lithium deuteride inner electrode

[jerryby]

Has anyone considered that the sputtering poisoning effect from the inner electrode might be mitigated by use of a LiD inner electrode?
In fact I wonder if the Tokomak people have considered tiling the machine with LiD?

[001userid]

What is the melting point and work function of LiD?
Joe Sal

[jerryby]

I Googled it yesterday and I think it is some 650degC. It is a brittle metal apparently and hard to work. I would guess the WF would be low since Li and hydrogen is not too far from Cs on the periodic chart (??). I was thinking today about plating lithium and then loading the film at low currents with deuterium. However Li film seem to not be stable based on their failure in Li ion batteries. There are some exotic processes (read expensive and need extensive development) in the patent literature whereby the film is under a protective coating. However, I'm not a chemist, but think of doing the wall and electrode plating in the reactor containment vessel.
However, even if a stable film could be plated, it is not clear how long it would last on the under electrode. I have never worked with LiD but I have worked with boral which also might make an electrode material.

[Edward Miller]

The Tok'ers have some info on liquid lithium walls.
I think LiD would be pretty tough for a Fusioneer since the good stuff is hard to get and doesn't like air or water.

From the wikipedia article on LiH
"It is a flammable solid, and is also very reactive to water, with which it reacts to produce lithium hydroxide (which is a corrosive strong alkali compound), and flammable hydrogen gas. It may ignite spontaneously in air, when at an elevated temperature."

[jerryby]

LiD is available from Alfa Aesar @ $48 for mg and $64.10 for 2g (2003-04 catalog). It is the form of lump/powder and is listed as air and moisture sensitive. Alfa probably can help with the handling. I think if its use has any chance of success, it must be argon sputtered inside the fusor in a side sputtering assembly. Cs deposition in a PM tube is kind of an example.

[Nick]

Well I know as of last time I takled to someone at MIT there using boron tiles
in the tokomak.

[Verp]

I think this is also an issue of vapor pressure, because if the chemical in question has too high a vapor pressure, the resulting gas is going to overwhelm any attempt at useful fusion.

Rod

[DaveC]

While the concept of a LiD "getter" for the sputtered metal from the inner electrode is appealing, it probably isn't worth the effort to implement, given that this simple spherical fusor design is sooo incapable of significant efficiency.

The way the typical spherical designs are built, the inner electrode cannot avoid being impacted by gas ions. Depending on the electrode materials, and their melting temperature, the fusor so constructed has some limiting current of sustainable operation, at any given voltage/pressure condition.

The original ion gunned fusors, made serious attempts to shoot ion beams through the inner electrode, not at it. This reduces the impact heating for at least the incoming ion pass. But does little for subsequent passes, assuming the ions don't merely go straight out the other side and reach the fusor wall and reverse direction.

What is interesting in the simulations I've done, is that the ions do not actually hit the wall, unless they are launched from outside the wall (ie: throught the outer fusor wall). Since with most of the fusors, the D+ ions are being created inside the shell, then they cannot actually reach the shell, unless they are involved in elastic collisions with other moving ions, in such a way as to receive a momentum boost along with a redirection.

It really pays to take some time to try to understand the ion and electron motions in the standard fusor that most folks are building. If the fusor is considered to be .. mostly.... a low pressure discharge device... then it will be clear that ... mostly... the outer shell heating is from electron collisions and heated neutral gases, and the inner electrode heating is from ion bombardment. The device strongly resembles a cold cathode type discharge tube.

All this suggests to me that probably these more exotic approaches to handling the sputtering may not be as useful, as reducing the sputtering directly by ion optics designs.

Dave Cooper

[Richard Hull]

Dave is pushing and re-enforcing what I have pushed for years. The outer shell just is not hit in the simple fusor by ANY ions at any time save for the statistically rare elastic collision ions!!!

Probably 75% of the major heating of the shell is due to electron bombardment at near full accelerator energy. The contribution from neutrals, mostly slow, is probably 20%. 4.9% is probably conduction related from the grid support. The remaining 0.1% is probably due to assorted miracles by ion impact (very slow).

