IEC Fusion Reactor
- Months of work: Apr 2009 – Sep 2010
- Approximate Build Time: 1.5 Years
- Max Voltage: 60kV
- Max Stored Energy: 0.5kJ
This project began at the beginning of 2010 when I was searching for a science research project. I found fusor.net, a community dedicated to amateur nuclear fusion. From there the project began.
The device is based on Philo Farnsworth’s device, the primary inventor of plasma inertial electrostatic confinement (IEC) fusion (along with Bob Hirsh and others). A negative high voltage is applied to a center grid which causes the atoms to become ionized. The chamber is in a vacuum during operation at roughly 10 microns of deuterium gas, although this can be quite a bit lower if an external ionizer is attached. The ions that are formed have a positive charge and are thus attracted to the negatively charged center of the grid. These ions are accelerated to a sufficient velocity to induce nuclear fusion turning the deuterium into helium or tritium, half of the reactions yield one and and the other half yield the other product.
Neutrons are released during the fusion reaction which is detected as proof of fusion. A BF3 neutron detector tube was being used early in the project with the signal being fed through a NIM discriminator and counter. During peak operation the device can produce roughly 1 million neutrons per second. Other detectors such as He3 tubes and a bubble dosimeter were later used for higher accuracy counting.
Reactor chamber and high voltage multiplier
Power transformers, power supply modulator, and deuterium gas supply
This is a view of inside the vacuum chamber. The small inner grid is put at the high negative voltage potential. The impacts of putting RF power on the outer grid wire is being researched.
A view from the chamber camera during operation. As the device warms up the inner grid becomes incandescent from the heat of the ion collisions with it.
Operating with two inner grids biased a few kV apart. This seemed to dramatically improve the focus so the inner grid would run at a much lower temperature. The static in the image is x-rays affecting the CCD camera. During peak runs, x-rays were greater than 10REM/hr at the viewport and the camera was almost entirely static. Lots of radiation behind the shields.
A 2.45ghz waveguide designed for ionizing the gas passing through the quartz tube, which will be under vacuum. More fun dremel machining here.
An improved magnetron based ionization source. This is a resonant cavity that acts as the “9th resonator” in a microwave oven magnetron, rather than being a waveguide. Worked much better than the waveguide, but still not operating at quite a low enough pressure to be all that useful.
Silver foil that was moderated and placed near the reactor during a run lasting about 10 minutes, yielding 67CPM on the geiger counter. This shows that the silver was being activated to an isotope then decaying back. I would guess the run was around 250,000n/s based on this activation yield.
Lots of neutron detectors. The detection tubes must be in a moderator (paraffin wax, HDPE, anything with lots of dense hydrogen) since the reaction is producing high energy 2.45MeV hard neutrons, but proportional counter tubes (He3, B10 lined, BF3) can only detect thermalized neutrons. Passing through several inches of paraffin wax will thermalize the neutrons so that they can be detected, which is what all the wax tubes are for.
Before I got a cylinder of deuterium gas from AirGas, I had to make my own via electrolysis. It had to be thoroughly dried after creating the gas so as to not contaminate the vacuum system and limit the rate of the fusion reaction. I used two stages of drying, a stack of drierite right above the electrolysis cell (shown above in the thin tube), followed by a cold-trap which ideally would be filled with LN2, but I just used ice water.
The electrolysis cell. The deuterium gas is captured up the center tube, and the oxygen is vented.
Early in the game, started out building the base setup with a friend. This is the setup we brought to my high school for the science fair. Took first place.