Asymetry in collected current on each hemisphere

For posts specifically relating to fusor design, construction, and operation.
Post Reply
Andrew Seltzman
Posts: 815
Joined: Sun Feb 01, 2004 8:02 pm
Real name: Andrew Seltzman
Contact:

Asymetry in collected current on each hemisphere

Post by Andrew Seltzman »

The mark 3 fusor has electrically isolated hemispheres (both hemispheres are insulated from each other and the vacuum system) allowing the collected ion/electron current in each hemisphere flowing to ground to be measured independently for examining if the asymmetry generated by the presence of the grid stalk insulator and ion injectors effects shell current distributions in the fusor.

The insulating break is made by using a viton o-ring shielded by a ceramic fabric limiter, the conflat bolts are insulated and the bolt rings are separated by thin fiberglass shims preventing direct electric contact between the flanges. As I will might be changing to a copper o-ring for the hemispheres in order to achieve better vacuum levels, I conducted some tests to see the effects.

Measurements were taken by connecting each hemisphere to ground through a multimeter and measuring the grid current with the power supply. The injectors are driven by DC-DC converters that separate them from ground leaving the only return path through the multimeters.

It was determined that for an insulated grid stalk, when the fusor is operating in glow discharge mode(18 mTorr) with no ion injectors on there is equal current collected on both hemispheres. At lower pressures(2.5mTorr) with all ion injectors on, there is definite difference in collected current on each hemisphere. With both hemispheres left floating, a single injector can drive them to about 180v difference, when shorted together through a multimeter, an injector can drive about 2mA from one hemisphere to another. Adding voltage to the grid will drive current to both hemispheres, superimposing it on top of the current flowing between hemispheres driven by the injectors.

Measurement setup
SAM_4454a.jpg
Electrical connections
SAM_4453a.jpg
Top injectors on showing ion current being collected in bottom hemisphere
SAM_4456a.jpg
Using injectors to null out current being collected in bottom hemisphere with grid current present
SAM_4462a.jpg
Floating hemispheres with grid current off showing injectors driving the hemispheres to 187v diffrence
SAM_4465a.jpg
Andrew Seltzman
www.rtftechnologies.org
User avatar
Steven Sesselmann
Posts: 2127
Joined: Wed Aug 10, 2005 9:50 pm
Real name: Steven Sesselmann
Location: Sydney - Australia
Contact:

Re: Asymetry in collected current on each hemisphere

Post by Steven Sesselmann »

Andrew,

Interesting experiment, where how did you hook up ground on the PSU?

Are you operating with a double grid?

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
Andrew Seltzman
Posts: 815
Joined: Sun Feb 01, 2004 8:02 pm
Real name: Andrew Seltzman
Contact:

Re: Asymetry in collected current on each hemisphere

Post by Andrew Seltzman »

The grid power supply ground is connected to the negative leads of the multi meters connected to the hemispheres. The positive leads are connected to the hemispheres which are isolated from the aluminum frame, vacuum system, and each other.

This is with a single grid.
Andrew Seltzman
www.rtftechnologies.org
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Asymetry in collected current on each hemisphere

Post by Richard Hull »

Nice effort, Andrew. Now to figure out what this means in a real scenario where fusion is done. Very interesting, indeed.

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
Post Reply

Return to “Fusor Construction & Operation (& FAQs)”