Spherical Cathode

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Dennis P Brown
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Spherical Cathode

Post by Dennis P Brown »

Well, I mounted a modest size sphere (about 2 inch diameter) in my chamber as the high voltage cathode. Not sure if this will improve the system's performance; still working on trying to get my 3He detector to work. So, can't do a comparison with my old cathode (a std cage.)

The plasma does appear more uniform compared to my old cage. Of course there are no 'hot spots' since there is no cage. I would hope that this type of cathode will result in fewer useless electrons in the plasma (electrons boiled off at a 'hot section' of the cathode wire (i.e. a section glowing red hot); resulting in a lot of electrons with too low a voltage.) The idea is then less wasted energy (power) so more deuterium ions can be created for a given power. Or at least that is the theory as someone here suggested.

My system was open to the air for a half an hour - so certainly water vapor contaminated the chamber. Despite that, the system powered up with no runaways nor any noticeable current fluctuations. As I raised the voltage to 30 kV, the current smoothly rose. Whether this is due to my system being extremely clean so that short exposure wasn't significant or possibly, the sphere does perform better then my original cage. Normally, there is a short 'seasoning' period after I open the chamber. Far too little data to draw any real conclusions but is interesting.
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JoeBallantyne
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Re: Spherical Cathode

Post by JoeBallantyne »

Any ions you create in that chamber, are just going to smash directly into the cathode essentially immediately after they are created.

Granted, most fusors have little if any recirculation, but a continuous surface cathode is guaranteed to have NONE. Ions will be directly attracted its surface, and will smash into it and lose their energy. Furthermore they will do so pretty much evenly spaced over the whole surface of the cathode, so no concentration of ions hitting in close the the same spot on the anode after they are thermalized and escape the potential well of the cathode as happens in hollow cathode, and solid cylindrical cathode fusors - which tend to focus the ions in a single beam.

I don't understand what improvements you are attempting to make to the conventional fusor by having a solid surface spherical cathode.

Joe.
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Dennis P Brown
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Re: Spherical Cathode

Post by Dennis P Brown »

Thanks for bring this issue up and discussing the problem in more detail - I didn't really address the purpose for this unusual approch to a cathode design. So, in answer to your post I will say: I'm not sure. Your issue is exactly why I desire to look into this question in an extreme manner - hopefully a spherical cathode stops all recirculation and I can then see exactly what happens to overall fusor performance.

Since recirculation is not necessarily a major or possibly (?) a significant source of fusion - as I understand it from some many posts here (and as you also suggested) - then what might be the primary source in a fusor? Since Richard and others have suggested that mostly imbedded deuterium atoms on surfaces that interact via collisions from deuterium ions striking these surfaces create the majority of fusion events, then a spherical solid cathode would not reduce performance and might even enhance such fusion rates (for a two reasons: more surface area and fewer lower energy electrons due to 'hot spots'.)

However, I agree that it is more then likely this design will not help but rather will hinder performance (getting good at that aspect of fusors.) Such a result is also useful information and will offer support that even for a fusor recirculation is a not insignificant source of neutrons.

Since it is trivial for my setup to interchange cathodes (with either a cage or solid sphere), I wish to look into this matter.

But in any case, until I get some neutron measurements (both cases) I certainly won't know. Regardless, doing this experiment might help settle that question: that is, which type of fusion process dominates in a fusor. Does using a standard cathode (i.e. cage design) using semi-free recirculation type cathode offer the best performance (even with 'hot spot' issues) or does a solid spherical cathode (less wasted ion energy) that depends almost solely on imbedded fusion offer better performance?

Using different fusor arrangements to aid in determining certain aspects of what is actually occurring relative to proposed models is the most logical methodology to help aid in clarifying such questions.
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Nicolas Krause
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Re: Spherical Cathode

Post by Nicolas Krause »

An interesting experiment Dennis, I hope it goes well. I'm curious, in standard fusors there's a star mode that occurs at certain pressure and voltage settings. It would seem obvious to me that the star mode requires a grid that the ions can pass through in some manner. However have you had any luck finding an analogous mode in your fusor? Perhaps there's some configuration of parameters where the plasma appears to circulate around the sphere?
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Richard Hull
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Re: Spherical Cathode

Post by Richard Hull »

An advantage of having been here since day one and having read every post ever written is that I remember Jon Rosenstiel has already used a solid sphere cathode in his old spherical fusor in a test related to reports from U of W years ago. It did fusion but no where near what he got with a cage wire grid. This ancient guy has ancient memories....How much longer will they be there for me to access?

Maybe he will chime in on his effort or you might search for that ancient post.

Edit:

Found it........! 2008 the wav file is still there and is really strange! Acoustic vibration of sphere in some relaxation oscillation mode???
"It Is a puzzlement." (Yul Brenner in the King and I)

viewtopic.php?p=16925&hilit=Rosenstiel+ ... rid#p16925

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Dennis P Brown
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Re: Spherical Cathode

Post by Dennis P Brown »

Thank you Richard for finding that post. Glad someone looked into that issue and interesting that this type of extra surface area decreases fusion rate; so some recirculation is occurring and useful in a fusor after all.

I did notice that they used a very small sphere. I might (or might not) try using my rather large sphere to see (which I am sure will occur) that a reduction still occurs compared to a cage (of similar size.)

I also intend (when I open the chamber again) to add a large wire grid (SS) to reduce the net 'effective' volume of my fusor. That is, adding a smaller grounded cage of wire inside the fusor allows a larger volume fusor to work like a fusor of much smaller 'apparent' volume. So this grounding cage does in fact allow a large volume fusor to operate at a much higher pressure and this extra gas does increase the fusion rate compared to the original fusor. Since that worked rather well in the past I really should have done that a while ago.
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