Technical Background on Focus Fusion
Focus Fusion operates using a dense plasma focus (DPF) with hydrogen-boron fuel. The fuel is in the form of decaborane (H14B10), a solid at room temperature which sublimates into a gas when heated to moderate temperatures of around 100 C. As in any fusion reaction, when the hydrogen nuclei (protons) and boron-11 nuclei collide at high enough velocities, a nuclear reaction occurs. In this case, three helium nuclei (also called alpha particles) are produced, which stream off in a concentrated beam, confined by powerful magnetic fields produced by the plasma itself.
While the plasma focus device has existed for 40 years, progress with the DPF has been impeded mainly by a lack of good quantitative theoretical models. There are too many parameters in the DPF to allow progress on a purely empirical basis: the anode and cathode radii, electrode length, shape of the anode and especially anode tip, length of insulator, charging voltage, fill pressure, fill gas, and so on. Without a good theory, DPF research is like wandering in a six-dimensional desert looking for small oases. This means that there has been, apart from our own work, no way of predicting in advance the size, density, magnetic field and ion and electron energies of the plasmoids (ultra-dense, self-confined blobs of plasma) in the DPF, given initial conditions.
LPP has developed a detailed quantitative theory of DPF operation, which has been successfully tested against experiments that we performed in collaboration with the University of Illinois in 1994 and with Texas A&M University in 2001. This theory, including important refinements that include magnetic effects gives us the ability, unique among DPF groups, to show in advance that hydrogen-boron fusion is feasible.
This allowed us, in the 2001 experiments, to achieve the temperature of over one billion degrees (ion energies of over 100 keV) that is needed to ignite hydrogen-boron fuel. In 2004, LPP performed a preliminary set of simulations that showed that net energy production is possible with a small Focus Fusion device. The simulations were better than expected in that net energy production is projected at a current of 2 MA (mega-amperes), well below the 3 MA that the device we are planning for Phase I can achieve.
The simulation showed that the ratio of fusion yield/gross input energy rose from 0.067% at 0.75 MA to 5% at 1 MA to 24% at 1.5 MA. The optimum case studied is for a current of 2.0 MA, cathode radius of 3.3 cm, and final magnetic field of 12 GG. This simulation case produced a beam that carried 97% of input energy and X-rays that carried 57% of input energy. In practical terms, this means that if the beam energy recovery efficiency is 90%, which is reasonable, net energy production occurs with X-ray energy recovery rates above 22%, which is easily achievable. Another practical energy-producing combination simulated used an 80% beam recovery and 80% X-ray recovery for an overall efficiency of 43%. In this example, the net electric energy production is 3.1 kJ per pulse, or 3.1 MW for a 1 kHz pulse rate.
This article further illustrates the the Focus Fusion energy flow with a Sankey diagram of the full cycle.
Our technical efforts are greatly enhanced by the unique new simulation tools being developed by our collaborator John Guillory of George Mason University. This approach allows us to simulate over the wide range of space and time scales (from centimeters to microns and from microseconds to picoseconds) needed to accurately model the DPF.
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