[Henning]

There are already some more suggestions from the Polywellers.
For the removal of copper residuals there are two suggestions:

As far as removal of the Copper from the chamber walls, a simple DC glow discharge with Ar or O2 should do the job. The glow discharge would be simple capacitive DC with the bias plate at 500 or 1000 V bias. The Ar or O2 gas flow should be at around 1-10 torr with a base pressure of 0.1 torr (need only a roughing pump).

Change to sapphire windows and scratching during cleaning becomes less of a problem. ‘Course the sapphire windows may be out-of-budget.

Alternatively, treat the glass windows as replaceable items and don’t bother cleaning them.

Sapphire windows shouldn’t be too expensive, though: http://www.sapphirewindows.com/
There are other suppliers, but this one quotes the price directly on the front page.

[Henning]

I’ve cross-posted this question on Talk-Polywell, and Giorgio already answered:

IR + UV lamps or Glow discharge with Argon.

See here:
http://www.vacuumlab.com/Articles/VacLab52.pdf

They could also contact directly the guys at vacuumlab.com for additional suggestions.

Keep a look on this thread, maybe more is coming in.

[Henning]

Rumors say it’s something between 50000 and 150000 USD, plus optional gear.

http://wallstreetrun.com/record-breaking-high-speed-camera-captures-the-world-at-1000000-frames-per-second-yahoo-news.htm
http://geeks.thedailywh.at/2011/08/09/million-fps-camera-of-the-day/
http://geekosophy.com/2011/08/09/meet-the-phantom-v1610-the-million-fps-camera/

Maybe still better than the Framing Camera on the LPPX wishlist: https://focusfusion.org/index.php/site/article/lppx_wishlist_-_donate_equipment

[Henning]

Tulse wrote: Cheap power makes a lot of things [em]possible[/em], but that doesn’t make all of them [em]attractive[/em].

Same holds true for colonies on moon and Mars.

[Henning]

markus7 wrote:
EDIT: I wonder if such an arrangement of 16 “spark plug plasma jets”, in addition to improving current sheath symmetry, might make it possible to eliminate using the main capacitor switches to trigger pulses. That is, the 16 outer cathode rods would, while running, be connected to the capacitors, and the “spark plug plasma jets” would take over the function of the vacuum switches, making them redundant. The function of the vacuum switches would be part of the fusor unit.

Generally a good idea, but I think the electrodes will shorten before the target voltage is reached, i.e. distance between cathode and anode are too short to hold back the sparks, as we try to reduce the diameter of the DPF and increase the amperage of the pulse (which goes along with the voltage). Anyone an idea how to reduce voltage and increase amperage? Well, by reducing inductance, which is somewhat one of the main goals…

[Henning]

I’ve got a different proposal for insulation material: Kapton.

The discussion is on the forum with the title Corona Resistant Kapton Insulation.

Henning wrote: I just stumbled over a heat resistant insulator, which maybe can be used in the DPF or switches.

It’s called Kapton. Maybe it’s already used by LPP anyway. But in case the insulation is an issue, I’m posting some information here.

Different versions of Kapton:
http://www2.dupont.com/Kapton/en_US/products/index.html

General overview:
http://www2.dupont.com/Kapton/en_US/assets/downloads/pdf/summaryofprop.pdf

The corona resistant version of Kapton:
http://www2.dupont.com/Kapton/en_US/assets/downloads/pdf/CR_H-54506-1.pdf

Insulation capability:
Electrical Strength: 291 kV/mm

One supplier is here (and there are others):
http://www.kaptontape.com/default.php

Henning wrote: Got some more from Wikipedia:

According to a NASA internal report, space shuttle “wires were coated with an insulator known as Kapton that tended to break down over time, causing short circuits and, potentially, fires.” The NASA Jet Propulsion Laboratory has considered Kapton as a good plastic support for solar sails because of its long duration in the space environment.

Kapton is also commonly used as a material for windows of all kinds at X-ray sources (synchrotron beam-lines and X-ray tubes) and X-ray detectors. Its high mechanical and thermal stability as well as its high transmittance to X-rays make it the preferred material. It is also relatively insensitive to radiation damage. Another prominent material for these purposes is beryllium.

The thermal conductivity of Kapton in temperatures from 0.5 to 5 kelvin is rather high κ = 4.638×10−3 T0.5678 W·m−1·K−1. This, together with its good dielectric qualities and its availability as thin sheets have made it a favorite material in cryogenics. Kapton is regularly used as an insulator in ultra-high vacuum environments due to its low outgassing rate.

So on the one hand Wikipedia states it has great mechanical properties, on the other hand it breaks down over time.

With a reply from pulser:

pulser wrote: Kapton is good for vacuum systems, but as mentioned will break down over time. Use 4x the thickness associated with dielectric strength for long term reliability.
Dealing with high voltages can be challenging. Use of semi-insulators will help with limiting electrostatic charge build-up and localized breakdown. I’ve found most people are not familiar with semi-insulators and the concept of what they do and how to use them is challenging even for electrical engineers working with high voltage devices for a living. Semi-insulators include materials like SIPOS and silicon rich silicon nitride (more like amorphous silicon than Si3N4). Carbon could also be used but I have no experience on the best form or deposition methods. Sheet resistances of 1e12 to 1e15ohms/sq are typical. Using alternating layers of semi-insulators and high dielectric strength insulators is a very good way to stand off very high fields even with ionization taking place creating localized high field spots. For pulsed applications such as this, much higher conductivity films could be utilized as long as the power dissipation does not cause significant self heating.

