So the coil to extract energy from the beam is really an energy recovery device, it’s the X-ray PV cells that will collect the surplus energy from the fusion ?

james:  That sounds like a reasonable explanation - most (some?) of the input is recovered from the ion beam and the X-rays are gravy.

Ivy:  I guess if Learner says heavy ions are more compressible, b-B11 might work better - I hope he’s right.

A thought on ion beam conversion efficiency:

It occurs to me that ions traveling through a coil to generate electricity might be analogous to wind passing through a wind turbine.  Thing is though, the maximum possible efficiency for a wind turbine is about 59% ie. no more than 59% of the kinetic energy of the wind passing through the turbine’s swept area can be recovered (sometimes referred to as the “Betz law”). 

http://en.wikipedia.org/wiki/Betz’_law

What is going on is that the wind must slow when it reacts with the turbine blades but cannot slow beyond a certain velocity as it must keep moving to get out of the way of the incoming wind behind it.  It seems to me that a similar situation might exist for a stream of ions traveling down the annulus of a coil or past a coil for that matter.  Maybe then the efficiency of ion to electrical energy conversion is similarly limited for the same reason??

NoSmoke - 29 January 2011 08:17 PM

If p-B11 does work, and works well, would p-N14 also be a good possibility (not sure if there would be any great incentive to go there though).

If the neutrons produced by p-B11 side reactions are not energetic enough to induce radioactivity, what happens to them (do they decay or just hang around)?

 

There is a good reason to prefer boron (atomic number 5) to nitrogen(atomic number 7) as a fuel. It’s the problem of minimizing x-ray emissions. X-ray emission increases with the square of the atomic number ... so boron has 25 times the x-ray emissions of hydrogen. Nitrogen would have 49 times the emissions of hydrogen. Almost twice as much.

Note: All this talk of x-rays can get confusing. These x-rays are not the reaction x-rays which we talk of harvesting for energy. (although some of them might be recaptured in this way) These are x-rays given of throughout the compression phase and reaction phase, and which tend to cool the reactants. They also tend to be somewhat softer (longer wavelength, less energy) than the reaction x-rays.

rickPS - 02 February 2011 02:39 PM

So the coil to extract energy from the beam is really an energy recovery device, it’s the X-ray PV cells that will collect the surplus energy from the fusion ?

to achieve the predicted system efficiency of 50%, you’ll want to use both.

NoSmoke - 04 February 2011 02:54 AM

A thought on ion beam conversion efficiency:

It occurs to me that ions traveling through a coil to generate electricity might be analogous to wind passing through a wind turbine.  Thing is though, the maximum possible efficiency for a wind turbine is about 59% ie. no more than 59% of the kinetic energy of the wind passing through the turbine’s swept area can be recovered (sometimes referred to as the “Betz law”). 

http://en.wikipedia.org/wiki/Betz’_law

What is going on is that the wind must slow when it reacts with the turbine blades but cannot slow beyond a certain velocity as it must keep moving to get out of the way of the incoming wind behind it.  It seems to me that a similar situation might exist for a stream of ions traveling down the annulus of a coil or past a coil for that matter.  Maybe then the efficiency of ion to electrical energy conversion is similarly limited for the same reason??

That is an interesting analogy. Although it is indeed the kinetic energy which is being harvested from the ion beam there seem to me to be a couple of fundamental differences in our favour. Firstly the cross sections of the ion nuclei are approximately 1e-10 smaller than molecules, so that collisions of decelerated ions with “full speed” ions are much rarer, and secondly, partly-decelerated ions still produce a pro rata voltage in the coil and can theoretically, other things being equal, be decelerated by the induced current right down to zero velocity.

Allan Brewer - 06 February 2011 11:03 PM

NoSmoke - 04 February 2011 02:54 AM

A thought on ion beam conversion efficiency:

It occurs to me that ions traveling through a coil to generate electricity might be analogous to wind passing through a wind turbine.  Thing is though, the maximum possible efficiency for a wind turbine is about 59% ie. no more than 59% of the kinetic energy of the wind passing through the turbine’s swept area can be recovered (sometimes referred to as the “Betz law”). 

http://en.wikipedia.org/wiki/Betz’_law

What is going on is that the wind must slow when it reacts with the turbine blades but cannot slow beyond a certain velocity as it must keep moving to get out of the way of the incoming wind behind it.  It seems to me that a similar situation might exist for a stream of ions traveling down the annulus of a coil or past a coil for that matter.  Maybe then the efficiency of ion to electrical energy conversion is similarly limited for the same reason??

That is an interesting analogy. Although it is indeed the kinetic energy which is being harvested from the ion beam there seem to me to be a couple of fundamental differences in our favour. Firstly the cross sections of the ion nuclei are approximately 1e-10 smaller than molecules, so that collisions of decelerated ions with “full speed” ions are much rarer, and secondly, partly-decelerated ions still produce a pro rata voltage in the coil and can theoretically, other things being equal, be decelerated by the induced current right down to zero velocity.

I see what you mean but I wonder if there is another factor to consider.  As the ions slow in the coil they will necessarily bunch up at the slow end and, although the ion cross section is much smaller than a molecule, they can still “see” each other via electrostatic repulsion, that repulsion being greater from the bunched up end than towards the coil entrance where the ion density will be lower.  Thus the slower ions will tend to slow down the faster upstream ions and the slower ions will have to maintain some velocity to get out of the way, similar to a wind turbine.  I think…....

this will probably yield a particle fountain, at the tail end. but, the alphas will eventually collide with something that will carry the charge away