Fusion Cross Sections

Giorgio · Post by **Giorgio** » Thu Apr 21, 2011 11:37 am

pB11
http://i155.photobucket.com/albums/s307 ... ct-l-1.jpg

3He + 3He
http://www.kayelaby.npl.co.uk/atomic_an ... _7_4a.html

6Li + 6Li (p+6Li and 3He+3He):
http://www.polywellnuclearfusion.com/Nu ... ctors.html

This should be about all you need to generate it.

KitemanSA · Post by **KitemanSA** » Thu Apr 21, 2011 12:09 pm

If
p + ⁶Li > ³He + ⁴He:
shouldn't
p + ⁷Li > 2 x ⁴He ?
what is the cross section for that?

Giorgio · Post by **Giorgio** » Thu Apr 21, 2011 12:40 pm

KitemanSA wrote:If
p + ⁶Li > ³He + ⁴He:
shouldn't
p + ⁷Li > 2 x ⁴He ?
what is the cross section for that?

If I remember correctly only a small percentage of p+7Li --> 2 x 4He.
Most of it will become 7Be + n.
In that case you will have side reactions n +7Li --> T + 4He + n

I think this is the reason why p + 7Li is not considered.

Giorgio · Post by **Giorgio** » Thu Apr 21, 2011 1:05 pm

KitemanSA wrote:If
p + ⁶Li > ³He + ⁴He:
shouldn't
p + ⁷Li > 2 x ⁴He ?
what is the cross section for that?

Check the section "Neutron blanket reactions":
http://www.kayelaby.npl.co.uk/atomic_an ... 4_7_4.html

Giorgio · Post by **Giorgio** » Thu Apr 21, 2011 3:27 pm

Colonel_Korg wrote:Thanks for the replies. But I still did not see the Li6+Li6 -> 3 He4 cross-section graph.

It's a composed reaction:
p+6Li --> Alpha + 3He
p+6Li --> Alpha + 3He
3He+3He--> Alpha + 2p

Hence 6Li + 6Li --> 3Alpha

Colonel_Korg wrote:Example: The peak of p+B11 is 550kV, but someone once told me that because B11 has 5 protons (charge of +5) then the voltage of 110kV is equivalent to the 550kV of kinetic energy. True or false?

True, the charge of 11B is 5, hence if you accellerate 11B to 110KeV its KE will be 110 *5=550 KeV

chrismb · Post by **chrismb** » Thu Apr 21, 2011 4:40 pm

Giorgio wrote:True, the charge of 11B is 5, hence if you accellerate 11B to 110KeV its KE will be 110 *5=550 KeV

Depends on what frame it's KE is significant.

e.g.; if a [lab-frame] 550keV 11B comes across a [lab-frame] stationary proton, the collision energy would be 45keV.

Homework for Korg; if a [lab-frame] 550keV 11B comes into collision with a [lab-frame] 110keV proton, what is the collision energy?

chrismb · Post by **chrismb** » Thu Apr 21, 2011 9:29 pm

Colonel_Korg wrote:Since a 550kV B11 colliding with a stationary proton is 45kV and a non stationary proton is moving at 110kV? then it would be 45kV + 110kV ?

Nice try. This is simple kinetics, easily looked up.... homework!

As for 6Li+6Li - which isn't easy to look up - the only reaction that comes up on the "National Nuclear Data Center" [sic!] database is 6Li+6Li->n+a+7Be, and no cross-sections are indicated for that reaction below ~1.5MeV, peak around 0.2 barn @ 6MeV. Not 'aneutronic' and not accessible as a fusion fuel, it seems.

If you're looking to determine the "best" aneutronic fuel, see what you think of p+15N. I gave an account of it in viewtopic.php?t=2808 (before it got dragged into some obscure pedantry).

KitemanSA · Post by **KitemanSA** » Fri Apr 22, 2011 1:35 am

Several decades ago the "Migma" reactor proposed a 3p + 2(6Li) > 3(4He) +3p reaction. Wonder what ever happened to that. I liked it cuz it was a di-lithium reaction!

Giorgio · Post by **Giorgio** » Fri Apr 22, 2011 8:16 am

chrismb wrote:As for 6Li+6Li - which isn't easy to look up - the only reaction that comes up on the "National Nuclear Data Center" [sic!] database is 6Li+6Li->n+a+7Be, and no cross-sections are indicated for that reaction below ~1.5MeV, peak around 0.2 barn @ 6MeV. Not 'aneutronic' and not accessible as a fusion fuel, it seems.

The only potential aneutronic possibility for 6Li fusion looks like it is via a proton middlestep to 3He as I indicated above.

chrismb wrote:If you're looking to determine the "best" aneutronic fuel, see what you think of p+15N. I gave an account of it in viewtopic.php?t=2808 (before it got dragged into some obscure pedantry).

That was an interesting thread, yet also on p+15N there is the shadow of potentially high bremsstrahlung losses.

chrismb · Post by **chrismb** » Fri Apr 22, 2011 9:27 am

Giorgio wrote: yet also on p+15N there is the shadow of potentially high bremsstrahlung losses.

Not just possible, I'd say certainly! You have to keep the 15N 'cool', along with their electrons, and let the protons do all the colliding. Non-Maxwellian and mitigations against thermalisation are therefore essential - a particular requirement for any fusion with Z>1 reactants.

D Tibbets · Post by **D Tibbets** » Fri Apr 22, 2011 3:48 pm

chrismb wrote:
Giorgio wrote: yet also on p+15N there is the shadow of potentially high bremsstrahlung losses.
Not just possible, I'd say certainly! You have to keep the 15N 'cool', along with their electrons, and let the protons do all the colliding. Non-Maxwellian and mitigations against thermalisation are therefore essential - a particular requirement for any fusion with Z>1 reactants.

Unless you cheat with quantum effects like DPF by LPP proposes. And, I don't think you need to keep the ions cool, only the relevent electrons (thus the cool central core electrons claimed for the Polywell)

Dan Tibbets