Page 1 of 1

From confinement, to jet mode, and star mode

Posted: Sun Dec 16, 2018 3:13 pm
by Samuel Low
Has anyone had any success in explaining the mechanism for how the fusor eventually transits to jet mode or star mode ultimately with a low enough pressure? Does voltage play a role? I would love to hear someone point me in the right direction to understanding this phenomenon, thank you!


Re: From confinement, to jet mode, and star mode

Posted: Mon Dec 17, 2018 12:51 pm
by Max_micklitsch
Dont quote me on this, but i believe it relies solely on the shape of the electrical element

Re: From confinement, to jet mode, and star mode

Posted: Mon Dec 17, 2018 3:16 pm
by Richard Hull
Indeed, much relies on the inner grid construction, but operational know-how, clean vacuum in the 10 micron and below range helps also. My avatar image is from a formal, tough to make, resistance welded geodesic. the image was taken about 1 year after I had fiddled with demo fusors. I had no help in these efforts, there was no fusor information on line. It was about a year before even the "songs" genesis of this forum was around. It was done all on my own.

Star mode, in and of itself, means nothing related to fusion. It means you have a well built grid of a certain type and that you have succeeded in obtaining a clean vacuum with a mechanical pump in any gas of your choice.

I include a couple images. All were images taken from a black and white video monitor's glass CRT screen in 1998 from a first run of fusor III. The bluish cast is due to the early low resolution digital camera I had.

Richard Hull

Re: From confinement, to jet mode, and star mode

Posted: Tue Dec 18, 2018 1:28 am
by Samuel Low
Ah, so if it relies purely on the geometry, then jet mode arises as a result of the "asymmetry" of the alignment of the inner grid? Since in reality we can't have something that is purely right smack in the middle; a little bit off centre and we would see electric fields weakened in one particular direction as compared to the rest - and that is where the corona discharge takes place - the path of least resistance. I will pepper a few more questions and thoughts here to leverage on the expertise of the fusioneers to satisfy my curious cravings to learn, if everyone doesn't mind :)

As the pressure reduces even further below 10 pascals, without any change in voltage or ambient temperature whatsoever, we would see the fusor phase from jet mode to star mode naturally. Why does this change occur? Is there any actual mechanics or research that has been done to study this transition? Why is it so dependent on pressure? Does the mean free path of each particle affect the ability for the fusor to engage into star versus jet mode?

What really flows through this corona (be it jet or star mode)? The electrons? Or the cations? I assume it has to be both by conservation of charges. My intuition tells me each "jet" represents a bridge where cations flow from the grounded or positive outer grid to the inner grid to get themselves confined in permanence, and electrons get repelled from the inner grid back to the positive grounded outer grid.

The continuity equation then implies that this flow rate of charges along these "jets" can only be limited by the current rating of the NST or power supply the user is operating at. Please correct me if this is wrong :)

Thank you for the replies Richard and Max - and Richard, that is one amazing photo of Fusor III, I would love to achieve that on my own one day but right now I'm still stuck on jet mode with a cheap run-off-the-mill chinese pump from Alibaba.

Re: From confinement, to jet mode, and star mode

Posted: Tue Dec 18, 2018 5:27 pm
by Richard Hull
Simon analysis shows this well.....Try


You can see the visible jets in the simulation based on grid geometry. (assuming all other conditions are correct and supportive)

I have an additional image of my current non-geodsic, three ring grid which is one of the Simon runs shown.

The jets are ions recombining in the stream and being re-ionized in the high energy streamlines. All of this produces increased light along the streamlines over the general glowing environment. Thus, we see the so called star mode

Richard Hull

Re: From confinement, to jet mode, and star mode

Posted: Thu Dec 20, 2018 5:30 am
by Samuel Low
Thanks for sharing Richard, those SIMION plots in the link you sent are very telling for why the edges of the stars form. My guess then is that "jet" mode comes as a result of asymmetrical positioning of the inner grid (so the electric fields lines are less "concentrated" on one end than the others, leaving an obvious choice of a path for particles who wish to attempt the jail-break).

It makes sense then that the lengths of each of these star spindles will increase greatly at a much lower pressure, due to the reduced mean free path.

Re: From confinement, to jet mode, and star mode

Posted: Fri Dec 21, 2018 11:50 am
by Dennis P Brown
You have a simple editing error - mean free path increases with lower pressure. We don't want to confuse readers not use to vacuum work.

Re: From confinement, to jet mode, and star mode

Posted: Tue Dec 25, 2018 7:08 pm
by Scott Moroch

The above simulation in SIMION clearly demonstrates the formation of star-mode. Only particular ions will be captured in stable, oscillatory orbits in an IEC device. Most are lost by collisions with the inner or outer grid.

Scott Moroch