Reply To: What can we do with $189 Billion?

[asymmetric_implosion]

People use optical methods for time of arrival of the current sheets. It is important to note that most plasma focus devices don’t rely on individual filaments but a uniform sheet of plasma. FoFu is somewhat unique in that respect. The methods are proven but they cannot measure the magnitude of the current or some relative measure of current in a meaningful way. B-dot probes, the most common magnetic probes for local B-field measurement, would be useful but they are shielded by plasma that is strongly dependent on local parameter that aren’t easy to diagnose so you cannot say if the measurement is “good” or not. Measurements using B-dots have been attempted with some success but the experiments are difficult and far from low cost if you think $50K is expensive. A fast framing camera can also be used but they are very expensive by the $50K standard. There are a number of paper in published literature that discuss these diagnostics since 2000. Papers by the NTU group on NX-2, PF-1000 papers published since 2009 and some work done by Moreno show these diagnostics in action. If you want a sort list of papers I can supply the information to download them.

The production of fusion reactions is a common thing in plasma focus devices. The applications for most groups is for producing neutrons for various applications so producing neutrons is not a problem. Most of the groups I mentioned above produce neutrons intentionally for those funding their work. Most of the groups are active based upon recent publications. If you aren’t going to use fusion fuel gases you need to pick a representative gas system. You can use H2 as a surrogate for D2 but you need twice the pressure which may change the way the filaments evolve. You can use heavier gases but the radiation emitted by the filaments changes which can impact the local environment by photoionization and secondary electron emission from the electrodes. Neon and Argon emit copious amounts of UV during their axial rundown.

The ion beam and electron beam do exit the pinch region in different directions. The electron beam hits the anodes so you have to make the anode hollow and put a beam diagnostic near the exit. The ion beam moves away from the anode and it is more straightforward to measure. People frequently use time of flight or ion spectrometers to measure the ion beam spectrum.

In my opinion, the best diagnostics package on a plasma focus right now is the PF-1000. They have multi-frame interferometry and neutron time of flight that allows them to reconstruct the ion distribution that generated the neutrons. The work is particularly relevant to FoFu research. I know Mr. Lerner does not put much faith in interferometry but it is an excellent diagnostic and it would address a number of the problems you are describing by measuring the electron density in its conventional form or the electron density gradient in a shearing form.

The problem with many of these experiments is the cost. As I said scientist are expensive and access to these facilities costs as well. There is a minimum contract value that most companies or big labs will accept because of admin costs will drain the contracts. I don’t know what you have in mind for low cost but I believe you mean a great deal of good will. General Electric has a rule about research. For every dollar spent on research, seven dollars are spent on development and $49 are spent on building the first working unit. A quick sum assuming ~$2M at the research base clear $100M pretty quickly. As with any fusion system, getting the plasma “right” is not the worst problem. The materials issues are the real problems. I suggest looking at materials issues if you want to do scaling down experiments because you can replicate the operating pressure of FoFu-1 and the current density at low cost. The erosion can be studied and the lifetime can be estimated.