MTd2 wrote:
Summing up, not even with Poseidon, which has banks of 750KJ and a voltage of 80KV, were capable of achieving more than 1.5MA of current in the pinch. This is real bad since it means a neutron yield one magnitude lower than what is desired for LPPX for an equipment with much higher capacity.

The figure of 1.5MA seems close to the Pease-Braginskii limit.
From Robson’s 1989 paper: link.aps.org/doi/10.1103/PhysRevLett.63.2816

The concept of the Pease-Braginskii current in a Z pinch is reexamined in the light of the anomalous resistivity that arises in a plasma when the electron drift velocity is greater than the ion sound speed. Radial profiles of density and current are derived on the assumption that anomalous resistivity will prevent the drift velocity from exceeding the sound speed. The value of the Pease-Braginskii current then depends upon the line density, and may be significantly greater than its classical value.

Basically this give a limit on the current a filament can carry where the radiation pressure outwards balances the pinch force inwards. For deuterium the figure is around 1.6MA. Normally it is assumed other instabilities will break up a filament well before it reaches this limit, but if you can delay their onset, or be fast enough that they haven’t had time to develop, it gives an upper limit due to the radiative effects.

I was wondering, since this figure though is related to the collisionality parameter know as the Coulomb Logarithm, which would be different for pB11. The peak attainable could be lower rather than higher. Although this limit for a single filament – we start with a pair of filaments per cathode. These merge together to eventually form one at the focus. So the total peak current can be higher when there are still many filaments, but as they merge the total current they can carry goes down. When the plasmoid forms, the strong magnetic field effect hypothesized to reduce the bremstrahlung in pB11 could increase the Pease-Braginskii current limit, but this may be too late to get any more energy into the plasmoid.

I guess the question is – Is the magnetic field strong enough by the time the last few filaments merge, to suppress the radiation enough to allow more current? Or is this completely irrelevant and I’m just extrapolating a bit too far.

That would indeed be frustrating if those limits really apply. Lee’s and Saw’s work is based on gas pressure of 3.5 torr and a time scale of 0-10 microseconds. It would be interesting to see the computed results if they used the latest figures from the LPP November 11 report showing a gas pressure of 13 torr.
The November 11 report also gives a possible explanation for the change in resistance.
November 11 report

MTd2 wrote:

Basically this give a limit on the current a filament can carry where the radiation pressure outwards balances the pinch force inwards. For deuterium the figure is around 1.6MA.

According to Sing Lee, this limit is due the impedance of the contracting plasma not due radiation pressure.

It can be overcome by increasing the voltage between the cathodes to high values, like above 90KV:

http://www.plasmafocus.net/IPFS/2010 Papers/2010 Pp2 IJER.doc

The Las Vegas DPF can do that:

https://focusfusion.org/index.php/site/article/july_switch_update/

Unfortunately, LPPX cannot…

The 1.6MA figure is a generic limit for a single current carrying filament of plasma (a Z-pinch) regardless of its size or origin.
The particular geometrical & electrical arrangement of a DPF is the topic of Sing Lee’s paper. The Pease-Braginskii current is not a hard limit, in that is cannot be exceeded. It is just that if the current is higher than the critical value for that fill gas, the filament will be unstable and begin to collapse because the pressure is no longer balanced.

Rezwan wrote: We need to start compiling this kind of discussion into a “ReNeW” document for the DPF, if there isn’t one out there already.

… “ReNeW” document?