Impact fusion concept has some outstanding features such as “standing off” and high drive efficiency. Historically, as people expected large projectile and excessively high ignition energy, the idea was abandoned because there is no way to accelerate a gram size projectile to necessary hyperspeed. Here we present a new approach, using a millimeter-size diamond bullet, and crystal solid DT methane as the fusion fuel. DT methane has twice DT concentration and five times alpha particle stopping power than DT ice. The smaller size of the bullet is to achieve a “fast ignition” like concept, instead of global compression of former schemes. The physics of this new impact fusion is discussed, and an estimation of ignition energy is presented. With all inborn advantages, impact fusion energy can be very promising.
Each fusion approach has its own problems, but there is one in common, i.e., some components and/or the confinement chamber wall are too close to the fusion spot/area. This will cause great damage to the cable, stand, optic lens, etc., and impose too heavy load to the reaction chamber wall. This is the notorious “standing-off” problem of fusion energy research, specially in inertial con¯nement schemes. Current main stream inertial fusion energy schemes, i.e., laser, Z-pinch, heavy ion,also share another major defect of low drive efficiency. In these schemes, typically less than 10 percent of the injected laser, ion beam, electrical energy can be converted into the hydrodynamic imploding energy.
Impact fusion schemes are free of the above two problems. They also have extra bene¯ts which are attractive to fusion researchers, such as no target pre-compression, propagating fusion burn, etc. In these schemes, a macroscopic (~ 1 g) projectile (bullet, or macron) is accelerated to a hyper-velocity of 200 to 1000 km/s, and shot to passive targets, to produce the high density and temperature required. However, the problem comes from the acceleration. As earlier researchers expected a rather large bullet (~ 1 g) and excessive projectile kinetic energy (10 ~ 50 MJ, depends on whether the impact compression is one dimensional or three, no mass acceleration method can reach even 1 thousandth of that energy.
* according to high energy charged particle stopping theories carbon ions have a stopping power to fusion alpha particle about 9 times larger than averaged DT ions.
* The ignition energy for a millimeter size diamond bullet is 1 ~ 2 MJ. This renders electrostatic linear acceleration a practical approach.
* The main purpose of the simulation is to estimate the ignition energy of the bullet. We found that a millimeter diamond bullet with the kinetic energy of 1 ~ 2 MJ, or at the speed of about 1000 km/s, is sufficient to initiate a propagating thermal nuclear burn. This is important, because in 1980s people believe one dimensional compression needs a 50 MJ bullet. This change can reduce the length of the linear accelerator from 10000
kilometer to less than 100 km.
* Surprisingly, if the fusion fuel is DT liquid or ice, the ignition energy is only 50% higher. We had expected a much higher ignition energy, for the stopping range in uncompressed DT ice plasma is 5 times longer. This is because the density shell can rise to the same density as in DT methane, and less electron and carbon means less radiation loss.
Advantages of this Approach
There are many features or advantages in this fusion
scheme which is not available in other fusion energy ideas.
For completeness, they are listed as follows:
* “Standing-off” and sustainable. There is no mess of destroyed parts, no close contact, no strong and unpleasant limit posed to reaction chamber wall. The wall can be build only according to thermal, mechanic, technical, and economical requirements.
* High hydrodynamic efficiency. 10 times higher than main stream schemes.
* No pre-compression, greatly simplified the whole system.
* Unlimited and easy tailored energy output, high output/input ratio.
* Extra confinement can be achieved by casing the target with heavy metals. High burn out ratio.
* Close harvest of the fusion energy and neutron. Unlike other fusion schemes, the space near the fusion point is free, we can put anything there to harvest the vast amount of energy or the hyper intensity neutrons. Utilizations like Deuterium breading of Tritium and Helium-3, Uranium-238 burning, radio-active waste treatment are now practical.
* Low-tech and economical accelerator. Low particle speed, low vacuum requirement, no magnets (particle controlled by electric field).
Crystal DT methane has higher DT concentration, stronger alpha particle stopping, and is easier to handle because the melting temperature is much higher than liquid or solid DT. DT methane can be a good option as fusion fuel in ICF. The high density and high stopping means less compression. Rayleigh-Taylor instability situation can be mitigated significantly. It can be very promising in volume ignition ideas, for the ignition temperature is low (1.5 keV), and radiation is not a problem.
Bremsstrahlung lost is the most significant issue in this scheme. If further studies shows this problem is too severe to overcome, we may have to go back to DT ice. Other potential DT compounds like LiDT, LiB(DT)4, have more electrons and the bremsstrahlung situation is even worse. However, even if the ignition energy is a little higher than DT ice, the easy handling of DT methane could make it a better choice.
Industrial Diamond Costs
Total industrial diamond output worldwide(2008) was estimated by the USGS to be about 4.62 billion carats valued between $1.65 and $2.00 billion.
Current industrial diamon price is about $0.16 per carat
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