not be the primary product. The availability of very high
temperature heat permits the consideration of another process of energy conversion
and that is the direct production of hydrogen from the thermal disassociation of
water. The known, and well researched, Sulfur–Iodine process and the high
temperature electrolysis process both produce hydrogen at about 50% efficiency.
Hydrogen is the key component in the production of synthetic fuels and can be
produced from SPS systems at a cost comparable to the cost of production from
reforming of natural gas. The hydrogen can be used directly as a fuel source or it
can be combined with carbon to form various hydrocarbons including gasoline,
kerosene (jet fuel), or diesel oil. Since these latter fuels support the existing
transportation infrastructure, we intend to focus our hydrogen output on production
of these synthetic fuel products.
The source of carbon can be biomass, or coal, or the CO2 in the atmosphere.
Evaluation of the technology for extracting CO2 from the atmosphere by the Los
Alamos National Laboratory concluded that this technology is now mature enough
that it is viable as a source of CO2. Since we have to dispose of waste heat in any
case, why not use the waste heat to drive a cooling tower that processes a large
volume of air and extracts the CO2 from it? Carbon from an atmospheric source is
slightly more expensive than carbon from coal, but the use of atmospheric carbon means that the liquid fuel we produce would become carbon neutral – the carbon
comes from the atmosphere and returns to the atmosphere again when the fuel is
The processes for conversion of hydrogen and CO2 to form synfuels is a mature
industrial process that has been used by Exxon-Mobil in the past and is currently
being used by Sasol to produce liquid fuels in plants in South Africa and Arabia.
Until now, the constraint for the production of synthetic fuels has been the
availability of an inexpensive source of hydrogen. The heat from an SPS will
remedy this shortcoming and make the synthesis of liquid fuel possible at a cost
less than the current cost of the same fuel from a crude oil feedstock.
Fusion power promises to be much more efficient than conventional electrical
power sources. A fission power plant converts about one third of the energy in the
fuel to useful power sent to the customer as electricity. This is because the Carnot
(ideal) efficiency is necessarily low since the energy conversion process for fission
is constrained by a low ratio of the input and output temperatures. The ambient
temperature of the environment outside the plant sets the output temperature, but
the input temperature in fission plants is constrained by the limits imposed on the
materials of the pressure vessel. The efficiency of energy conversion in other
fusion systems encounters similar temperature constraints. Their chamber designs
perform similar roles, which lead to similar temperature constraints on their
materials, which need to operate slightly above the temperature of the steam that
will drive the turbines.
In contrast, FPC’s chamber system produces very high temperature heat at the
same time that the chamber operates at uniquely low temperatures. For initial
operations, we base our revenue estimates on the conservative use of conventional
electricity generation using steam turbine systems. However, the high temperatures
phases that the lithium passes through in each fusion power sequence can be
exploited to raise the efficiency by implementing advanced energy conversion
The earliest of the advanced techniques to be implemented will be high
temperature gas turbines, as illustrated in Figure T-5. By transferring the heat at
the highest temperature, near the condensation temperature of lithium, to a gas such as helium, the efficiency would reach the higher levels that are a well-known
advantage of combined-cycle power plants fired by natural gas.
Exciting prospects for further efficiency increases in the future involve the direct
conversion that becomes a possibility because of the existence of a plasma state
during the first phase of the lithium’s cycle. (Figure T-6) Because the
temperature of this plasma will be above 20,000 oC, 50 percent or more of the heat
can be converted “off the top” before the lithium temperature decreases (by further
expansion and mixing with lithium rain) to be compatible with the steel tubes of
heat exchangers. Considering the ideal efficiency of a thermodynamic process
starting at 20,000 oC, overall efficiencies as high as 90 percent are seen to be
possible. This underscores the fact that releasing fusion energy will not be the end
of the story, but the beginning of a continuous improvement process, as has been
the history with steam power, internal combustion, and even batteries. Most
remarkably, these prospects for developing extraordinarily high efficiencies, which
depend on having extraordinarily high temperatures, are made possible by the
design that keeps the temperature of the structural materials of FPC’s chamber at
extraordinarily low levels.
Hundreds of accelerators exist in the world. All are designed using ordinary
materials that are readily available. The materials needed for our Heavy Ion
Fusion accelerator will be no different than for these other machines. The
accelerator will be longer than Stanford’s original SLAC accelerator (built in the1960s) or Germany’s UNILAC (built in the 1970s), but it will continue to use the
latest versions of the same technology. The precision tunneling employed in the
construction of large accelerators will be applied to the design and construction of
the first SPS, as well as all of its successors.
The ion source system is a unique element in the FPC design. It will use heavy
isotopes rather than electrons or protons as used in most accelerators. But this
technology is also mature. Heavy ion accelerators operate at numerous
laboratories in the US, Europe, and Asia. Our system will be different in that we
will use a multiplicity of single-isotope ion sources. This requires a supply of the
specific isotopes of the elements we plan to use – xenon, tin, lead, and mercury –
elements chosen first to achieve the requirements for fusion ignition and second for
their abundance of isotopes within the mass range that we want to use. Most
likely, preparation of these single isotope supplies will be special for our project.
The materials and technologies used to construct the reaction chambers are
common to many high-stress, high-temperature applications, such as in refineries,
metal processing industries, and rocket engines. Because our chamber operates at
temperatures lower than any other power plant based on heat, and because the
hazards of radiation are very much lower (in kind and amount) than in fission
power plants, we anticipate some relaxation of the expensive “N-stamp” required
for fission systems. We expect to benefit, however, from the excellent steels and
processes that have been developed for fission systems, including those for liquid
metal heat exchangers.
No special or 'magic' materials are needed. FPC's chamber does not face the problem posed by fusion’s high-energy neutrons for most of the other fusion chamber concepts. The protection of the system from the fusion neutrons is based on our unique use of the lithium needed to generate the tritium fuel. Our system for
handling lithium benefits from experience that dates from early in the space
program and from liquid metal fission systems, as well as from fusion energy
Lithium was considered a rare and hazardous metal until recently. The use of
lithium in batteries for electronic equipments, and even electric automobiles, has
changed much of that. Safe handling and packaging processes have been
developed and the metal is now in many household goods, from cameras to
computers. Its supply has expanded as well and it is now produced in quantities
needed to supply the start-up of several fusion power plants per year. For long-term operations, and for the build out of the fusion energy system worldwide, we
will extract lithium from seawater.
Modern engineering design is highly dependent on computational technology in
roles from computer assisted drafting to detailed component modeling and
manufacture. This project is no exception. We will design and model all aspects
of the system in a computer prior to construction. Besides assuring that all
components fit together, this will build the end-to-end model to simulate operation
of the system and define flow of data for precise and safe system control.
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