as with any engine the fuel must be delivered…shoveled into a steam engine,carburated into a gasoline engine, pumped int a turbine,injected into a diesel. in each case the variables are minimized and controlled .
what scheme of fuel delivery is fofu 1 going to implement?
What form of boron solid liquid or gas?
in the event that boron fouling or chamber contamination becomes an issue is there an alternate fuel delivery scheme?
FoFu1 is a research device, not intended for power production. At the very low pressures inside the device, the problem is taking enough fuel out (prior to a shot), not putting it in.
AFAIK, the fuel in the “production model” will be decaborane gas. It will decompose into 14 H and 10 B in the plasmoid. Decaborane liquifies at about 216°C, solidifies at ~97°C. IIRC, the chamber will hold a mild vacuum (plasma) at about 500°C.
Fouling should not be a problem as long as the temp is kept up, I’d guess.
If decaborane is used for trials this means that fouling will likely occur as the chamber temperatures are at room temperature. I was wondering if a solid fuel rod of solid boron was placed in the area of plasmoid formation that it could supply as much boron as required. since the plasmoid has lots of little electrons whizzing about and little hydrogen ions zipping round and round they could crash directly into a stationary object. I had an idea of a mechanism like a mechanical pencil with a boron filament that could be replenished by a little click if you wanted more, just protruding through the end of the anode. a kind of fusion fuel dispenser. this way the only gas in the chamber would be hydrogen and hopefully a growing amount of helium. boron has a high melting temperature so with a billion degree electron stripping off a few boron atoms or fusing on the side of the filament you will not have a noxious fouling gas to contend with. I believe the fuel density would go up considerably into the solid realm without having to change many parameters. in this way the hydrogen gas pressure would be the only parameter to adjust. that is if the plasmoid doesn’t care if it has a boron stick in one end.
I know that as the work is progressing and plans have been made to use decaborane, is there a material that could be painted on or used as a liner in order to make it easy to clean the chamber after testing? maybe some sort of liner or spray on non stick cooking oil? lol..
Boron fouling might be an issue for the chamber walls, electrodes and insulator. Once the decaborane is converted to a plasma, it will decompose. People observe this in methane PFs. The chemical bonds break in the high temperature, high density plasma. There is no reason for the carbon to grab back four hydrogen atoms. Decaborane will be the same. Boron could coat every surface or form a debris dust. Devices that fire many shots observe dust formation in the vacuum chamber as electrode and insulator material is converted to plasma and then solidifies from the plasma as it cools. Even if the chamber is held at temperature, the boron will still plate out unless there is chemistry that demands for the formation of a gaseous form or boron. I don’t know the answer for sure but I doubt it. If boron readily formed a gas with hydrogen the tokamek guys would already know about it. It was common practice to coat the inside of tokamek with boron for a time.
I find it hard to believe that the fuel will be evacuated between shots if the repetition rate is much greater than 1 Hz. Continuous feed and pump is done for inert gases for high repetition rate PF devices in lithography. I’d imagine a similar strategy would be implemented at the power plant level. Most of the fuel gas could be recycled. It would be interesting to fire a few shots and see how much the gas pressure drops for gases that chemically react and are likely to have solid products. Methane or acetylene seem like good choices as carbon is inert but very messy in terms of vacuum as carbon holds onto everything. Black powder all over the place isn’t very appealing either.
This is a difficult problem. It will take some creative solutions to keep everything working correctly.
Brian H wrote: IIRC, the chamber will hold a mild vacuum (plasma) at about 500°C.
if i remember correctly, Eric said contents should be kept above 1000°C, between shots.
