Yet another demo fusor (first runs)
Posted: Sat Aug 05, 2017 5:03 pm
This post describes my demo fusor and shows its first runs. I have been reading things in this forums for a while, but I decided to build something only when I found a bell jar at a reasonable price on ebay.
I started making the fusor around the bell: first, from an aluminium plate, four holes were drilled (three for pump, vacuum gauge and gas inlet, all ¼” SAE, and one for the electric feedthrough): Then a viton sheet was put between the aluminium plate and the bell jar, and an electric feedthrough was built form a spark candle: Vacuum grease is applied on both sides of the viton sheet. A cylindric inner grid was built and connected with a bolt to the spark candle: the grid is made of harmonic steel wires kept together by 5 cents coin (euro cents has a 12 star circle, quite easy to find where to put six holes!).
This is the final setup (I had to build a wooden support for the fusor), you can see also the ground grid (that is a spring of harmonic steel): The electric power supplier is an unbranded unit, with knobs that can adjust voltage between 5 and 30 kV and current protection from 5 mA to 10 mA: I plan to build a HV voltmeter to check indications, but, if you trust the knobs, all the following pictures are obtainted at 5-7 kV with 7mA limit.
Vacuum is obtained with an air conditioning vacuum pump, and checked with a digital gauge (with a 200 micron Hg resolution). Unfortunately the minimum pressure I could achieve was 3.6 mm Hg: I think this can be due to poor pump or water contamination (lot of fog coming out of the pump…), since the chamber can maintain vacuum at its minimum pressure for about 6 hours.
These are a couple of pictures of the plasma obtained at 3.6-3.8 mmHg, the plasmoid has a nice clessidra shape: Another picture: Here is a run without the ground grid (and a little higher pressure) showing discharges rising from the plate: During the first run I also built a guard around the bell (it has, in fact, imperfections) that was removed since it doesn’t heat and seems to survive vacuum safely.
Future plans are to try different gases (all there runs used air), to build an HV-voltmeter to check input voltage, and possibly to improve vacuum. Best everybody,
LT.
I started making the fusor around the bell: first, from an aluminium plate, four holes were drilled (three for pump, vacuum gauge and gas inlet, all ¼” SAE, and one for the electric feedthrough): Then a viton sheet was put between the aluminium plate and the bell jar, and an electric feedthrough was built form a spark candle: Vacuum grease is applied on both sides of the viton sheet. A cylindric inner grid was built and connected with a bolt to the spark candle: the grid is made of harmonic steel wires kept together by 5 cents coin (euro cents has a 12 star circle, quite easy to find where to put six holes!).
This is the final setup (I had to build a wooden support for the fusor), you can see also the ground grid (that is a spring of harmonic steel): The electric power supplier is an unbranded unit, with knobs that can adjust voltage between 5 and 30 kV and current protection from 5 mA to 10 mA: I plan to build a HV voltmeter to check indications, but, if you trust the knobs, all the following pictures are obtainted at 5-7 kV with 7mA limit.
Vacuum is obtained with an air conditioning vacuum pump, and checked with a digital gauge (with a 200 micron Hg resolution). Unfortunately the minimum pressure I could achieve was 3.6 mm Hg: I think this can be due to poor pump or water contamination (lot of fog coming out of the pump…), since the chamber can maintain vacuum at its minimum pressure for about 6 hours.
These are a couple of pictures of the plasma obtained at 3.6-3.8 mmHg, the plasmoid has a nice clessidra shape: Another picture: Here is a run without the ground grid (and a little higher pressure) showing discharges rising from the plate: During the first run I also built a guard around the bell (it has, in fact, imperfections) that was removed since it doesn’t heat and seems to survive vacuum safely.
Future plans are to try different gases (all there runs used air), to build an HV-voltmeter to check input voltage, and possibly to improve vacuum. Best everybody,
LT.