Monolithic cathode planned to achieve plasma purity, higher density
Posted by Ivy / Trackback / August 07, 2013 / in News
Our latest round of experiments have convinced us that we will not be able to achieve the level of purity in the plasma we need for high density as long as we have joints between metal pieces in the cathode. Even with our very careful use of indium, sufficient contact resistance remains to cause significant vaporization of copper. So, despite the additional expense involved, we have decided to upgrade the cathode to a single monolithic piece of tungsten. This single piece will incorporate the cathode plate, the cathode rods and the underlying plate that attaches to the transmission plates that carry the current back to the capacitors. Thus the plate will only have a current connection outside the vacuum chamber. Both our experimental experience and materials theory indicates that vaporization from the tungsten itself should be minimized, and should fall well below the requirements we need. As far as we know, such monolithic construction is new for plasma focus device design.
However, a key consideration in the new cathode design is the brittleness of tungsten. Complex tungsten pieces like ours are formed by sintering—pressing together tungsten powder. This process does not give the tungsten its full strength and makes it vulnerable to sudden impacts. When the current flows through the electrode, the magnetic field will force the cathode outwards while it pinches the anode inwards. So we have to design the new cathode to withstand repetitive sudden stresses of this sort. On possible design involves replacing the rods with vanes that will be much more resistant to stresses, as shown here.
One of our student research associates this summer, Arya Ghaseminejad, is helping to prepare various design alternatives. These will be tested with CAD simulations with the help of LPP Board of Advisor member Rudy Fritsch. In this way we can ensure in advance that a new and more expensive monolithic cathode will also be long-lasting.
In order to measure in real time the amount of metal impurities in the plasma, we have purchased a digital UV spectrometer. From the ratios of the strengths of the bright lines produces by deuterium and by the metals we should be able to calculate the impurity levels for each shot. Our other student research associate, Kyle Lindhiemer, will be calibrating this spectrometer and we will probably be doing some shots with the old cathode to get a baseline comparison for our monolithic model.
- See more at:
http://lawrencevilleplasmaphysics.co....YHCPCBLi.dpuf
Moving the goal posts closer: quantum “herding”
Posted by Ivy / Trackback / August 07, 2013 / in News
Increasing the density of the plasmoid is the “long pole” in our fusion tent—what we need to do to get to net energy production. We know we must increase density a long way from our current results. But now it seems the goal post have moved somewhat nearer. New theoretical calculations indicate that an effect that was left out of previous calculation increases the fusion reaction rate at high magnetic fields and thus requires only about one third the plasma density we previously calculated. This reduces the improvement needed in density from about 10,000-fold to about 3,000-fold.
The new calculation is again based on the quantum magnetic field effect that LPP Chief Scientist Eric Lerner first applied to the dense plasma focus in 2003. This effect causes ions—nuclei—moving in extremely strong magnetic fields to transfer energy slowly to electrons. Back in 2003, we realized that this would keep the electrons cooler, so they would radiate less x-ray energy, making it easier to achieve the extremely high temperature needed for hydrogen-boron fusion. But until recently, we overlooked another beneficial effect.
In a typical plasma at low magnetic field, the nuclei move almost randomly on the microscopic level, so when two nuclei collide only about one third of their energy is directed along the line that connects them. But recently, we realized that at very high magnetic fields, the situation is different. The nuclei in that case are moving almost exactly along the direction of the magnetic fields. So when they collide head-on, their full energy goes into the collision. Since the fusion reaction rate rise with energy, up to a very high energy, the more-head on collisions speed up the reactions for a given density. Equally, they allow the same reaction rate at a lower plasma density.
The reason this alignment along the magnetic field line happens at very high magnetic fields is because the quantum magnetic field effect operates only for ions moving in the same direction as the electrons—along the field lines. If the ions randomly move across the field lines, they lose energy much more rapidly to the electrons, forcing the ions back onto the field lines. Thus the electrons, through the quantum effect, act as sheep dogs, herding the ions in the magnetic field direction, where they collide with each other head-on.
The result is to allow us to reach net energy production with somewhat less demanding density conditions—making our path shorter and easier. We’ll be publishing a paper on this in the coming months.
- See more at:
http://lawrencevilleplasmaphysics.co....7e8PLvcS.dpuf