Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Grid potential problems
Date: Sep 03, 9:33 pm
Poster: Al Dovigi

On Sep 03, 9:33 pm, Al Dovigi wrote:

Dear Fusion Researchers,

I am attempting to build a fusor to experiment with and am running into
some trouble. I hope you can help steer me in the right direction:
I have constructed a crude vacuum chamber and electrode for my fusor
project. I have copies of Farnsworth's patents and am trying to model my
project after his description. The problem I am running into is
obtaining a high voltage across my electrodes.
Farnsworth describes a 15 amp current flow across his at voltages as
high as 140 Kv. This is a very high power and such a device would be
actively cooled as he describes.

My power supply is capable of 30 kV and up to 30 ma. I am trying to
limit the power input to 10 ma and 25 Kv to give me a total power in of
250 watts. I have been able to pump the vacuum down to 10-5 Torr but
with no resistors the direct current only gives me a kV at best???
The only way I can get my grid potential up to 20 Kv is to place a 200 M
ohm resistor after my cathode to ground. Needless to say I've blown
quite a few resistors that way.
Am I doing this right???

Did Farnsworth use a resistor to keep his Cathode potential so high? He
doesn't show this in his patent? He would need an internal resistance of
his device of at least 10 K ohms since even with a high vacuum in the
10-7 Torr area there would still be little internal resistance at that
voltage, then once a plasma is generated the resistance would drop
further as the plasma is a good conductor.

If I understand the theory correctly the grid is at a high potential
with respect to ground and the electron space charge building up inside
the cathode, and this is the region where the ions oscillate?

Even using the Child-Langmuir equation with a perfect vacuum a 30 Kv
potential and a 10 ma current with an inter electrode separation of .01
meters my electrode surface area has to be just 100 microns x 100
microns. I'm sure Farnsworth's electrodes had a much higher surface

Am I missing anything here?

Thank you in advance for your help

Al Dovigi