Methane or acetylene seem like good choices as carbon is inert but very messy in terms of vacuum as carbon holds onto everything. Black powder all over the place isn’t very appealing either.
carbon will conduct electricity…. just take a pencil and draw lines from any 2 points on your distributor cap and run your engine. it just won’t be the same. I am still excited to see decaborane or alternative boron fuel introduced.. science is fun.
since boron is used in glassware could it be formed into strands much like glass fiber? I have a boron fiber fishing rod so i believe the same concept could be implemented.
could a small hole be drilled in the center of the anode and wedge some boron filaments in it for a test with just hydrogen gas.
There are still a lot of unexplored possibilities if decaborane has unanticipated issues. Pentaborane, for example, is gaseous at room temperature.
Boron can be made conducting as well so same problem as carbon. It can gum up the insulator and ruin the breakdown along the insulator. Any gas that can decompose into a solid has the potential to gum up the process. This is a common problem in the semiconductor industry with silane and large molecules that contain silicon. I think you will get some shots before it becomes a problem but operating at steady state could be challenging. High temperature will only improve the bonding of boron atoms and grow dense thin films.
This is a common problem in the semiconductor industry with silane and large molecules that contain silicon.
so what was/is the fix for protecting working parts from deposition of unwanted materials.
I would think that any material coming from a plasma would have an electrostatic charge for a short time. Maybe an electrostatic dust collector inside the chamber could collect the boron dust. It would be interesting to try it with acetylene first to see if carbon dust could be collected that way.
The fix is to send out the chamber for cleaning or implementing a cleaning gas mixture involving fluorine or other extremely reactive gas that can volatilize the contaminant. The problem in a reactor environment is the shutdown time to clean. It could take minutes to hours to coat the parts and then hours to clean them. The “on time” for a coal fire plant or nuclear plant is typically rated at more than 90%. That would be hard to accomplish if coating takes hours and the cleaning takes hours. The alternative would be to run parallel fusion “light bulbs” driven by the same pulse power. One bulb is on while the other is cleaned. I don’t know the boron deposition rate but it is probably an important experiment to try in the near term. The reason to try carbon it is more conducting and dealing with it is low risk from a human stand point.
The boron will be a plasma when it is emitted by the pinch. It will plate out onto something before dust forms. No time to nucleate particles when transit times are less than 10 us. That is not to say the coating will not flake off as dust on a longer time scale. Electrostatic collection might be feasible on particles that have fallen off the walls. The real problem is will the insulator get coated. You need a clean insulator for the PF to work correctly.
Maybe low pressure oxygen could be admitted to the chamber and the plasma system fired a few times. The highly reactive oxygen plasma should oxidize the boron into B2O3. Boron oxides may chemically combine with the insulator. I don’t know if that would be an improvement or not.
It would be interesting to try an oxygen plasma on a carbon coating to see the effect.
Francisl wrote: Maybe low pressure oxygen could be admitted to the chamber and the plasma system fired a few times. The highly reactive oxygen plasma should oxidize the boron into B2O3. Boron oxides may chemically combine with the insulator. I don’t know if that would be an improvement or not.
It would be interesting to try an oxygen plasma on a carbon coating to see the effect.
Wikipedia has two articles listed as Plasma cleaning and Plasma ashing that may be useful. Cleaning carbon is easy. Removing boron may be harder. An aggressive oxygen plasma could damage the metal electrodes so they would have to be protected. Argon or helium plasmas may be more practical. This has been mentioned in other posts about removing contaminants from the chamber.
An automated cleaning system could be designed for a commercial unit.
Oxygen might not be aggressive enough. The beauty of carbon is oxygen turns carbon into CO2 which is easily pumped from the chamber. Boron forms a stable solid oxide. Fluorine can form a boron gas but it is highly toxic and fluorine attacks almost everything. The key question is the etch rate vs the deposition rate. Fluorine is commonly used in semiconductor chamber cleaning so the recipe exists. An question to pose would be using a mixture of BF3 (toxic boron gas) and hydrogen as fuel. The fluorine would attack the electrodes, but it would also keep the boron in gas form. I guess it would be a trade off in which gets you first, boron build up or electrode/chamber erosion.