How's the new tungsten cathode working out?

[Andrew Palfreyman]

All quiet for about a month. Hopefully progress remains positive.

[Ivy Matt]

This is the latest news I’ve heard:

https://www.facebook.com/focusfusion/posts/10155623932255258

On June 2nd the tungsten electrodes were mounted to FF-1 and waiting for the vacuum chamber to be attached.

Some developments are announced in these places:

https://www.facebook.com/focusfusion
https://twitter.com/focusfusion
https://twitter.com/lppx

[cmatofte]

Nearly every day I check lppfusion.com and this forum thread hoping to see something along the lines of: “If you are heavily invested in oil, now might be the time to get out. Huge announcement to follow!” 🙂

Any status updates?

[Andrew Palfreyman]

Latest report
http://us8.campaign-archive1.com/?u=87935f5eb37481cdcd48cf498&id=52e1f80838&e=a62ed3a024
highlights important impurity issues.
“An alternative source might be a very thin layer of tungsten oxide—too thin to be seen or removed during the electrodes’ cleaning. Tungsten oxide dissociates at 1970 C, far below tungsten’s vaporization point of 5500 C, so an oxide layer will be far more fragile. The oxide layer might well give rise to the tungsten in the plasma as well. If this is the case, repeated firing will burn the oxide layer off and impurities will fall.”

Looking here (assuming this is the correct oxide – there are several)
https://en.wikipedia.org/wiki/Tungsten_trioxide
it seems that a hydrogen gas treatment at moderate temperature might be a shortcut to getting rid of this surface layer, if indeed this be the problem.

WO3 + 3 H2 → W + 3 H2O (550 – 850 °C)

But repeated firing to get a feel for the asymptote seems the most reasonable short-term course of action.
It might be enough.

[Henning]

How fast would the tungsten re-oxidise? It’s maybe worth to get the oxygen off, but when the electrodes get installed, the tungsten re-oxidises. But maybe the layer is thinner, and the rest can be blast off with fewer shots.

Or filling the vacuum chamber with hot hydrogen. But here the Mylar (PE) insulation wouldn’t survive.

[Andrew Palfreyman]

I’m sure Dr. Lerner has already realised that the forthcoming beryllium electrodes may also be prone to similar surface oxidation. Not being a chemist myself (but a physics-trained engineer), sounding the alarm is about all I’m good at on this one 🙂

[Tim1]

I was wondering if any Nitrogen showed up in the optical spectra from the Focus Fusion shots. The cathode wasn’t quite as dense as tungsten. Could air or some other gas be trapped in voids left from the sintering process? Could this explain the pressure pops after firing?

[igorsoares]

What if the electrodes were covered in a layer of insulator, leaving only the upper and lower tips exposed to the plasma.
Wouldn’t it be able to “trap” most of the “escaping” atoms?

[JimmyT]

As the filaments form and migrate toward the end of the electrode they grow and merge. I think that at least the inner surface of the outer electrodes have to remain exposed to facilitate this.

[Andrew Palfreyman]

No news for over a month. Are we stuck?

[meemoe_uk]

Well, in my experience of waiting for news, longer waits than expected are due to 1 of 2 reasons
a) Somethings gone wrong
b) Big step forward, so extra time is spent polishing all the results so they are presentable to high brow journals.

From what we know from the July 9th news, both (a) and (b) are possible.

I was thinking about the impurities problem : Is increasing the pressure amount of fuel in the chamber a viable way of reducing the percentage of impurities in the plasmoids?

[Lerner]

The tungsten cathode, which had an oxide layer, took a hot ammonia bath and came out clean! Next: reassembly and more shots.

[Andrew Palfreyman]

Excellent news. Do we know which oxide was prevalent and what the re-formation rate is projected to be?

[Lerner]

Yes–it will not re-form at room temperature. It was exposed to high temperatures during manufacture. When firing, there will be no oxygen in the chamber.

[meemoe_uk]

> In addition, we are working out theoretically ways to transfer more of the energy from the electron beam to the heating of plasmoid, leaving less available to damage the anode. This work involves mixing in heavier gases and is still under way.

What about increasing the pressure?

[Author]

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