Aneutronic Fusion Approaches
Comparison with Other Aneutronic Approaches
Latest IEC results show large continuing lead by DPFs in fusion yield
Currently there are three experimental approaches to aneutronic fusion with hydrogen-boron fuel, in addition to other conceptual approaches which have not yet reached the experimental stage. They are the dense plasma focus device, used by LPPF; Tri Alpha’s field reversed configuration, discussed below, and inertial electrostatic confinement or IEC, used by EMC2’s Polywell devices and by academic groups like that at the University of Wisconsin, Madison (UWM).
While the EMC2 effort has not published anything in recent years, UWM has been publishing and LPPF Chief Scientist Lerner was able to get some updates on the field from Dr. John Santarius, one of the leaders of the UWM team. These updates showed that in terms of fusion output per unit of energy input, plasma focus devices still have large lead over IEC devices. This of course does not mean that our Focus Fusion approach will necessarily win the race to net energy production, but it is a reflection of where things stand now.
Dr. Santarius reports that their best results with deuterium fuel are 20,000 neutrons per joule of energy input. By comparison, FF-1’s best results with the same fuel are 150 billion neutrons for 60,000 joules input, or 2.5 million neutrons per joule. So, at the moment, plasma focus devices produce over 100 times more fusion energy per unit input energy than do IEC devices. (Not that our results are yet good enough. We are aiming for thousands of times better than we now get.)
IEC devices operate by trapping ions within an electrostatic field. The field also accelerates them to high energy, so like DPF devices, they can get to the ion energies needed to burn hydrogen-boron fuel. However, at the moment, very little of the fusion energy in an IEC comes from hot ions colliding with hot ions, as it does in the DPF. Rather, the ions collide with the cold background gas. The problem with that, as IEC researchers are aware, is that the energy output only increases proportional to the energy input, not faster. Net energy then gets no closer with increasing input.
If, on the other hand, ions collide with ions, each ion encounters more collisions, so the energy output can increase as the square of the energy input or even faster, then net energy gets closer with more power input. For this to happen with IEC, experiments will have to develop better vacuums to reduce background collisions and, most difficult, there will have to be far fewer collisions of ions with the device structure itself.
While IEC is certainly worth researching, the comparison again confirms that research with the plasma focus is still the path closest to achieving net energy with aneutronic fusion—the only known route to cheap, clean, safe, and unlimited energy.
Comparison with Tri Alpha Energy
Tri Alpha Energy, which is pursuing aneutronic fusion with a different device from the plasma focus, presented their past year’s progress with a half-dozen poster presentations at the American Physical Society’s Plasma Physics conference in October, 2012. The clear and thorough presentation of their results was due to a new openness by their management, according to several of the researchers participating. Tri Alpha’s device, called a field reversed configuration, or FRC, generates two large rings of plasma and heats them with an externally accelerated ion beam. Their most recent results show that they have confined plasma at about 100 eV energy (equivalent to 1.1 million degrees C) for about 2 milliseconds at a density of 2×1013 ions/cm3.
While this temperature is too low to produce measurable fusion energy, a rough measure of overall progress is the product of these three numbers, called “nτT”, which for Tri Alpha is 4×1012 eVsec/cm3. By comparison, LPPF’s FF-1 with an ion energy of 160 keV, confinement time of about 30 ns and density of 3×1019 ions/cm3 has a nτT product of 1.4×1017 eVsec/cm3, a factor of about 30,000 larger than that of Tri Alpha. This puts LPPF far closer to the goal of net energy for now. Tri Alpha has raised about $140 million in private investments and works with a staff of 30 physicists. Considering that Tri Alpha has raised $140 million with 30,000 times more modest results, and LPPF has raised $3 million, we feel that LPPF is a real bargain—the best buy in fusion!