Jim Kovalchick 11/05 observations

[Jim Kovalchick]

I am still taking a moment now and then to keep improving my new fusor because I don't yet have stable operations at neutron magnitudes sufficient to measurably activate. Here are a few observations I have:
1. My stem connection appears to be the source of some vicious arcing at -30 kV. This is limiting my stability and top end neutron counts to roughly 200,000 neutrons per second. I am using a piece of stainless tubing as a crimp. I think I need to cover it over with alumina to keep it cooler.
2. My plasma concentration as indicated by brightness in the center of my grid does not seem concentrated. In fact there seems to be two minor bright spots with some diffuse additional concentration. I sent some pictures to my son to look at, and his immediate reaction was that there seems to be an overall cloudiness in the chamber without a clear concentration by star mode. I believe this may the result of asymmetry of my grid position in the conflat T.
3. Once I get above about -20 kV, the pressure in my chamber steadily drops causing me to have to chase current with constant adjustments. I believe this is a result of my chamber being relatively long with lots of metal to the point that heating is uneven. I think I am still baking out the chamber even though my chamber is very tight. I recently found my chamber less than 700 millitorr after over a week sitting idle.

I decided to start addressing some of these issues one at a time starting with grid shape and position. I have created a new grid out of tungsten. This time I am using only one continuous piece of wire wrapped in a cage with no crosses. I am still using the same stem connection method, but I will address that in the future. I also positioned the grid further into the center of my chamber. I am hoping this helps with both bake-out and with plasma symmetry. I have attached some photos to show some early results. The plasma was taken at high pressure, low voltage.

[Richard Hull]

I am assuming you are using flowing d2 gas as all successful fusors do?

I checked and my fusor leaks down to about 12 torr after only 24 hours of down time. Quite a leak! Yet, you saw it perform to a million n/sec a few weeks ago and activate silver nicely. Leaks of my kind, (severe for any vacuumist!), are absolutely no impedement to doing fusion provided operational awareness and control is exercised.

The key to doing good fusion is to constantly adjust the gas pressure to limit runaway current and yet reach ever higher voltages. (assumes excellent insulation on the HV input stalk.) The higher the D2 pressure at fusion volatages, the more fusion is to be had.

I doubt that precision symmetry has a whole lot to do with anything beyond assuring proper HV standoff distances from the shell. Naturally, the cathode should be as close to centered in the chamber as possible. Eyeball accurate is close enough.

Richard Hull