I am getting the parts together to make a DPF device. I noticed the Focus fusion device has a copper tube and an array of copper posts at the cathode I am kind of stretched for cash so I was wondering it the device has to be copper or if any metal will do. I am thinking of using Black Iron sewer pipe and rebar because they are readily available at any Hardware store.
If you are strapped for cash at this point then I’m concerned that you may take other shortcuts. This will not be cheap unles you have access to good salvage equipment. A functioning unit can produce radio frequency interference and some x-rays and you need to take precautions.
Copper is used because it is an excellent conductor of electricity and heat. It has a reasonably low level of corrosion. You can make a demonstrator unit using iron parts but the metal needs to be shiny bright and iron tends to rust easily. Your power supply will be the most expensive part and it needs to supply a large enough current at high voltage to give you a satisfactory demonstration. The dimensions and gas pressure are important elements too as has been explained in other posts.
Please do NOT try to build a DPF unless you have some knowledge of and experience with high voltage equipment. If you do have this, then there is a new simple and very small Indian design. I’ll post the reference shortly.
As a Power pro ( USAF) I have experience with high voltage equipment and am reasonably competent around hot equipment. I didn’t think about the corrosion aspect of black iron pipe but could see how that would be a major problem. Would cast aluminum work better, I live near Reading Cast Aluminum, so I have a supplier here in PA. The caps maybe a problem but I hear Ebay is a good source for high farad caps.
You really need to use copper or stainless steel for the electrodes. If your library has access I suggest you look at this design as a way to build a really cheap DPF. It has a finite lifetime, but should be a good start. The budget is in the tens of dollars.