Heavy Ion Fusion Process
Heavy ion accelerator drivers can provide the energetic ignition beams needed for Inertial Confinement Fusion (ICF) that are beyond the capabilities of laser technologies. These accelerator systems also possess the repetition rate, efficiency, and durability needed for power production.
Fusion power is not a distant hope. It is at our doorstep. In fact, it could have been done a decade or more ago. The requirements for practical fusion power are known, but the ramifications of using known accelerator technology on the timeline to fruition are widely misinterpreted. National priorities in 1979, when the HIF ICF process was initially ready to be pursued, were not in favor of fusion, and consummation of this effort has been delayed until now - when priorities for a new energy source are paramount.
A known technology with a known solution that can solve our greatest known problem - the lack of a viable future energy supply.
In the ICF approach known as Heavy Ion Fusion (HIF), beams of high-energy heavy ions provide the energy to compress and ignite fusion fuel. The processes are intense and brief; the fuel “burns” in the brief moment before it dissipates—less than a billionth of a second . Development of inertial confinement fusion (ICF) began in 1962, shortly after the invention of the pulsed (Q-switched) ruby laser. In 1976, a special workshop called by the US Energy Research and Development Administration (now DOE) concluded that the technology of high energy particle accelerators holds all the capabilities required for power production using ICF.
The engineering attributes of particle accelerators are essential for economic power production. In routine operation, accelerators convert electricity from the mains to beam energy with high efficiency; pulse (unless d.c.) many times per second; and last until supplanted by new accelerator technology. These attributes complete the picture for power plants, but more basic is the ability of heavy ions to provide ignition beams with the robustness needed to achieve ignition with confidence.
Fuel compression is the key to scaling fusion explosions down. When the fusion burn starts in fuel that has been compressed to high density, the fusion reactions heat the fuel to still higher temperature, which accelerates the reaction rate. The surrounding fuel ignites in a “propagating burn”, resulting in the fusion energy output being many times the input for ignition. ICF research has demonstrated fuel compression to hundreds of times the density of solid hydrogen isotopes.
The degree of compression already demonstrated in ICF research is sufficient for Heavy Ion Fusion using the FPC driver. This is because HIF will employ the process known as fast ignition, the benefits of which are shown in the figure above. Representing the results of fifty years of intensely exploring the limits of compression, the curve labeled "Fast ignition (laser)" illustrates the boost that the National Ignition Facility would get if a laser could achieve fast ignition. The obstacle to laser-driven fast ignition is the inability of laser light to penetrate matter at normal solid density. In contrast, heavy ion beams penetrate solid matter according to physics that has been in standard practice for three-quarters of a century.
A decisive factor is the physics of how the beam energy couples into the fuel target. The figure above shows the large increase in the ratio of energy out to energy in (“gain”) that results from separating the process of fuel compression from that of ignition. This process called “fast ignition” is analogous to using a blasting cap to ignite a stick of dynamite; compressing the fuel renders it “explodable”, the “fast ignition” spark sets it off. But the NIF “point design” in the figure shows that fast ignition by laser is, as put by the leader of the NIF program, “futuristic”, owing to the exquisite complexity of the physics proposed to get some of the laser energy from its stopping point in “underdense” matter to where it is needed in the compressed fuel. In stark contrast, heavy ions can access the ideal location in the compressed fuel via the “classical physics” known since Neils Bohr provided the formula in 1926. With beams carrying the energy needed for ignition, and having the ability to put the energy in the right places in the target, and being created by technology having efficiency and engineering robustness, HIF has the “right stuff” for fusion power.
At the time that President Reagan said: “Now, the same scientists that brought us these terrible weapons will make them impotent and obsolete.”, those same words could have been used to announce that the US would defuse the tensions of the world by developing an abundant source of affordable energy that was not prone to the inevitable tensions arising from nature’s capricious placement of fossil fuel resources.
The figure below illustrates the essence of the challenge of power production from inertial confinement fusion (ICF). In real terms as well as qualitative, the essential requirement is to displace the use of a fission explosion to ignite a much smaller fusion explosion. The conventional process for miniaturization of any invention is to reduce the size in moderate steps. In the absence of a large driver, development of ICF has been dominated by scaling up laser technology. The blue shaded region illustrates the limitations of lasers.
When accelerators demonstrated storage of megajoules of beam energy (approximately the energy from a stick of dynamite) in 1975, and it was realized that accelerating heavy ions instead of protons (hydrogen nuclei) would cause such energy to deposit efficiency in ICF’s small targets, the accelerator community came forward to join with their colleagues in the ICF community to achieve fusion power in a joint effort.
Fusion power is not a distant hope. It is currently a realizable technology, FPC's fusion technology can be applied today. It can, and will, solve our energy problem.
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