How LPPX could overcome the Dynamical neutron saturation?

[MTd2]

Lerner is aware of this issue!!!

http://denseplasmafocus.org/index.php/forums/viewthread/443/

I wonder how he will overcome this.

[Francisl]

I am guessing that Eric will optimize his current setup, gather data and test his theories, project where he needs to go from here, all the while trying to gather support and funding to make the next big advance.

[Aeronaut]

Francisl wrote: I am guessing that Eric will optimize his current setup, gather data and test his theories, project where he needs to go from here, all the while trying to gather support and funding to make the next big advance.

Eric’s response to Lee’s challenge strongly suggests to me that shorter electrodes are the most practical way to reduce inductance in the present LPPX setup, which is designed to be practical (not necessarily easy) to replace any part(s) should the need arise.

A less practical yet glaringly obvious way to reduce system inductance would be to place the cap bank above the HV delivery plates to reduce their mass and inductance by placing the caps in a grid array as close to the anode pin as the switches will allow. Since the test cell lacks the ceiling height and a crane, it isn’t practical in this stage of development.

A ‘porcupine’ looking modified spherical cap bank geometry might be able to move the switches even closer to the anode pin while delivering a uniform distance from each switch to the anode. The physical result in my mind’s eye is a forest of unistrut or 80/20 (much more professional looking than unistrut, imo, and it’s much easier to work with for many reasons) supports and braces. Ugghh.

The most elegant and aesthetically-pleasing solution could be to mount at least the caps below-grade, preferably with their cradles pre-cast in the new concrete. But to get from here to there requires solutions to the spark plug and switching issues. Just thinking out loud here…

[MTd2]

According to Sing Lee, if you are using the Sing Lee model, no matter what you do, you will face the same limitation. The use of the axial field is the way to find a loophole inside Lee`s theory. But it seems that the axial field just enhances slightly the saturation limit. What I see as a solution is just to double the voltage. Everything is kept the same, the energy stored in the banks is enough. The axial field should be 10x stronger due the faster speed of the arriving current, but that would be a great thing since it would be above the background magnetic noise.

[Aeronaut]

Sing Lee’s equivalent circuit diagram and labels rely heavily on the word ‘fraction’. The backplate’s inductance and current fractions are significant contributors to the machine’s performance or lack thereof. Have any of his students reported any experiments to reduce backplate inductance? I remember reading one that proved a short metal plate was a lower inductance capacitor conductor than the standard issue wire, for instance.

I’ve sketched cap bank geometries a few times since my last post. Danged frustrating things to put close together! It’s starting to look like a 3 by 3 or 3 by 4 array might be the lowest impedance HV system…

[Francisl]

Is the DPF well enough insulated to withstand 90 KV?

[MTd2]

Aeronaut wrote: Sing Lee’s equivalent circuit diagram and labels rely heavily on the word ‘fraction’. The backplate’s inductance and current fractions are significant contributors to the machine’s performance or lack thereof. Have any of his students reported any experiments to reduce backplate inductance?

It was tested in several different kinds of DPF devices. The limitation is inherent to all kinds of Sing Lee`s variations. What was not tested though it was the regime of 90KV. Las Vegas DPF will attempt to study this region.

[Aeronaut]

Sing Lee’s description of his understanding of DPF theory, combined with playing with his simulator, taught me a lot in a hurry. I heartily recommend it as a bridge to a more complete understanding of DPF theory. The low current, low voltage variety which seems best suited for making tuned X-ray and neutron bursts.

Anything we as a DPF community can do to reduce the system inductance will pay off handsomely by keeping open the option of using any voltage(s) an experimenter so desires, up to around 100kV. This is the easiest way to significantly extend useful cap bank life, since firing 90kV shots is going to kill a cap bank within a year at LPP’s average shot rate.

Caps are built in a job shop environment, not warehoused. They aren’t cheap, and the delivery time for a set of 12 would make a slow boat from China look fast. This could be a legitimate reason for the Las Vegas machine’s budget being much higher than LPP’s.

[Lerner]

Right now, we think that we will get to a demonstration of feasibility at around 2.8 MA, which is below Lee’s limit. Going much beyond our planned 45 kV will involve significant changes to the facility–power supply, capacitors, insulation, etc. Of course, as a practical matter, if we got very close and were on a rising curve, we should be able to stop and make major changes to increase voltage. Hopefully, that won’t be needed.

[MTd2]

According to table 1, table 3 and Figure 7 of this paper:

http://www.plasmafocus.net/IPFS/2010 Papers/Energies PP.pdf

Saturation occurs for 1.5MA. So, if you discharge more than 1.5MA, at low voltages, the pinch won’t achieve more than 1MA, and it doesn’t matter what configuration is used.

[Aeronaut]

MTd2 wrote: According to table 1, table 3 and Figure 7 of this paper:

http://www.plasmafocus.net/IPFS/2010 Papers/Energies PP.pdf

Saturation occurs for 1.5MA. So, if you discharge more than 1.5MA, at low voltages, the pinch won’t achieve more than 1MA, and it doesn’t matter what configuration is used.

The page isn’t directly linkable (returns a 404 file not found error) but I was able to find the 2010 papers page. Which title are you referring to on that page?

[Rezwan]

zapkitty 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?

“Research Needs Workshop” More at this post.

[Francisl]

Aeronaut wrote:

According to table 1, table 3 and Figure 7 of this paper:

http://www.plasmafocus.net/IPFS/2010 Papers/Energies PP.pdf

Saturation occurs for 1.5MA. So, if you discharge more than 1.5MA, at low voltages, the pinch won’t achieve more than 1MA, and it doesn’t matter what configuration is used.

The page isn’t directly linkable (returns a 404 file not found error) but I was able to find the 2010 papers page. Which title are you referring to on that page?

Try this, copy and paste:

http://www.plasmafocus.net/IPFS/2010 Papers/Energies PP.pdf

[MTd2]

The reason for this saturation is caused by the design of the DPF. When a EM magnetic pulse runs through the cathode, it charges and push a thin layer of gas ahead of it. The gas becomes hot, a plasma, and moves fast. This means that there is transfer of energy between the pulse and the plasma mainly in 2 ways: inducing a current in the plasma and by giving it kinetic energy. The latter is a dynamical source of resistance since the speed of the plasma is high, and mostly doesn`t vary much, independently of the variation of the parameters of the DPF device, at least in the window of 15-50KW: up to 100km/s, at the tip of the cathodes, comparable to the Sun`s plasma velocity. This dynamical resistance has about 7 mili Ohm. So, the bigger the current, the bigger the loss of energy. The remaining current for the plasma pinch is small, given that most of it was lost in heat.

The solution to this problem is the same that is used for long distance electrical lines, meaning, using higher voltage to minimize losses.

[Aeronaut]

Yep, that link worked like a charm. The stray resistance is an intriguing aspect to try to reduce. I’m glad to see that Lee’s included the Filipov design, also, since the rest of the case always seems to lead to shorter electrodes.

Long distance transmission lines double the voltage to reduce the current by 50%. Using P=(I^2) R, doubling the transmission voltage results in 25% of the losses. Not sure how this relates to raising voltage to raise current…

[Author]

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