Step 1: Assemble the Vacuum Chamber

A quality high vacuum chamber is required for the fusor to operate. Sometimes an appropriate chamber can be found on eBay, but generally it is best to make one. Parts can be scrounged for several hundred dollars, or purchased new for $500+.

Get two stainless steel hemispheres, purchase two corresponding conflat-flanges (8" flanges in my case), bore out holes for accessory flanges, and then TIG weld it all together. Flanges are typically either of the KF or the conflat style. Conflat can be seen in the image below as the flanges with bolts, and KF (kwik-flange) are seen as those with only clamps holding an o-ring on the mating surface. Only weld on the inside, never on the outside (since virtual leaks can be formed if both inside and outside are welded). If you've never TIG welded before, it would be wise to have someone with experience do it as the welds must be flawless with no pin-sized holes or porous areas to hold a vacuum.

After machining, thoroughly clean the chamber and avoid getting fingerprints in it since these will outgas, which means at vacuum pressure molecules in the oil of finger prints or machining oil will become vapor and make it hard to maintain plasma stability or reach a good ultimate vacuum level.

Step 2: Prepare the High Vacuum Pump

Install the oil diffusion pump (or turbo pump if you have a bit of luck scrounging or a higher budget). Fill the pump with quality diffusion pump oil to whatever fill level the pump documentation suggests, attach the inlet to a valve which then connects to the chamber (see diagram), and attach the outlet to a mechanical backing pump capable of reaching at least around 75 microns (any higher and the diffusion pump will not operate properly or the oil will oxidize quickly).

Make sure the pump is sufficiently cooled, many oil diffusion pumps require water cooling, smaller ones such as the one pictured can get by with a decent air flow.

Once this is assembled, turn on the mechanical pump and wait for the vacuum to reach at least 75 microns. Next you can test the high vacuum pump by turning on the boiler on the diffusion pump. After it warms up (could take a while), the vacuum should rapidly drop below the single micron range.

Step 3: Build Inner Grid

The inner grid (where the high voltage is applied) must now be built and attached to a high voltage feedthrough.

It is best to use a metal such as tungsten for the grid wires since it has a very high melting point, and the grid will get extremely hot during high power runs.

This can be built however you wish, as long as it resembles a spherical shape of roughly 1-1.5 inches in diameter (for a 6-8" chamber), it should work fine.

The grid should be internally attached to an electrical feedthrough such as the one pictured in the second image. This feedthrough needs to be rated for the cathode voltage that will be used, typically 40kv is a good target voltage.

Step 4: Assemble the Deuterium System

Deuterium gas is used as the fuel for this fusion reactor. You will need to purchase a tank of this gas (unless you wish to do electrolysis on heavy water, this process will not be documented here but nothing more than a small Hoffman Apparatus is required - higher purity gas can be gotten from a compressed tank).

Attach a high pressure regulator directly to the tank, add an extremely fine-metering needle valve after this (or a laser drilled orifice in the range of 5 microns), then attach this to the chamber. A ball valve can also be installed between the regulator and the needle valve since needle valves are not shutoff valves.

See the attached diagram now updated with the deuterium handling system.

Step 5: High Voltage

If you can purchase a power supply (occasionally but not commonly found surplus) appropriate for fusion use, the high voltage becomes very simple. Simply take the output of the 40kv negative supply and attach it to the chamber with a physically large high voltage 50-100k ohm ballast resistor in series (large enough that its length will not flash-over if 40kv is applied to it in a plasma run-away or arc discharge).

The difficulty is that it is often difficult if not impossible to find an appropriate fully assembled DC supply of this voltage level that is affordable to the amateur scientist.

Pictured is my high frequency ferrite transformer pair, with a 4-stage multiplier seen behind it.

If a fully assembled power supply (typically manufactured by either Glassman or Spellman), there are a few options: -Find an x-ray transformer, and if necessary either reverse the rectifiers for negative polarity or add rectifiers if it has none (an x-ray transformer core won't have rectifiers, it probably will if it is in its oil tank) -Build a switching high frequency ferrite power supply. This is what I did, however it requires a bit of EE experience since several aspects must be resonant and if it is ever taken out of tune, the transistors will burn out. Probably not the best option for people with little electrical background.

Step 6: Setup Neutron Detection

The proof of fusion (and a quantitative analysis of how much fusion) is obtained through detecting neutron radiation, the byproduct of a D-D fusion reaction. There are three options which will be described. They are in order of descending ease of setup.

-A Neutron Bubble Dosimeter A bubble dosimeter is a small unit with a gel in it that forms bubbles when ionized by neutron radiation. This is the easiest form of neutron detection available since all you have to do is unscrew the top and set it next to the fusor. Some of the drawbacks are that it is an integrative detector which means all you get is a total neutron emission number over the time that it was used, rather than an instantaneous neutron rate. Additionally, they are somewhat hard to get since the only company to make them is Bubbletech in Canada, which has a minimum order of 3 with steep shipping and handling (expect to spend $700+ if ordering directly from them not in a group buy). Additionally, they tend to be fairly worn out after a year of shelf life (although I've kept mine in a refrigerated storage container at 50*F and it seems to be like new after I think more than a year). The advantage is that calibration data is provided with purchase and of course it is easy.

-Silver Activation When silver is placed near the reactor (with a moderator [paraffin wax, water, HDPE, etc] between it and the neutron source, since only thermal neutrons will activate the material) it becomes slightly radioactive with decent neutron fluxes. It has a short half life of only a few minutes, but if you quickly put a geiger counter next to the silver, counts can be detected. In my best runs, I have gotten a piece of silver to about 250CPM over background on a CDV-700 geiger-counter. The disadvantages of this are that it requires a decent neutron flux (at least about 100,000 neutrons/s) which is above the average "beginner's first run" neutron rate. Also, it is somewhat difficult to calibrate, and the counts can't be taken until after the fusor has been shut off.

-A Proportional Tube Tubes can be purchased which are filled with either BF3 or Helium-3 (some very old tubes are Boron-10 lined inert gas tubes). These tubes, similar to a geiger counter, can be used with a counting device to detect electrical pulses when neutrons pass through the tube. Either an all-in-one counter can be used, often made by a company called Ludlum, or a modular counting system can be made using NIM modules. The tube is surrounded by about 2 inches of moderating material such as wax or water. This is by far the most accurate and useful form of neutron detection, however the cost of a new tube is prohibitive to most people, and they are extremely rare on the surplus market. Also, counting equipment can become quite costly.

NIM Configuration: If you chose to make a NIM setup as I