But I think that break-down is the result of real mechanical stress, and the wear over time is measured in years — much more than it’s needed for the experiments. The only thing is that it’s not as mechanically flexible as Mylar (biaxially oriented PET film). But for protecting the insulator within the switch or even DPF, this might be a good candidate (if it doesn’t introduce more non-symmetries).

[Henning]

Got some more from Wikipedia:

According to a NASA internal report, space shuttle “wires were coated with an insulator known as Kapton that tended to break down over time, causing short circuits and, potentially, fires.” The NASA Jet Propulsion Laboratory has considered Kapton as a good plastic support for solar sails because of its long duration in the space environment.

Kapton is also commonly used as a material for windows of all kinds at X-ray sources (synchrotron beam-lines and X-ray tubes) and X-ray detectors. Its high mechanical and thermal stability as well as its high transmittance to X-rays make it the preferred material. It is also relatively insensitive to radiation damage. Another prominent material for these purposes is beryllium.

The thermal conductivity of Kapton in temperatures from 0.5 to 5 kelvin is rather high κ = 4.638×10−3 T0.5678 W·m−1·K−1. This, together with its good dielectric qualities and its availability as thin sheets have made it a favorite material in cryogenics. Kapton is regularly used as an insulator in ultra-high vacuum environments due to its low outgassing rate.

So on the one hand Wikipedia states it has great mechanical properties, on the other hand it breaks down over time.

[Henning]

So we have it here again: filaments. Of a million degrees hot.

Formed by what? Gravity? Electrical fields? If it’s electrical fields, then it’s pretty much as Eric describes in BBNH.

[Henning]

Impaler: I like your idea of replacement to also include the fuel. I don’t know if the business model will be implemented, but it’s an option which is maybe worth thinking about. But if it slows down the adaption of FF, it probably won’t be implemented.

Milemaster: Erm, I don’t really know how you would build a laser electrode, especially one that is energy efficient. Lasers aren’t really efficient. For the electrode material Eric more thinking about Beryllium, which is transparent to x-rays. The higher you get with atomic numbers, the less transparent the material gets (at least somewhat generally).

[Henning]

Not bad, but for my taste it’s too much of “If we have free energy, we can do so much stuff”, i.e. separation of hydrogen and oxygen.

Anyway, I thought the main problem of molten salt reactors are the corrosion of pipes. Anybody a different opinion?

[Henning]

Timing.

… lasers inject their energy within nanoseconds, compared with milliseconds for spark plugs.

That’s what makes it interesting for focus fusion.

I don’t know whether they’re strong enough to ionise the switch fill gas as required. But multiple shots possibly can add up (maybe not):

The laser is not strong enough to light the leanest fuel mixtures with a single pulse. By using several 800-picosecond-long pulses, however, they can inject enough energy to ignite the mixture completely.

[Henning]

Tulse wrote: This may have been discussed elsewhere, but why is the anode a single cylinder, rather than a set of rods like the cathodes?

This hasn’t been discussed in the forum yet, only the other way round: Why is the outer electrode made out of rods? Old-day DPFs had a hollow cylinder as outer electrode, modern DPFs have those rods. It helps forming of the filaments (if I remember correctly).

Maybe a sawtooth shaped inner electrode would help guiding those filaments? Maybe not. Maybe they break if guided too tightly.

[Henning]

redsnapper wrote: BTW – we have trouble building conventional photovoltaic devices with efficiencies higher than 25% – and we’ve been working at this, perhaps only semi-seriously, for the last 40 years. It does seem to me we might be ridiculously optmistic to think we can convert 80% of Xrays into electricity as early as three years from now. Is the argument that the entropy of Xrays is so much lower than that of visible light, that there’s reason for optimism

The problem with visible light is, it comes with low energy that needs to push up the electron one valence layer. See band gap for more details.

The x-ray photovoltaic works differently: it uses a potential gap (if I understood it correctly) of the several layers of the onion.

Might not explain it completely. Maybe someone else has better words for that…

[Henning]

redsnapper wrote: electrodes themselves (for example: highly-conductive, Xray-transparent, ceramic electrodes that can handle 2000 degC; better yet, virtual electrodes that can handle 500MdegC)

Read: quite-conductive (36 nΩ·m, compared to 16.78 nΩ·m of copper at 20 °C), x-ray-transparent, beryllium electrodes that can handle 2400 °C

The electrodes never get into contact with the 500 M°C (actually 2 G°C) pinch.

[Henning]

That x-ray transparent fluid (helium gas, I don’t know at which pressure it gets fluid, but I suspect the pressure has to be extremely high at 1000K) is required for cooling the electrodes (canals within the electrodes), and also the onion (also with canals).

Maybe also lithium would be possible: https://focusfusion.org/index.php/forums/viewthread/457/#4213

The patent has a drawing of the onion with canals in it for cooling (figure 13). Look for a reference in the text to figure 13.

[Author]

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