The electron heating is the most efficient energy transfer in the entire system. The MFP of electrons is extreme compared to large slow neutrals or richocetting slowed ions.

Folks have to remember that ions just can't go any closer to the shell than their point of creation via any electrostatic regime in the device. Only a mechanical hit would do this and would have its greatest statistical possibilty on very slow, decelerating ions already near the shell in their electrostatic orbital regime. Thus the energy of impact would be low and the heating value also low compared to the torrent of unassailed high energy electrons created throughout the volume and doomed to hit only the outer shell. Not many misses in this latter regime. Ultimately, a lot of heat based on input energy winds up at the shell through many processes. To my knowledge this remains unquantized by experiment.

Obviously, in an ideal calorimetric bomb test, the water would record 100.000000000001% of the input energy delivered to the bomb's water. The device is over unity due to fusion.

This is a device that transforms electrical energy into kinetic energy of mass in motion. As 99.9999999999% of the mass remains in the vessel, all kinetic energy will be downconverted to heat. This will ultimately make its way through various paths to the shell.

Richard Hull

[JohnCuthbert]

The vapour pressure is probably a moot point for a more or less ionic solid. OTOH the dissociation pressure of the hydride LiH reaches 10 mmHg at about 550C and 1 bar at about 1000C. If the deuterated version were very different then this would be a neat way of separating the 2 isotopes so I bet it isn't.
I don't think this stuff woud survive very long on the grid of a working fusor.

[Frank Sanns]

Agreed but there is one factor that I think is being left out and that is the difference between energy and momentum. Momentum is a vector; that is it has both magnitude and direction. Energy on the other hand only has magnitude.

What this means is that ions not only may have enough energy but WILL have enough energy to go farther than the distance from the inner grid (gee, are you guys still using grids?) and the outer wall. The reason is that the inner grid (are you guys still using grids?) looks like a point far away but is not a point up close. So as the ions zip through the inner grid (are you guys still using grids?) then the ion deflects somewhat and has some tangential component to its velocity (energy). On the next path, the ion will now have velocity of the energy of its original fall to the inner grid (.....?) PLUS the tangential velocity. You can see that after just a few passes that there will be a rotational character to the ion velocity and the overall velocity will actually go up beyond the input energy (voltage). This is not a violation of any physics laws as the velocity is gained as in a multiple path accelerator, by sucessive pushes via the electric field. Energy has to be put in to get the gain but the applied peak voltage stays the same.

Frank S.

[001userid]

Frank,

When working from a vector to a tangential, back to a vector, The magnitudes of the initial vector and the final vector should stay the same, unless potential was changed DURING the tangential travel.
Magnitude doesn't change unless you can alter potential for that blink of an instant of tangential velocity.

Joe Sal

[DaveC]

Joe - to Frank's point, ( and I see yours which is also valid and correct)... energy exchanges between colliding particles will occur, and when they do, a re-distribution of both energy and momentum occurs.

In the obvious case of two particles of similar mass colliding head-on, one initially at rest, and the other in motion, the velocities will generally be exchanged, with the moving mass becoming stationary and the mass at rest now being accelerated to the same velocity of the other particle.

However, in the aggregate, summed over all gas ions, the average velocity at the fusor shell, should be zero.

So, I think you are both correct, in different ways.


Dave Cooper

[Frank Sanns]

I did not mean to suggest a rotating vortex inside the fusor. On the contrary. But I do think the ion paths are not linear out and linear back like springs. To my thinking there are complex paths that are linked to collisions as Dave has suggested but also because of wire inner grids The voltage is sweeping as a function of time as we are using unfiltered or modestly filtered power supplies. There is a time varied voltage sweep that is going on that will be prevelent on consecutive paths only to reverse 120 times per second.

Frank S.

[001userid]

Without a solid set voltage, The "Slingshot effect" will contribute to sending many ions into the wall. I do agree that paths are complex depending on both birth place and collisions.
Joe Sal