Boron Fuel Injection

Alchemist · Post by **Alchemist** » Thu May 15, 2008 7:35 pm

I know the issue of fuel injection and precise control has been brought up several times, and I have an idea that might help solve the issue, at least in a P + B11 fueled reactor.

What I envision is a metal upside-down T-shaped chamber attached to the reactor via a vacuum / fuel-feed line that connects to the "stem" of the T. One end of the T contains solid/powdered boron fuel, followed by a vacuum air lock mechanism for reloading the boron fuel without contaminating the fuel supply with stray atmospheric gasses. The opposite end of the T is capped with a thick "lens" of high-grade optical glass capable of withstanding the high vacuum inside the machine. The glass will allow an external laser to fire into the chamber vaporizing a minute amount of the powdered boron. The entire T-shaped chamber, and the boron inside, can be charged to the necessary level to ionize the boron as it is vaporized by the laser. (Using a UV laser could possibly contribute to the ionization although I don't know how efficient that would be.)

Using this setup, the amount of boron fuel fed into the system could be precisely controlled by adjusting the frequency and duration of laser pulses.

KeithChard · Post by **KeithChard** » Fri Aug 22, 2008 8:00 pm

Alchemist

You were right to bring up this much neglected topic. Do we use powdered boron, solid amorphous boron, bars of crystalline boron or some other form? Is a laser the right tool for ionising it? How do we keep up with supplying fuel to a vacuum vessel in a radiation zone?

I can only suggest that a year or more supply should be available in a magazine that is located within the vacuum system with an automatic reloading system.

Much more thought and good ideas required!

D Tibbets · Post by **D Tibbets** » Sat Aug 23, 2008 1:17 am

I'm not sure you can ionize the boron befor it is inside the magrid. If ionized (positive charge) outside the grid it would be repelled by the positively charged magrid. I'm thinking that the boron would need to enter within the magrid as a neutral gas befor being ionized by the electrons, microwaves, lasers, etc; or if 'pre-ionized', injected with an ion gun.

KeithChard · Post by **KeithChard** » Sat Aug 23, 2008 6:58 am

D Tibbets.

That makes things very difficult. Boron melts at 2349K and boils at 4200k although that is probably at normal pressure. I think it may sublime at low pressure. It looks like an ion gun may be part of the solution, as you suggest.

D Tibbets · Post by **D Tibbets** » Sat Aug 23, 2008 9:06 am

I've seen posts here mentioning at least one boron compound that is a gas at room temperature- Diborane I beleive - http://en.wikipedia.org/wiki/Diborane
that is made up of boron and hydrogen. I understand that it is nasty stuff. but since hydrogen is the only other ingrediant it might not contaminate the reacter.

Dan Tibbets

drmike · Post by **drmike** » Sat Aug 23, 2008 1:50 pm

Hydrogen is the other component of the reaction, so diborane would be pure fuel. The nastyness part might be why you would not want to use it.

D Tibbets · Post by **D Tibbets** » Sat Aug 23, 2008 2:08 pm

Yes, it has the advantage of being a complete fuel. What I should have said was - no unwanted contaminates, and if the three to one ratio of hydrogen/boron in the molecule is not to high. Are you better off with a 1: 1 ratio, 2: 1, 10: 1 ?

Dan Tibbets

drmike · Post by **drmike** » Sat Aug 23, 2008 6:06 pm

I suspect it depends on the temperature distribution. If you can have a high spread with the protons, then more is probably better. You increase the probability of a fusion that way. It would be an interesting problem to study.

KeithChard · Post by **KeithChard** » Sun Aug 24, 2008 2:22 pm

Decaborane B10 H14 appears to be less unpleasant. It is a solid at normal tepearature, melts at 100C and boils at 215C. Would it decompose and ionise readily? Would there not be an excess of protons?
I know that an excess is desirable but use of these boron compounds would cause that excess to build continuously.

JohnSmith · Post by **JohnSmith** » Sun Aug 24, 2008 2:51 pm

I imagine we might have to purge the system occasionally anyway. Not sure what that would do to performance.

drmike · Post by **drmike** » Sun Aug 24, 2008 3:42 pm

Yes, it would ionize easily. I don't think excess hydrogen is too much a problem for the plasma, but it might be a problem for the steel walls. Hydrogen makes steel brittle, and I'd think you'd want to make sure you keep the excess from getting into the outer walls too much. If it works to get fuel in, we can find a way to deal with the extra hydrogen to prevent premature failure of the vacuum chamber. I think it's an interesting thing to look at.

MSimon · Post by **MSimon** » Sun Aug 24, 2008 5:07 pm

Current thinking is that a hydrogen to boron ratio of 10:1 would minimize energy losses.

KeithChard · Post by **KeithChard** » Mon Aug 25, 2008 7:17 pm

M.Simon,

If fuel is added at 10 p to 1 B and is converted to alphas in the ratio of 1 p to 1 B there will be much more than 10 p to 1 B very quickly. In fact any fuel with an excess of p over B will quickly exceed 10:1 in the well.

I think independent control of p and B will be necessary unless we invent a way of removing excess p.

MSimon · Post by **MSimon** » Mon Aug 25, 2008 10:25 pm

KeithChard wrote:M.Simon,

If fuel is added at 10 p to 1 B and is converted to alphas in the ratio of 1 p to 1 B there will be much more than 10 p to 1 B very quickly. In fact any fuel with an excess of p over B will quickly exceed 10:1 in the well.

I think independent control of p and B will be necessary unless we invent a way of removing excess p.

Yes.

icarus · Post by **icarus** » Wed Aug 27, 2008 3:47 am

So proton ion gun(s) and boron-11 ion gun(s) seem like a possible solution for the fuel mixing/input rate?

Some kind of feed-thru for the cathodes as they ablate maybe? ... or simple change out rotation type of replacement using multiple injection guns?