Demonstration Fusor

A Demonstration Fusor is a simplified version of a fusor, designed, as the name implies, to demonstrate the principle of Inertial Electrstatic Confinement without actually performing fusion. Both the voltages used, and the levels of vacuum reached, are usually not sufficient for actual fusion. The residual gas in the chamber is air, not deuterium.

A Demonstration Fusor is usually the first step toward actual fusion, and the majority of amateurs do not get past this stage. (Going further requires better vacuum equipment, a higher voltage power supply, more sophisticated vacuum metering, a source of Deuterium, and equipment for neutron detection and counting. Shielding from x-ray radiation also becomes a factor because of the higher voltages used)

The equipment as initially assembled in the Haylett garage. The power supply and the vacuum gauge are both out of view.

The meters (photographed later on) indicating 7839 volts, and 6.74 milliamperes.

PLASMA! The faint glow of plasma forming around the inner grid as pressure is lowered.

A clearly formed plasma “bugle”.

At slightly lower pressure, the bugle becomes an electron beam, and begins localized heating of the bell jar wall (Not good!).

As the pressure falls still further, the voltage rises and the current decreases.
By around 7500 to 8000 volts, all signs of the bugle and electron beam are gone, and a star begins to form.

As the pressure drops further, the voltage continues to rise,  the current continues to fall, and the plasma star gets dimmer.

At around 9500 volts, the plasma extinguishes. At that moment, the current drops to essentially zero, and the voltage climbs to the power supply’s maximum – around 10,700 volts.


An Excellent Example of STAR MODE in a Demonstration Fusor

Although still just a demonstration fusor, and still using air rather than deuterium, a clearly formed “fusion star” is visible with a ray coming out of the center of each opening in the grid.

Records were unfortunately lost, but the operating voltage at the time of the photo is believed to have been around 15,000 volts, with a current of between 3 and 4 mA. At this time we still did not have a calibrated pressure gauge available.

The inner grid used was slightly smaller than the first inner grid. The power supply still used a 15,000 volt, 30 mA neon sign transformer, but with the center tap ground removed so that the full 15,000 volts could be rectified with a full-wave bridge rectifier. The output was then filtered with a 35,000 volt, 30 nF cap. and current limited with a resistance of approx. 70 K ohms. The rectifier and resistors were kept submerged in oil.

Open-circuit voltage of this power supply is close to 22,000 Volts DC when supplied with 140 volts A.C. from a Variac.


Next: Nuclear Fusion in the basement